A fast ceramic mixed OH-/H+ ionic conductor for low temperature fuel cells

A fast ceramic mixed OH-/H+ ionic conductor for low temperature fuel cells | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article A fast ceramic mixed OH - /H + ionic conductor for low temperature fuel cells Shanwen Tao, Peimiao Zou, Dinu Iuga, Shigang Chen, Mengfei Zhang, and 1 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-1885173/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 30 Jan, 2024 Read the published version in Nature Communications → Version 1 posted You are reading this latest preprint version Abstract OH - and H + ionic conductors are important electrolyte materials for electrochemical devices such as fuel cells. The high cost of the best low temperature H + ionic conductor, Nafion membrane, and the poor chemical compatibility with CO 2 in air of alkaline membrane based on quaternary ammonium groups have seriously affected the large-scale application of low temperature fuel cells. Here we show the discovery of a fast ceramic mixed OH - /H + conductor, perovskite oxide SrZr 0.8 Y 0.2 O 3-δ , which exhibits a high ionic conductivity of approximately 0.01 S cm -1 at 90°C when measured in water and wet air, sufficient to be used as electrolyte for low temperature fuel cells. The ionic conductivity is stable in wet air during the measured 130 hours. The ionic conduction was also demonstrated by near ambient temperature solid oxide fuel cells (NAT-SOFCs). This opens a window on discovering new ionic conducting materials for low temperature fuel cells. Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Full Text Fuel cells are important electrochemical devices to convert chemical energy in fuels into electricity at high efficiency. There are different types of fuel cells based on various ionic conducting electrolytes, with a wide operating temperature from near ambient temperature (£100 °C) (NAT) such as around 80°C for proton exchange membrane fuel cells (PEMFCs), to high temperature such as 500–900°C for solid oxide fuel cells (SOFCs) 1 . SOFCs have been developed for stationary power generation while poor durability, due to materials sublimation and cross-diffusion at high operating temperature, is the major obstacle for the large-scale applications 2 . The typical electrolyte materials for SOFCs are doped ZrO 2 or CeO 2 with fluorite structure or doped BaCeO 3 /BaZrO 3 /LaGaO 3 with perovskite structure 1,3-7 . The representative high temperature proton conductors based on doped perovskite oxides BaCeO 3 /BaZrO 3 was discovered by Iwahara in 1980 and 1990’s respectively 3,7 , while the high temperature O 2- ion conductor based on doped LaGaO 3 was discovered by Ishihara in 1994 4 . However, the ionic conductivity of these oxides is not high enough when the operating temperature is below 500°C 1 . To solve this problem, it is desired to reduce the operating temperature of SOFCs, ideally to NAT. The first task to achieve NAT operation of SOFCs is to identify good H + / O 2- /OH - ionic conducting materials to be used as the electrolyte. It has been reported that doped zirconates such as BaZr 0.8 Y 0.2 O 3- d are robust proton conductors with ionic conductivity above 10 -4 Scm -1 at a temperature above 600 °C 7,8 . However, the proton conductivity of perovskite zirconates are normally measured in wet air or wet H 2 by passing the gases through room temperature water with moisture contents of 3 mol% 8 . On the other hand, the OH - ionic conductivity of alkaline membranes are measured in water 9 . For oxide ionic conductors, it was reported that high open circuit voltage (OCV) of an electrochemical cell with 8 mol% Y 2 O 3 stabilized ZrO 2 or Ce 0.8 Sm 0.2 O 2- d pellets with grain size of 15 nm was used as the electrolyte while one side is merged in water 10 . To the best of our knowledge, report on measuring ionic conductivity of oxides in liquid water is scarce. In our research, it was found that Y-doped SrZrO 3 , SrZr 0.8 Y 0.2 O 3-δ exhibits high ionic conductivity of approximately 0.01 S cm -1 at 90°C when exposed in water or wet air, which opens a window on developing solid oxide ionic conductors for applications in NAT-SOFCs. Creation Of Pathways For Ions In Perovskite Oxide Srzryo For a good ionic conductor, it is desired to have pathways for the diffusion of ions. With the existence of pathways, the concentration of charge carriers must be sufficient in order to achieve high ionic conductivity. For doped zirconates, it is widely accepted that the oxygen vacancies and the associated proton defects during the reaction between oxygen vacancy and steam (or water) forms the pathways for the proton conduction 11 , 12 . The schematic diagram on how to form the pathways in a perovskite oxide is shown in Fig. 1 . Perovskite oxide SrZrO 3 was chosen as the parent phase. When part of Zr at the B-site in SrZrO 3 is replaced by Y, for charge compensation, positively charged oxygen vacancies ( \({V}_{O}^{\bullet \bullet }\) ) are formed. For charge balance, the negatively charged \({Y}_{Zr}^{{\prime }}\) defects are formed simultaneously. It can be described by Kröger-Vink notations. $$2{Zr}_{Zr}^{\times }+{O}_{O}^{\times }+{Y}_{2}{O}_{3}\to 2Zr{O}_{2}+2{Y}_{Zr}^{{\prime }}+{V}_{O}^{\bullet \bullet }$$ 1 When this Y doped SrZrO 3 , with a general formula of SrZr 1 − x Y x O 3−δ , meets water or steam, proton defects \({OH}_{O}^{\bullet }\) will be formed. $${V}_{O}^{\bullet \bullet }+{O}_{O}^{\times }+{H}_{2}O\to 2{OH}_{O}^{\bullet }$$ 2 At high temperatures, typically above 600°C, the mobility of formed proton defects increases leading to high protonic conductivity in doped BaCeO 3 /BaZrO 3 3 . The ionic conductivity of Y-doped SrZrO 3 , SrZr 0.95 Y 0.05 O 3−δ is approximately 7.0 ⋅ 10 − 4 S cm − 1 at 600°C, which is not high enough for use as electrolyte for NAT-SOFCs 13 . In order to improve the ionic conductivity at low temperatures, it is necessary to increase the concentration of charge carriers, i.e., the proton defects. Therefore, we synthesized SrZr 1 − x Y x O 3−δ (x = 0, 0.1, 0.2) samples (Fig. 2 a and Methods) and put the samples in liquid water to maximize the interaction between water and oxygen vacancies to maximize the concentration of proton defects. When the concentration of these proton defects is high enough, the neighbouring proton defects may couple or exchange with each other, in the form of H + or OH − ions, forming a continuous pathway, resulting in high OH − /H + ionic conductivity. Materials Characterizations Of Srzryo Based on the analysis above, it is anticipated that, doped zirconates may exhibit high ionic conductivity in water or, in the presence of high partial pressure of steam, \(p{H}_{2}O\) . At 100°C, the bulk proton conductivity of BaZr 0.8 Y 0.2 O 3−δ is in the order of 10 − 5 S cm − 1 in air, too low to be used as electrolyte for NAT-SOFCs 14 . In reported papers, at the same temperature, generally Y-doped BaZrO 3 exhibits higher ionic conductivity than those for Y-doped SrZrO 3 because doped BaZrO 3 has larger lattice volume thus more ‘free volume’ for diffusion/jumping of ions in the lattice 13 , 14 . To identify the effect of A-site ions on the ionic conductivity of Y-doped zirconates, three compounds with AZr 0.8 Y 0.2 O 3−δ where A = Ca, Sr, Ba were synthesized. X-ray diffraction (XRD) experiments indicate both CaZr 0.8 Y 0.2 O 3−δ and BaZr 0.8 Y 0.2 O 3−δ are single phases while there is a small amount of secondary phase SrY 2 O 4 in SrZr 0.8 Y 0.2 O 3−δ (Supplementary Fig. 1 and Supplementary Table 1). The SrY 2 O 4 second phase was also observed in SrZr 0.8 Y 0.2 O 3−δ when synthesised by pulsed layer deposition method 15 and was commonly existed in Y doped perovskite oxides such as Sr(Ce 0.6 Zr 0.4 ) 0.8 Y 0.2 O 3 16 and Sr(Ti 0.9 Y 0.1 )O 3 17 . The primary particle size of SrZr 0.8 Y 0.2 O 3−δ was about 200–250 nm and an agglomeration of some particles was observed by both scanning electron microscopy (SEM) and annular dark – field scanning transmission electron microscopy (ADF-STEM) (Fig. 2 b,c). In Fig. 2 d, the two labelled spacings were associated with the (200) and (004) lattice planes of the orthorhombic phase of SrZrO 3 (ICDD:04-014-8276), respectively. The EDX elemental maps clearly show that the amount of secondary phase is small and Sr, Zr, Y and O elements are distributed evenly in the grains (Fig. 2 e,f). The spacing labelled in Supplementary Fig. 2c was associated with the (200) lattice plane of the orthorhombic phase of SrY 2 O 4 (ICDD:01-074-0264), confirming the Y-rich area of the SrZr 0.8 Y 0.2 O 3−δ sample was the SrY 2 O 4 phase (Supplementary Fig. 2). Removal Of Second Phase Sryo From The Samples It has been reported that the secondary phase of the sample, SrY 2 O 4 , may react with water at high temperature to form SrCO 3 , Sr(OH) 2 ⋅8H 2 O and gel phase Y(OH) 3 18 . Therefore, before the conductivity measurements, SrZr 1 − x Y x O 3−δ samples were heated in hot water at 90°C for 20 hours and washed for three times in order to get rid of second phase SrY 2 O 4 and the hydrated soluble product Sr(OH) 2 ⋅8H 2 O. From STEM and EDX analysis of pre-washed SrZr 0.8 Y 0.2 O 3−δ samples (Fig. 3 a-c and Supplementary Fig. 3), the measured spacing in Fig. 3 c was associated with the (002) lattice plane of the orthorhombic phase of SrZrO 3 (ICDD:04-014-8276). This indicates the perovskite phase is stable after hot water treatment at 90°C while second phase SrY 2 O 4 has been successfully removed. In addition, STEM and EDX results indicate the presence of an amorphous material in the Y-rich area B (Supplementary Fig. 3b), which is likely to be Y(OH) 3 . This amorphous stays on the grain boundary or presents as isolated particles among perovskite particles (marked area in Fig. 3 a). The elemental analysis of SrZr 0.8 Y 0.2 O 3−δ samples before and after being washed in hot water also confirmed that the soluble hydrolysis products Sr(OH) 2 ⋅8H 2 O had been removed (Supplementary Table 2). The complete hydrolysis of SrY 2 O 4 at 90°C was also confirmed by XRD analyses (Supplementary Fig. 4). All samples for conductivity measurements were treated in water at 90°C for 20 hours (repeated three times) to get rid of second phase SrY 2 O 4 . Conductivity And Importance Of Hydration The measurement of traditional protonic conducting perovskite oxides such as doped zirconates or cerates are normally measured in wet air or wet H 2 , passing the gas through room temperature water with steam partial pressure of 0.03 bar, i.e., 3 mol% steam in the humidified air or hydrogen. Their conductivity at NAT is very low 14 . According to our analysis above (Fig. 1 and Eqs. 1 & 2 ), the water or steam concentration mentioned in reported papers may not be enough to form sufficient proton defects in order to form continuous pathways for OH − /H + ions. Therefore, we decided to directly measure the conductivity and ion transfer number of the prepared and pre-washed AZr 0.8 Y 0.2 O 3−δ (A = Ca, Sr, Ba) pellets in water (Supplementary Fig. 5), which is the method commonly used for conductivity measurement in alkaline membranes 9 . At room temperature, the conductivity of un-washed SrZr 0.8 Y 0.2 O 3−δ pellet in water kept increasing against time (Supplementary Fig. 6). It increased from 2.96 ⋅ 10 − 4 S cm − 1 to 2.28 ⋅ 10 − 3 S cm − 1 in 10 hours indicating hydration to form proton defects is extremely important (Eq. 2 ). After ageing in water at room temperature, the ionic conductivity of SrZr 0.8 Y 0.2 O 3−δ in water, is already higher than the protonic conductivity of SrZr 0.95 Y 0.05 O 3−δ , 7.0 ⋅ 10 − 4 S cm − 1 , at 600°C when measured in H 2 13 . The conductivity of SrY 2 O 4 is stable at room temperature indicating hydrolysis does not happen at this temperature. Its conductivity is 1.7 ⋅ 10 − 4 S cm − 1 , is only 7.5% of that for fully hydrated SrZr 0.8 Y 0.2 O 3−δ , thus the high ionic conductivity of un-washed SrZr 0.8 Y 0.2 O 3−δ in water at room temperature is mainly due to the hydration of SrZr 0.8 Y 0.2 O 3−δ (Supplementary Fig. 6c). To rule out the possible contribution of residual Y 2 O 3 or Y(OH) 3 in the pre-washed SrZr 0.8 Y 0.2 O 3−δ sample, conductivities of pure Y 2 O 3 and Y(OH) 3 in water were measured indicating they have very low ionic conductivity (Supplementary Fig. 7) thus will have little contribution to the observed high ionic conductivity of SrZr 0.8 Y 0.2 O 3−δ at elevated temperatures. The interaction between oxygen vacancy and water was also confirmed by Raman spectra (Fig. 3 d). The peaks in the 600–900 cm − 1 region are slightly wider when the SrZr 0.8 Y 0.2 O 3−δ sample is wetter. When the hydration level of SrZr 0.8 Y 0.2 O 3−δ sample is higher, the Raman peak shifts towards higher values (734 cm − 1 ), which is consistent with the Raman features of proton insertion in oxygen vacancies 19 . Among the three AZr 0.8 Y 0.2 O 3−δ (A = Ca, Sr, Ba) oxides, it was found that sample SrZr 0.8 Y 0.2 O 3−δ exhibits the highest ionic conductivity (Fig. 4 a). The jumping or diffusion of ions in a lattice, not only related to the high concentration of proton defects, but also to the ‘free volume’ and jumping distance between neighbouring available sites (Fig. 1 ). In general, large lattice parameters or bond length means higher ‘free volume’, favouring the mobility of ions, while longer jumping distance for ions will reduce the mobility. These two effects are opposite on the ionic conductivity. Therefore, there must be an optimised lattice size, which exhibits the highest ionic conductivity. In the AZr 0.8 Y 0.2 O 3−δ (A = Ca, Sr, Ba) series, sample SrZr 0.8 Y 0.2 O 3−δ exhibits the highest ionic conductivity. This is consistent with the observed proton conductivity of AZr 0.95 In 0.05 O 3−δ (A = Ca, Sr, Ba) in H 2 at a temperature of 600–1000°C 7 . In order to work out the types of charge carries, low temperature concentration cell measurement was applied to work out the conduction ions (Supplementary Fig. 8 and Supplementary Discussion 1) 20 . It was found that, in water, SrZr 0.8 Y 0.2 O 3−δ is a mixed OH − /H + ion conductor while the ion transfer number for anion OH − ions is higher (Supplementary Table 3). Therefore, both H + and OH − ions are mobile in hydrated SrZr 0.8 Y 0.2 O 3−δ when it is exposed in liquid water. This is very different from the conventional doped zirconates which is known as mixed H + /O 2− ionic conduction at temperature above 500°C 21 . In this study, it has been observed that, not only protons, but OH − ions may also jump or diffuse via the oxygen vacancies or proton defects after hydrated with liquid water. The OH − ionic conduction was also previously proposed in similar perovskite oxides SrCe 0.95 Yb 0.05 O 3−δ and BaCe 1 − x Gd x O 3−δ in the presence of water vapour at high temperature (> 500°C) while the observed ionic conduction was very low because pH 2 O is not high enough 22 , 23 . In order to confirm the importance of oxygen vacancies, the ionic conductivity of SrZrO 3 and SrZr 0.9 Y 0.1 O 3−δ in water was also investigated. XRD results indicate that SrZrO 3 is a single phase, while both SrZr 0.9 Y 0.1 O 3−δ and SrZr 0.8 Y 0.2 O 3−δ contain a small amount of second phase SrY 2 O 4 (Supplementary Figs. 1c,9). Among the three oxides, the order of conductivity and transfer number is SrZr 0.8 Y 0.2 O 3−δ > SrZr 0.9 Y 0.1 O 3−δ > SrZrO 3 (Fig. 4 b). This is because SrZr 0.8 Y 0.2 O 3−δ has the highest doping level thus the highest concentration of oxygen vacancies (Eq. 1 ), thus more proton defects (Eq. 2 ) leading to the highest ionic conductivity. In water, the ionic conductivity of sample SrZr 0.8 Y 0.2 O 3−δ is 3.28 ⋅ 10 − 3 S cm − 1 at 25°C, 9.71 ⋅ 10 − 3 S cm − 1 at 90°C respectively with ion transfer number higher than 0.995. This is sufficient to be used as electrolyte for fuel cells and electrolysers at 90°C when thin film technology used for conventional SOFC is applied. For fuel cell applications, the cathode side may be exposed to wet O 2 or wet air. Therefore it is very important to measure the ionic conductivity in wet air. Different from the conventional humidified air with 3% H 2 O for conductivity measurement, we pass the air through 100°C boiling water in order to fully humidify the oxides while the real temperature of the oxide pellet was recorded by a thermocouple next to the sample. The conductivity of SrZr 0.8 Y 0.2 O 3−δ in wet air at 90°C is 1.1 ⋅ 10 − 2 S cm − 1 while it suddenly drops at above 100°C (Fig. 4 c and Supplementary Fig. 10a-c). This means the high ionic conductivity of SrZr 0.8 Y 0.2 O 3−δ is related to the presence of liquid water. At 70°C, the conductivity of SrZr 0.8 Y 0.2 O 3−δ in wet air is stable at 0.01 S cm − 1 for the measured 130 hours (Fig. 4 d), which is reflected in the a.c. impedance spectra (Supplementary Fig. 10d,e). This indicates the ceramic ionic conductor SrZr 0.8 Y 0.2 O 3−δ has excellent stability in humidified air. After conductivity measurements, the chemical composition was still perovskite oxide, confirmed by XRD and element mapping (Supplementary Fig. 11). Pre-washed SrZr 0.8 Y 0.2 O 3−δ sample contains 2% residual SrCO 3 due to hydrolysis of SrY 2 O 4 and the SrCO 3 remains 2% in SrZr 0.8 Y 0.2 O 3−δ sample after conductivity measurement in air at 70°C for 130 hours indicating excellent chemical compatibility with CO 2 in air. Kinetic Isotope Effect For proton conducting materials, the conductivity in D 2 O will be reduced due to the decreased mobility of D + ions 7 , 24 . This is also called the kinetic isotope effect (KIE). The conductivity of SrZr 0.8 Y 0.2 O 3−δ in pure D 2 O was also measured to investigate its ability on proton conduction (Fig. 4 e and Supplementary Discussion 2). At 90°C, the conductivity in H 2 O is 5.28 time of that in D 2 O, which is reflected in the a.c. impedance spectra in Supplementary Fig. 12. For pure proton conductors, the kinetic isotope effect (KIE) is usually no less than 1.4 for Grotthuss mechanism, while it is close to 1.2 for vehicle mechanism 24 . As the KIE is much larger than 1.4, it is presumed that SrZr 0.8 Y 0.2 O 3−δ is a not a pure protonic conductor.. The activation energy of SrZr 0.8 Y 0.2 O 3−δ in H 2 O and D 2 O was 0.201±0.008 eV and 0.169±0.005eV respectively (Fig. 4 f). It is slightly higher than the 0.17eV for Nafion membrane in H 2 O 2 4 and within the range of activity energy for OH − conducting polymers (0.12–0.26 eV) 25 . The activation energy of doped SrZrO 3 at low (< 100°C) in this study is much different from reported doped SrZrO 3−δ at high temperature with the range of 0.4–0.6 eV at 700–1000°C when the dominant charge carriers are H + and O 2− ions 13 , which indicates the charge carriers in liquid water may be different. This explains why the hydrated SrZr 0.8 Y 0.2 O 3−δ is a mixed OH − /H + conductor, while the transfer number for OH − ions is higher than that for cations, H + ions (Supplementary Table 3). The particle size remained unchanged after sample SrZr 0.8 Y 0.2 O 3−δ had been measured in water, D 2 O or wet air (Supplementary Fig. 13), further confirmed the chemical stability of the sample. Solid State Nmr Measurements In order to further investigate the conduction mechanism of SrZr 0.8 Y 0.2 O 3−δ in water, solid state nuclear magnetic resonance (NMR) has been employed to study the dry and partially hydrated SrZr 0.8 Y 0.2 O 3−δ . Figure 5 a shows the solid state 1 H NMR spectra of dry (red) and partially hydrated (blue) SrZr 0.8 Y 0.2 O 3−δ . The 1 H spectrum of dry SrZr 0.8 Y 0.2 O 3−δ shows three resolved signals at 4.4, 3.5 and 0.7 ppm that can be assigned to H 2 O, OH − groups bound on defects or surface and, H + bound to oxygen of the Sr-O-Y or Sr-O-Zr environments, respectively. Akin assignments of proton signals on similar samples have been reported 26 − 28 . As the sample gets partially hydrated the 1 H signal increases dramatically and shows two broad peaks at 4.6 and 2.3 ppm which can be assigned to water at 4.6 ppm and to signals from OH − and H + moieties and their exchange at 2.3 ppm. The deconvolution of the partially hydrated sample is shown on Supplementary Fig. 14. The fast MAS experiments were performed with a 1.3 mm probe that has limited variable temperature capabilities. Figure 5 b shows the solid state 1 H NMR (MAS 60 kHz) spectra of partially hydrated (top) and dry (bottom) SrZr 0.8 Y 0.2 O 3−δ measured with the sample at -5 o C (blue) and + 30 o C (red). On both samples the water peak shifts slightly with the temperature (approximately 0.1 ppm / 10 o C) 29 . At both temperatures, the dry and the wet samples, the signals assigned to OH − and to H + are getting broader as the temperature increases which suggests the presence of exchange between the two moieties. 1 H nuclear overhauser effect spectroscopy (NOESY) spectra of the dry and hydrated samples are shown on Fig. 5 c,d and prove proximity between different 1 H moieties. We have also performed 89 Y MAS NMR experiments on the partially hydrated sample as shown on Fig. 5 e. The 89 Y direct polarization (DP) signal measured with a spin echo experiment shows two broad signals at 370 and 160 ppm indicating Y sites are coordinated by 6, 7 and 8 oxygen atoms 30 , 31 . The 1 H- 89 Y cross polarization (CP) spectrum shows two 89 Y signals at 219 and 130 ppm (mainly 7 and 8 coordinated sites) in proximity to 1 H nuclei. The 1 H- 89 Y heteronuclear correlation experiment, performed on the partially hydrated sample is displayed in Fig. 5 f. It shows that the 89 Y signals correlates with the 1 H signal at 2.3 ppm which we assign to the OH − and H + exchange signal. This indicates the mobile OH − and H + ions are associated with Y 3+ sites since Y 3+ doping introduces oxygen vacancies in the SrZrO 3 lattice, as shown in Fig. 1 and Eq. 1 . This is also consistent with the Raman results (Supplementary Fig. 15 and Supplementary Discussion 3). In water, the real composition of hy drated SrZr 1 − x Y x O 3−δ is hydrated or unhydrated oxyhydroxide (z = 0), with a general formula, SrZr 1 − x Y x O 3−y (OH) 2y ⋅zH 2 O. The OH − ions are presented in the form of protonic defects, \({OH}_{O}^{\bullet }\) , which are associated with oxygen vacancies. The exchange and coupling of OH − and H + ions in hydrated SrZr 0.8 Y 0.2 O 3−δ has been confirmed by solid state NMR observation for a better understanding of the conduction mechanism in water. Fuel Cell Demonstration To further confirm the ionic conduction of SrZr 0.8 Y 0.2 O 3−δ , a H 2 /air fuel cell and an NH 3 /air fuel cell using SrZr 0.8 Y 0.2 O 3−δ pellet as the electrolyte were constructed (Supplementary Fig. 16). Figure 6 a shows the OCV of the H 2 /air fuel cell at a temperature of 20°C. The OCV gradually increased against time in the first three hours due to hydration then reached a stable value of 1.07 V. This is fairly close to the theoretical value of a H 2 /O 2 fuel cell (1.23 V at 25°C) considering humidified air instead of pure O 2 is used at the cathode. From this OCV result, it can be deduced that SrZr 0.8 Y 0.2 O 3−δ is almost a nearly pure ionic conductor at 20°C in wet atmosphere. At 20°C, a maximum current density of 1.25 mA cm − 2 with maximum power density of 0.34 mW cm − 2 was achieved respectively (Supplementary Fig. 17). This key experiment indicates it is possible to develop NAT-SOFCs for different applications. The main purpose for this experiment is to confirm the OH − /H + ionic conduction of SrZr 0.8 Y 0.2 O 3−δ electrolyte thus the performance was not optimised. Ammonia was also used as the fuel for this type of NAT- SOFC (Fig. 6 b). When using 35 wt% ammonia solution as a fuel, the current density of the fuel cell using SrZr 0.8 Y 0.2 O 3−δ electrolyte was similar to the fuel cell using commercial anion exchange membrane (AEM) (Supplementary Fig. 18). Considering the thickness difference between SrZr 0.8 Y 0.2 O 3−δ pellet (1300 µm) and AEM (50 µm), the conductivity of SrZr 0.8 Y 0.2 O 3−δ pellet, estimated from the series resistance of the a.c. impedance spectra of the fuel cells, is higher than the commercial AEM (Supplementary Fig. 19). The observed low ionic conductivity of commercial AEM is due to its poor chemical compatibility with CO 2 in air. It has been reported that adding KOH in ammonia solution can significantly improve the fuel cell performance when alkaline membrane was used as the electrolyte 32 , 33 . 35 wt% ammonia solution with added 3M KOH was used as the fuel for a direct ammonia fuel cell based on SrZr 0.8 Y 0.2 O 3−δ electrolyte. The relevant I-V curves and a.c. impedance spectra of the direct ammonia fuel cell are shown in Fig. 6 c,d. At 90°C, a maximum power density of 30 mW cm − 2 was achieved. Compared to reported work in DAFCs, the power density is relatively low due to the thick electrolyte (1.3mm) and not optimised solid to solid electrolyte/electrode interface while wet air instead of wet O 2 was used at the cathode. In this study, the good ionic conduction of SrZr 0.8 Y 0.2 O 3−δ near ambient temperature has been demonstrated by both hydrogen and ammonia fuel cells. Conclusions In summary, the mixed OH − /H + conduction of perovskite oxides such as SrZr 0.8 Y 0.2 O 3−δ with ionic conductivity around 0.01 S cm − 1 at 90°C in water and humidified air was discovered. XRD and ADF-STEM confirm the formation and stability of perovskite phase. Solid state NMR study reveals that the transfer of OH − and H + ions is coupled with dopant Y 3+ ions at the B-sites indicating oxygen vacancies play important role for the ionic conduction, similar to their high H + /O 2− conductivity at high temperature (typically ≥ 500°C). The discovery of low temperature mixed OH − /H + ionic conduction in oxide materials opens a window on discovering new low temperature OH − /H + ionic conducting materials in oxides or other ceramic materials. Similar phenomenon was also observed in doped cerates while the investigation is on-going. Methods Synthesis of SrZr 1 − x Y x O 3−δ (x = 0, 0.1, 0.2) The perovskite oxides SrZr 0.8 Y 0.2 O 3−δ were synthesized by a combustion method. 10.80 g of Sr(NO 3 ) 2 (98%, Alfa Aesar), 3.83 g of Y(NO 3 ) 3 ∙6H 2 O (99.9%, Alfa Aesar), 13.15 g of ZrOCl 2 ∙8H 2 O (98%, Alfa Aesar) and 5 mL of nitric acid (70%, Sigma Aldrich) were directly dissolved in deionized water to prepare a mixed solution. Then 38.81 g of citric acid (99+%, Alfa Aesar) was added into the solution and magnetically stirred at 90°C for 12 hours on a hot plate to form a gel. Then the gel was dried at a constant temperature of 400°C for 1 hour to be ignited for combustion. After the organic components in the mixture burned off, the powder was ground in an agate mortar and calcined in air at 400°C for 3 hours, then 1000°C for 2 hours. After this, the as-prepared powder was reground and pressed into pellets with a diameter of 13 mm and 20 mm respectively under a pressure of 6 tons, and then sintered in air at 1300°C for 24 hours with a heating/cooling rate of 5°C/min to form SrZr 0.8 Y 0.2 O 3−δ phase 34 . The perovskite oxides SrZrO 3 and SrZr 0.9 Y 0.1 O 3−δ were synthesized with the same combustion method. The stoichiometric molar ratio of Sr(NO 3 ) 2 , Y(NO 3 ) 3 ∙6H 2 O and ZrOCl 2 ∙8H 2 O with a small amount of nitric acid were used in precursor solution. The molar ratio of citric acid to total metal ions was 2:1 35 . The target perovskite phase was obtained after pelletized and fired at 1300°C for 24 hours, the same as for preparation of SrZr 0.8 Y 0.2 O 3−δ . The as-prepared pellets with diameter of about 13 mm were used for conductivity measurements while those with diameter of about 20 mm were used for concentration cell and fuel cell measurements. Synthesis Of Azryo (A = ca, Ba) The perovskite oxides CaZr 0.8 Y 0.2 O 3−δ and BaZr 0.8 Y 0.2 O 3−δ were synthesized by the same combustion process. 11.93 g of Ca(NO 3 ) 2 ∙4H 2 O (99%, Sigma Aldrich) or 13.20 g of Ba(NO 3 ) 2 (99%, Sigma Aldrich) was used as precursors respectively to synthesize AZr 0.8 Y 0.2 O 3−δ (A = Ca, Ba). The usage of other precursors and igniting conditions were the same as for SrZr 0.8 Y 0.2 O 3−δ . The CaZr 0.8 Y 0.2 O 3−δ phase was formed after fired in air at 1300°C for 4 hours. The BaZr 0.8 Y 0.2 O 3−δ phase was formed after fired in air at 1500°C for 4 hours. Synthesis Of Sryo And Y(Oh) In order to identify the effect of the secondary phase SrY 2 O 4 in SrZr 0.8 Y 0.2 O 3−δ on the ionic conductivity, the single phase SrY 2 O 4 was synthesised by the same combustion method. 6.48 g of Sr(NO 3 ) 2 (98%, Alfa Aesar), 23.00 g of Y(NO 3 ) 3 ∙6H 2 O (99.9%, Alfa Aesar) and 34.93 g of citric acid (99+%, Alfa Aesar) were directly dissolved in deionized water and the mixed solution was magnetically stirred at 80°C for 12 hours on a hot plate to form a gel. The igniting conditions were the same as for SrZr 0.8 Y 0.2 O 3−δ . The target SrY 2 O 4 sample was obtained after pelletized and fired in air at 1300°C for 24 hours. In order to rule out the contribution of the hydrolysis products of SrY 2 O 4 on the conductivity measurement, Y(OH) 3 sample was chemical deposited through the reaction between 0.5 mol L − 1 Y(NO 3 ) 3 ∙6H 2 O (99.9%, Alfa Aesar) and 1.5 mol L − 1 of NaOH (98%, Alfa Aesar). The synthesized powder was thoroughly washed and dried at 60°C for 8 hours, and then pelletized for conductivity measurement. The commercial Y 2 O 3 (99.9%, Alfa Aesar) powder was also pelletized and fired at 1300°C for 4 hours to be measured its conductivity in water. (Supplementary Fig. 7 and Supplementary Discussion 4) Structural Characterizations The X-ray diffraction (XRD) was carried out on a third generation Malvern Panalytical Empyrean equipped with multicore (iCore/dCore) optics and a Pixcel3D detector operating in 1D scanning mode with a Cu Kα radiation (1.5419 Å) to identify the crystalline phases present in the samples. The diffraction scans were collected over a 2θ range from 5° to 100° at a step size of 0.013° with a counting time of 110 s per step and were analysed using the Malvern Panalytical Highscore Plus 4.9 software and the latest ICDD PDF-4 + database. Rietveld refinement of the representative perovskite oxides was carried out by GSAS and EXPGUI. Scanning electron microscopy (SEM) observation of the microstructure was carried out on a Zeiss SUPRA 55-VP scanning microscope. Energy dispersive X-ray spectroscopy (EDX) was used to analyse the cross section of pellets and determine the element composition of the samples through elemental mapping analyses. Annular dark field (ADF) and bright field (BF) scanning transmission electron microscopy (STEM) imaging and energy dispersive X-ray spectroscopy (EDX) elemental mapping were carried out on a double aberration corrected JEOL ARM200F TEM, operated at 200 kV, equipped with a 100 mm 2 Oxford Instruments windowless EDX detector. The SrZr 0.8 Y 0.2 O 3−δ powders for TEM measurement were ground from sintered pellets. Some pellets were washed in water at 90°C for three times to get rid of the second phase SrY 2 O 4 and hydrated products and then ground into powders, labelled as washed SrZr 0.8 Y 0.2 O 3−δ sample. It is noted that Cu, Cr and C signals are artefacts generated during the STEM-EDX acquisition. Raman spectra at room temperature were recorded on a Renishaw inVia Reflex Raman Microscope equipped with DPSS laser at 532 nm (10% power nominally 2 mW) and Renishaw CCD detector. Objective of X50 LWD and an acquisition time of 10 seconds was used during testing. For these measurements, the pellets were cleaved, and the fracture surface was analysed. The sample washed in water at 90°C and dried in oven for overnight was labelled as partially hydrated sample, while the sample dried in air for a moment before Raman measurement was labelled as hydrated sample. Solid-state Nmr Spectra Measurements All SrZr 0.8 Y 0.2 O 3−δ powder samples for solid state NMR measurements were heated in hot water at 90°C for 20 hours and washed to get rid of second phase SrY 2 O 4 and the hydrated products. This process was repeated three times for each sample. The as-treated powder was dried in a fume cupboard at room temperature overnight, labelled as partially hydrated sample. Some of the as-treated powder was dried in a vacuum oven at 120°C overnight to get rid of the hydrated water. This sample was labelled as dry SrZr 0.8 Y 0.2 O 3−δ sample. Nuclear Magnetic Resonance were performed on a Bruker Avance Neo spectrometer with a Larmor frequency of 850.2 MHz and 41.6 MHz for 1 H and 89 Y, respectively using a 1.3 mm Bruker triple resonance HXY probe spinning a 60 kHz and a 4 mm Bruker double resonance HX low gamma probe spinning at 8 kHz. The 89 Y spectra were referenced to solid Y(NO 3 ) 3 ∙6H 2 O with the 89 Y peak set to -53.2 ppm. The 1 H NMR spectra were referenced to 1 H peak of solid adamantane set to 1.8 ppm. 89 Y MAS spectra were acquired with a spin echo pulse sequence with a 90 and 180 pulses set to 6 µs and 12 µs, respectively and with cross polarization experiment with 6 ms contact time. 1 H MAS (60 kHz) NMR spectra were measured using a background suppression pulse sequence consisting of a 180 pulse followed by two 90 pulses. Measurements Of Ion Conductivity And Ion Transfer Number To measure the conductivity of sintered oxide pellets with diameter around 13 mm, two side surfaces of a pellet (~ 2 mm in thickness) are coated by Silver Conductive Ink (Alfa Aesar) to form Ag electrodes. The Ag painting layers were dried in an oven at 130°C for 150 minutes. A sandwich-structure cell with a layer of pellet between two layers of silver mesh was then immobilized in a home-made jig. Since the conduction of hydroxide ion requires water or steam as a medium, the ionic conductivity was measured either in a beaker fulfilled with deionized water (Supplementary Fig. 5) or in a sealed quartz tube in which the humidified compressed air was passing through. For the conductivity measurements in water, the temperature of water was detected and controlled by a hot plate connected with thermocouple. For the conductivity measurements in wet air, the compressed air was humidified by passing through boiling water at a flow rate of 100 mL min − 1 and then flowed into the jig sealed in a vertical furnace to be heated from 20 to 600°C. The temperature of wet air around the pellet was read by a thermocouple linked to Solartron 1470E CellTest System. Before the conductivity measurements, all the pellets were heated in hot water at 90°C for 20 hours and washed to get rid of second phase SrY 2 O 4 and the hydrated products. This process was repeated three times for each sample. Electronic conductivity of the pellet was measured by a pseudo four-terminal DC method on a Solartron 1470E CellTest System. To work out the resistance caused by electronic conduction, 1 V constant DC voltage was applied on the pellet. After the current had been saturated, the direct current electrical resistance (R DC ) was calculated from applied voltage (V) and saturated current (I sat ) 24 . Then the electrical conductivity (σ e ) was calculated on the basis of thickness, λ, and effective cross-sectional area of the electrolyte pellet, A, as follows: 24 R DC =V/I sat , σ e = λ /(R DC ×A). Electrochemical impedance spectrum (EIS) was acquired using a Solartron 1455 frequency response analyser (FRA) with 10 mV amplitude and frequency range of 1 MHz to 0.01 Hz to measure total conductivities (σ t ). Based on the relation between electronic conductivity and total conductivity, the ionic conductivity σ i is calculated as: σ i = σ t - σ e The electronic conduction transfer number (t e ) is σ e /σ t × 100%. Then the corresponding ion transfer number (t i ) can be measured as follows: t i = (1-σ e /σ t ) ×100% Identification Of The Charge Carrier In Ionic Conductors In order to determine which ion was conducted by the solid ionic conductors, a concentration cell with Ag/Ag 2 O electrodes was made according to the method described in a previous report 20 . A perovskite oxide pellet was clamped between two chambers of the H-cell filled with NaOH solution (Supplementary Fig. 8). A Nafion™ 212 membrane (FuelCellStore) and an anion exchange membrane (Fumapem FAA, FuelCellStore) purchased commercially were measured for comparison (details in Supplementary Discussion 1). Kie Measurements The SrZr 0.8 Y 0.2 O 3−δ electrolyte pellet was firstly treated in deionized water at 90℃ for 20 hours (repeated three times), and then dried in a vacuum oven at 120°C overnight to remove the adsorbed water as much as possible. The conductivity was then measured after the pre-treated pellet being stored in deuterium water (D 2 O) for overnight. The kinetic isotope effect (KIE) is the ratio of ion conductivity of pellets in H 2 O to the that in D 2 O 24 . Electrode Preparation For Fuel Cell Measurement Plain carbon fiber cloth (0.35 mm thickness, E-TEK) was used as the substrate for the catalysts. The carbon cloth electrode (1×1 cm 2 ) was sonicated in diluted hydrochloric acid, deionized water, and isopropanol for 1 min respectively. PtIr/C catalysts (20 wt% of metals loading) were prepared by the borohydride reduction process 36 using K 2 PtCl 6 (Pt 39.6%, Thermo Scientific™), IrCl 3 ∙3H 2 O (53–56% Ir, Thermo Scientific™) and Vulcan XC72 carbon black as precursors. The atomic ratio of Pt:Ir is 50:50. The catalyst ink was made up of 80 mg PtIr/C powder, 500 µL isopropanol and 145 µL 5 wt% Nafion solution. The ink slurry was ultrasonicated for 1 h and then brushed onto the pre-treated carbon cloth. The electrode was dried in an oven at 80°C. The loading of PtIr was about 1.2 mg cm − 2 . The Pt/C electrode (20 wt% Pt on carbon black, Alfa Aesar) was prepared in the same way and the loading of Pt was about 1.3 mg cm − 2 . Hydrogen Fuel Cell Fabrication And Measurements A SrZr 0.8 Y 0.2 O 3−δ pellet (1.8mm of thickness, 19.2mm of diameter) was employed as the electrolyte. The symmetric hydrogen fuel cell was assembled using Pt/C electrode as both the anode and cathode. The loading of Pt is about 1.3 mg cm − 2 . The effective area of the fuel cell was 1 × 1 cm 2 . Hydrogen gas was passing through a humidifier to flow into the anode at 5 mL min − 1 , whilst 20 mL min − 1 humidified compressed air was flowing into the cathode field of fuel cell system. The pressure of both hydrogen and compressed air is at ambient pressure. The polarization curves and power density curves were measured through a Solartron 1287A electrochemical interface controlled by electrochemical software Corr-Ware/CorrView. The EIS data of the fuel cell was collected by the Solartron 1260A Electrochemical Station at a frequency range of 1 MHz to 0.01 Hz and fixed potential of 10 mV bias. Direct Ammonia Fuel Cell Fabrication And Measurements A SrZr 0.8 Y 0.2 O 3−δ pellet (1.3mm of thickness, 19.2mm of diameter) was used as the electrolyte. PtIr/C and Pt/C electrode was used as ammonia oxidation reaction (AOR) anode and oxygen reduction reaction (ORR) cathode respectively in direct ammonia fuel cell measurements. The loading of PtIr was about 1.2 mg cm − 2 and the loading of Pt was about 1.3 mg cm − 2 . The effective area of the fuel cell was 1 × 1 cm 2 . An ammonia solution, i.e., 35 wt% NH 3 H 2 O or 35 wt% NH 3 H 2 O + 3 M KOH, was pumped at flow rate of 1 mL min − 1 into anode channels. Compressed air was passing through 100°C humidifier at 20 mL min − 1 then into the cathodic chamber. The pressure of both ammonia solution at the anode and compressed air at the cathode is at ambient pressure. The fuel cell performance was measured by a Solartron 1287A Electrochemical Interface coupled with a Solartron 1260 controlled by electrochemical software CorrWare/CorrView and Z-Plot/Z-view. The a.c. impedance was measured in the frequency range between 1 MHz and 0.01 Hz at the amplitude of the a.c. signal 10 mV. The polarization curves were obtained at different temperatures of fuel cell and a scan rate of 5 mV s − 1 was used in the measurements. The commercial anion exchange membrane (Fumapem FAA-3-50, FuelCellStore) with 50 µm thickness was also employed in fuel cell measurements for a comparison. 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Supplementary Files SrZr0.8Y0.2O3ionicconductorNEV50supplementarydoubleblinded.docx This file contains Supplementary Figs. 1–19, Discussions 1–4, Tables 1-3 and References 1-13. Cite Share Download PDF Status: Published Journal Publication published 30 Jan, 2024 Read the published version in Nature Communications → Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-1885173","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":141734937,"identity":"dae79d1a-17a7-446d-a74c-d6342ef0da3b","order_by":0,"name":"Shanwen 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1","display":"","copyAsset":false,"role":"figure","size":197990,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eThe proposed schematic diagram for the formation of pathways for OH\u003c/strong\u003e\u003csup\u003e\u003cstrong\u003e-\u003c/strong\u003e\u003c/sup\u003e\u003cstrong\u003e/H\u003c/strong\u003e\u003csup\u003e\u003cstrong\u003e+\u003c/strong\u003e\u003c/sup\u003e\u003cstrong\u003e ions in SrZr\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e0.8\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eY\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e0.2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eO\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e3-d\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003e enabled by water/steam.\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-1885173/v1/bada6e758ffb865d1e4d15ba.png"},{"id":27393398,"identity":"6c0e0925-777f-4be0-85ee-debe45fff47d","added_by":"auto","created_at":"2022-10-05 19:48:52","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":403421,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eThe characterizations of doped zirconates.\u003c/strong\u003e \u003cstrong\u003ea\u003c/strong\u003e, XRD patterns of SrZr\u003csub\u003e1-x\u003c/sub\u003eY\u003csub\u003ex\u003c/sub\u003eO\u003csub\u003e3-d\u003c/sub\u003e (x = 0, 0.1, 0.2). \u003cstrong\u003eb-f\u003c/strong\u003e, SEM and TEM analysis of SrZr\u003csub\u003e0.8\u003c/sub\u003eY\u003csub\u003e0.2\u003c/sub\u003eO\u003csub\u003e3-d\u003c/sub\u003e powders.\u003cstrong\u003e \u003c/strong\u003e(\u003cstrong\u003eb\u003c/strong\u003e) SEM image, (\u003cstrong\u003ec\u003c/strong\u003e) ADF-STEM image, (\u003cstrong\u003ed\u003c/strong\u003e) high resolution ADF-STEM image taken from marked area in \u003cstrong\u003ec\u003c/strong\u003e (inset: corresponding FFT of the image), (\u003cstrong\u003ee\u003c/strong\u003e) Integrated EDX spectra from the STEM-EDX analysis in \u003cstrong\u003ef\u003c/strong\u003e, (\u003cstrong\u003ef\u003c/strong\u003e) BF-STEM image and the corresponding EDX maps of Sr, Zr, Y, O.\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-1885173/v1/3db12d84455fdd76079d0ac5.png"},{"id":27393401,"identity":"7f400247-6e8d-41e2-b34f-784ac6cf5521","added_by":"auto","created_at":"2022-10-05 19:48:52","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":292732,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eTEM and Raman characterizations of washed SrZr\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e0.8\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eY\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e0.2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eO\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e3-d\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003e. a-c\u003c/strong\u003e, TEM analysis of washed SrZr\u003csub\u003e0.8\u003c/sub\u003eY\u003csub\u003e0.2\u003c/sub\u003eO\u003csub\u003e3-d\u003c/sub\u003e powders.\u003cstrong\u003e \u003c/strong\u003e(\u003cstrong\u003ea\u003c/strong\u003e) BF-STEM image and the corresponding EDX maps of Sr, Zr, Y, O, (\u003cstrong\u003eb\u003c/strong\u003e) ADF-STEM image, (\u003cstrong\u003ec\u003c/strong\u003e) High resolution ADF-STEM image taken from marked area in \u003cstrong\u003eb\u003c/strong\u003e (inset: corresponding FFT of the image). \u003cstrong\u003ed\u003c/strong\u003e, Raman spectra of SrZr\u003csub\u003e0.8\u003c/sub\u003eY\u003csub\u003e0.2\u003c/sub\u003eO\u003csub\u003e3-d\u003c/sub\u003e samples with different hydration levels.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-1885173/v1/d1ff8f0192875bbb041c975e.png"},{"id":27393400,"identity":"0a569c34-d870-4eb4-a58a-39950d03f4b4","added_by":"auto","created_at":"2022-10-05 19:48:52","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":123145,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eThe ionic conductivity of doped zirconates under different conditions.\u003c/strong\u003e \u003cstrong\u003ea\u003c/strong\u003e, AZr\u003csub\u003e0.8\u003c/sub\u003eY\u003csub\u003e0.2\u003c/sub\u003eO\u003csub\u003e3-d\u003c/sub\u003e (A = Ca, Sr, Ba) in water. \u003cstrong\u003eb\u003c/strong\u003e, SrZr\u003csub\u003e1-x\u003c/sub\u003eY\u003csub\u003ex\u003c/sub\u003eO\u003csub\u003e3-d\u003c/sub\u003e (x = 0, 0.1, 0.2) in water. \u003cstrong\u003ec\u003c/strong\u003e, SrZr\u003csub\u003e0.8\u003c/sub\u003eY\u003csub\u003e0.2\u003c/sub\u003eO\u003csub\u003e3-d\u003c/sub\u003e in wet air at different temperatures. \u003cstrong\u003ed\u003c/strong\u003e, Stability of the conductivity of SrZr\u003csub\u003e0.8\u003c/sub\u003eY\u003csub\u003e0.2\u003c/sub\u003eO\u003csub\u003e3-d\u003c/sub\u003e in wet air at 70°C. \u003cstrong\u003ee\u003c/strong\u003e,\u003cstrong\u003ef\u003c/strong\u003e, Conductivity (\u003cstrong\u003ee\u003c/strong\u003e) and activation energy (\u003cstrong\u003ef\u003c/strong\u003e) of SrZr\u003csub\u003e0.8\u003c/sub\u003eY\u003csub\u003e0.2\u003c/sub\u003eO\u003csub\u003e3-d\u003c/sub\u003e in H\u003csub\u003e2\u003c/sub\u003eO and D\u003csub\u003e2\u003c/sub\u003eO.\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-1885173/v1/0d5d11dd7e19f07aad7574e6.png"},{"id":27393397,"identity":"a3d9d988-05a8-4abf-ba56-28e24c382f8c","added_by":"auto","created_at":"2022-10-05 19:48:52","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":91977,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eSolid state NMR spectra of dry and partially hydrated SrZr\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e0.8\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eY\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e0.2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eO\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e3-d\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003e .\u003c/strong\u003e \u003cstrong\u003ea\u003c/strong\u003e, The solid state \u003csup\u003e1\u003c/sup\u003eH NMR spectra of dry (red) and partially hydrated (blue) SrZr\u003csub\u003e0.8\u003c/sub\u003eY\u003csub\u003e0.2\u003c/sub\u003eO\u003csub\u003e3-d\u003c/sub\u003e. \u003cstrong\u003eb\u003c/strong\u003e, The solid state \u003csup\u003e1\u003c/sup\u003eH NMR (MAS 60 kHz) spectra of partially hydrated (top) and dry (bottom) SrZr\u003csub\u003e0.8\u003c/sub\u003eY\u003csub\u003e0.2\u003c/sub\u003eO\u003csub\u003e3-d \u003c/sub\u003eperformed whit the rotors kept at -5 \u003csup\u003eo\u003c/sup\u003eC (blue) and +30 \u003csup\u003eo\u003c/sup\u003eC (red). \u003cstrong\u003ec\u003c/strong\u003e,\u003cstrong\u003ed\u003c/strong\u003e, \u003csup\u003e1\u003c/sup\u003eH-\u003csup\u003e1\u003c/sup\u003eH NOESY correlation spectra (MAS 60 kHz) of dry (\u003cstrong\u003ec\u003c/strong\u003e) and partially hydrated (\u003cstrong\u003ed\u003c/strong\u003e) SrZr\u003csub\u003e0.8\u003c/sub\u003eY\u003csub\u003e0.2\u003c/sub\u003eO\u003csub\u003e3-d \u003c/sub\u003emixing time (\u003cstrong\u003ec\u003c/strong\u003e) 0.1 s and (\u003cstrong\u003ed\u003c/strong\u003e) 1 s. \u003cstrong\u003ee\u003c/strong\u003e, \u003csup\u003e89\u003c/sup\u003eY MAS at 8 kHz DP spectrum measured with a spin echo (red) and cross polarization (blue) from \u003csup\u003e1\u003c/sup\u003eH of partially hydrated SrZr\u003csub\u003e0.8\u003c/sub\u003eY\u003csub\u003e0.2\u003c/sub\u003eO\u003csub\u003e3-d\u003c/sub\u003e. \u003cstrong\u003ef\u003c/strong\u003e, \u003csup\u003e1\u003c/sup\u003eH-\u003csup\u003e89\u003c/sup\u003eY heteronuclear correlation experiment obtained with 6 ms cross polarization, MAS 8 kHz.\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-1885173/v1/965e90cc20390ab919fdbc35.png"},{"id":27393402,"identity":"658401bc-2174-4ca2-aac1-554fd6a615b3","added_by":"auto","created_at":"2022-10-05 19:48:52","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":174970,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eFuel cell measurements when SrZr\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e0.8\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eY\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e0.2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eO\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e3-d\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003e was used as electrolyte. a\u003c/strong\u003e, The OCV change against time of a H\u003csub\u003e2\u003c/sub\u003e/air fuel cell at 20°C. \u003cstrong\u003eb\u003c/strong\u003e, Working principle of low temperature SOFCs for an NH\u003csub\u003e3\u003c/sub\u003e/air fuel cell. \u003cstrong\u003ec\u003c/strong\u003e,\u003cstrong\u003ed\u003c/strong\u003e, The performance (\u003cstrong\u003ec\u003c/strong\u003e) and impedance (\u003cstrong\u003ed\u003c/strong\u003e) of an NH\u003csub\u003e3\u003c/sub\u003e/air fuel cell (35 wt% NH\u003csub\u003e3\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003eO solution + 3 M KOH as the fuel) at different temperatures, enlarged impedance spectra is displayed in insert.\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-1885173/v1/052571f58f38b466696643b4.png"},{"id":50415551,"identity":"11288295-ac36-4197-babd-fad3c904d7ac","added_by":"auto","created_at":"2024-01-31 08:11:59","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1742178,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-1885173/v1/e26bc3c4-c8ed-4a5e-8497-a3c7ea3c3114.pdf"},{"id":27393675,"identity":"07704778-2902-48dd-be67-a3169a3163db","added_by":"auto","created_at":"2022-10-05 19:53:52","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":9014371,"visible":true,"origin":"","legend":"\u003cp\u003eThis file contains Supplementary Figs. 1–19, Discussions 1–4, Tables 1-3 and References 1-13.\u003c/p\u003e","description":"","filename":"SrZr0.8Y0.2O3ionicconductorNEV50supplementarydoubleblinded.docx","url":"https://assets-eu.researchsquare.com/files/rs-1885173/v1/dbe3059a86fc2d88732109c1.docx"}],"financialInterests":"\u003cb\u003eYes\u003c/b\u003e there is potential Competing Interest.","formattedTitle":"\u003cp\u003eA fast ceramic mixed OH\u003csup\u003e-\u003c/sup\u003e/H\u003csup\u003e+\u003c/sup\u003e ionic conductor for low temperature fuel cells\u003c/p\u003e","fulltext":[{"header":"Full Text","content":"\u003cp\u003eFuel cells are important electrochemical devices to convert chemical energy in fuels into electricity at high efficiency. There are different types of fuel cells based on various ionic conducting electrolytes, with a wide operating temperature from near ambient temperature (\u0026pound;100 \u0026deg;C) (NAT) such as around 80\u0026deg;C for proton exchange membrane fuel cells (PEMFCs), to high temperature such as 500\u0026ndash;900\u0026deg;C for solid oxide fuel cells (SOFCs)\u003csup\u003e1\u003c/sup\u003e. SOFCs have been developed for stationary power generation while poor durability, due to materials sublimation and cross-diffusion at high operating temperature, is the major obstacle for the large-scale applications\u003csup\u003e2\u003c/sup\u003e. The typical electrolyte materials for SOFCs are doped ZrO\u003csub\u003e2\u003c/sub\u003e or CeO\u003csub\u003e2\u003c/sub\u003e with fluorite structure or doped BaCeO\u003csub\u003e3\u003c/sub\u003e/BaZrO\u003csub\u003e3\u003c/sub\u003e/LaGaO\u003csub\u003e3\u003c/sub\u003e with perovskite structure\u003csup\u003e1,3-7\u003c/sup\u003e. The representative high temperature proton conductors based on doped perovskite oxides BaCeO\u003csub\u003e3\u003c/sub\u003e/BaZrO\u003csub\u003e3\u003c/sub\u003e was discovered by Iwahara in 1980 and 1990\u0026rsquo;s respectively\u003csup\u003e3,7\u003c/sup\u003e, while the high temperature O\u003csup\u003e2-\u003c/sup\u003e ion conductor based on doped LaGaO\u003csub\u003e3\u003c/sub\u003e was discovered by Ishihara in 1994\u003csup\u003e4\u003c/sup\u003e. However, the ionic conductivity of these oxides is not high enough when the operating temperature is below 500\u0026deg;C\u003csup\u003e1\u003c/sup\u003e. To solve this problem, it is desired to reduce the operating temperature of SOFCs, ideally to NAT. The first task to achieve NAT operation of SOFCs is to identify good H\u003csup\u003e+\u003c/sup\u003e / O\u003csup\u003e2-\u003c/sup\u003e /OH\u003csup\u003e-\u003c/sup\u003e ionic conducting materials to be used as the electrolyte.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eIt has been reported that doped zirconates such as BaZr\u003csub\u003e0.8\u003c/sub\u003eY\u003csub\u003e0.2\u003c/sub\u003eO\u003csub\u003e3-\u003c/sub\u003e\u003csub\u003ed\u003c/sub\u003e are robust proton conductors with ionic conductivity above 10\u003csup\u003e-4\u003c/sup\u003e Scm\u003csup\u003e-1\u003c/sup\u003e at a temperature above 600 \u0026deg;C\u003csup\u003e7,8\u003c/sup\u003e. However, the proton conductivity of perovskite zirconates are normally measured in wet air or wet H\u003csub\u003e2\u003c/sub\u003e by passing the gases through room temperature water with moisture contents of 3 mol%\u003csup\u003e8\u003c/sup\u003e. On the other hand, the OH\u003csup\u003e-\u003c/sup\u003e ionic conductivity of alkaline membranes are measured in water\u0026nbsp;\u003csup\u003e9\u003c/sup\u003e. For oxide ionic conductors, it was reported that high open circuit voltage (OCV) of an electrochemical cell with 8 mol% Y\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e stabilized ZrO\u003csub\u003e2\u003c/sub\u003e or Ce\u003csub\u003e0.8\u003c/sub\u003eSm\u003csub\u003e0.2\u003c/sub\u003eO\u003csub\u003e2-\u003c/sub\u003e\u003csub\u003ed\u003c/sub\u003e pellets with grain size of 15 nm was used as the electrolyte while one side is merged in water\u003csup\u003e10\u003c/sup\u003e. To the best of our knowledge, report on measuring ionic conductivity of oxides in liquid water is scarce. In our research, it was found that Y-doped SrZrO\u003csub\u003e3\u003c/sub\u003e, SrZr\u003csub\u003e0.8\u003c/sub\u003eY\u003csub\u003e0.2\u003c/sub\u003eO\u003csub\u003e3-\u0026delta;\u003c/sub\u003e exhibits high ionic conductivity of approximately 0.01 S cm\u003csup\u003e-1\u003c/sup\u003e at 90\u0026deg;C when exposed in water or wet air, which opens a window on developing solid oxide ionic conductors for applications in NAT-SOFCs.\u0026nbsp;\u003c/p\u003e\n\u003ch3\u003eCreation Of Pathways For Ions In Perovskite Oxide Srzryo\u003c/h3\u003e\n\u003cp\u003eFor a good ionic conductor, it is desired to have pathways for the diffusion of ions. With the existence of pathways, the concentration of charge carriers must be sufficient in order to achieve high ionic conductivity. For doped zirconates, it is widely accepted that the oxygen vacancies and the associated proton defects during the reaction between oxygen vacancy and steam (or water) forms the pathways for the proton conduction\u003csup\u003e\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e,\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u003c/sup\u003e. The schematic diagram on how to form the pathways in a perovskite oxide is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. Perovskite oxide SrZrO\u003csub\u003e3\u003c/sub\u003e was chosen as the parent phase. When part of Zr at the B-site in SrZrO\u003csub\u003e3\u003c/sub\u003e is replaced by Y, for charge compensation, positively charged oxygen vacancies (\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({V}_{O}^{\\bullet \\bullet }\\)\u003c/span\u003e\u003c/span\u003e) are formed. For charge balance, the negatively charged \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({Y}_{Zr}^{{\\prime }}\\)\u003c/span\u003e\u003c/span\u003e defects are formed simultaneously. It can be described by Kr\u0026ouml;ger-Vink notations.\u003cdiv id=\"Equ1\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ1\" name=\"EquationSource\"\u003e\n$$2{Zr}_{Zr}^{\\times }+{O}_{O}^{\\times }+{Y}_{2}{O}_{3}\\to 2Zr{O}_{2}+2{Y}_{Zr}^{{\\prime }}+{V}_{O}^{\\bullet \\bullet }$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e1\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eWhen this Y doped SrZrO\u003csub\u003e3\u003c/sub\u003e, with a general formula of SrZr\u003csub\u003e1\u0026thinsp;\u0026minus;\u0026thinsp;x\u003c/sub\u003eY\u003csub\u003ex\u003c/sub\u003eO\u003csub\u003e3\u0026minus;δ\u003c/sub\u003e, meets water or steam, proton defects \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({OH}_{O}^{\\bullet }\\)\u003c/span\u003e\u003c/span\u003e will be formed.\u003cdiv id=\"Equ2\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ2\" name=\"EquationSource\"\u003e\n$${V}_{O}^{\\bullet \\bullet }+{O}_{O}^{\\times }+{H}_{2}O\\to 2{OH}_{O}^{\\bullet }$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e2\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eAt high temperatures, typically above 600\u0026deg;C, the mobility of formed proton defects increases leading to high protonic conductivity in doped BaCeO\u003csub\u003e3\u003c/sub\u003e/BaZrO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e3\u003c/sup\u003e. The ionic conductivity of Y-doped SrZrO\u003csub\u003e3\u003c/sub\u003e, SrZr\u003csub\u003e0.95\u003c/sub\u003eY\u003csub\u003e0.05\u003c/sub\u003eO\u003csub\u003e3\u0026minus;δ\u003c/sub\u003e is approximately 7.0 \u0026sdot; 10\u003csup\u003e\u0026minus;\u0026thinsp;4\u003c/sup\u003e S cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e at 600\u0026deg;C, which is not high enough for use as electrolyte for NAT-SOFCs\u003csup\u003e\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u003c/sup\u003e. In order to improve the ionic conductivity at low temperatures, it is necessary to increase the concentration of charge carriers, i.e., the proton defects. Therefore, we synthesized SrZr\u003csub\u003e1\u0026thinsp;\u0026minus;\u0026thinsp;x\u003c/sub\u003eY\u003csub\u003ex\u003c/sub\u003eO\u003csub\u003e3\u0026minus;δ\u003c/sub\u003e (x\u0026thinsp;=\u0026thinsp;0, 0.1, 0.2) samples (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea and Methods) and put the samples in liquid water to maximize the interaction between water and oxygen vacancies to maximize the concentration of proton defects. When the concentration of these proton defects is high enough, the neighbouring proton defects may couple or exchange with each other, in the form of H\u003csup\u003e+\u003c/sup\u003e or OH\u003csup\u003e\u0026minus;\u003c/sup\u003e ions, forming a continuous pathway, resulting in high OH\u003csup\u003e\u0026minus;\u003c/sup\u003e/H\u003csup\u003e+\u003c/sup\u003e ionic conductivity.\u003c/p\u003e\n\u003ch3\u003eMaterials Characterizations Of Srzryo\u003c/h3\u003e\n\u003cp\u003eBased on the analysis above, it is anticipated that, doped zirconates may exhibit high ionic conductivity in water or, in the presence of high partial pressure of steam, \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(p{H}_{2}O\\)\u003c/span\u003e\u003c/span\u003e. At 100\u0026deg;C, the bulk proton conductivity of BaZr\u003csub\u003e0.8\u003c/sub\u003eY\u003csub\u003e0.2\u003c/sub\u003eO\u003csub\u003e3\u0026minus;δ\u003c/sub\u003e is in the order of 10\u003csup\u003e\u0026minus;\u0026thinsp;5\u003c/sup\u003e S cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e in air, too low to be used as electrolyte for NAT-SOFCs\u003csup\u003e\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e\u003c/sup\u003e. In reported papers, at the same temperature, generally Y-doped BaZrO\u003csub\u003e3\u003c/sub\u003e exhibits higher ionic conductivity than those for Y-doped SrZrO\u003csub\u003e3\u003c/sub\u003e because doped BaZrO\u003csub\u003e3\u003c/sub\u003e has larger lattice volume thus more \u0026lsquo;free volume\u0026rsquo; for diffusion/jumping of ions in the lattice\u003csup\u003e\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e,\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e\u003c/sup\u003e. To identify the effect of A-site ions on the ionic conductivity of Y-doped zirconates, three compounds with AZr\u003csub\u003e0.8\u003c/sub\u003eY\u003csub\u003e0.2\u003c/sub\u003eO\u003csub\u003e3\u0026minus;δ\u003c/sub\u003e where A\u0026thinsp;=\u0026thinsp;Ca, Sr, Ba were synthesized. X-ray diffraction (XRD) experiments indicate both CaZr\u003csub\u003e0.8\u003c/sub\u003eY\u003csub\u003e0.2\u003c/sub\u003eO\u003csub\u003e3\u0026minus;δ\u003c/sub\u003e and BaZr\u003csub\u003e0.8\u003c/sub\u003eY\u003csub\u003e0.2\u003c/sub\u003eO\u003csub\u003e3\u0026minus;δ\u003c/sub\u003e are single phases while there is a small amount of secondary phase SrY\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e in SrZr\u003csub\u003e0.8\u003c/sub\u003eY\u003csub\u003e0.2\u003c/sub\u003eO\u003csub\u003e3\u0026minus;δ\u003c/sub\u003e (Supplementary Fig.\u0026nbsp;1 and Supplementary Table\u0026nbsp;1). The SrY\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e second phase was also observed in SrZr\u003csub\u003e0.8\u003c/sub\u003eY\u003csub\u003e0.2\u003c/sub\u003eO\u003csub\u003e3\u0026minus;δ\u003c/sub\u003e when synthesised by pulsed layer deposition method\u003csup\u003e\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u003c/sup\u003e and was commonly existed in Y doped perovskite oxides such as Sr(Ce\u003csub\u003e0.6\u003c/sub\u003eZr\u003csub\u003e0.4\u003c/sub\u003e)\u003csub\u003e0.8\u003c/sub\u003eY\u003csub\u003e0.2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e16\u003c/sup\u003e and Sr(Ti\u003csub\u003e0.9\u003c/sub\u003eY\u003csub\u003e0.1\u003c/sub\u003e)O\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e17\u003c/sup\u003e. The primary particle size of SrZr\u003csub\u003e0.8\u003c/sub\u003eY\u003csub\u003e0.2\u003c/sub\u003eO\u003csub\u003e3\u0026minus;δ\u003c/sub\u003e was about 200\u0026ndash;250 nm and an agglomeration of some particles was observed by both scanning electron microscopy (SEM) and annular dark \u0026ndash; field scanning transmission electron microscopy (ADF-STEM) (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb,c). In Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ed, the two labelled spacings were associated with the (200) and (004) lattice planes of the orthorhombic phase of SrZrO\u003csub\u003e3\u003c/sub\u003e (ICDD:04-014-8276), respectively. The EDX elemental maps clearly show that the amount of secondary phase is small and Sr, Zr, Y and O elements are distributed evenly in the grains (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ee,f). The spacing labelled in Supplementary Fig.\u0026nbsp;2c was associated with the (200) lattice plane of the orthorhombic phase of SrY\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e (ICDD:01-074-0264), confirming the Y-rich area of the SrZr\u003csub\u003e0.8\u003c/sub\u003eY\u003csub\u003e0.2\u003c/sub\u003eO\u003csub\u003e3\u0026minus;δ\u003c/sub\u003e sample was the SrY\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e phase (Supplementary Fig.\u0026nbsp;2).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e\n\u003ch3\u003eRemoval Of Second Phase Sryo From The Samples\u003c/h3\u003e\n\u003cp\u003eIt has been reported that the secondary phase of the sample, SrY\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e, may react with water at high temperature to form SrCO\u003csub\u003e3\u003c/sub\u003e, Sr(OH)\u003csub\u003e2\u003c/sub\u003e\u0026sdot;8H\u003csub\u003e2\u003c/sub\u003eO and gel phase Y(OH)\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e18\u003c/sup\u003e. Therefore, before the conductivity measurements, SrZr\u003csub\u003e1\u0026thinsp;\u0026minus;\u0026thinsp;x\u003c/sub\u003eY\u003csub\u003ex\u003c/sub\u003eO\u003csub\u003e3\u0026minus;δ\u003c/sub\u003e samples were heated in hot water at 90\u0026deg;C for 20 hours and washed for three times in order to get rid of second phase SrY\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e and the hydrated soluble product Sr(OH)\u003csub\u003e2\u003c/sub\u003e\u0026sdot;8H\u003csub\u003e2\u003c/sub\u003eO. From STEM and EDX analysis of pre-washed SrZr\u003csub\u003e0.8\u003c/sub\u003eY\u003csub\u003e0.2\u003c/sub\u003eO\u003csub\u003e3\u0026minus;δ\u003c/sub\u003e samples (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea-c and Supplementary Fig.\u0026nbsp;3), the measured spacing in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ec was associated with the (002) lattice plane of the orthorhombic phase of SrZrO\u003csub\u003e3\u003c/sub\u003e (ICDD:04-014-8276). This indicates the perovskite phase is stable after hot water treatment at 90\u0026deg;C while second phase SrY\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e has been successfully removed. In addition, STEM and EDX results indicate the presence of an amorphous material in the Y-rich area B (Supplementary Fig.\u0026nbsp;3b), which is likely to be Y(OH)\u003csub\u003e3\u003c/sub\u003e. This amorphous stays on the grain boundary or presents as isolated particles among perovskite particles (marked area in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea). The elemental analysis of SrZr\u003csub\u003e0.8\u003c/sub\u003eY\u003csub\u003e0.2\u003c/sub\u003eO\u003csub\u003e3\u0026minus;δ\u003c/sub\u003e samples before and after being washed in hot water also confirmed that the soluble hydrolysis products Sr(OH)\u003csub\u003e2\u003c/sub\u003e\u0026sdot;8H\u003csub\u003e2\u003c/sub\u003eO had been removed (Supplementary Table\u0026nbsp;2). The complete hydrolysis of SrY\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e at 90\u0026deg;C was also confirmed by XRD analyses (Supplementary Fig.\u0026nbsp;4). All samples for conductivity measurements were treated in water at 90\u0026deg;C for 20 hours (repeated three times) to get rid of second phase SrY\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e\n\u003ch3\u003eConductivity And Importance Of Hydration\u003c/h3\u003e\n\u003cp\u003eThe measurement of traditional protonic conducting perovskite oxides such as doped zirconates or cerates are normally measured in wet air or wet H\u003csub\u003e2\u003c/sub\u003e, passing the gas through room temperature water with steam partial pressure of 0.03 bar, i.e., 3 mol% steam in the humidified air or hydrogen. Their conductivity at NAT is very low\u003csup\u003e\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e\u003c/sup\u003e. According to our analysis above (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e and Eqs.\u0026nbsp;\u003cspan refid=\"Equ1\" class=\"InternalRef\"\u003e1\u003c/span\u003e \u0026amp;\u003cspan refid=\"Equ2\" class=\"InternalRef\"\u003e2\u003c/span\u003e), the water or steam concentration mentioned in reported papers may not be enough to form sufficient proton defects in order to form continuous pathways for OH\u003csup\u003e\u0026minus;\u003c/sup\u003e/H\u003csup\u003e+\u003c/sup\u003e ions. Therefore, we decided to directly measure the conductivity and ion transfer number of the prepared and pre-washed AZr\u003csub\u003e0.8\u003c/sub\u003eY\u003csub\u003e0.2\u003c/sub\u003eO\u003csub\u003e3\u0026minus;δ\u003c/sub\u003e (A\u0026thinsp;=\u0026thinsp;Ca, Sr, Ba) pellets in water (Supplementary Fig.\u0026nbsp;5), which is the method commonly used for conductivity measurement in alkaline membranes \u003csup\u003e\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u003c/sup\u003e. At room temperature, the conductivity of un-washed SrZr\u003csub\u003e0.8\u003c/sub\u003eY\u003csub\u003e0.2\u003c/sub\u003eO\u003csub\u003e3\u0026minus;δ\u003c/sub\u003e pellet in water kept increasing against time (Supplementary Fig.\u0026nbsp;6). It increased from 2.96 \u0026sdot; 10\u003csup\u003e\u0026minus;\u0026thinsp;4\u003c/sup\u003e S cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e to 2.28 \u0026sdot; 10\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e S cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e in 10 hours indicating hydration to form proton defects is extremely important (Eq.\u0026nbsp;\u003cspan refid=\"Equ2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). After ageing in water at room temperature, the ionic conductivity of SrZr\u003csub\u003e0.8\u003c/sub\u003eY\u003csub\u003e0.2\u003c/sub\u003eO\u003csub\u003e3\u0026minus;δ\u003c/sub\u003e in water, is already higher than the protonic conductivity of SrZr\u003csub\u003e0.95\u003c/sub\u003eY\u003csub\u003e0.05\u003c/sub\u003eO\u003csub\u003e3\u0026minus;δ\u003c/sub\u003e, 7.0 \u0026sdot; 10\u003csup\u003e\u0026minus;\u0026thinsp;4\u003c/sup\u003e S cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, at 600\u0026deg;C when measured in H\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e13\u003c/sup\u003e. The conductivity of SrY\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e is stable at room temperature indicating hydrolysis does not happen at this temperature. Its conductivity is 1.7 \u0026sdot; 10\u003csup\u003e\u0026minus;\u0026thinsp;4\u003c/sup\u003e S cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, is only 7.5% of that for fully hydrated SrZr\u003csub\u003e0.8\u003c/sub\u003eY\u003csub\u003e0.2\u003c/sub\u003eO\u003csub\u003e3\u0026minus;δ\u003c/sub\u003e, thus the high ionic conductivity of un-washed SrZr\u003csub\u003e0.8\u003c/sub\u003eY\u003csub\u003e0.2\u003c/sub\u003eO\u003csub\u003e3\u0026minus;δ\u003c/sub\u003e in water at room temperature is mainly due to the hydration of SrZr\u003csub\u003e0.8\u003c/sub\u003eY\u003csub\u003e0.2\u003c/sub\u003eO\u003csub\u003e3\u0026minus;δ\u003c/sub\u003e (Supplementary Fig.\u0026nbsp;6c). To rule out the possible contribution of residual Y\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e or Y(OH)\u003csub\u003e3\u003c/sub\u003e in the pre-washed SrZr\u003csub\u003e0.8\u003c/sub\u003eY\u003csub\u003e0.2\u003c/sub\u003eO\u003csub\u003e3\u0026minus;δ\u003c/sub\u003e sample, conductivities of pure Y\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e and Y(OH)\u003csub\u003e3\u003c/sub\u003e in water were measured indicating they have very low ionic conductivity (Supplementary Fig.\u0026nbsp;7) thus will have little contribution to the observed high ionic conductivity of SrZr\u003csub\u003e0.8\u003c/sub\u003eY\u003csub\u003e0.2\u003c/sub\u003eO\u003csub\u003e3\u0026minus;δ\u003c/sub\u003e at elevated temperatures.\u003c/p\u003e \u003cp\u003eThe interaction between oxygen vacancy and water was also confirmed by Raman spectra (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ed). The peaks in the 600\u0026ndash;900 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e region are slightly wider when the SrZr\u003csub\u003e0.8\u003c/sub\u003eY\u003csub\u003e0.2\u003c/sub\u003eO\u003csub\u003e3\u0026minus;δ\u003c/sub\u003e sample is wetter. When the hydration level of SrZr\u003csub\u003e0.8\u003c/sub\u003eY\u003csub\u003e0.2\u003c/sub\u003eO\u003csub\u003e3\u0026minus;δ\u003c/sub\u003e sample is higher, the Raman peak shifts towards higher values (734 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e), which is consistent with the Raman features of proton insertion in oxygen vacancies\u003csup\u003e\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eAmong the three AZr\u003csub\u003e0.8\u003c/sub\u003eY\u003csub\u003e0.2\u003c/sub\u003eO\u003csub\u003e3\u0026minus;δ\u003c/sub\u003e (A\u0026thinsp;=\u0026thinsp;Ca, Sr, Ba) oxides, it was found that sample SrZr\u003csub\u003e0.8\u003c/sub\u003eY\u003csub\u003e0.2\u003c/sub\u003eO\u003csub\u003e3\u0026minus;δ\u003c/sub\u003e exhibits the highest ionic conductivity (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea). The jumping or diffusion of ions in a lattice, not only related to the high concentration of proton defects, but also to the \u0026lsquo;free volume\u0026rsquo; and jumping distance between neighbouring available sites (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). In general, large lattice parameters or bond length means higher \u0026lsquo;free volume\u0026rsquo;, favouring the mobility of ions, while longer jumping distance for ions will reduce the mobility. These two effects are opposite on the ionic conductivity. Therefore, there must be an optimised lattice size, which exhibits the highest ionic conductivity. In the AZr\u003csub\u003e0.8\u003c/sub\u003eY\u003csub\u003e0.2\u003c/sub\u003eO\u003csub\u003e3\u0026minus;δ\u003c/sub\u003e (A\u0026thinsp;=\u0026thinsp;Ca, Sr, Ba) series, sample SrZr\u003csub\u003e0.8\u003c/sub\u003eY\u003csub\u003e0.2\u003c/sub\u003eO\u003csub\u003e3\u0026minus;δ\u003c/sub\u003e exhibits the highest ionic conductivity. This is consistent with the observed proton conductivity of AZr\u003csub\u003e0.95\u003c/sub\u003eIn\u003csub\u003e0.05\u003c/sub\u003eO\u003csub\u003e3\u0026minus;δ\u003c/sub\u003e (A\u0026thinsp;=\u0026thinsp;Ca, Sr, Ba) in H\u003csub\u003e2\u003c/sub\u003e at a temperature of 600\u0026ndash;1000\u0026deg;C \u003csup\u003e\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eIn order to work out the types of charge carries, low temperature concentration cell measurement was applied to work out the conduction ions (Supplementary Fig.\u0026nbsp;8 and Supplementary Discussion 1)\u003csup\u003e\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e\u003c/sup\u003e. It was found that, in water, SrZr\u003csub\u003e0.8\u003c/sub\u003eY\u003csub\u003e0.2\u003c/sub\u003eO\u003csub\u003e3\u0026minus;δ\u003c/sub\u003e is a mixed OH\u003csup\u003e\u0026minus;\u003c/sup\u003e/H\u003csup\u003e+\u003c/sup\u003e ion conductor while the ion transfer number for anion OH\u003csup\u003e\u0026minus;\u003c/sup\u003e ions is higher (Supplementary Table\u0026nbsp;3). Therefore, both H\u003csup\u003e+\u003c/sup\u003e and OH\u003csup\u003e\u0026minus;\u003c/sup\u003e ions are mobile in hydrated SrZr\u003csub\u003e0.8\u003c/sub\u003eY\u003csub\u003e0.2\u003c/sub\u003eO\u003csub\u003e3\u0026minus;δ\u003c/sub\u003e when it is exposed in liquid water. This is very different from the conventional doped zirconates which is known as mixed H\u003csup\u003e+\u003c/sup\u003e/O\u003csup\u003e2\u0026minus;\u003c/sup\u003e ionic conduction at temperature above 500\u0026deg;C\u003csup\u003e\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e\u003c/sup\u003e. In this study, it has been observed that, not only protons, but OH\u003csup\u003e\u0026minus;\u003c/sup\u003e ions may also jump or diffuse via the oxygen vacancies or proton defects after hydrated with liquid water. The OH\u003csup\u003e\u0026minus;\u003c/sup\u003e ionic conduction was also previously proposed in similar perovskite oxides SrCe\u003csub\u003e0.95\u003c/sub\u003eYb\u003csub\u003e0.05\u003c/sub\u003eO\u003csub\u003e3\u0026minus;δ\u003c/sub\u003e and BaCe\u003csub\u003e1\u0026thinsp;\u0026minus;\u0026thinsp;x\u003c/sub\u003eGd\u003csub\u003ex\u003c/sub\u003eO\u003csub\u003e3\u0026minus;δ\u003c/sub\u003e in the presence of water vapour at high temperature (\u0026gt;\u0026thinsp;500\u0026deg;C) while the observed ionic conduction was very low because pH\u003csub\u003e2\u003c/sub\u003eO is not high enough\u003csup\u003e\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e,\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eIn order to confirm the importance of oxygen vacancies, the ionic conductivity of SrZrO\u003csub\u003e3\u003c/sub\u003e and SrZr\u003csub\u003e0.9\u003c/sub\u003eY\u003csub\u003e0.1\u003c/sub\u003eO\u003csub\u003e3\u0026minus;δ\u003c/sub\u003e in water was also investigated. XRD results indicate that SrZrO\u003csub\u003e3\u003c/sub\u003e is a single phase, while both SrZr\u003csub\u003e0.9\u003c/sub\u003eY\u003csub\u003e0.1\u003c/sub\u003eO\u003csub\u003e3\u0026minus;δ\u003c/sub\u003e and SrZr\u003csub\u003e0.8\u003c/sub\u003eY\u003csub\u003e0.2\u003c/sub\u003eO\u003csub\u003e3\u0026minus;δ\u003c/sub\u003e contain a small amount of second phase SrY\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e (Supplementary Figs.\u0026nbsp;1c,9). Among the three oxides, the order of conductivity and transfer number is SrZr\u003csub\u003e0.8\u003c/sub\u003eY\u003csub\u003e0.2\u003c/sub\u003eO\u003csub\u003e3\u0026minus;δ\u003c/sub\u003e \u0026gt; SrZr\u003csub\u003e0.9\u003c/sub\u003eY\u003csub\u003e0.1\u003c/sub\u003eO\u003csub\u003e3\u0026minus;δ\u003c/sub\u003e \u0026gt; SrZrO\u003csub\u003e3\u003c/sub\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eb). This is because SrZr\u003csub\u003e0.8\u003c/sub\u003eY\u003csub\u003e0.2\u003c/sub\u003eO\u003csub\u003e3\u0026minus;δ\u003c/sub\u003e has the highest doping level thus the highest concentration of oxygen vacancies (Eq.\u0026nbsp;\u003cspan refid=\"Equ1\" class=\"InternalRef\"\u003e1\u003c/span\u003e), thus more proton defects (Eq.\u0026nbsp;\u003cspan refid=\"Equ2\" class=\"InternalRef\"\u003e2\u003c/span\u003e) leading to the highest ionic conductivity. In water, the ionic conductivity of sample SrZr\u003csub\u003e0.8\u003c/sub\u003eY\u003csub\u003e0.2\u003c/sub\u003eO\u003csub\u003e3\u0026minus;δ\u003c/sub\u003e is 3.28 \u0026sdot; 10\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e S cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e at 25\u0026deg;C, 9.71 \u0026sdot; 10\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e S cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e at 90\u0026deg;C respectively with ion transfer number higher than 0.995. This is sufficient to be used as electrolyte for fuel cells and electrolysers at 90\u0026deg;C when thin film technology used for conventional SOFC is applied.\u003c/p\u003e \u003cp\u003eFor fuel cell applications, the cathode side may be exposed to wet O\u003csub\u003e2\u003c/sub\u003e or wet air. Therefore it is very important to measure the ionic conductivity in wet air. Different from the conventional humidified air with 3% H\u003csub\u003e2\u003c/sub\u003eO for conductivity measurement, we pass the air through 100\u0026deg;C boiling water in order to fully humidify the oxides while the real temperature of the oxide pellet was recorded by a thermocouple next to the sample. The conductivity of SrZr\u003csub\u003e0.8\u003c/sub\u003eY\u003csub\u003e0.2\u003c/sub\u003eO\u003csub\u003e3\u0026minus;δ\u003c/sub\u003e in wet air at 90\u0026deg;C is 1.1 \u0026sdot; 10\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e S cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e while it suddenly drops at above 100\u0026deg;C (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ec and Supplementary Fig.\u0026nbsp;10a-c). This means the high ionic conductivity of SrZr\u003csub\u003e0.8\u003c/sub\u003eY\u003csub\u003e0.2\u003c/sub\u003eO\u003csub\u003e3\u0026minus;δ\u003c/sub\u003e is related to the presence of liquid water. At 70\u0026deg;C, the conductivity of SrZr\u003csub\u003e0.8\u003c/sub\u003eY\u003csub\u003e0.2\u003c/sub\u003eO\u003csub\u003e3\u0026minus;δ\u003c/sub\u003e in wet air is stable at 0.01 S cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e for the measured 130 hours (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ed), which is reflected in the a.c. impedance spectra (Supplementary Fig.\u0026nbsp;10d,e). This indicates the ceramic ionic conductor SrZr\u003csub\u003e0.8\u003c/sub\u003eY\u003csub\u003e0.2\u003c/sub\u003eO\u003csub\u003e3\u0026minus;δ\u003c/sub\u003e has excellent stability in humidified air. After conductivity measurements, the chemical composition was still perovskite oxide, confirmed by XRD and element mapping (Supplementary Fig.\u0026nbsp;11). Pre-washed SrZr\u003csub\u003e0.8\u003c/sub\u003eY\u003csub\u003e0.2\u003c/sub\u003eO\u003csub\u003e3\u0026minus;δ\u003c/sub\u003e sample contains 2% residual SrCO\u003csub\u003e3\u003c/sub\u003e due to hydrolysis of SrY\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e and the SrCO\u003csub\u003e3\u003c/sub\u003e remains 2% in SrZr\u003csub\u003e0.8\u003c/sub\u003eY\u003csub\u003e0.2\u003c/sub\u003eO\u003csub\u003e3\u0026minus;δ\u003c/sub\u003e sample after conductivity measurement in air at 70\u0026deg;C for 130 hours indicating excellent chemical compatibility with CO\u003csub\u003e2\u003c/sub\u003e in air.\u003c/p\u003e\n\u003ch3\u003eKinetic Isotope Effect\u003c/h3\u003e\n\u003cp\u003eFor proton conducting materials, the conductivity in D\u003csub\u003e2\u003c/sub\u003eO will be reduced due to the decreased mobility of D\u003csup\u003e+\u003c/sup\u003e ions \u003csup\u003e\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e,\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e\u003c/sup\u003e. This is also called the kinetic isotope effect (KIE). The conductivity of SrZr\u003csub\u003e0.8\u003c/sub\u003eY\u003csub\u003e0.2\u003c/sub\u003eO\u003csub\u003e3\u0026minus;δ\u003c/sub\u003e in pure D\u003csub\u003e2\u003c/sub\u003eO was also measured to investigate its ability on proton conduction (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ee and Supplementary Discussion 2). At 90\u0026deg;C, the conductivity in H\u003csub\u003e2\u003c/sub\u003eO is 5.28 time of that in D\u003csub\u003e2\u003c/sub\u003eO, which is reflected in the a.c. impedance spectra in Supplementary Fig.\u0026nbsp;12. For pure proton conductors, the kinetic isotope effect (KIE) is usually no less than 1.4 for Grotthuss mechanism, while it is close to 1.2 for vehicle mechanism\u003csup\u003e\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e\u003c/sup\u003e. As the KIE is much larger than 1.4, it is presumed that SrZr\u003csub\u003e0.8\u003c/sub\u003eY\u003csub\u003e0.2\u003c/sub\u003eO\u003csub\u003e3\u0026minus;δ\u003c/sub\u003e is a not a pure protonic conductor..\u003c/p\u003e \u003cp\u003eThe activation energy of SrZr\u003csub\u003e0.8\u003c/sub\u003eY\u003csub\u003e0.2\u003c/sub\u003eO\u003csub\u003e3\u0026minus;δ\u003c/sub\u003e in H\u003csub\u003e2\u003c/sub\u003eO and D\u003csub\u003e2\u003c/sub\u003eO was 0.201\u0026plusmn;0.008 eV and 0.169\u0026plusmn;0.005eV respectively (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ef). It is slightly higher than the 0.17eV for Nafion membrane in H\u003csub\u003e2\u003c/sub\u003eO\u003csup\u003e2\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e\u003c/sup\u003e and within the range of activity energy for OH\u003csup\u003e\u0026minus;\u003c/sup\u003e conducting polymers (0.12\u0026ndash;0.26 eV)\u003csup\u003e\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e\u003c/sup\u003e. The activation energy of doped SrZrO\u003csub\u003e3\u003c/sub\u003e at low (\u0026lt;\u0026thinsp;100\u0026deg;C) in this study is much different from reported doped SrZrO\u003csub\u003e3\u0026minus;δ\u003c/sub\u003e at high temperature with the range of 0.4\u0026ndash;0.6 eV at 700\u0026ndash;1000\u0026deg;C when the dominant charge carriers are H\u003csup\u003e+\u003c/sup\u003e and O\u003csup\u003e2\u0026minus;\u003c/sup\u003e ions \u003csup\u003e\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u003c/sup\u003e, which indicates the charge carriers in liquid water may be different. This explains why the hydrated SrZr\u003csub\u003e0.8\u003c/sub\u003eY\u003csub\u003e0.2\u003c/sub\u003eO\u003csub\u003e3\u0026minus;δ\u003c/sub\u003e is a mixed OH\u003csup\u003e\u0026minus;\u003c/sup\u003e/H\u003csup\u003e+\u003c/sup\u003e conductor, while the transfer number for OH\u003csup\u003e\u0026minus;\u003c/sup\u003e ions is higher than that for cations, H\u003csup\u003e+\u003c/sup\u003e ions (Supplementary Table\u0026nbsp;3).\u003c/p\u003e \u003cp\u003eThe particle size remained unchanged after sample SrZr\u003csub\u003e0.8\u003c/sub\u003eY\u003csub\u003e0.2\u003c/sub\u003eO\u003csub\u003e3\u0026minus;δ\u003c/sub\u003e had been measured in water, D\u003csub\u003e2\u003c/sub\u003eO or wet air (Supplementary Fig.\u0026nbsp;13), further confirmed the chemical stability of the sample.\u003c/p\u003e\n\u003ch3\u003eSolid State Nmr Measurements\u003c/h3\u003e\n\u003cp\u003eIn order to further investigate the conduction mechanism of SrZr\u003csub\u003e0.8\u003c/sub\u003eY\u003csub\u003e0.2\u003c/sub\u003eO\u003csub\u003e3\u0026minus;δ\u003c/sub\u003e in water, solid state nuclear magnetic resonance (NMR) has been employed to study the dry and partially hydrated SrZr\u003csub\u003e0.8\u003c/sub\u003eY\u003csub\u003e0.2\u003c/sub\u003eO\u003csub\u003e3\u0026minus;δ\u003c/sub\u003e. Figure\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ea shows the solid state \u003csup\u003e1\u003c/sup\u003eH NMR spectra of dry (red) and partially hydrated (blue) SrZr\u003csub\u003e0.8\u003c/sub\u003eY\u003csub\u003e0.2\u003c/sub\u003eO\u003csub\u003e3\u0026minus;δ\u003c/sub\u003e. The \u003csup\u003e1\u003c/sup\u003eH spectrum of dry SrZr\u003csub\u003e0.8\u003c/sub\u003eY\u003csub\u003e0.2\u003c/sub\u003eO\u003csub\u003e3\u0026minus;δ\u003c/sub\u003e shows three resolved signals at 4.4, 3.5 and 0.7 ppm that can be assigned to H\u003csub\u003e2\u003c/sub\u003eO, OH\u003csup\u003e\u0026minus;\u003c/sup\u003e groups bound on defects or surface and, H\u003csup\u003e+\u003c/sup\u003e bound to oxygen of the Sr-O-Y or Sr-O-Zr environments, respectively. Akin assignments of proton signals on similar samples have been reported\u003csup\u003e26\u0026thinsp;\u0026minus;\u0026thinsp;28\u003c/sup\u003e. As the sample gets partially hydrated the \u003csup\u003e1\u003c/sup\u003eH signal increases dramatically and shows two broad peaks at 4.6 and 2.3 ppm which can be assigned to water at 4.6 ppm and to signals from OH\u003csup\u003e\u0026minus;\u003c/sup\u003e and H\u003csup\u003e+\u003c/sup\u003e moieties and their exchange at 2.3 ppm. The deconvolution of the partially hydrated sample is shown on Supplementary Fig.\u0026nbsp;14. The fast MAS experiments were performed with a 1.3 mm probe that has limited variable temperature capabilities. Figure\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eb shows the solid state \u003csup\u003e1\u003c/sup\u003eH NMR (MAS 60 kHz) spectra of partially hydrated (top) and dry (bottom) SrZr\u003csub\u003e0.8\u003c/sub\u003eY\u003csub\u003e0.2\u003c/sub\u003eO\u003csub\u003e3\u0026minus;δ\u003c/sub\u003e measured with the sample at -5\u003csup\u003eo\u003c/sup\u003eC (blue) and +\u0026thinsp;30\u003csup\u003eo\u003c/sup\u003eC (red). On both samples the water peak shifts slightly with the temperature (approximately 0.1 ppm / 10\u003csup\u003eo\u003c/sup\u003eC)\u003csup\u003e29\u003c/sup\u003e. At both temperatures, the dry and the wet samples, the signals assigned to OH\u003csup\u003e\u0026minus;\u003c/sup\u003e and to H\u003csup\u003e+\u003c/sup\u003e are getting broader as the temperature increases which suggests the presence of exchange between the two moieties. \u003csup\u003e1\u003c/sup\u003eH nuclear overhauser effect spectroscopy (NOESY) spectra of the dry and hydrated samples are shown on Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ec,d and prove proximity between different \u003csup\u003e1\u003c/sup\u003eH moieties.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eWe have also performed \u003csup\u003e89\u003c/sup\u003eY MAS NMR experiments on the partially hydrated sample as shown on Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ee. The \u003csup\u003e89\u003c/sup\u003eY direct polarization (DP) signal measured with a spin echo experiment shows two broad signals at 370 and 160 ppm indicating Y sites are coordinated by 6, 7 and 8 oxygen atoms\u003csup\u003e\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e,\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e\u003c/sup\u003e. The \u003csup\u003e1\u003c/sup\u003eH-\u003csup\u003e89\u003c/sup\u003eY cross polarization (CP) spectrum shows two \u003csup\u003e89\u003c/sup\u003eY signals at 219 and 130 ppm (mainly 7 and 8 coordinated sites) in proximity to \u003csup\u003e1\u003c/sup\u003eH nuclei. The \u003csup\u003e1\u003c/sup\u003eH-\u003csup\u003e89\u003c/sup\u003eY heteronuclear correlation experiment, performed on the partially hydrated sample is displayed in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ef. It shows that the \u003csup\u003e89\u003c/sup\u003eY signals correlates with the \u003csup\u003e1\u003c/sup\u003eH signal at 2.3 ppm which we assign to the OH\u003csup\u003e\u0026minus;\u003c/sup\u003e and H\u003csup\u003e+\u003c/sup\u003e exchange signal. This indicates the mobile OH\u003csup\u003e\u0026minus;\u003c/sup\u003e and H\u003csup\u003e+\u003c/sup\u003e ions are associated with Y\u003csup\u003e3+\u003c/sup\u003e sites since Y\u003csup\u003e3+\u003c/sup\u003e doping introduces oxygen vacancies in the SrZrO\u003csub\u003e3\u003c/sub\u003e lattice, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e and Eq.\u0026nbsp;\u003cspan refid=\"Equ1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. This is also consistent with the Raman results (Supplementary Fig.\u0026nbsp;15 and Supplementary Discussion 3). In water, the real composition of hy\u003cspan type=\"Underline\" class=\"Underline\" name=\"Emphasis\"\u003edrated SrZr\u003c/span\u003e\u003csub\u003e\u003cspan type=\"Underline\" class=\"Underline\" name=\"Emphasis\"\u003e1\u0026thinsp;\u0026minus;\u0026thinsp;x\u003c/span\u003e\u003c/sub\u003e\u003cspan type=\"Underline\" class=\"Underline\" name=\"Emphasis\"\u003eY\u003c/span\u003e\u003csub\u003e\u003cspan type=\"Underline\" class=\"Underline\" name=\"Emphasis\"\u003ex\u003c/span\u003e\u003c/sub\u003eO\u003csub\u003e3\u0026minus;δ\u003c/sub\u003e is hydrated or unhydrated oxyhydroxide (z\u0026thinsp;=\u0026thinsp;0), with a general formula, SrZr\u003csub\u003e1\u0026thinsp;\u0026minus;\u0026thinsp;x\u003c/sub\u003eY\u003csub\u003ex\u003c/sub\u003eO\u003csub\u003e3\u0026minus;y\u003c/sub\u003e(OH)\u003csub\u003e2y\u003c/sub\u003e\u0026sdot;zH\u003csub\u003e2\u003c/sub\u003eO. The OH\u003csup\u003e\u0026minus;\u003c/sup\u003e ions are presented in the form of protonic defects, \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({OH}_{O}^{\\bullet }\\)\u003c/span\u003e\u003c/span\u003e, which are associated with oxygen vacancies. The exchange and coupling of OH\u003csup\u003e\u0026minus;\u003c/sup\u003e and H\u003csup\u003e+\u003c/sup\u003e ions in hydrated SrZr\u003csub\u003e0.8\u003c/sub\u003eY\u003csub\u003e0.2\u003c/sub\u003eO\u003csub\u003e3\u0026minus;δ\u003c/sub\u003e has been confirmed by solid state NMR observation for a better understanding of the conduction mechanism in water.\u003c/p\u003e\n\u003ch3\u003eFuel Cell Demonstration\u003c/h3\u003e\n\u003cp\u003eTo further confirm the ionic conduction of SrZr\u003csub\u003e0.8\u003c/sub\u003eY\u003csub\u003e0.2\u003c/sub\u003eO\u003csub\u003e3\u0026minus;δ\u003c/sub\u003e, a H\u003csub\u003e2\u003c/sub\u003e/air fuel cell and an NH\u003csub\u003e3\u003c/sub\u003e/air fuel cell using SrZr\u003csub\u003e0.8\u003c/sub\u003eY\u003csub\u003e0.2\u003c/sub\u003eO\u003csub\u003e3\u0026minus;δ\u003c/sub\u003e pellet as the electrolyte were constructed (Supplementary Fig.\u0026nbsp;16). Figure\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ea shows the OCV of the H\u003csub\u003e2\u003c/sub\u003e/air fuel cell at a temperature of 20\u0026deg;C. The OCV gradually increased against time in the first three hours due to hydration then reached a stable value of 1.07 V. This is fairly close to the theoretical value of a H\u003csub\u003e2\u003c/sub\u003e/O\u003csub\u003e2\u003c/sub\u003e fuel cell (1.23 V at 25\u0026deg;C) considering humidified air instead of pure O\u003csub\u003e2\u003c/sub\u003e is used at the cathode. From this OCV result, it can be deduced that SrZr\u003csub\u003e0.8\u003c/sub\u003eY\u003csub\u003e0.2\u003c/sub\u003eO\u003csub\u003e3\u0026minus;δ\u003c/sub\u003e is almost a nearly pure ionic conductor at 20\u0026deg;C in wet atmosphere. At 20\u0026deg;C, a maximum current density of 1.25 mA cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e with maximum power density of 0.34 mW cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e was achieved respectively (Supplementary Fig.\u0026nbsp;17). This key experiment indicates it is possible to develop NAT-SOFCs for different applications. The main purpose for this experiment is to confirm the OH\u003csup\u003e\u0026minus;\u003c/sup\u003e/H\u003csup\u003e+\u003c/sup\u003e ionic conduction of SrZr\u003csub\u003e0.8\u003c/sub\u003eY\u003csub\u003e0.2\u003c/sub\u003eO\u003csub\u003e3\u0026minus;δ\u003c/sub\u003e electrolyte thus the performance was not optimised.\u003c/p\u003e \u003cp\u003eAmmonia was also used as the fuel for this type of NAT- SOFC (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eb). When using 35 wt% ammonia solution as a fuel, the current density of the fuel cell using SrZr\u003csub\u003e0.8\u003c/sub\u003eY\u003csub\u003e0.2\u003c/sub\u003eO\u003csub\u003e3\u0026minus;δ\u003c/sub\u003e electrolyte was similar to the fuel cell using commercial anion exchange membrane (AEM) (Supplementary Fig.\u0026nbsp;18). Considering the thickness difference between SrZr\u003csub\u003e0.8\u003c/sub\u003eY\u003csub\u003e0.2\u003c/sub\u003eO\u003csub\u003e3\u0026minus;δ\u003c/sub\u003e pellet (1300 \u0026micro;m) and AEM (50 \u0026micro;m), the conductivity of SrZr\u003csub\u003e0.8\u003c/sub\u003eY\u003csub\u003e0.2\u003c/sub\u003eO\u003csub\u003e3\u0026minus;δ\u003c/sub\u003e pellet, estimated from the series resistance of the a.c. impedance spectra of the fuel cells, is higher than the commercial AEM (Supplementary Fig.\u0026nbsp;19). The observed low ionic conductivity of commercial AEM is due to its poor chemical compatibility with CO\u003csub\u003e2\u003c/sub\u003e in air. It has been reported that adding KOH in ammonia solution can significantly improve the fuel cell performance when alkaline membrane was used as the electrolyte\u003csup\u003e\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e,\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e\u003c/sup\u003e. 35 wt% ammonia solution with added 3M KOH was used as the fuel for a direct ammonia fuel cell based on SrZr\u003csub\u003e0.8\u003c/sub\u003eY\u003csub\u003e0.2\u003c/sub\u003eO\u003csub\u003e3\u0026minus;δ\u003c/sub\u003e electrolyte. The relevant I-V curves and a.c. impedance spectra of the direct ammonia fuel cell are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ec,d. At 90\u0026deg;C, a maximum power density of 30 mW cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e was achieved. Compared to reported work in DAFCs, the power density is relatively low due to the thick electrolyte (1.3mm) and not optimised solid to solid electrolyte/electrode interface while wet air instead of wet O\u003csub\u003e2\u003c/sub\u003e was used at the cathode. In this study, the good ionic conduction of SrZr\u003csub\u003e0.8\u003c/sub\u003eY\u003csub\u003e0.2\u003c/sub\u003eO\u003csub\u003e3\u0026minus;δ\u003c/sub\u003e near ambient temperature has been demonstrated by both hydrogen and ammonia fuel cells.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e"},{"header":"Conclusions","content":"\u003cp\u003eIn summary, the mixed OH\u003csup\u003e\u0026minus;\u003c/sup\u003e/H\u003csup\u003e+\u003c/sup\u003e conduction of perovskite oxides such as SrZr\u003csub\u003e0.8\u003c/sub\u003eY\u003csub\u003e0.2\u003c/sub\u003eO\u003csub\u003e3\u0026minus;δ\u003c/sub\u003e with ionic conductivity around 0.01 S cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e at 90\u0026deg;C in water and humidified air was discovered. XRD and ADF-STEM confirm the formation and stability of perovskite phase. Solid state NMR study reveals that the transfer of OH\u003csup\u003e\u0026minus;\u003c/sup\u003e and H\u003csup\u003e+\u003c/sup\u003eions is coupled with dopant Y\u003csup\u003e3+\u003c/sup\u003e ions at the B-sites indicating oxygen vacancies play important role for the ionic conduction, similar to their high H\u003csup\u003e+\u003c/sup\u003e/O\u003csup\u003e2\u0026minus;\u003c/sup\u003e conductivity at high temperature (typically \u0026ge; 500\u0026deg;C). The discovery of low temperature mixed OH\u003csup\u003e\u0026minus;\u003c/sup\u003e/H\u003csup\u003e+\u003c/sup\u003e ionic conduction in oxide materials opens a window on discovering new low temperature OH\u003csup\u003e\u0026minus;\u003c/sup\u003e/H\u003csup\u003e+\u003c/sup\u003e ionic conducting materials in oxides or other ceramic materials. Similar phenomenon was also observed in doped cerates while the investigation is on-going.\u003c/p\u003e"},{"header":"Methods","content":"\u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003eSynthesis of SrZr\u003csub\u003e1\u0026thinsp;\u0026minus;\u0026thinsp;x\u003c/sub\u003eY\u003csub\u003ex\u003c/sub\u003eO\u003csub\u003e3\u0026minus;δ\u003c/sub\u003e (x\u0026thinsp;=\u0026thinsp;0, 0.1, 0.2)\u003c/h2\u003e \u003cp\u003eThe perovskite oxides SrZr\u003csub\u003e0.8\u003c/sub\u003eY\u003csub\u003e0.2\u003c/sub\u003eO\u003csub\u003e3\u0026minus;δ\u003c/sub\u003e were synthesized by a combustion method. 10.80 g of Sr(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e (98%, Alfa Aesar), 3.83 g of Y(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e3\u003c/sub\u003e∙6H\u003csub\u003e2\u003c/sub\u003eO (99.9%, Alfa Aesar), 13.15 g of ZrOCl\u003csub\u003e2\u003c/sub\u003e∙8H\u003csub\u003e2\u003c/sub\u003eO (98%, Alfa Aesar) and 5 mL of nitric acid (70%, Sigma Aldrich) were directly dissolved in deionized water to prepare a mixed solution. Then 38.81 g of citric acid (99+%, Alfa Aesar) was added into the solution and magnetically stirred at 90\u0026deg;C for 12 hours on a hot plate to form a gel. Then the gel was dried at a constant temperature of 400\u0026deg;C for 1 hour to be ignited for combustion. After the organic components in the mixture burned off, the powder was ground in an agate mortar and calcined in air at 400\u0026deg;C for 3 hours, then 1000\u0026deg;C for 2 hours. After this, the as-prepared powder was reground and pressed into pellets with a diameter of 13 mm and 20 mm respectively under a pressure of 6 tons, and then sintered in air at 1300\u0026deg;C for 24 hours with a heating/cooling rate of 5\u0026deg;C/min to form SrZr\u003csub\u003e0.8\u003c/sub\u003eY\u003csub\u003e0.2\u003c/sub\u003eO\u003csub\u003e3\u0026minus;δ\u003c/sub\u003e phase\u003csup\u003e\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eThe perovskite oxides SrZrO\u003csub\u003e3\u003c/sub\u003e and SrZr\u003csub\u003e0.9\u003c/sub\u003eY\u003csub\u003e0.1\u003c/sub\u003eO\u003csub\u003e3\u0026minus;δ\u003c/sub\u003e were synthesized with the same combustion method. The stoichiometric molar ratio of Sr(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e, Y(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e3\u003c/sub\u003e∙6H\u003csub\u003e2\u003c/sub\u003eO and ZrOCl\u003csub\u003e2\u003c/sub\u003e∙8H\u003csub\u003e2\u003c/sub\u003eO with a small amount of nitric acid were used in precursor solution. The molar ratio of citric acid to total metal ions was 2:1\u003csup\u003e35\u003c/sup\u003e. The target perovskite phase was obtained after pelletized and fired at 1300\u0026deg;C for 24 hours, the same as for preparation of SrZr\u003csub\u003e0.8\u003c/sub\u003eY\u003csub\u003e0.2\u003c/sub\u003eO\u003csub\u003e3\u0026minus;δ\u003c/sub\u003e.\u003c/p\u003e \u003cp\u003eThe as-prepared pellets with diameter of about 13 mm were used for conductivity measurements while those with diameter of about 20 mm were used for concentration cell and fuel cell measurements.\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eSynthesis Of Azryo (A = ca, Ba)\u003c/h3\u003e\n\u003cp\u003eThe perovskite oxides CaZr\u003csub\u003e0.8\u003c/sub\u003eY\u003csub\u003e0.2\u003c/sub\u003eO\u003csub\u003e3\u0026minus;δ\u003c/sub\u003e and BaZr\u003csub\u003e0.8\u003c/sub\u003eY\u003csub\u003e0.2\u003c/sub\u003eO\u003csub\u003e3\u0026minus;δ\u003c/sub\u003e were synthesized by the same combustion process. 11.93 g of Ca(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e∙4H\u003csub\u003e2\u003c/sub\u003eO (99%, Sigma Aldrich) or 13.20 g of Ba(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e (99%, Sigma Aldrich) was used as precursors respectively to synthesize AZr\u003csub\u003e0.8\u003c/sub\u003eY\u003csub\u003e0.2\u003c/sub\u003eO\u003csub\u003e3\u0026minus;δ\u003c/sub\u003e (A\u0026thinsp;=\u0026thinsp;Ca, Ba). The usage of other precursors and igniting conditions were the same as for SrZr\u003csub\u003e0.8\u003c/sub\u003eY\u003csub\u003e0.2\u003c/sub\u003eO\u003csub\u003e3\u0026minus;δ\u003c/sub\u003e. The CaZr\u003csub\u003e0.8\u003c/sub\u003eY\u003csub\u003e0.2\u003c/sub\u003eO\u003csub\u003e3\u0026minus;δ\u003c/sub\u003e phase was formed after fired in air at 1300\u0026deg;C for 4 hours. The BaZr\u003csub\u003e0.8\u003c/sub\u003eY\u003csub\u003e0.2\u003c/sub\u003eO\u003csub\u003e3\u0026minus;δ\u003c/sub\u003e phase was formed after fired in air at 1500\u0026deg;C for 4 hours.\u003c/p\u003e\n\u003ch3\u003eSynthesis Of Sryo And Y(Oh)\u003c/h3\u003e\n\u003cp\u003eIn order to identify the effect of the secondary phase SrY\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e in SrZr\u003csub\u003e0.8\u003c/sub\u003eY\u003csub\u003e0.2\u003c/sub\u003eO\u003csub\u003e3\u0026minus;δ\u003c/sub\u003e on the ionic conductivity, the single phase SrY\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e was synthesised by the same combustion method. 6.48 g of Sr(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e (98%, Alfa Aesar), 23.00 g of Y(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e3\u003c/sub\u003e∙6H\u003csub\u003e2\u003c/sub\u003eO (99.9%, Alfa Aesar) and 34.93 g of citric acid (99+%, Alfa Aesar) were directly dissolved in deionized water and the mixed solution was magnetically stirred at 80\u0026deg;C for 12 hours on a hot plate to form a gel. The igniting conditions were the same as for SrZr\u003csub\u003e0.8\u003c/sub\u003eY\u003csub\u003e0.2\u003c/sub\u003eO\u003csub\u003e3\u0026minus;δ\u003c/sub\u003e. The target SrY\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e sample was obtained after pelletized and fired in air at 1300\u0026deg;C for 24 hours.\u003c/p\u003e \u003cp\u003eIn order to rule out the contribution of the hydrolysis products of SrY\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e on the conductivity measurement, Y(OH)\u003csub\u003e3\u003c/sub\u003e sample was chemical deposited through the reaction between 0.5 mol L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e Y(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e3\u003c/sub\u003e∙6H\u003csub\u003e2\u003c/sub\u003eO (99.9%, Alfa Aesar) and 1.5 mol L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e of NaOH (98%, Alfa Aesar). The synthesized powder was thoroughly washed and dried at 60\u0026deg;C for 8 hours, and then pelletized for conductivity measurement. The commercial Y\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e (99.9%, Alfa Aesar) powder was also pelletized and fired at 1300\u0026deg;C for 4 hours to be measured its conductivity in water. (Supplementary Fig.\u0026nbsp;7 and Supplementary Discussion 4)\u003c/p\u003e\n\u003ch3\u003eStructural Characterizations\u003c/h3\u003e\n\u003cp\u003eThe X-ray diffraction (XRD) was carried out on a third generation Malvern Panalytical Empyrean equipped with multicore (iCore/dCore) optics and a Pixcel3D detector operating in 1D scanning mode with a Cu Kα radiation (1.5419 \u0026Aring;) to identify the crystalline phases present in the samples. The diffraction scans were collected over a 2θ range from 5\u0026deg; to 100\u0026deg; at a step size of 0.013\u0026deg; with a counting time of 110 s per step and were analysed using the Malvern Panalytical Highscore Plus 4.9 software and the latest ICDD PDF-4\u0026thinsp;+\u0026thinsp;database. Rietveld refinement of the representative perovskite oxides was carried out by GSAS and EXPGUI.\u003c/p\u003e \u003cp\u003eScanning electron microscopy (SEM) observation of the microstructure was carried out on a Zeiss SUPRA 55-VP scanning microscope. Energy dispersive X-ray spectroscopy (EDX) was used to analyse the cross section of pellets and determine the element composition of the samples through elemental mapping analyses.\u003c/p\u003e \u003cp\u003eAnnular dark field (ADF) and bright field (BF) scanning transmission electron microscopy (STEM) imaging and energy dispersive X-ray spectroscopy (EDX) elemental mapping were carried out on a double aberration corrected JEOL ARM200F TEM, operated at 200 kV, equipped with a 100 mm\u003csup\u003e\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e Oxford Instruments windowless EDX detector. The SrZr\u003csub\u003e0.8\u003c/sub\u003eY\u003csub\u003e0.2\u003c/sub\u003eO\u003csub\u003e3\u0026minus;δ\u003c/sub\u003e powders for TEM measurement were ground from sintered pellets. Some pellets were washed in water at 90\u0026deg;C for three times to get rid of the second phase SrY\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e and hydrated products and then ground into powders, labelled as washed SrZr\u003csub\u003e0.8\u003c/sub\u003eY\u003csub\u003e0.2\u003c/sub\u003eO\u003csub\u003e3\u0026minus;δ\u003c/sub\u003e sample. It is noted that Cu, Cr and C signals are artefacts generated during the STEM-EDX acquisition.\u003c/p\u003e \u003cp\u003eRaman spectra at room temperature were recorded on a Renishaw inVia Reflex Raman Microscope equipped with DPSS laser at 532 nm (10% power nominally 2 mW) and Renishaw CCD detector. Objective of X50 LWD and an acquisition time of 10 seconds was used during testing. For these measurements, the pellets were cleaved, and the fracture surface was analysed. The sample washed in water at 90\u0026deg;C and dried in oven for overnight was labelled as partially hydrated sample, while the sample dried in air for a moment before Raman measurement was labelled as hydrated sample.\u003c/p\u003e\n\u003ch3\u003eSolid-state Nmr Spectra Measurements\u003c/h3\u003e\n\u003cp\u003eAll SrZr\u003csub\u003e0.8\u003c/sub\u003eY\u003csub\u003e0.2\u003c/sub\u003eO\u003csub\u003e3\u0026minus;δ\u003c/sub\u003e powder samples for solid state NMR measurements were heated in hot water at 90\u0026deg;C for 20 hours and washed to get rid of second phase SrY\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e and the hydrated products. This process was repeated three times for each sample. The as-treated powder was dried in a fume cupboard at room temperature overnight, labelled as partially hydrated sample. Some of the as-treated powder was dried in a vacuum oven at 120\u0026deg;C overnight to get rid of the hydrated water. This sample was labelled as dry SrZr\u003csub\u003e0.8\u003c/sub\u003eY\u003csub\u003e0.2\u003c/sub\u003eO\u003csub\u003e3\u0026minus;δ\u003c/sub\u003e sample.\u003c/p\u003e \u003cp\u003eNuclear Magnetic Resonance were performed on a Bruker Avance Neo spectrometer with a Larmor frequency of 850.2 MHz and 41.6 MHz for \u003csup\u003e1\u003c/sup\u003eH and \u003csup\u003e89\u003c/sup\u003eY, respectively using a 1.3 mm Bruker triple resonance HXY probe spinning a 60 kHz and a 4 mm Bruker double resonance HX low gamma probe spinning at 8 kHz. The \u003csup\u003e89\u003c/sup\u003eY spectra were referenced to solid Y(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e3\u003c/sub\u003e∙6H\u003csub\u003e2\u003c/sub\u003eO with the \u003csup\u003e89\u003c/sup\u003eY peak set to -53.2 ppm. The \u003csup\u003e1\u003c/sup\u003eH NMR spectra were referenced to \u003csup\u003e1\u003c/sup\u003eH peak of solid adamantane set to 1.8 ppm. \u003csup\u003e89\u003c/sup\u003eY MAS spectra were acquired with a spin echo pulse sequence with a 90 and 180 pulses set to 6 \u0026micro;s and 12 \u0026micro;s, respectively and with cross polarization experiment with 6 ms contact time. \u003csup\u003e1\u003c/sup\u003eH MAS (60 kHz) NMR spectra were measured using a background suppression pulse sequence consisting of a 180 pulse followed by two 90 pulses.\u003c/p\u003e\n\u003ch3\u003eMeasurements Of Ion Conductivity And Ion Transfer Number\u003c/h3\u003e\n\u003cp\u003eTo measure the conductivity of sintered oxide pellets with diameter around 13 mm, two side surfaces of a pellet (~\u0026thinsp;2 mm in thickness) are coated by Silver Conductive Ink (Alfa Aesar) to form Ag electrodes. The Ag painting layers were dried in an oven at 130\u0026deg;C for 150 minutes. A sandwich-structure cell with a layer of pellet between two layers of silver mesh was then immobilized in a home-made jig. Since the conduction of hydroxide ion requires water or steam as a medium, the ionic conductivity was measured either in a beaker fulfilled with deionized water (Supplementary Fig.\u0026nbsp;5) or in a sealed quartz tube in which the humidified compressed air was passing through. For the conductivity measurements in water, the temperature of water was detected and controlled by a hot plate connected with thermocouple. For the conductivity measurements in wet air, the compressed air was humidified by passing through boiling water at a flow rate of 100 mL min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and then flowed into the jig sealed in a vertical furnace to be heated from 20 to 600\u0026deg;C. The temperature of wet air around the pellet was read by a thermocouple linked to Solartron 1470E CellTest System.\u003c/p\u003e \u003cp\u003eBefore the conductivity measurements, all the pellets were heated in hot water at 90\u0026deg;C for 20 hours and washed to get rid of second phase SrY\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e and the hydrated products. This process was repeated three times for each sample.\u003c/p\u003e \u003cp\u003eElectronic conductivity of the pellet was measured by a pseudo four-terminal DC method on a Solartron 1470E CellTest System. To work out the resistance caused by electronic conduction, 1 V constant DC voltage was applied on the pellet. After the current had been saturated, the direct current electrical resistance (R\u003csub\u003eDC\u003c/sub\u003e) was calculated from applied voltage (V) and saturated current (I\u003csub\u003esat\u003c/sub\u003e)\u003csup\u003e\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e\u003c/sup\u003e. Then the electrical conductivity (σ\u003csub\u003ee\u003c/sub\u003e) was calculated on the basis of thickness, λ, and effective cross-sectional area of the electrolyte pellet, A, as follows:\u003csup\u003e\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e\u003c/sup\u003e\u003c/p\u003e \u003cp\u003eR\u003csub\u003eDC\u003c/sub\u003e=V/I\u003csub\u003esat\u003c/sub\u003e,\u003c/p\u003e \u003cp\u003eσ\u003csub\u003ee\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;λ /(R\u003csub\u003eDC\u003c/sub\u003e\u0026times;A).\u003c/p\u003e \u003cp\u003eElectrochemical impedance spectrum (EIS) was acquired using a Solartron 1455 frequency response analyser (FRA) with 10 mV amplitude and frequency range of 1 MHz to 0.01 Hz to measure total conductivities (σ\u003csub\u003et\u003c/sub\u003e). Based on the relation between electronic conductivity and total conductivity, the ionic conductivity σ\u003csub\u003ei\u003c/sub\u003e is calculated as:\u003c/p\u003e \u003cp\u003eσ\u003csub\u003ei\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;σ\u003csub\u003et\u003c/sub\u003e - σ\u003csub\u003ee\u003c/sub\u003e\u003c/p\u003e \u003cp\u003eThe electronic conduction transfer number (t\u003csub\u003ee\u003c/sub\u003e) is σ\u003csub\u003ee\u003c/sub\u003e/σ\u003csub\u003et\u003c/sub\u003e\u0026thinsp;\u0026times;\u0026thinsp;100%. Then the corresponding ion transfer number (t\u003csub\u003ei\u003c/sub\u003e) can be measured as follows:\u003c/p\u003e \u003cp\u003et\u003csub\u003ei\u003c/sub\u003e = (1-σ\u003csub\u003ee\u003c/sub\u003e/σ\u003csub\u003et\u003c/sub\u003e) \u0026times;100%\u003c/p\u003e\n\u003ch3\u003eIdentification Of The Charge Carrier In Ionic Conductors\u003c/h3\u003e\n\u003cp\u003eIn order to determine which ion was conducted by the solid ionic conductors, a concentration cell with Ag/Ag\u003csub\u003e2\u003c/sub\u003eO electrodes was made according to the method described in a previous report \u003csup\u003e\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e\u003c/sup\u003e. A perovskite oxide pellet was clamped between two chambers of the H-cell filled with NaOH solution (Supplementary Fig.\u0026nbsp;8). A Nafion\u0026trade; 212 membrane (FuelCellStore) and an anion exchange membrane (Fumapem FAA, FuelCellStore) purchased commercially were measured for comparison (details in Supplementary Discussion 1).\u003c/p\u003e\n\u003ch3\u003eKie Measurements\u003c/h3\u003e\n\u003cp\u003eThe SrZr\u003csub\u003e0.8\u003c/sub\u003eY\u003csub\u003e0.2\u003c/sub\u003eO\u003csub\u003e3\u0026minus;δ\u003c/sub\u003e electrolyte pellet was firstly treated in deionized water at 90℃ for 20 hours (repeated three times), and then dried in a vacuum oven at 120\u0026deg;C overnight to remove the adsorbed water as much as possible. The conductivity was then measured after the pre-treated pellet being stored in deuterium water (D\u003csub\u003e2\u003c/sub\u003eO) for overnight. The kinetic isotope effect (KIE) is the ratio of ion conductivity of pellets in H\u003csub\u003e2\u003c/sub\u003eO to the that in D\u003csub\u003e2\u003c/sub\u003eO \u003csup\u003e\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e\n\u003ch3\u003eElectrode Preparation For Fuel Cell Measurement\u003c/h3\u003e\n\u003cp\u003ePlain carbon fiber cloth (0.35 mm thickness, E-TEK) was used as the substrate for the catalysts. The carbon cloth electrode (1\u0026times;1 cm\u003csup\u003e\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e) was sonicated in diluted hydrochloric acid, deionized water, and isopropanol for 1 min respectively. PtIr/C catalysts (20 wt% of metals loading) were prepared by the borohydride reduction process \u003csup\u003e\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e\u003c/sup\u003e using K\u003csub\u003e2\u003c/sub\u003ePtCl\u003csub\u003e6\u003c/sub\u003e (Pt 39.6%, Thermo Scientific\u0026trade;), IrCl\u003csub\u003e3\u003c/sub\u003e∙3H\u003csub\u003e2\u003c/sub\u003eO (53\u0026ndash;56% Ir, Thermo Scientific\u0026trade;) and Vulcan XC72 carbon black as precursors. The atomic ratio of Pt:Ir is 50:50. The catalyst ink was made up of 80 mg PtIr/C powder, 500 \u0026micro;L isopropanol and 145 \u0026micro;L 5 wt% Nafion solution. The ink slurry was ultrasonicated for 1 h and then brushed onto the pre-treated carbon cloth. The electrode was dried in an oven at 80\u0026deg;C. The loading of PtIr was about 1.2 mg cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e. The Pt/C electrode (20 wt% Pt on carbon black, Alfa Aesar) was prepared in the same way and the loading of Pt was about 1.3 mg cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e.\u003c/p\u003e\n\u003ch3\u003eHydrogen Fuel Cell Fabrication And Measurements\u003c/h3\u003e\n\u003cp\u003eA SrZr\u003csub\u003e0.8\u003c/sub\u003eY\u003csub\u003e0.2\u003c/sub\u003eO\u003csub\u003e3\u0026minus;δ\u003c/sub\u003e pellet (1.8mm of thickness, 19.2mm of diameter) was employed as the electrolyte. The symmetric hydrogen fuel cell was assembled using Pt/C electrode as both the anode and cathode. The loading of Pt is about 1.3 mg cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e. The effective area of the fuel cell was 1 \u0026times; 1 cm\u003csup\u003e\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e. Hydrogen gas was passing through a humidifier to flow into the anode at 5 mL min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, whilst 20 mL min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e humidified compressed air was flowing into the cathode field of fuel cell system. The pressure of both hydrogen and compressed air is at ambient pressure. The polarization curves and power density curves were measured through a Solartron 1287A electrochemical interface controlled by electrochemical software Corr-Ware/CorrView. The EIS data of the fuel cell was collected by the Solartron 1260A Electrochemical Station at a frequency range of 1 MHz to 0.01 Hz and fixed potential of 10 mV bias.\u003c/p\u003e\n\u003ch3\u003eDirect Ammonia Fuel Cell Fabrication And Measurements\u003c/h3\u003e\n\u003cp\u003eA SrZr\u003csub\u003e0.8\u003c/sub\u003eY\u003csub\u003e0.2\u003c/sub\u003eO\u003csub\u003e3\u0026minus;δ\u003c/sub\u003e pellet (1.3mm of thickness, 19.2mm of diameter) was used as the electrolyte. PtIr/C and Pt/C electrode was used as ammonia oxidation reaction (AOR) anode and oxygen reduction reaction (ORR) cathode respectively in direct ammonia fuel cell measurements. The loading of PtIr was about 1.2 mg cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e and the loading of Pt was about 1.3 mg cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e. The effective area of the fuel cell was 1 \u0026times; 1 cm\u003csup\u003e\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e. An ammonia solution, i.e., 35 wt% NH\u003csub\u003e3\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003eO or 35 wt% NH\u003csub\u003e3\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003eO\u0026thinsp;+\u0026thinsp;3 M KOH, was pumped at flow rate of 1 mL min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e into anode channels. Compressed air was passing through 100\u0026deg;C humidifier at 20 mL min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e then into the cathodic chamber. The pressure of both ammonia solution at the anode and compressed air at the cathode is at ambient pressure. The fuel cell performance was measured by a Solartron 1287A Electrochemical Interface coupled with a Solartron 1260 controlled by electrochemical software CorrWare/CorrView and Z-Plot/Z-view. The a.c. impedance was measured in the frequency range between 1 MHz and 0.01 Hz at the amplitude of the a.c. signal 10 mV. The polarization curves were obtained at different temperatures of fuel cell and a scan rate of 5 mV s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e was used in the measurements. The commercial anion exchange membrane (Fumapem FAA-3-50, FuelCellStore) with 50 \u0026micro;m thickness was also employed in fuel cell measurements for a comparison.\u003c/p\u003e\n\u003ch3\u003eData Availability\u003c/h3\u003e\n\u003cp\u003eThe data that support the findings of this study are available from the corresponding author upon reasonable request.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eSteele, B. C. H. \u0026amp; Heinzel, A. Materials for fuel-cell technologies. 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Stable SrCo\u003csub\u003e0.7\u003c/sub\u003eFe\u003csub\u003e0.2\u003c/sub\u003eZr\u003csub\u003e0.1\u003c/sub\u003eO\u003csub\u003e3-δ\u003c/sub\u003e cathode material for proton conducting solid oxide fuel cell reactors. International Journal of Hydrogen Energy \u003cb\u003e43\u003c/b\u003e, 7511\u0026ndash;7514 (2018).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAssump\u0026ccedil;\u0026atilde;o, M. H. \u003cem\u003eet al.\u003c/em\u003e Direct ammonia fuel cell performance using PtIr/C as anode electrocatalysts. International Journal of Hydrogen Energy \u003cb\u003e39\u003c/b\u003e, 5148\u0026ndash;5152 (2014).\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"nature-portfolio","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"","title":"Nature Portfolio","twitterHandle":"","acdcEnabled":false,"dfaEnabled":false,"editorialSystem":"ejp","reportingPortfolio":"","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"","lastPublishedDoi":"10.21203/rs.3.rs-1885173/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-1885173/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eOH\u003csup\u003e-\u003c/sup\u003e and H\u003csup\u003e+\u003c/sup\u003e ionic conductors are important electrolyte materials for electrochemical devices such as fuel cells. The high cost of the best low temperature H\u003csup\u003e+\u003c/sup\u003e ionic conductor, Nafion membrane, and the poor chemical compatibility with CO\u003csub\u003e2\u003c/sub\u003e in air of alkaline membrane based on quaternary ammonium groups have seriously affected the large-scale application of low temperature fuel cells. Here we show the discovery of a fast ceramic mixed OH\u003csup\u003e-\u003c/sup\u003e/H\u003csup\u003e+\u003c/sup\u003e conductor, perovskite oxide SrZr\u003csub\u003e0.8\u003c/sub\u003eY\u003csub\u003e0.2\u003c/sub\u003eO\u003csub\u003e3-δ\u003c/sub\u003e, which exhibits a high ionic conductivity of approximately 0.01 S cm\u003csup\u003e-1\u003c/sup\u003e at 90°C when measured in water and wet air, sufficient to be used as electrolyte for low temperature fuel cells. The ionic conductivity is stable in wet air during the measured 130 hours. The ionic conduction was also demonstrated by near ambient temperature solid oxide fuel cells (NAT-SOFCs). This opens a window on discovering new ionic conducting materials for low temperature fuel cells.\u003c/p\u003e","manuscriptTitle":"A fast ceramic mixed OH-/H+ ionic conductor for low temperature fuel cells","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2022-10-05 19:48:50","doi":"10.21203/rs.3.rs-1885173/v1","editorialEvents":[],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"nature-communications","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"NCOMMS","sideBox":"Learn more about [Nature Communications](http://www.nature.com/ncomms/)","snPcode":"","submissionUrl":"https://mts-ncomms.nature.com/","title":"Nature Communications","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"ejp","reportingPortfolio":"Nature Communications","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"df5e4972-bd10-4c9c-b972-d885fdd52aec","owner":[],"postedDate":"October 5th, 2022","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2024-01-31T08:11:52+00:00","versionOfRecord":{"articleIdentity":"rs-1885173","link":"https://doi.org/10.1038/s41467-024-45060-1","journal":{"identity":"nature-communications","isVorOnly":false,"title":"Nature Communications"},"publishedOn":"2024-01-30 05:00:00","publishedOnDateReadable":"January 30th, 2024"},"versionCreatedAt":"2022-10-05 19:48:50","video":"","vorDoi":"10.1038/s41467-024-45060-1","vorDoiUrl":"https://doi.org/10.1038/s41467-024-45060-1","workflowStages":[]},"version":"v1","identity":"rs-1885173","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-1885173","identity":"rs-1885173","version":["v1"]},"buildId":"_2-kVJe1T_tPrBINL-cwx","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}