Internal steam generation via mixed ion-conducting fuel cell for methane reforming at 600ºC

Internal steam generation via mixed ion-conducting fuel cell for methane reforming at 600ºC | 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 Research Article Internal steam generation via mixed ion-conducting fuel cell for methane reforming at 600ºC Ok Sung Jeon, Myung Sik Choi This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6550800/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 20 Jun, 2025 Read the published version in Journal of Electroceramics → Version 1 posted 10 You are reading this latest preprint version Abstract Fuel cells provide efficient and eco-friendly alternatives to traditional combustion-based power generation. Among various types, protonic ceramic fuel cell (PCFC) has emerged as promising candidates due to their ability to operate at lower temperature and feasibility for methane usage. Although solid oxide fuel cell (SOFC) naturally generates steam at the anode during operation, PCFC necessitates the installation of an external steam generator to for mitigating carbon coke formation and incomplete conversion. This study introduces a novel mixed ion-conducting fuel cell (MIFC) design for internal steam generating in the anode side of PCFC. The MIFC was fabricated with BaZr 0.1 Ce 0.7 Y 0.1 Yb 0.1 O 3-δ (BZCYYb) as a proton conductor and Sm 0.2 Ce 0.8 O 2-δ (SDC) as an oxide ion conductor via dip-coating leveraging the shrinkage difference and coating slurry viscosities. The layered structure of the MIFC significantly improved maximum power densities of 0.40 W cm -2 for hydrogen and 0.20 W cm -2 for methane at 600 o C. The layered MIFC also achieved highly table performance at long-term methane reforming at 0.1 A cm -2 for 50 hours. Internal steam generation from the layered structure contributed to higher power densities and mitigated coke formation. The results highlight its potential for applications using hydrocarbon fuels. Protonic ceramic fuel cell mixed ion-conducting shrinkage steam methane Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 1. Introduction Hydrogen is regarded as a promising energy carrier that aligns with the goals of green and clean mobility. Approximately 70% of global hydrogen production relies on natural gas and methane derived from fossil fuels and coal, which remain the dominant sources for large-scale production. [1] Among various hydrogen energy conversion systems, solid oxide fuel cell (SOFC) is particularly promising due to their high efficiency and low pollutant emissions. [2–5] Moreover, SOFC offers greater fuel flexibility compared to low-temperature polymer electrolyte membrane fuel cell (PEMFC) which require high-purity of hydrogen. SOFC can theoretically operate with methane, thereby broadening their potential range of applications. [6] Methane is advantageous for transportation applications with substantially less unit price and high volumetric energy density. In addition, since the direct utilization of methane eliminates the need for external reformers simplifying the system and reducing its overall size and cost, direct methane-fueled SOFC has attracted significant attention. [7] In order to be economically competitive and commercially viable, SOFC technologies should achieve significant breakthroughs in materials development. [8] In particular, the operating temperature needs to be reduced to intermediate temperature (400 o C-650 o C) for minimizing material degradation, lowering the risk of gas leakage and allowing the use of less expensive components. [9–13] Proton-conducting electrolyte is favorable to operate at low temperature due to perovskite-type crystal structures facilitating proton transfer with reduced activation energy. L. Yang et al. reported new type of proton conductor, BaZr 0.1 Ce 0.7 Y 0.2−x Yb x O 3−δ (BZCYYb), which exhibited higher conductivity than Ba(Zr 0.1 Ce 0.7 Y 0.2 )O 3−δ (BZCY) as well as conventional oxide ion conductors such as yttria-stabilized zirconia (YSZ) and gadolinium doped ceria (GDC) at low operating temperatures. [6,14] Ni/BZCYYb serves as conventional anode for direct methane-fueled protonic ceramic fuel cell (PCFC), but Ni species is highly susceptible to coke formation and lowering the temperature exacerbates methane reforming with the conversion. [15] Methane reacts with steam in highly endothermic reaction to produce syngas (CO + H 2 ), while the CO generated subsequently undergoes exothermic water-gas shift (WGS) reaction with steam to produce additional H 2 and CO 2 . [16] Since the additional production in hydrogen is consumed in electrochemical reactions directly contributing to the power output of PCFC and coke formation is primarily driven by CO disproportionation in accordance with the Boudouard reaction, containing steam in the feedstock promotes both enhanced power output and suppressed the coke formation despite lower methane conversion. [17] Furthermore, proton-conducting electrolytes facilitate the formation and incorporation of hydroxyl groups into oxygen vacancies followed by proton migration from steam via Grotthuss-like mechanism. Therefore, providing steam to the anode side of the PCFC with high steam-to-carbon (S/C) ratio plays a key role in operation of PCFC at low temperature. [18] The steam generation process in PCFC is fundamentally the reverse counterpart of that in SOFC. (Fig. 1 ) In SOFC, methane at the anode reacts with oxide ions transported from the cathode through oxide ion-conducting electrolyte which produce electrons, steam and gaseous product at the anode side. As opposed to SOFC, methane is efficiently dehydrogenated to produce protons at the anode of PCFC and subsequently migrate through the proton-conducting electrolyte to the cathode, where they react with oxygen to generate steam. The undesired steam generation in the cathode side in PCFC necessitates the construction of an external steam generator, thereby compromising the cost efficiency and simplicity of direct methane-fueled PCFC. [19] In order to facilitate the internal provision of steam to the anode side of the PCFC during operation, oxide ion-conducting electrolyte must be applied to the cell. Hence, we introduced new electrolyte structure to provide internal steam to the anode of direct methane fueled mixed ion-conducting fuel cell (MIFC) in this study. The main framework of developed internal steam-generating MIFCs consisted of Sm 0.2 Ce 0.8 O 2-δ (SDC)-coated porous Ni/BZCYYb anode, porous BZCYYb/SDC and dense SDC bilayer electrolyte, and porous La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3-δ (LSCF)/SDC cathode. The cell design was implemented via dip-coating using the differences in slurry viscosities and shrinkage behavior between BZCYYb and SDC. The developed MIFC exhibited power density of approximately 0.40 W cm -2 with H 2 and 0.20 W cm -2 with CH 4 at 600 o C. It also retained stable operation of approximately 0.9 V at 0.1 A cm -2 for 50 hours. These results demonstrate the potential of internal steam generation by structural design of MIFC for methane reforming and further performance enhancement is expected through coating conditions and compositional optimization. 2. Experimental 2.1. Synthesis of BZCYYb, SDC, LSCF BZCYYb powder with nominal composition of BaZr 0.1 Ce 0.7 Y 0.1 Yb 0.1 O 3−δ was synthesized by solid-state reaction. BaCO 3 , ZrO 2 , CeO 2 , Y 2 O 3 and Yb 2 O 3 powders were mixed in line with stoichiometric composition and ball-milled in ethanol for 24 hours, drying in oven for 24 hours, and calcination at 1100 o C for 10 hours. These steps were repeated once to completely remove carbonate materials. SDC powder with nominal composition of Sm 0.2 Ce 0.8 O 2−δ was synthesized by pechini method. Sm(NO 3 ) 3 ·6H 2 O and Ce(NO 3 ) 3 ·6H 2 O precursors were dissolved in distilled water with adequate mole fraction and stirring for 1 hour at room temperature. Citric acid (CA) and ethylene glycol (EG) were added into the solution containing the metal salts (M) ([CA]/[M] = 1 and [EG]/[CA] = 4) and then vigorous stirring was carried out at 100 o C. The polymeric sol was burned out at about 200 o C and then the powder was calcined at 900 o C for 3 hours. LSCF powder with nominal composition of La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3−δ was synthesized by solid-state method. The stoichiometric amount of the metal oxides was ball-milled in ethanol for 24 hours and then dried at 60 o C for 24 h. The dried powders were calcined at 900 o C for 3 hours. 2.1. Fabrication of NiO/BZCYYb anode pellet NiO, BZCYYb and carbon black as pore former were ball-milled in ethanol for 24 hours and then dried at 80 o C for 12 hours. The ratio of NiO to BZCYYb was 6:4 and 10% of the carbon black for the NiO powder was added into the mixture. As-prepared mixture was pressed at 50 MPa to fabricate disk-like anode supports with a diameter of 2.5 cm and partially sintered at 1100 o C for 3 hours. 2.2. Slurry for dip-coating The electrolyte slurries of BZCYYb and SDC were prepared by ball-milling. The electrolyte powder (BZCYYb or SDC) was ball-milled with EFKA 4340 as dispersant in mixed toluene/isopropyl alcohol (IPA) for 12 hours. Subsequently, dibutylphthalate (DBP) and Triton-X as plasticizer, and polyvinyl butyral (PVB) as binder were added to the suspension. The viscosities of slurries were controlled by amounts of electrolyte powder composition (5g or 20 g). (Table 1 ) The designated amounts of electrolyte powder were added into the suspension, and then it was finally ball-milled for 24 hours. Table 1 The compositions and viscosities of BZCYYb and SDC electrolyte slurries used for dip-coating onto anode pellets. Contents Toluene IPA Powder EFKA-4340 PVB Triton-X DBP Viscosity BZCYYb Slurry 33.6 ml 67.2 ml 20 g 0.4 ml 2 g 0.4 ml 2 ml - SDC Slurry 1 33.6 ml 67.2 ml 5 g 0.4 ml 2 g 0.4 ml 2 ml 12.0 cP SDC Slurry 2 33.6 ml 67.2 ml 20 g 0.4 ml 2 g 0.4 ml 2 ml 599 cP 2.3. Fabrication of mixed MIFC As-prepared BZCYYb/SDC (4:1) electrolyte slurry was coated on the NiO/BZCYYb anode pellet by dip-coating process. The coated half-cell was fully sintered at 1450 o C for 3 hours. The LSCF/SDC (4:6) cathode paste was coated on the BZCYYb electrolyte side and the cell was finally sintered at 1200 o C for 2 hours. 2.4. Fabrication of layered MIFC BZCYYb slurry was coated on the NiO/BZCYYb anode by dip-coating process. Additionally, SDC slurries with low viscosity (Slurry 1) and high viscosity (Slurry 2) were subsequently coated on the as-prepared half-cell. These cells were fully sintered at 1450 o C for 3 hours. The LSCF/SDC cathode paste was coated on the electrolyte and the cell was finally sintered at 1200 o C for 2 hours. 2.5. Characterizations The crystal structures of the BZCYYb and SDC electrolyte were determined by X-ray diffraction (XRD, Rigaku, D/Max-2200 model) with Cu Kα radiation at wave length of 1.54 Å. In order to observe shrinkage behavior of the BZCYYb and SDC electrolyte, the pellets with 12.7 mm of diameter, 2.5 mm of thickness and 0.65 g of weight were prepared and sintered at 1450 o C for 3 hours. Specific shrinkage behaviors were further investigated using dilatometer (DIL 402C, Netzch Ins.) from ambient temperature to 1450°C with ramping rate of 5 o C min − 1 in air. The viscosity of the slurry was measured using a Brookfield DV2T viscometer with the rotating speeds ranging from 20 rpm to 200 rpm. Field emission scanning electron microscopy (FE-SEM, JEOL, JSM-6701F model) and energy dispersive X-ray were used to observe the surface and cross-sectional morphologies of the electrolytes and cells. Individual cells (2 cm x 2 cm) with the electrode area of 1.1 cm 2 were used in the cell test. Two Pt mesh were attached to each of the anodes and cathodes and Pt paste was used only on the cathodes side as current collector. Pyrex sealant was utilized to adhere the cell to zirconia tube in testing apparatus. The temperature was gradually increased to 850 o C, and remained for 30 minutes to ensure complete sealing. The temperature was naturally reduced to 800 o C, and hydrogen gas was fed into the anode for 3 hours to reduce nickel oxide to nickel metal. The electrochemical test of cells were performed at 600 o C. The flow rates of air, hydrogen and methane were 400 sccm, 200 sccm and 40 sccm, respectively. The electrochemical analysis was carried out by using a FC Impedance meter (Kikusi, KFM-2030 model) and versatile multichannel potentiostat (VSP,Biologic,VMP3B-10 model). The frequency range was varied from 100 kHz to 0.1 Hz with the applied AC amplitude of 35 mV. 3. Results & Discussion Two types of electrolytes, BZCYYb as a proton conductor and SDC as an oxide ion conductor, were synthesized by solid-state reaction and sol-gel method, respectively. In order to confirm the secondary phases formation in as-prepared electrolytes and their mixture, the respective crystalline structures of these electrolytes and the mixture after the pelletizing under 50 MPa and sintering at 1450 o C for 3 hours were observed by X-ray diffraction (XRD). (Fig. 2 ) BZCYYb and SDC electrolytes were successfully synthesized in the reference states as perovskite and fluorite structures without the formation of undesirable secondary phases. It was also demonstrated that those two electrolytes remained their distinct crystalline structures after the sintering of BZCYYb and SDC mixture. This implies that the mixture of BZCYYb and SDC slightly influenced on their ionic conductivities and respective conduction behaviors as proton conduction for BZCYYb and oxide ion conduction for SDC even after being sintered simultaneously. The shrinkage of those electrolyte pellets after the sintering were measured by volumetric change. The shrinkages of the BZCYYb and SDC electrolytes were about 8.07% and 39.8%, respectively. (Fig. 3 a) While BZCYYb is typically sintered at 1500–1600 o C, [19] SDC could achieve 95% of density even at 1400 o C. [20] Due to the significant difference in the inherent sintering behaviors of BZCYYb and SDC, the addition of SDC to BZCYYb pellets is expected to act as sintering aid which leads to complete densification below 1500 o C. [21] The effects of addition of SDC to BZCYYb on shrinkage behavior was further investigated during the sintering of electrolyte pellets through dilatometry. (Fig. 3 b) The sintering of BZCYYb primarily initiated around 1100 o C and continued gradually to 1450 o C. This gradual increase elucidated the existence of residual porosity and incomplete densification in the BZCYYb pellet. With addition of SDC, the main sintering of pellet occurred at lower temperature around 1040 o C in comparison with the BZCYYb. Furthermore, the BZCYYb/SDC pellet exhibited a steep increase in shrinkage and reached − 21.3% at 1450 o C, whereas the shrinkage of the BZCYYb pellet attained only − 16.2%. Consequently, though poor sintering of BZCYYb at 1450 o C could induce pore formation in the pellet, this issue could be alleviated by the addition of SDC. The internal steam-generating MIFC was fabricated by simple dip-coating method using these shrinkage differences. Dip-coated half-cells with diverse slurries were sintered at 1450 o C for 3 hours. The surficial morphology of this BZCYYb coated half-cell was shown in Fig. 4 a. The significant quantities of pores apparently formed on the surface of half-cell and would be primarily attributed to the low shrinkage of BZCYYb at 1450 o C. The two different viscosities of SDC slurries were prepared to remain porous structure and form dense surface on this BZCYYb layer. The SDC slurry 1 and slurry 2 were 12.0 cP and 599 cP, respectively. (Table 1 ) Upon additional dip-coating with SDC low-viscosity slurry 1, the assistance of densification during sintering at 1450 o C for 3 hours led to narrow the pores on the surface of the half-cell. (Fig. 4 b) However, the residual pores on the surface half-cell were still observed on the surface. It presumed that low-viscosity SDC slurry can penetrated into the porous NiO/BZCYYb during dip-coating leaving only slight coverage on the anode surface with large pores remaining. In comparison with SDC slurry 1, using the SDC slurry 2 including higher viscosity led to acquire the dense surface as shown in Fig. 4 c. The less void concentration of coated layer using SDC slurry 2 caused these morphological differences. Furthermore, SDC slurry 2 might have difficulties to penetrate into the both anode and electrolyte of the half-cell due to the high viscosity. For fabricating half-cell of MIFC, the porous BZCYYb layer was initially dip-coated on the as-prepared anode pellet. Thereafter, SDC slurry 1 and slurry 2 also subsequently covered on this half-cell and additionally sintered at 1450 o C for 3 hours. The cross-sectional SEM image of the half-cell of MIFC was shown in Fig. 5 a. The backscattered electrons in the SEM image clearly distinguished between the electrolyte and Ni. The brightness of electrolyte and Ni particles separated into the bright and dark regions, respectively. The anode layer at the bottom of the half-cell exhibited large pores with heterogeneous distribution of Ni and electrolyte particles. The distinguishable Ni, Ba, Sm and Ce signals in the energy dispersive X-ray (EDS) mapping clearly demonstrated the anode region. (Fig. 5 b) The upper region of the anode layer in the cross-sectional SEM image corresponded to the electrolyte layers of which thickness was 18 µm comprising porous ~ 10 µm-thick layer (Yellow box A) and ~ 6 µm-thick dense layer (Yellow box B). The configuration of porous BZCYYb layer was arisen from poor shrinkage as shown in Fig. 4 a. Furthermore, the dip-coating slurry 1 spread slight portion of SDC uniformly across entire layers as indicated by the Sm signal in Fig. 5 b. The yellow arrow in the magnified SEM image of the yellow box A revealed that the surface of the micro-sized BZCYYb was decorated with incorporated SDC nanoparticles. (Fig. 5 c) The SDC slurries also densified the top side of the BZCYYb layer which had been caused by the effect of SDC acting as sintering aid for BZCYYb as mentioned in Fig. 4 b. Similar to typical sintering aids located at grain boundaries, [22] the healed grain boundaries of BZCYYb were also confirmed in the magnified SEM image of yellow box B. (Fig. 4 d) As a result, layered mixed ionic-conducting electrolyte with porous BZCYYb layer was successfully fabricated by exploiting differences in shrinkage behavior and slurry viscosities through simple dip-coating method. To verify the importance of layered structure of MIFC, the dip-coating of mixed BZCYYb and SDC electrolyte was also conducted to prepare the reference cell in the simple way. Figure 6 presented the I-V curves and impedance spectra of the mixed MIFC and layered MIFC at 600 o C with H 2 fuel. The mixed MIFC exhibited poor open circuit voltage (OCV) of 0.92 V, whereas the layered MIFC had reasonable OCV of 1.06 V. (Fig. 6 a) This phenomenon was mainly attributed to the intrinsic characteristics of SDC. It has been widely reported that the reduction of Ce 4+ to Ce 3+ in SDC significantly increased electronic conductivity during SOFC operation, thereby leading to decrease in OCV. [23] Thus, the mixed MIFC with large portions of SDC in electrolyte layer could follow the characteristics of SDC. On the other hand, in the case of the layered MIFC, the inter-diffusion between BZCYYb and SDC during sintering resulted in the thin layer of doped barium cerate and zirconate at the interface, which successfully inhibited the electronic conduction of SDC and improved the OCV. [24] Although the slope in the I-V curve of the mixed MIFC sharply decreased in the ohmic polarization region with the increase in current density as well, that of the layered MIFC dropped gradually. These resulted in divergent maximum power densities of 0.16 W cm − 2 for the mixed MIFC and 0.40 W cm − 2 for the layered MIFC, respectively. The layered MIFC had significantly lower ohmic resistance of 0.54 Ohm cm 2 compared to that of mixed MIFC even though the absolute value was not detected in the mixed MIFC due to the range of measured frequency. (Fig. 6 b) This corresponded well to the sharp ohmic losses detected in the polarization curve of the mixed MIFC. I–V curves for the MIFCs with methane were also detected as shown in Fig. 7 . The OCV of the mixed MIFC and layered MIFC remained with feedstock change about 0.92 V and 1.06 V, respectively. (Fig. 7 a) The observed current densities were lower than the case of hydrogen due to the smaller ΔG of the methane reforming reaction compared with the hydrogen/air reaction. [25] The maximum power densities of mixed MIFC and layered MIFC were 0.10 W cm − 2 and 0.20 W cm − 2 , respectively. The decrease in the power density of the MIFCs with methane was ascribed to slower electrochemical oxidation of methane than that of hydrogen. The further impedance measurements were conducted to figure out the different resistances associated with MIFC operation on hydrogen and methane fuel. (Fig. 7 b) The main differences in impedance spectra occurred at the high-frequency region. The resistance in the high-frequency region for methane was noticeably higher than that for hydrogen in the mixed MIFC. In contrast, the resistance in this region showed only slight increase in the layered MIFC. The resistance in high-frequency region is assigned to fuel oxidation reaction at the anode. [26] Since the rapid supplying of oxide ions from dispersed SDC in the anode can promote oxidation of methane. [27] Furthermore, generating steam at the anode also can participate in the methane reforming reactions. [28] The ohmic resistances of the MIFCs were also higher during methane operation due to the reduction in the local cell temperature caused by the endothermic methane reforming reactions, which in turn led to lower ionic conductivity of the electrolyte. [29] Considering these results, the internal steam generation was primarily responsible for higher power density with the methane fuel. Long-term operation with methane at 600 o C under constant current density of 0.1 A cm − 2 was carried out for both the mixed and layered MIFCs. (Fig. 8a) The layered MIFC maintained stable operation for 50 hours, whereas the mixed MIFC deteriorated within 2 hours. In the course of long-term operation, it was confirmed that the layered MIFC generated and coagulated at the anode side. (Fig. 8b) These results obviously indicated that the internal steam generation by layered structure of MIFC enhanced the coke tolerance. 4. Conclusions The new design of mixed ion conducting fuel cell was introduced in this study. The MIFC was successfully fabricated using BZCYYb as a proton conductor and SDC as an oxide ion conductor through simple dip-coating method. The significant difference in shrinkage between BZCYYb and SDC at 1450 o C enabled to render the electrolyte surface porous or dense. Leveraging these distinct sintering behaviors and slurry viscosities, the two types of mixed and layered MIFC were manufactured and compared to highlight the importance of internal steam generation at the anode side. The layered MIFC demonstrated significantly higher stability and power density compared to the mixed MIFC. The maximum power densities for the mixed and layered MIFCs were 0.16 W cm -2 and 0.40 W cm -2 at 600 o C for H 2 , and 0.10 W cm -2 and 0.20 W cm -2 at 600 o C for methane, respectively. While the voltage of the mixed MIFC sharply dropped within 2 hours, the layered MIFC maintained stable performance for 50 hours during methane reforming at 600°C under 0.1 A cm -2 . The internal steam generation in the layered structure contributed to higher power densities and reduced coke formation. These results highlighted the potential of the layered MIFC to enhance fuel cell performance, particularly in applications using hydrocarbon fuels. Declarations Acknowledgements This research was supported by the National Research Foundation of Korea (NRF) grant funded by the Ministry of Science and ICT (MSIT) (RS-2021-NR060108). 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Wachsman, Mitigating electronic conduction in ceria-based electrolytes via external structure design, Adv. Funct. Mater. 34 (2024) 2308123. https://doi.org/10.1002/adfm.202308123. M. Liu, D. Ding, Y. Bai, T. He, M. Liu, An efficient SOFC based on samaria-doped ceria (SDC) electrolyte, J. Electrochem. Soc. 159 (2012) B661. https://doi.org/10.1149/2.032206jes. W. G. Coors, Protonic ceramic fuel cells for high-efficiency operation with methane, J. Power Sources 118 (2003) 150-156. https://doi.org/10.1016/S0378-7753(03)00072-7. Direct operation of solid oxide fuel cells with methane fuel, Solid State Ion. 176 (2005) 1827-1835. https://doi.org/10.1016/j.ssi.2005.05.008. Z. Tao, G. Houa, N. Xu, Q. Zhang and H. Ding, A mixed proton-oxide ion-electron conducting anode for highly coking-resistant solid oxide fuel cells, Electrochim. Acta 150 (2014) 55-61. https://doi.org/10.1016/j.electacta.2014.10.126. K. P. Recknagle, E. M. Ryan, B. J. Koeppel, L. A. Mahoney and M. A. Khaleel, Modeling of electrochemistry and steam–methane reforming performance for simulating pressurized solid oxide fuel cell stacks, J. Power Sources 195 (2010) 6637-6644. https://doi.org/10.1016/j.jpowsour.2010.04.024. W. A. Rosensteel, S. M. BabiniecD. D. Storjohann, J. Persky, N. P. Sullivan, Use of anode barrier layers in tubular solid-oxide fuel cells for robust operation on hydrocarbon fuels, J. Power Sources 205 (2012) 108-113. https://doi.org/10.1016/j.jpowsour.2012.01.035. Additional Declarations No competing interests reported. Cite Share Download PDF Status: Published Journal Publication published 20 Jun, 2025 Read the published version in Journal of Electroceramics → Version 1 posted Editorial decision: Revision requested 18 May, 2025 Reviews received at journal 12 May, 2025 Reviewers agreed at journal 08 May, 2025 Reviews received at journal 03 May, 2025 Reviewers agreed at journal 03 May, 2025 Reviewers agreed at journal 02 May, 2025 Reviewers invited by journal 01 May, 2025 Editor assigned by journal 30 Apr, 2025 Submission checks completed at journal 30 Apr, 2025 First submitted to journal 28 Apr, 2025 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. 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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-6550800","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":451395108,"identity":"88af572e-7f95-4cbd-b1c6-06a94a3a4c19","order_by":0,"name":"Ok Sung Jeon","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAy0lEQVRIiWNgGAWjYHCCBCD+L8fAwNwAZDATrYXZmIGBkXgtIMCc2EC0Fn7+Aw8ffNzBlr7h+MHGDwwV1okNhLRIzkhINpx5hid3w5nEZgmGM+mEtRjcYEiT5m2TyN1wg7FBgrHtMBFazh9I/83bZpBucIOx+QfjP2K0HEhIY+ZtS0gAammTYGwgQgvIL5Iz2w4A/ZPYZpFwLN2YoBZ+/jOJHz62HZDnO3748I0PNdayBLUwMPAkINgJuBShAvYDxKkbBaNgFIyCkQsAOXVBug6n3IQAAAAASUVORK5CYII=","orcid":"","institution":"University of California Los Angeles","correspondingAuthor":true,"prefix":"","firstName":"Ok","middleName":"Sung","lastName":"Jeon","suffix":""},{"id":451395109,"identity":"4b412893-823d-4da9-8125-e989eeb4a0d6","order_by":1,"name":"Myung Sik Choi","email":"","orcid":"","institution":"Kyungpook National University","correspondingAuthor":false,"prefix":"","firstName":"Myung","middleName":"Sik","lastName":"Choi","suffix":""}],"badges":[],"createdAt":"2025-04-28 21:08:07","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-6550800/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6550800/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1007/s10832-025-00420-1","type":"published","date":"2025-06-20T15:57:16+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":82070032,"identity":"fe31512a-67b4-4ac4-98ae-30879b087a74","added_by":"auto","created_at":"2025-05-06 13:09:08","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":188677,"visible":true,"origin":"","legend":"\u003cp\u003eSchematic illustrations of steam generating mechanism of conventional solid oxide fuel cell (SOFC), protonic ceramic fuel cell (PCFC) and internal steam-generating mixed ion-conducting fuel cell (MIFC).\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-6550800/v1/b1be2fa32c8ff2bd3fe5e506.png"},{"id":82070040,"identity":"5c13877b-ecc1-47ec-a208-6eb1572f0f04","added_by":"auto","created_at":"2025-05-06 13:09:09","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":87962,"visible":true,"origin":"","legend":"\u003cp\u003eX-ray diffraction (XRD) patterns of BZCYYb, SDC and BZCYYb/SDC pellets sintered at 1450 \u003csup\u003eo\u003c/sup\u003eC for 3 hours.\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-6550800/v1/869904313420c99d07f38f49.png"},{"id":82070033,"identity":"26362736-1acd-4d87-af84-7b8e610444d8","added_by":"auto","created_at":"2025-05-06 13:09:08","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":96182,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Shrinkages of respective BZCYYb and SDC electrolyte pellets after the sintering at 1450 \u003csup\u003eo\u003c/sup\u003eC for 3 hours and (b) dilatometry curves of BZCYYb and BZCYYb/SDC pellets.\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-6550800/v1/73cf5e410f3472f2c24db002.png"},{"id":82070071,"identity":"cd7e9e3d-1619-4f7d-a207-56e7115ba7b2","added_by":"auto","created_at":"2025-05-06 13:09:11","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":201243,"visible":true,"origin":"","legend":"\u003cp\u003eScanning electron microscopy (SEM) images of the surface of (a) dip-coated BZCYYb pellet, (b) additional SDC coating on dip-coated BZCYYb pellet with slurry 1 and (c) additional SDC coating on dip-coated SDC/BZCYYb pellet with slurry 2. The all pellets were sintered at 1450 \u003csup\u003eo\u003c/sup\u003eC for 3 hours.\u003c/p\u003e","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-6550800/v1/0ca56d0b6423291d804dda68.png"},{"id":82070095,"identity":"3cd2da2b-586c-435e-bb28-2b24488795eb","added_by":"auto","created_at":"2025-05-06 13:09:13","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":496008,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Cross-sectional SEM image and (b) energy dispersive X-ray (EDS) mapping of the half-cell of the layered internal steam-generating MIFC. The magnified SEM images of the half-cell of the MIFC in the region of (c) yellow box A and (d) yellow box B.\u003c/p\u003e","description":"","filename":"floatimage5.png","url":"https://assets-eu.researchsquare.com/files/rs-6550800/v1/950b68c03fd14be90122970d.png"},{"id":82070045,"identity":"2f5ae87b-43ef-4ac0-bb8e-65eb450582c6","added_by":"auto","created_at":"2025-05-06 13:09:10","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":140102,"visible":true,"origin":"","legend":"\u003cp\u003e(a) I-V curves and (b) impedance spectra of the mixed MIFC and layered MIFC at 600 \u003csup\u003eo\u003c/sup\u003eC with H\u003csub\u003e2\u003c/sub\u003e fuel.\u003c/p\u003e","description":"","filename":"floatimage6.png","url":"https://assets-eu.researchsquare.com/files/rs-6550800/v1/4a929e846bfab9f4a36c8270.png"},{"id":82070075,"identity":"7ff9e70f-deef-4d6f-acb4-2f0301fa5994","added_by":"auto","created_at":"2025-05-06 13:09:12","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":139495,"visible":true,"origin":"","legend":"\u003cp\u003e(a) I-V curves and (b) impedance spectra of the mixed MIFC and layered MIFC at 600 \u003csup\u003eo\u003c/sup\u003eC with CH\u003csub\u003e4\u003c/sub\u003e fuel.\u003c/p\u003e","description":"","filename":"floatimage7.png","url":"https://assets-eu.researchsquare.com/files/rs-6550800/v1/82edc84dd075d02f62297a51.png"},{"id":82070080,"identity":"0d882185-ac81-4bef-b318-5e7b5568a300","added_by":"auto","created_at":"2025-05-06 13:09:12","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":145044,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Long-term stability of the mixed MIFC and layered MIFC at 600 \u003csup\u003eo\u003c/sup\u003eC with CH\u003csub\u003e4\u003c/sub\u003e fuel applying current density of 0.1 A cm\u003csup\u003e-2\u003c/sup\u003e and (b) photograph of the steam generation at the anode outlet.\u003c/p\u003e","description":"","filename":"floatimage8.png","url":"https://assets-eu.researchsquare.com/files/rs-6550800/v1/75efcd1d1b1aae05450a210a.png"},{"id":85231419,"identity":"8d7302c3-42a3-4c17-8d2f-fac20079d8fe","added_by":"auto","created_at":"2025-06-23 16:07:40","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2059916,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6550800/v1/a85b8de8-c6ed-4440-90ac-6712b9e9d751.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"\u003cp\u003eInternal steam generation via mixed ion-conducting fuel cell for methane reforming at 600ºC\u003c/p\u003e","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eHydrogen is regarded as a promising energy carrier that aligns with the goals of green and clean mobility. Approximately 70% of global hydrogen production relies on natural gas and methane derived from fossil fuels and coal, which remain the dominant sources for large-scale production. [1] Among various hydrogen energy conversion systems, solid oxide fuel cell (SOFC) is particularly promising due to their high efficiency and low pollutant emissions. [2\u0026ndash;5] Moreover, SOFC offers greater fuel flexibility compared to low-temperature polymer electrolyte membrane fuel cell (PEMFC) which require high-purity of hydrogen. SOFC can theoretically operate with methane, thereby broadening their potential range of applications. [6] Methane is advantageous for transportation applications with substantially less unit price and high volumetric energy density. In addition, since the direct utilization of methane eliminates the need for external reformers simplifying the system and reducing its overall size and cost, direct methane-fueled SOFC has attracted significant attention. [7]\u003c/p\u003e \u003cp\u003eIn order to be economically competitive and commercially viable, SOFC technologies should achieve significant breakthroughs in materials development. [8] In particular, the operating temperature needs to be reduced to intermediate temperature (400 \u003csup\u003eo\u003c/sup\u003eC-650 \u003csup\u003eo\u003c/sup\u003eC) for minimizing material degradation, lowering the risk of gas leakage and allowing the use of less expensive components. [9\u0026ndash;13] Proton-conducting electrolyte is favorable to operate at low temperature due to perovskite-type crystal structures facilitating proton transfer with reduced activation energy. L. Yang et al. reported new type of proton conductor, BaZr\u003csub\u003e0.1\u003c/sub\u003eCe\u003csub\u003e0.7\u003c/sub\u003eY\u003csub\u003e0.2\u0026minus;x\u003c/sub\u003eYb\u003csub\u003ex\u003c/sub\u003eO\u003csub\u003e3\u0026minus;δ\u003c/sub\u003e (BZCYYb), which exhibited higher conductivity than Ba(Zr\u003csub\u003e0.1\u003c/sub\u003eCe\u003csub\u003e0.7\u003c/sub\u003eY\u003csub\u003e0.2\u003c/sub\u003e)O\u003csub\u003e3\u0026minus;δ\u003c/sub\u003e (BZCY) as well as conventional oxide ion conductors such as yttria-stabilized zirconia (YSZ) and gadolinium doped ceria (GDC) at low operating temperatures. [6,14]\u003cdiv class=\"BlockQuote\"\u003e\u003cp\u003eNi/BZCYYb serves as conventional anode for direct methane-fueled protonic ceramic fuel cell (PCFC), but Ni species is highly susceptible to coke formation and lowering the temperature exacerbates methane reforming with the conversion. [15] Methane reacts with steam in highly endothermic reaction to produce syngas (CO\u0026thinsp;+\u0026thinsp;H\u003csub\u003e2\u003c/sub\u003e), while the CO generated subsequently undergoes exothermic water-gas shift (WGS) reaction with steam to produce additional H\u003csub\u003e2\u003c/sub\u003e and CO\u003csub\u003e2\u003c/sub\u003e. [16] Since the additional production in hydrogen is consumed in electrochemical reactions directly contributing to the power output of PCFC and coke formation is primarily driven by CO disproportionation in accordance with the Boudouard reaction, containing steam in the feedstock promotes both enhanced power output and suppressed the coke formation despite lower methane conversion. [17] Furthermore, proton-conducting electrolytes facilitate the formation and incorporation of hydroxyl groups into oxygen vacancies followed by proton migration from steam via Grotthuss-like mechanism. Therefore, providing steam to the anode side of the PCFC with high steam-to-carbon (S/C) ratio plays a key role in operation of PCFC at low temperature. [18]\u003c/p\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"BlockQuote\"\u003e \u003cp\u003eThe steam generation process in PCFC is fundamentally the reverse counterpart of that in SOFC. (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e) In SOFC, methane at the anode reacts with oxide ions transported from the cathode through oxide ion-conducting electrolyte which produce electrons, steam and gaseous product at the anode side. As opposed to SOFC, methane is efficiently dehydrogenated to produce protons at the anode of PCFC and subsequently migrate through the proton-conducting electrolyte to the cathode, where they react with oxygen to generate steam. The undesired steam generation in the cathode side in PCFC necessitates the construction of an external steam generator, thereby compromising the cost efficiency and simplicity of direct methane-fueled PCFC. [19] In order to facilitate the internal provision of steam to the anode side of the PCFC during operation, oxide ion-conducting electrolyte must be applied to the cell. Hence, we introduced new electrolyte structure to provide internal steam to the anode of direct methane fueled mixed ion-conducting fuel cell (MIFC) in this study. The main framework of developed internal steam-generating MIFCs consisted of Sm\u003csub\u003e0.2\u003c/sub\u003eCe\u003csub\u003e0.8\u003c/sub\u003eO\u003csub\u003e2-δ\u003c/sub\u003e (SDC)-coated porous Ni/BZCYYb anode, porous BZCYYb/SDC and dense SDC bilayer electrolyte, and porous La\u003csub\u003e0.6\u003c/sub\u003eSr\u003csub\u003e0.4\u003c/sub\u003eCo\u003csub\u003e0.2\u003c/sub\u003eFe\u003csub\u003e0.8\u003c/sub\u003eO\u003csub\u003e3-δ\u003c/sub\u003e (LSCF)/SDC cathode. The cell design was implemented via dip-coating using the differences in slurry viscosities and shrinkage behavior between BZCYYb and SDC. The developed MIFC exhibited power density of approximately 0.40 W cm\u003csup\u003e-2\u003c/sup\u003e with H\u003csub\u003e2\u003c/sub\u003e and 0.20 W cm\u003csup\u003e-2\u003c/sup\u003e with CH\u003csub\u003e4\u003c/sub\u003e at 600 \u003csup\u003eo\u003c/sup\u003eC. It also retained stable operation of approximately 0.9 V at 0.1 A cm\u003csup\u003e-2\u003c/sup\u003e for 50 hours. These results demonstrate the potential of internal steam generation by structural design of MIFC for methane reforming and further performance enhancement is expected through coating conditions and compositional optimization.\u003c/p\u003e \u003c/div\u003e \u003c/p\u003e"},{"header":"2. Experimental","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1. Synthesis of BZCYYb, SDC, LSCF\u003c/h2\u003e \u003cp\u003eBZCYYb powder with nominal composition of BaZr\u003csub\u003e0.1\u003c/sub\u003eCe\u003csub\u003e0.7\u003c/sub\u003eY\u003csub\u003e0.1\u003c/sub\u003eYb\u003csub\u003e0.1\u003c/sub\u003eO\u003csub\u003e3\u0026minus;δ\u003c/sub\u003e was synthesized by solid-state reaction. BaCO\u003csub\u003e3\u003c/sub\u003e, ZrO\u003csub\u003e2\u003c/sub\u003e, CeO\u003csub\u003e2\u003c/sub\u003e, Y\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e and Yb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e powders were mixed in line with stoichiometric composition and ball-milled in ethanol for 24 hours, drying in oven for 24 hours, and calcination at 1100 \u003csup\u003eo\u003c/sup\u003eC for 10 hours. These steps were repeated once to completely remove carbonate materials. SDC powder with nominal composition of Sm\u003csub\u003e0.2\u003c/sub\u003eCe\u003csub\u003e0.8\u003c/sub\u003eO\u003csub\u003e2\u0026minus;δ\u003c/sub\u003e was synthesized by pechini method. Sm(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e3\u003c/sub\u003e\u0026middot;6H\u003csub\u003e2\u003c/sub\u003eO and Ce(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e3\u003c/sub\u003e\u0026middot;6H\u003csub\u003e2\u003c/sub\u003eO precursors were dissolved in distilled water with adequate mole fraction and stirring for 1 hour at room temperature. Citric acid (CA) and ethylene glycol (EG) were added into the solution containing the metal salts (M) ([CA]/[M]\u0026thinsp;=\u0026thinsp;1 and [EG]/[CA]\u0026thinsp;=\u0026thinsp;4) and then vigorous stirring was carried out at 100 \u003csup\u003eo\u003c/sup\u003eC. The polymeric sol was burned out at about 200 \u003csup\u003eo\u003c/sup\u003eC and then the powder was calcined at 900 \u003csup\u003eo\u003c/sup\u003eC for 3 hours. LSCF powder with nominal composition of La\u003csub\u003e0.6\u003c/sub\u003eSr\u003csub\u003e0.4\u003c/sub\u003eCo\u003csub\u003e0.2\u003c/sub\u003eFe\u003csub\u003e0.8\u003c/sub\u003eO\u003csub\u003e3\u0026minus;δ\u003c/sub\u003e was synthesized by solid-state method. The stoichiometric amount of the metal oxides was ball-milled in ethanol for 24 hours and then dried at 60 \u003csup\u003eo\u003c/sup\u003eC for 24 h. The dried powders were calcined at 900 \u003csup\u003eo\u003c/sup\u003eC for 3 hours.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.1. Fabrication of NiO/BZCYYb anode pellet\u003c/h2\u003e \u003cp\u003eNiO, BZCYYb and carbon black as pore former were ball-milled in ethanol for 24 hours and then dried at 80 \u003csup\u003eo\u003c/sup\u003eC for 12 hours. The ratio of NiO to BZCYYb was 6:4 and 10% of the carbon black for the NiO powder was added into the mixture. As-prepared mixture was pressed at 50 MPa to fabricate disk-like anode supports with a diameter of 2.5 cm and partially sintered at 1100 \u003csup\u003eo\u003c/sup\u003eC for 3 hours.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.2. Slurry for dip-coating\u003c/h2\u003e \u003cp\u003eThe electrolyte slurries of BZCYYb and SDC were prepared by ball-milling. The electrolyte powder (BZCYYb or SDC) was ball-milled with EFKA 4340 as dispersant in mixed toluene/isopropyl alcohol (IPA) for 12 hours. Subsequently, dibutylphthalate (DBP) and Triton-X as plasticizer, and polyvinyl butyral (PVB) as binder were added to the suspension. The viscosities of slurries were controlled by amounts of electrolyte powder composition (5g or 20 g). (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e) The designated amounts of electrolyte powder were added into the suspension, and then it was finally ball-milled for 24 hours.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eThe compositions and viscosities of BZCYYb and SDC electrolyte slurries used for dip-coating onto anode pellets.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"9\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c9\" colnum=\"9\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eContents\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eToluene\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eIPA\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003ePowder\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eEFKA-4340\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003ePVB\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eTriton-X\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c8\"\u003e \u003cp\u003eDBP\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c9\"\u003e \u003cp\u003eViscosity\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eBZCYYb\u003c/b\u003e\u003c/p\u003e \u003cp\u003e\u003cb\u003eSlurry\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e33.6 ml\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e67.2 ml\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e20 g\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.4 ml\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e2 g\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e0.4 ml\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e2 ml\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eSDC\u003c/b\u003e\u003c/p\u003e \u003cp\u003e\u003cb\u003eSlurry 1\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e33.6 ml\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e67.2 ml\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e5 g\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.4 ml\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e2 g\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e0.4 ml\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e2 ml\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e12.0 cP\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eSDC\u003c/b\u003e\u003c/p\u003e \u003cp\u003e\u003cb\u003eSlurry 2\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e33.6 ml\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e67.2 ml\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e20 g\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.4 ml\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e2 g\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e0.4 ml\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e2 ml\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e599 cP\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e2.3. Fabrication of mixed MIFC\u003c/h2\u003e \u003cp\u003eAs-prepared BZCYYb/SDC (4:1) electrolyte slurry was coated on the NiO/BZCYYb anode pellet by dip-coating process. The coated half-cell was fully sintered at 1450 \u003csup\u003eo\u003c/sup\u003eC for 3 hours. The LSCF/SDC (4:6) cathode paste was coated on the BZCYYb electrolyte side and the cell was finally sintered at 1200 \u003csup\u003eo\u003c/sup\u003eC for 2 hours.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e2.4. Fabrication of layered MIFC\u003c/h2\u003e \u003cp\u003eBZCYYb slurry was coated on the NiO/BZCYYb anode by dip-coating process. Additionally, SDC slurries with low viscosity (Slurry 1) and high viscosity (Slurry 2) were subsequently coated on the as-prepared half-cell. These cells were fully sintered at 1450 \u003csup\u003eo\u003c/sup\u003eC for 3 hours. The LSCF/SDC cathode paste was coated on the electrolyte and the cell was finally sintered at 1200 \u003csup\u003eo\u003c/sup\u003eC for 2 hours.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003e2.5. Characterizations\u003c/h2\u003e \u003cp\u003eThe crystal structures of the BZCYYb and SDC electrolyte were determined by X-ray diffraction (XRD, Rigaku, D/Max-2200 model) with Cu Kα radiation at wave length of 1.54 \u0026Aring;. In order to observe shrinkage behavior of the BZCYYb and SDC electrolyte, the pellets with 12.7 mm of diameter, 2.5 mm of thickness and 0.65 g of weight were prepared and sintered at 1450 \u003csup\u003eo\u003c/sup\u003eC for 3 hours. Specific shrinkage behaviors were further investigated using dilatometer (DIL 402C, Netzch Ins.) from ambient temperature to 1450\u0026deg;C with ramping rate of 5 \u003csup\u003eo\u003c/sup\u003eC min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e in air. The viscosity of the slurry was measured using a Brookfield DV2T viscometer with the rotating speeds ranging from 20 rpm to 200 rpm. Field emission scanning electron microscopy (FE-SEM, JEOL, JSM-6701F model) and energy dispersive X-ray were used to observe the surface and cross-sectional morphologies of the electrolytes and cells. Individual cells (2 cm x 2 cm) with the electrode area of 1.1 cm\u003csup\u003e2\u003c/sup\u003e were used in the cell test. Two Pt mesh were attached to each of the anodes and cathodes and Pt paste was used only on the cathodes side as current collector. Pyrex sealant was utilized to adhere the cell to zirconia tube in testing apparatus. The temperature was gradually increased to 850 \u003csup\u003eo\u003c/sup\u003eC, and remained for 30 minutes to ensure complete sealing. The temperature was naturally reduced to 800 \u003csup\u003eo\u003c/sup\u003eC, and hydrogen gas was fed into the anode for 3 hours to reduce nickel oxide to nickel metal. The electrochemical test of cells were performed at 600 \u003csup\u003eo\u003c/sup\u003eC. The flow rates of air, hydrogen and methane were 400 sccm, 200 sccm and 40 sccm, respectively. The electrochemical analysis was carried out by using a FC Impedance meter (Kikusi, KFM-2030 model) and versatile multichannel potentiostat (VSP,Biologic,VMP3B-10 model). The frequency range was varied from 100 kHz to 0.1 Hz with the applied AC amplitude of 35 mV.\u003c/p\u003e \u003c/div\u003e"},{"header":"3. Results \u0026 Discussion","content":"\u003cp\u003e \u003c/p\u003e \u003cp\u003eTwo types of electrolytes, BZCYYb as a proton conductor and SDC as an oxide ion conductor, were synthesized by solid-state reaction and sol-gel method, respectively. In order to confirm the secondary phases formation in as-prepared electrolytes and their mixture, the respective crystalline structures of these electrolytes and the mixture after the pelletizing under 50 MPa and sintering at 1450 \u003csup\u003eo\u003c/sup\u003eC for 3 hours were observed by X-ray diffraction (XRD). (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e) BZCYYb and SDC electrolytes were successfully synthesized in the reference states as perovskite and fluorite structures without the formation of undesirable secondary phases. It was also demonstrated that those two electrolytes remained their distinct crystalline structures after the sintering of BZCYYb and SDC mixture. This implies that the mixture of BZCYYb and SDC slightly influenced on their ionic conductivities and respective conduction behaviors as proton conduction for BZCYYb and oxide ion conduction for SDC even after being sintered simultaneously.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe shrinkage of those electrolyte pellets after the sintering were measured by volumetric change. The shrinkages of the BZCYYb and SDC electrolytes were about 8.07% and 39.8%, respectively. (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea) While BZCYYb is typically sintered at 1500\u0026ndash;1600 \u003csup\u003eo\u003c/sup\u003eC, [19] SDC could achieve 95% of density even at 1400 \u003csup\u003eo\u003c/sup\u003eC. [20] Due to the significant difference in the inherent sintering behaviors of BZCYYb and SDC, the addition of SDC to BZCYYb pellets is expected to act as sintering aid which leads to complete densification below 1500 \u003csup\u003eo\u003c/sup\u003eC. [21] The effects of addition of SDC to BZCYYb on shrinkage behavior was further investigated during the sintering of electrolyte pellets through dilatometry. (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb) The sintering of BZCYYb primarily initiated around 1100 \u003csup\u003eo\u003c/sup\u003eC and continued gradually to 1450 \u003csup\u003eo\u003c/sup\u003eC. This gradual increase elucidated the existence of residual porosity and incomplete densification in the BZCYYb pellet. With addition of SDC, the main sintering of pellet occurred at lower temperature around 1040 \u003csup\u003eo\u003c/sup\u003eC in comparison with the BZCYYb. Furthermore, the BZCYYb/SDC pellet exhibited a steep increase in shrinkage and reached \u0026minus;\u0026thinsp;21.3% at 1450 \u003csup\u003eo\u003c/sup\u003eC, whereas the shrinkage of the BZCYYb pellet attained only \u0026minus;\u0026thinsp;16.2%. Consequently, though poor sintering of BZCYYb at 1450 \u003csup\u003eo\u003c/sup\u003eC could induce pore formation in the pellet, this issue could be alleviated by the addition of SDC.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe internal steam-generating MIFC was fabricated by simple dip-coating method using these shrinkage differences. Dip-coated half-cells with diverse slurries were sintered at 1450 \u003csup\u003eo\u003c/sup\u003eC for 3 hours. The surficial morphology of this BZCYYb coated half-cell was shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea. The significant quantities of pores apparently formed on the surface of half-cell and would be primarily attributed to the low shrinkage of BZCYYb at 1450 \u003csup\u003eo\u003c/sup\u003eC. The two different viscosities of SDC slurries were prepared to remain porous structure and form dense surface on this BZCYYb layer. The SDC slurry 1 and slurry 2 were 12.0 cP and 599 cP, respectively. (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e) Upon additional dip-coating with SDC low-viscosity slurry 1, the assistance of densification during sintering at 1450 \u003csup\u003eo\u003c/sup\u003eC for 3 hours led to narrow the pores on the surface of the half-cell. (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eb) However, the residual pores on the surface half-cell were still observed on the surface. It presumed that low-viscosity SDC slurry can penetrated into the porous NiO/BZCYYb during dip-coating leaving only slight coverage on the anode surface with large pores remaining. In comparison with SDC slurry 1, using the SDC slurry 2 including higher viscosity led to acquire the dense surface as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ec. The less void concentration of coated layer using SDC slurry 2 caused these morphological differences. Furthermore, SDC slurry 2 might have difficulties to penetrate into the both anode and electrolyte of the half-cell due to the high viscosity.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFor fabricating half-cell of MIFC, the porous BZCYYb layer was initially dip-coated on the as-prepared anode pellet. Thereafter, SDC slurry 1 and slurry 2 also subsequently covered on this half-cell and additionally sintered at 1450 \u003csup\u003eo\u003c/sup\u003eC for 3 hours. The cross-sectional SEM image of the half-cell of MIFC was shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ea. The backscattered electrons in the SEM image clearly distinguished between the electrolyte and Ni. The brightness of electrolyte and Ni particles separated into the bright and dark regions, respectively. The anode layer at the bottom of the half-cell exhibited large pores with heterogeneous distribution of Ni and electrolyte particles. The distinguishable Ni, Ba, Sm and Ce signals in the energy dispersive X-ray (EDS) mapping clearly demonstrated the anode region. (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eb) The upper region of the anode layer in the cross-sectional SEM image corresponded to the electrolyte layers of which thickness was 18 \u0026micro;m comprising porous\u0026thinsp;~\u0026thinsp;10 \u0026micro;m-thick layer (Yellow box A) and ~\u0026thinsp;6 \u0026micro;m-thick dense layer (Yellow box B). The configuration of porous BZCYYb layer was arisen from poor shrinkage as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea. Furthermore, the dip-coating slurry 1 spread slight portion of SDC uniformly across entire layers as indicated by the Sm signal in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eb. The yellow arrow in the magnified SEM image of the yellow box A revealed that the surface of the micro-sized BZCYYb was decorated with incorporated SDC nanoparticles. (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ec) The SDC slurries also densified the top side of the BZCYYb layer which had been caused by the effect of SDC acting as sintering aid for BZCYYb as mentioned in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eb. Similar to typical sintering aids located at grain boundaries, [22] the healed grain boundaries of BZCYYb were also confirmed in the magnified SEM image of yellow box B. (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ed) As a result, layered mixed ionic-conducting electrolyte with porous BZCYYb layer was successfully fabricated by exploiting differences in shrinkage behavior and slurry viscosities through simple dip-coating method.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eTo verify the importance of layered structure of MIFC, the dip-coating of mixed BZCYYb and SDC electrolyte was also conducted to prepare the reference cell in the simple way. Figure\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e presented the I-V curves and impedance spectra of the mixed MIFC and layered MIFC at 600 \u003csup\u003eo\u003c/sup\u003eC with H\u003csub\u003e2\u003c/sub\u003e fuel. The mixed MIFC exhibited poor open circuit voltage (OCV) of 0.92 V, whereas the layered MIFC had reasonable OCV of 1.06 V. (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ea) This phenomenon was mainly attributed to the intrinsic characteristics of SDC. It has been widely reported that the reduction of Ce\u003csup\u003e4+\u003c/sup\u003e to Ce\u003csup\u003e3+\u003c/sup\u003e in SDC significantly increased electronic conductivity during SOFC operation, thereby leading to decrease in OCV. [23] Thus, the mixed MIFC with large portions of SDC in electrolyte layer could follow the characteristics of SDC. On the other hand, in the case of the layered MIFC, the inter-diffusion between BZCYYb and SDC during sintering resulted in the thin layer of doped barium cerate and zirconate at the interface, which successfully inhibited the electronic conduction of SDC and improved the OCV. [24] Although the slope in the I-V curve of the mixed MIFC sharply decreased in the ohmic polarization region with the increase in current density as well, that of the layered MIFC dropped gradually. These resulted in divergent maximum power densities of 0.16 W cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e for the mixed MIFC and 0.40 W cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e for the layered MIFC, respectively. The layered MIFC had significantly lower ohmic resistance of 0.54 Ohm cm\u003csup\u003e2\u003c/sup\u003e compared to that of mixed MIFC even though the absolute value was not detected in the mixed MIFC due to the range of measured frequency. (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eb) This corresponded well to the sharp ohmic losses detected in the polarization curve of the mixed MIFC.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eI\u0026ndash;V curves for the MIFCs with methane were also detected as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e. The OCV of the mixed MIFC and layered MIFC remained with feedstock change about 0.92 V and 1.06 V, respectively. (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003ea) The observed current densities were lower than the case of hydrogen due to the smaller ΔG of the methane reforming reaction compared with the hydrogen/air reaction. [25] The maximum power densities of mixed MIFC and layered MIFC were 0.10 W cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e and 0.20 W cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e, respectively. The decrease in the power density of the MIFCs with methane was ascribed to slower electrochemical oxidation of methane than that of hydrogen. The further impedance measurements were conducted to figure out the different resistances associated with MIFC operation on hydrogen and methane fuel. (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003eb) The main differences in impedance spectra occurred at the high-frequency region. The resistance in the high-frequency region for methane was noticeably higher than that for hydrogen in the mixed MIFC. In contrast, the resistance in this region showed only slight increase in the layered MIFC. The resistance in high-frequency region is assigned to fuel oxidation reaction at the anode. [26] Since the rapid supplying of oxide ions from dispersed SDC in the anode can promote oxidation of methane. [27] Furthermore, generating steam at the anode also can participate in the methane reforming reactions. [28] The ohmic resistances of the MIFCs were also higher during methane operation due to the reduction in the local cell temperature caused by the endothermic methane reforming reactions, which in turn led to lower ionic conductivity of the electrolyte. [29] Considering these results, the internal steam generation was primarily responsible for higher power density with the methane fuel.\u003c/p\u003e \u003cp\u003eLong-term operation with methane at 600 \u003csup\u003eo\u003c/sup\u003eC under constant current density of 0.1 A cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e was carried out for both the mixed and layered MIFCs. (Fig. 8a) The layered MIFC maintained stable operation for 50 hours, whereas the mixed MIFC deteriorated within 2 hours. In the course of long-term operation, it was confirmed that the layered MIFC generated and coagulated at the anode side. (Fig. 8b) These results obviously indicated that the internal steam generation by layered structure of MIFC enhanced the coke tolerance.\u003c/p\u003e"},{"header":"4. Conclusions","content":"\u003cp\u003eThe new design of mixed ion conducting fuel cell was introduced in this study. The MIFC was successfully fabricated using BZCYYb as a proton conductor and SDC as an oxide ion conductor through simple dip-coating method. The significant difference in shrinkage between BZCYYb and SDC at 1450 \u003csup\u003eo\u003c/sup\u003eC enabled to render the electrolyte surface porous or dense. Leveraging these distinct sintering behaviors and slurry viscosities, the two types of mixed and layered MIFC were manufactured and compared to highlight the importance of internal steam generation at the anode side. The layered MIFC demonstrated significantly higher stability and power density compared to the mixed MIFC. The maximum power densities for the mixed and layered MIFCs were 0.16 W cm\u003csup\u003e-2\u003c/sup\u003e and 0.40 W cm\u003csup\u003e-2\u003c/sup\u003e at 600 \u003csup\u003eo\u003c/sup\u003eC for H\u003csub\u003e2\u003c/sub\u003e, and 0.10 W cm\u003csup\u003e-2\u003c/sup\u003e and 0.20 W cm\u003csup\u003e-2\u003c/sup\u003e at 600 \u003csup\u003eo\u003c/sup\u003eC for methane, respectively. While the voltage of the mixed MIFC sharply dropped within 2 hours, the layered MIFC maintained stable performance for 50 hours during methane reforming at 600\u0026deg;C under 0.1 A cm\u003csup\u003e-2\u003c/sup\u003e. The internal steam generation in the layered structure contributed to higher power densities and reduced coke formation. These results highlighted the potential of the layered MIFC to enhance fuel cell performance, particularly in applications using hydrocarbon fuels.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis research was supported by the National Research Foundation of Korea (NRF) grant funded by the Ministry of Science and ICT (MSIT) (RS-2021-NR060108). This research was also supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (RS-2024-00462805).\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;\u003cstrong\u003eCompeting interests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare no competing interests.\u003c/p\u003e\n"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eL. Fan, C. Li, P. V. Aravind, W. Cai, M. Han, N. 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Rosensteel, S. M. BabiniecD. D. Storjohann, J. Persky, N. P. Sullivan, Use of anode barrier layers in tubular solid-oxide fuel cells for robust operation on hydrocarbon fuels, \u003cem\u003eJ. Power Sources\u003c/em\u003e 205 (2012) 108-113. https://doi.org/10.1016/j.jpowsour.2012.01.035.\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"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":"journal-of-electroceramics","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"jecr","sideBox":"Learn more about [Journal of Electroceramics](https://link.springer.com/journal/10832)","snPcode":"10832","submissionUrl":"https://submission.nature.com/new-submission/10832/3","title":"Journal of Electroceramics","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Protonic ceramic fuel cell, mixed ion-conducting, shrinkage, steam, methane","lastPublishedDoi":"10.21203/rs.3.rs-6550800/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6550800/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eFuel cells provide efficient and eco-friendly alternatives to traditional combustion-based power generation. Among various types, protonic ceramic fuel cell (PCFC) has emerged as promising candidates due to their ability to operate at lower temperature and feasibility for methane usage. Although solid oxide fuel cell (SOFC) naturally generates steam at the anode during operation, PCFC necessitates the installation of an external steam generator to for mitigating carbon coke formation and incomplete conversion. This study introduces a novel mixed ion-conducting fuel cell (MIFC) design for internal steam generating in the anode side of PCFC. The MIFC was fabricated with BaZr\u003csub\u003e0.1\u003c/sub\u003eCe\u003csub\u003e0.7\u003c/sub\u003eY\u003csub\u003e0.1\u003c/sub\u003eYb\u003csub\u003e0.1\u003c/sub\u003eO\u003csub\u003e3-δ\u003c/sub\u003e (BZCYYb) as a proton conductor and Sm\u003csub\u003e0.2\u003c/sub\u003eCe\u003csub\u003e0.8\u003c/sub\u003eO\u003csub\u003e2-δ\u003c/sub\u003e (SDC) as an oxide ion conductor via dip-coating leveraging the shrinkage difference and coating slurry viscosities. The layered structure of the MIFC significantly improved maximum power densities of 0.40 W cm\u003csup\u003e-2\u003c/sup\u003e for hydrogen and 0.20 W cm\u003csup\u003e-2\u003c/sup\u003e for methane at 600 \u003csup\u003eo\u003c/sup\u003eC. The layered MIFC also achieved highly table performance at long-term methane reforming at 0.1 A cm\u003csup\u003e-2\u003c/sup\u003e for 50 hours. Internal steam generation from the layered structure contributed to higher power densities and mitigated coke formation. The results highlight its potential for applications using hydrocarbon fuels.\u003c/p\u003e","manuscriptTitle":"Internal steam generation via mixed ion-conducting fuel cell for methane reforming at 600ºC","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-05-06 13:08:55","doi":"10.21203/rs.3.rs-6550800/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2025-05-18T16:05:03+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-05-12T10:21:33+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"238193883986752512806235416380128033864","date":"2025-05-08T17:44:28+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-05-03T08:38:45+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"204151950940234975313895690084855388798","date":"2025-05-03T07:31:53+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"53515471506964799896521510540826005571","date":"2025-05-02T12:39:21+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-05-01T06:58:10+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-05-01T02:07:07+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-05-01T02:05:46+00:00","index":"","fulltext":""},{"type":"submitted","content":"Journal of Electroceramics","date":"2025-04-28T21:02:30+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"journal-of-electroceramics","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"jecr","sideBox":"Learn more about [Journal of Electroceramics](https://link.springer.com/journal/10832)","snPcode":"10832","submissionUrl":"https://submission.nature.com/new-submission/10832/3","title":"Journal of Electroceramics","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"d81738f1-45e6-4d39-be06-64dde92beefb","owner":[],"postedDate":"May 6th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2025-06-23T16:03:31+00:00","versionOfRecord":{"articleIdentity":"rs-6550800","link":"https://doi.org/10.1007/s10832-025-00420-1","journal":{"identity":"journal-of-electroceramics","isVorOnly":false,"title":"Journal of Electroceramics"},"publishedOn":"2025-06-20 15:57:16","publishedOnDateReadable":"June 20th, 2025"},"versionCreatedAt":"2025-05-06 13:08:55","video":"","vorDoi":"10.1007/s10832-025-00420-1","vorDoiUrl":"https://doi.org/10.1007/s10832-025-00420-1","workflowStages":[]},"version":"v1","identity":"rs-6550800","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6550800","identity":"rs-6550800","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}