An efficient Turing-type Ag2Se-CoSe2 multi-interfacial oxygen-evolving electrocatalyst

An efficient Turing-type Ag2Se-CoSe2 multi-interfacial oxygen-evolving electrocatalyst | 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 An efficient Turing-type Ag 2 Se-CoSe 2 multi-interfacial oxygen-evolving electrocatalyst Xiao-Long Zhang, Peng-Peng Yang, Ya-Rong Zheng, Yu Duan, Shaojin Hu, and 13 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-39890/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Although the Turing structures, or stationary reaction-diffusion patterns, have received increasing attention in biology and chemistry, making such unusual patterns on inorganic solids is fundamentally challenging. We report a simple cation exchange approach to produce Turing-type Ag2Se on CoSe2 nanobelts relied on diffusion-driven instability. The resultant Turing-type Ag2Se-CoSe2 material is highly effective to catalyze the oxygen evolution reaction (OER) in alkaline electrolytes with an 84.5% anodic energy efficiency. Electrochemical measurements show that the intrinsic OER activity correlates linearly with the length of Ag2Se-CoSe2 interfaces, determining that such Turing-type interfaces are more active sites for OER. Combing X-ray absorption and computational simulations, we ascribe the excellent OER performance to the optimized adsorption energies for critical oxygen-containing intermediates at the unconventional interfaces. Our work offers opportunities for creating Turing structures in other inorganic nanomaterials with unexplored catalytic abilities. Materials Chemistry Materials Engineering Catalysis Ag2Se-CoSe2 multi-interfacial oxygen-evolving electrocatalyst Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Introduction Almost seven decades ago, Alan Turing predicted the chemical reaction-diffusion model, in which a pair of activator and inhibitor can interact and self-regulate to form spatiotemporal stationary patterns 1 . This reaction-diffusion model has become a classic mechanism for morphogenesis in biological 2,3 ( e.g. , skin patterns of the pufferfish; Fig. 1a) and chemical systems 4 . In experiments on chemical systems, previous research has led to stationary Turing patterns occurred in the chlorite-iodide-malonic acid 5-7 (CIMA) and the Belousov-Zhabotinsky 8,9 (BZ) reactions. Later, a number of two- and three-dimensional Turing structures was investigated in chemical 10,11 and living systems 12,13 . Very recently, Tan and co-workers reported the preparation of a Turing-type polyamide membrane, which shows markedly enhanced water-salt separation performance compared to the conventional desalination membranes 14 . Creating Turing structures in chemical systems currently remains a huge challenge. The difficulty comes from the necessary requirement that the reaction-diffusion process should evolve far from thermodynamic equilibrium 1,15,16 , in which the inhibitors have a higher diffusion coefficient than the activators, leading to short-range activation and long-range inhibition 17 (Fig. 1b). Nevertheless, in homogeneous media, most chemical reactions involve small molecules with similar or inappropriately differing diffusion coefficients 18,19 . Such difficulty can, in principle, be overcome by introducing an unreactive reagent that reversibly binds the activator species, thus causing suitable differences in the diffusion coefficients 6,7,14 . This has been demonstrated via coupling starch or polyvinyl alcohol with triiodide (activator) in the CIMA reaction 7 . Although considerable progress, there is no observation of stationary Turing patterns in inorganic solid nanomaterials has been reported thus far. Here, we report the first experimental demonstration of Turing-type silver selenide (Ag 2 Se) nanostructures that patterned on cobalt diselenide (CoSe 2 ) nanobelts by reacting Ag + ions with previously synthesized CoSe 2 (ref. 20) in a diethylenetriamine (DETA)-deionized water (DIW) binary solution at room temperature. The conversion from CoSe 2 to Ag 2 Se is a thermodynamic driving process 21,22 , in which the low-mobility CoSe 2 is the activator and the fast-diffusing Ag + ions are the inhibitor 23 , thus resulting in a diffusion-driven instability and forming Turing structures. The resultant new material possesses rich Turing-type Ag 2 Se-CoSe 2 interfaces, which manifest excellent activity for electrocatalytic oxygen evolution reaction (OER). Moreover, we show the high robustness of the Turing-type Ag 2 Se nanostructures under harsh OER process. The observed OER performances can be attributed to the large number of Turing interfaces, which are experimentally and computationally confirmed as more favorable sites for the adsorption of oxygen-containing OER intermediates. Results Synthesis and characterization of Turing-type Ag 2 Se-CoSe 2 Stationary Turing patterns have been widely observed in living systems 12,13,15 , such as diodon holocanthus (commonly known as the pufferfish; Fig. 1a). The striped patterns in the pufferfish inspired that a high density of interfaces are likely created when Turing structure can be made in inorganic materials. Chemical transformation of one inorganic solid to another by atom exchange in solution is generally considered as a reaction-diffusion process 24 . This transformation, also known as ion-exchange reaction, has previously been used to pattern solids on nanoscale, leading to new materials with higher compositional and structural complexity 25 . We hypothesize here that cation exchange may offer the ability to generate a Turing pattern once the diffusion coefficients of two cations are appropriately different. We want to react CoSe 2 nanobelts with Ag + ions to produce Ag 2 Se, considering that the conversion to Ag 2 Se is thermodynamically favored with a driving force of around -1000 kJ mol -1 in the bulk 26 . The previously developed CoSe 2 nanobelts 20 (Supplementary Fig. 1) are the material of choice because they can provide adequate surface regions for the development of Turing structures. In a typical synthesis, the as-synthesized CoSe 2 nanobelts were dispersed in a mixture of DETA and DIW (2/1, v/v) under vigorous stirring. After completely dispersing, AgNO 3 was added and the reaction solution was continuously stirred at room temperature for 4 hours. In this system, CoSe 2 is the activator, and AgNO 3 is the inhibitor (Fig. 1b). The reaction starts when the fast-diffusing Ag + comes to the CoSe 2 surface and replaces Co 2+ ions in the solid phase. Because the markedly lower diffusion of Co 2+ , this activator initially replaced by the locally available Ag + inhibitor. As the reaction proceeds, more Co 2+ activator diffuses to exchange with nearby inhibitor, and eventually a Turing-type Ag 2 Se pattern forms across the surface of the CoSe 2 nanobelts (Fig. 1c). We note that the diffusion coefficient of Ag + ions is ~10 -5 cm 2 s -1 (ref. 23), orders of magnitude higher than that of Co 2+ ions in CoSe 2 . Such differences in the diffusion coefficients of the two species thus meet the requirement of activator/inhibiotr-mediated patterning, which result in the unusual Turing structures (Fig. 1c). We examined the surface morphology of the as-synthesized sample by scanning electron microscopy (SEM), which shows regular striped patterns over the entire CoSe 2 support (Fig. 2a, Supplementary Fig. 2). Transmission electron microscopy (TEM; Fig. 2b) and scanning TEM (STEM; Fig. 2c) studies reveal that very refined and interconnected Ag 2 Se networks grew on CoSe 2 , forming the nanoscale Turing-type structures. To visualize the Ag 2 Se-CoSe 2 interfacial structure, we performed high-angle annular dark-field STEM (HAADF-STEM). Figure 2d validates the formation of distinct solid-state interface with the contrast mainly from the difference in atomic number between Ag 2 Se and CoSe 2 (Supplementary Fig. 3). The dashed circles in Figure 2d highlight different lattice configurations, and their corresponding fast Fourier transform (FFT) patterns feature cubic CoSe 2 (Fig. 2e) and orthorhombic Ag 2 Se (Fig. 2f), respectively. Energy-dispersive X-ray spectrum (EDX) elemental mappings further evidence that Ag 2 Se developed on the CoSe 2 support, where Ag appears only in the Turing-patterned regions (Supplementary Figs. 4, 5). Additionally, our X-ray diffraction (XRD; Supplementary Fig. 6a) measurements confirm the combination of cubic CoSe 2 (JCPDS 09-0234) and orthorhombic Ag 2 Se (JCPDS 24-1041) phases, consistent with the Raman results (Supplementary Fig. 6b). We carried out a series of control experiments to explore the formation of Turing-type Ag 2 Se-CoSe 2 structure. Despite cation exchange is commonly prohibited at room temperature in the bulk phase, results show that our reaction happened at room temperature with a fast rate. This phenomenon could be ascribed to the reduced reaction barrier in nanosized materials 27 , as well as the favorable thermodynamic driving force for forming Ag 2 Se (ref. 26). We tracked the evolution of the Turing structures as a function of reaction time (Supplementary Figs. 7, 8). The diffusion-driven instability allowed this Turing structures to develop well at mere 1 h; markedly prolonging the reaction time to 12 h resulted in a hollowed-out structure. Moreover, the concentration of AgNO 3 appears to be also critical (Supplementary Figs.9-11). At low Ag + concentration, the transformation reaction initiated only at the edges of CoSe 2 nanobelts where the Co 2+ diffusion is easier because of the energy minimization. The addition of excess Ag + would cause the formation of over-carved material. Our experiments thus reveal that reacting 7.84 mmol L -1 AgNO 3 with CoSe 2 at room temperature for 4 h yields the optimal Turing-type Ag 2 Se-CoSe 2 structure. We investigated the physicochemical properties of the novel Turing-type Ag 2 Se-CoSe 2 material by multiple characterization techniques. Differential scanning calorimetry (DSC) in Figure 2g exhibits a pair of endothermic (located at 417 K) and exothermal (located at 360 K) peaks for the Ag 2 Se-CoSe 2 , which could be the result of a phase transition from low-temperature cubic to high-temperature superionic phase of Ag 2 Se (ref. 28) (Insets in Fig. 2g). This superionic conducting phase transition of Ag 2 Se-CoSe 2 thus hints at potentially high cation mobility of the new structure 29 . Electrical conductivity tests as a function of temperature reveal consistently higher conductivity of the Ag 2 Se-CoSe 2 than that of metallic CoSe 2 (Fig. 2h). Such conductivity enhancement suggests that the Turing-type Ag 2 Se-CoSe 2­ interfaces facilitate electron transfer. Moreover, we performed the work function measurement of Ag 2 Se, CoSe 2 , and Ag 2 Se-CoSe 2 by ultraviolet photoelectron spectroscopy (UPS; Fig. 2i). The results show a lower work function of 3.73 eV for Ag 2 Se-CoSe 2 , versus 3.93 eV for CoSe 2 and 4.24 eV for Ag 2 Se, indicating a modulated electronic structure of Ag 2 Se-CoSe 2 that permit an easier electron transfer, in line with conductivity results 30 . OER performance of Turing-type Ag 2 Se-CoSe 2 catalyst The boosted electron transfer property of Ag 2 Se-CoSe 2 prompted us to explore this new structure for negotiating the sluggish OER catalysis, considering that decent OER activities have been observed previously on CoSe 2 -based catalysts 31-34 . We compared the OER activity of our Turing-type Ag 2 Se-CoSe 2 catalyst with that of four references CoSe 2 , Ag 2 Se, NiFe LDH, and 20 wt% Ir/C catalysts. Rotating disk electrode (RDE) measurements in O 2 -saturated 0.1 M KOH exhibit that Ag 2 Se-CoSe 2 needs an overpotential of mere 221 mV at 10 mA cm -2 , which increased to 399 mV for CoSe 2 , 350 mV for NiFe LDH, and 393 mV for Ir/C (Fig. 3a). By sharp contrast, Ag 2 Se itself affects negligible OER activity. Tafel analysis (Fig. 3b) yields a slope of 52, 175, 66 and 101 mV decade -1 for Ag 2 Se-CoSe 2 , CoSe 2 , NiFe LDH and Ir/C catalyst, respectively. A considerably smaller slope achieved in Ag 2 Se-CoSe 2 implies markedly enhanced kinetics for OER. We also conducted electrochemical impedance spectroscopy (EIS) at 340 mV overpotential to probe the charge transfer resistance ( R ct ) for these catalysts. Our measurements (Supplementary Fig. 12) exhibit that the R ct of Ag 2 Se-CoSe 2 is ~13 ohms, versus ~41, 18573, 30, 148 ohms for CoSe 2 , Ag 2 Se, NiFe LDH and Ir/C catalyst, respectively. The smaller R ct for Ag 2 Se-CoSe 2 suggests an improved charge transfer between the catalyst surface and sorbates ( e.g. , O 2 2- and O 2- ) in the OER process 35 . This result agrees well with our double-layer capacitance ( C dl ) measurements (Supplementary Figs. 13) that give the largest C dl value for Ag 2 Se-CoSe 2 , which also matches with our conductivity and work function results that Ag 2 Se-CoSe 2 allows more favorable electron transfer. We systematically assessed the OER performances of the Ag 2 Se-CoSe 2 catalysts that synthesized at different reaction times and Ag + concentrations, results of which we show in Supplementary Figures 14 to 16. We uncovered that Ag 2 Se-CoSe 2 with unique Turing-type structure gives the optimal catalytic property, so the rich Turing interfaces aforementioned could be responsible for the superior OER activity. We also underscore that the performance gained from the RDE testing here ranks among the superb for the OER electrocatalysts reported previously (Supplementary Fig. 17). Besides activity, the Ag 2 Se-CoSe 2 catalyst also exhibits excellent operating stability (Supplementary Figs. 18 and 19). For example, our multistep chronopotentiometry recorded at 10, 30 and 50 mA cm -2 reveals mere a small decay over 70 h of continuous electrolysis (Supplementary Fig. 19). To verify the hypothesis that Turing-type Ag 2 Se-CoSe 2 interfaces are more OER active sites, we plotted the exchange current density ( j 0 ; the most inherent measure of OER activity 36,37 ) of each sample versus the Ag 2 Se interface length and the Ag 2 Se covered area (Figs. 3c and d, Supplementary Figs. 20-22), respectively. We find that the j 0 increases linearly as the interface length is increased (Fig. 3c). When plotting versus the Ag 2 Se covered area, a volcano-shaped dependence of the j 0 was obtained (Fig. 3d), further revealing that the reaction rate is directly proportional to the amount of interface sites. These results thus elucidate that the OER reaction takes place more energetically at the Ag 2 Se-CoSe 2 interfaces. We used gas chromatography (GC) to detect and quantify the O 2 product evolved from the Ag 2 Se-CoSe 2 -docerated carbon paper electrode at 10 mA cm -2 . The measured O 2 gas perfectly matches with the theoretical value, corresponding to a Faradaic efficiency of ~100% (Fig. 3e). As a result, we achieved a high anodic energy efficiency up to 84.5%, which far exceeds that of CoSe 2 (73.7%) and also compares favorably to 76.2% for NiFe LDH and 74.4% for Ir/C catalyst (Fig. 3f), respectively. Spectroscopic studies of the Turing-type Ag 2 Se-CoSe 2 catalyst We now study the impact of Ag 2 Se-CoSe 2 interfaces on the electronic structure and catalytic character by using diverse spectroscopic techniques. Prior reports have demonstrated that orthorhombic Ag 2 Se contains Ag (1) occurring in tetrahedral coordination and Ag (2) in triangular coordination 38 (Supplementary Fig. 23). Our valence band spectrum of Ag 2 Se reveals two intensive features at 5.31 and 6.15 eV (Fig. 4a), originating from Ag (1) 5 d and Ag (2) 5 d states 39 , respectively. When forming interfaces with CoSe 2 , a large negative shift (~190 mV) of the Ag (1) 5 d state is observed, whereas the Ag (2) 5 d feature is undisturbed. This result suggests that Ag + coordinates tetrahedrally with Se 2- at the novel Turing-type interfaces (Supplementary Fig. 24). Figure 4b presents the Co K-edge X-ray absorption near-edge structure (XANES), which shows that the absorption edge of Ag 2 Se-CoSe 2 is shifted to a lower energy versus CoSe 2 because of charge transfer from Ag 2 Se to Co (Supplementary Fig. 25) 40 . Extended X-ray absorption fine structure (EXAFS) spectra (Fig. 4c) of Ag 2 Se-CoSe 2 and CoSe 2 are similar, both showing a peak at ~2.04 Å that ascribed to Co-Se (ref. 33). After OER, two distinct peaks appear in EXAFS spectra: the former at 1.47 Å is due to Co-O, and the latter 2.40 Å is attributed to Co-Co, indicating the formation of CoOOH because of surface self-reconstruction of Ag 2 Se-CoSe 2 catalyst during OER (ref. 41). Intriguingly, the peak at 2.04 Å, characteristic of CoSe 2 , is still observed after OER (Fig. 4c). By contrast, single CoSe 2 undergoes a complete surface self-reconstruction to form CoOOH after OER (Supplementary Fig. 26). The EXAFS wavelet transform (Fig. 4d) analyses－a technique that can discriminate the backscattering atoms－further verify that Co-Se bond (~ 7.82 Å -1 in k space) remains in Ag 2 Se-CoSe 2 after OER. Unexpectedly, our Ag 3 d X-ray photoelectron spectroscopy (XPS) analysis (Fig. 4e) reveals that the Ag valence state is unaltered after we performed OER on Ag 2 Se-CoSe 2 catalyst at a 221 mV overpotential (10 mA cm -2 ) for 12 h. Moreover, the signal from Ag-Se bond (at 54.2 eV) 42 in Se 3 d (Fig. 4f, Supplementary Fig. 27) further supports that Ag 2 Se phase survives after OER, agreeing with Se K-edge XANES results (Fig. 4g, Supplementary Fig. 28). By contrast, only oxidized Se species 43 were detected from single CoSe 2 catalyst after OER (Fig. 4f), suggesting a complete surface self-reconstruction to CoOOH. On the basis of above results, we become clear about the nature at the Turing-type Ag 2 Se-CoSe 2 interfaces. In the reaction-diffusion system, Ag + ions replace the Co 2+ ions in CoSe 2 nanobelts and tetrahedrally coordinates with Se 2- , creating Turing-type Ag 2 Se-CoSe 2 interfaces where the e g filling of adjacent Co cations is increased. This hence causes a near-unity e g occupancy of surface Co cations, leading to enhanced OER activity 40,44 . Moreover, such interfaces also show extreme structural robustness against harsh OER corrosion (Fig. 4h). Density functional theory calculations To better understand the catalytic nature of the Ag 2 Se-CoSe 2 interfaces, we carried out density functional theory (DFT) calculations. On the basis of experimental characterizations above, we created the Ag 2 Se-CoSe 2 model by bridging Ag 2 Se (112) and CoSe 2 (210) surfaces; regions remote to the interface were replaced with CoOOH to represent the catalyst during OER (Supplementary Figs. 29, 30). Detailed reaction-pathway calculations (Fig. 5a) reveal that the desorption of *OOH to generate O 2 on CoSe 2 (210) is kinetically hindered because of the high barrier of 2.976 eV. On the interface sites, the rate-determining *OOH intermediate is reduced by 0.904 eV, which gives a weaker *OOH adsorption, consistent with our Bader charge analysis 45 (Supplementary Fig. 31). DFT calculations further predict that the Co-O bond length increases from 1.79 to 1.84 Å on the Ag 2 Se-CoSe 2 interface (Supplementary Fig. 32), which explains the weaker *OOH adsorption on Ag 2 Se-CoSe 2 interface relative to CoSe 2 . A plot of the electron density difference (Fig. 5b) displays that the donation of electrons from the Ag 2 Se to nearby Co sites occurs at the interface, which permits e g -orbital occupancy of Co closer to unity and thus enhanced OER activity 40,44 , matching well with our XANES measurements. Moreover, the calculated projected density of states (PDOS; Fig. 5c) shows that the d -band center of Co atom in Ag 2 Se-CoSe 2 deviates more from the Fermi level than that of single CoSe 2 (210), further evidencing the weak binding of *OOH intermediate on the Ag 2 Se-CoSe 2 interfaces 46 . Lastly, to examine the O 2 binding abilities of Ag 2 Se-CoSe 2 and CoSe 2 catalysts, we performed the temperature-programmed desorption analysis. Figure 5d shows that Ag 2 Se-CoSe 2 gives a lower O 2 onset desorption temperature of 111 o C versus single CoSe 2 (195 o C), which we consider to benefit the rate-determining *OOH desorption step for improved O 2 release. Thus, our results, both experimentally and computationally, have demonstrated that the Turing-type Ag 2 Se-CoSe 2 interfaces are more energetically favored to catalyze the OER. Conclusion Chemical Turing patterns in inorganic nanomaterials have not yet been reported. Here we demonstrate that Turing-driven morphogenesis occurs in a cation exchange process, which was originated from the appropriate differences between the diffusion coefficients of Ag + and Co 2+ (diffused from CoSe 2 ), creating stationary Ag 2 Se Turing patterns on CoSe 2 nanobelts. The obtained new material comprises abundant Turing-structured Ag 2 Se-CoSe 2 interfaces, which enable excellent OER electrocatalytic activity and stability in alkaline electrolyte. Our work opens the possibility of producing stationary reaction-diffusion patterns in inorganic solids that would not otherwise have such structures. Furthermore, the unusual engineered interfaces may see application in a wider spectrum of electrocatalytic processes. Methods Material synthesis All chemicals are of analytical grade and were used as received without further purification. Synthesis of CoSe 2 /DETA nanobelts The CoSe 2 /DETA nanobelts were synthesized by a hydrothermal method using our previously developed method 20 . Briefly, 0.249 g Co(AC) 2 ⋅H 2 O and 0.173 g Na 2 SeO 3 were added into a mixed solution (40 ml) with a volume ratio of V DETA /V DIW = 2:1 (DIW = deionzed water). After stirring for 30 min, the obtained wine solution was transferred into a Teflon-lined autoclave, which was sealed and maintained at 180 o C for 17 h. The resulting CoSe 2 nanobelts were carefully washed and dried before use. Synthesis of Turing-type Ag 2 Se-CoSe 2 catalyst The Turing-type Ag 2 Se-CoSe 2 was prepared through an ion-exchange reaction. Briefly, 20 mg freshly made CoSe 2 nanobelts was added into a mixed solution (15 mL) with a volume ratio of V DETA /V DIW = 2:1. After completely dispersing, 20 mg AgNO 3 was added and drastically stirring at room temperature for 4 h, the obtained Turing-type Ag 2 Se-CoSe 2 powder was carefully washed and dried before use. Material characterizations X-ray powder diffraction (XRD) was obtained from a Philips X’Pert Pro Super X-ray diffractometer with Cu Kα radiation (λ = 1.54178 Å). The morphology of the samples was achieved by SEM (Zersss Supra 40) and TEM (Hitachi H7650). The STEM and HAADF images, SAED, and EDX elemental mappings were measured on JEMARM 200F Atomic Resolution Analytical Microscope with an acceleration voltage of 200 kV. Raman spectra were taken on a Raman microscope (Renishaw®) excited with a 514 nm excitation laser. ICP-AES data were investigated by an Optima 7300 DV instrument. Ultraviolet-photoelectron spectroscopy was obtained at the BL11U beamline of National Synchrotron Radiation Laboratory in Hefei, China. The X-ray absorption spectra of Co L-edges were taken on the BL10B beamline of National Synchrotron Radiation Laboratory in Hefei (China). The X-ray absorption spectra of Co and Se K-edges were carried out at the beamline 14W1 of Shanghai synchrotron Radiation Laboratory (China). XPS was performed on an X-ray photoelectron spectrometer (ESCALab MKII) with an X-ray source (Mg Kα hυ =1253.6 eV). The O 2 - temperature-programmed desorption analysis (TPD) measurements were taken on AutoChem II 2920. The electrical conductivity measurements were measured by using the standard four probe transport measurement on commercial apparatus of Physical Property Measurement System (Quantum Design, PPMS). Differential scanning calorimetry (DSC) cycling curves were carried out by the NETZSCH DSC Q2000 with a heating/cooling rate of 5 K min −1 between 273 and 473 K. Electrochemical measurements All the electrochemical measurements were performed in a standard three-electrode cell at ambient temperature connected to a VSP-300 potentiostat (BioLogic, France). Ag/AgCl (3.5 M KCl) electrode and graphite rod were used as the reference and counter electrodes, respectively. The potentials reported in this work were normalized versus the RHE through a standard RHE calibration (E = E Ag/AgCl + 0.97 V). A rotating disk electrode (RDE) with glassy carbon (PINE, 5.00 mm diameter, disk area: 0.196 cm 2 ) was used as the working electrode. To make the working electrodes, 5 mg catalyst powder was dispersed in 1 ml of 1:3 v/v isopropanol/DIW mixture with 20 μL Nafion solution (5 wt%), which was ultrasonicated to yield a homogeneous ink. Then, 8 μL catalyst ink was pipetted onto the glassy carbon disk to ensure the catalyst loading of ~0.2 mg cm -2 . The fresh electrolytes (0.1 M KOH) were bubbled with pure oxygen for 30 min before measurements. The electrodes were pre-cycled between 0 and 0.8 V vs. Ag/AgCl at a sweep rate of 100 mV s −1 for 30 cycles until reaching the stable state, then the OER polarization curves were recorded at a sweep rate of 2 mV s -1 and 1600 r.p.m (to remove the O 2 bubbles formed in situ ) at ambient temperature. The EIS measurement was performed in the same configuration at 340 mV overpotential over a frequency range from 100 KHz to 100 mHz at the amplitude of the sinusoidal voltage of 5 mV. The polarization curves were re-plotted as overpotential ( η ) versus log current (log j ) to get Tafel plots to assess the HER kinetics of investigated catalysts. The Tafel slope ( b ) can be obtained by fitting the linear portion of the Tafel plots to the Tafel equation ( ). The exchange current density ( j 0 ) were calculated from Tafel curves using extrapolation method. The values of mass activity (A mg -1 ) were calculated from the catalyst loading m (0.2 mg cm -2 ) and the current density of 10 mA cm -2 : mass activity = j / m . The Ag 2 Se-CoSe 2 -modified carbon paper (catalyst loading: ~0.20 mg cm −2 ) was used as working electrode to conduct chronopotentiometry experiments. The O 2 product, evolved from the Ag 2 Se-CoSe 2 -docerated carbon paper electrode at 10 mA cm -2 , was detected and quantified by gas chromatography. The accelerated stability measurements were carried out by potential cycling between 0 and 0.6 V Ag/AgCl at a sweep rate of 100 mV s −1 . After cycling, the resultant electrode was used for polarization curves with a sweep rate of 2 mV s −1 . To estimate the double-layer capacitance, cyclic voltammograms were measured at different sweep rates in the potential region of 1.25-1.35 versus RHE at ambient temperature. All the polarization curves were corrected with i R compensation that resulted from the solution resistance. Anodic energy efficiency calculations Anodic energy efficiency was calculated via the following formula 47 : (see Formula 1 in the Supplementary Files) where E 0 is the equilibrium cell potential for water decomposition (E 0 = 1.23 V). FE is the Faradaic efficiency for H 2 O to O 2 conversion, and η ,an is the overpotential at the anode and was measured at 10 mA cm -2 in this work. DFT calculations The overall OER process includes four elementary steps that follow: (see Reactions 1-4 in the Supplemental Files) Here, (*) denotes the –OH terminated CoSe 2 or Ag 2 Se- CoSe 2 surface. We used –OH groups to replace the unsaturated Se atoms as models to represent the surface hydroxylation of CoSe 2 or Ag 2 Se-CoSe 2 , because the whole structure is well maintained. These are similar to the –OH groups terminated surface of oxide models 48 . It is more convenient to calculate the thermochemistry of the OER under acidic condition. Following Bajdich et al. 49 , we consider the following elementary steps: (see Reactions 5-8 in the Supplemental Files) Reactions 5-8 are thermodynamically equivalent to reactions 1-4 shown above. The Gibbs free energy changes are calculated as follows: (see Changes in the Supplemental Files) The G values are calculated by: (see Formula 2 in the Supplemental Files) E DFT is the total energy from the DFT calculation. E ZPE is the zero-point energy, S is the entropy and T is the temperature (298K). The energy of is got from the energy of using the standard hydrogen electrode (SHE). The bond energy is calculated by: (see Formula 3 in the Supplemental Files) The density functional theory calculations were performed by Vienna ab initio simulation package (VASP) 50 program with projector augmented wave (PAW) method and the kinetic energy cut off was set to be 500 eV. The convergence criterion for the electronic self-consistent iteration was set to be 10 -4 eV. The atomic positions were fully relaxed until the force on each atom is less than 0.02 eV Å -1 . The Perdew-Burke-Ernzerhof (PBE) 51 generalized gradient approximation (GGA) exchange-correlation functional was used throughout. The slab model of CoSe 2 (210) surface was constructed based on the optimized crystal structure and we selected the right Ag 2 Se cluster anchored on the CoSe 2 (210) surface. The vacuum layer was set to be 15 Å to ensure the separation between slabs. Declarations Acknowledgements: This work was supported by the funding support from the National Natural Science Foundation of China (Grants 21975237 and 51702312), the National Basic Research Program of China (Grant 2018YFA0702001), the Fundamental Research Funds for the Central Universities (WK2340000076), and the Recruitment Program of Global Youth Experts. This work was partially performed at the USTC Center for Micro and Nanoscale Research and Fabrication. Author Contributions: M.-R.G. conceived and supervised the project. X.-L.Z. and P.-P.Y. performed the experiments, collected and analyzed the data. X.-S.Z. and J.-F.Z. performed XPS and UPS measurements. X.-L.Z., S.-J.H and X.Z. carried out the DFT calculations. T.M., F.-Y.G., Z.-Z.W., Z.-Z.N., Y.-R.Z., X.-X.Y., R.W., Y.D., C.G., L.-P.C. and S.Q. helped with electrochemical data collection and analysis. M.-R.G. and X.-L.Z. co-wrote the manuscript. All authors discussed the results and commented on the manuscript. Additional information: Supplementary information is available in the online version of the paper. Correspondence and requests for materials should be addressed to M.R.G. Competing financial interests: The authors declare no competing financial interests. References 1 Turing, A. M. The chemical basis of morphogenesis. Phil. Trans. R. Soc. Lond. B 237 , 37-72 (1952). 2 Meinhardt, H. Models of biological pattern formation . (Academic Press, 1982). 3 Murray, J. D. 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Supplementary Files SITuringtypecatalyst.pdf Supplementary Information Formulas.pdf Cite Share Download PDF Status: Posted 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-39890","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":767843,"identity":"c4e2c1b8-3487-4a6b-8c96-fc731ff1e78b","order_by":0,"name":"Xiao-Long Zhang","email":"","orcid":"https://orcid.org/0000-0002-5596-0776","institution":"University of Science and Technology of China","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Xiao-Long","middleName":"","lastName":"Zhang","suffix":""},{"id":767844,"identity":"e1d07b6c-3170-4cd9-a69b-553243e62118","order_by":1,"name":"Peng-Peng 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04:46:00","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-39890/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-39890/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":1567440,"identity":"c502efc6-61cb-41ca-b546-ecd3f9025fa6","added_by":"auto","created_at":"2020-07-15 16:11:35","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":137217,"visible":true,"origin":"","legend":"Formation of Turing-type structures. a, Photograph of the skin of a pufferfish, showing stationary Turing patterns. b, Schematic diagram of activator-inhibitor interaction in a reaction-diffusion process. Reactions leading to Turing-type structures depend on competing activation (purple) and inhibition (green) kinetic pathways. c, Schematic illustration of the formation of inorganic Turing system via ion-exchange reaction. In this system, CoSe2 is the activator, and AgNO3 is the inhibitor. The different diffusion coefficients between Co2+ in CoSe2 and Ag+ ions drive the formation of Turing-type Ag2Se patterns on the surface of CoSe2 nanobelts. ","description":"","filename":"1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-39890/v1/1.jpg"},{"id":1567441,"identity":"ca3906dd-130f-4922-8029-f38851becfcb","added_by":"auto","created_at":"2020-07-15 16:11:35","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":163216,"visible":true,"origin":"","legend":"Physical characterization of Turing-type Ag2Se-CoSe2. a-c, SEM (a), TEM (b), and STEM (c) images of the Ag2Se-CoSe2. Scale bars, 400 nm (a), 250 nm (b), 50 nm (c). d, Atomic-resolution HAADF-STEM image showing the interface ofAg2Se-CoSe2. Scale bar, 2 nm. e, f, FFT patterns of CoSe2 (e) and Ag2Se area (f), which taken from the regions marked by the dashed white and red circles, respectively. g, DSC thermogram of Ag2Se-CoSe2. Insets show the model of the cubic (top) and orthorhombic (down) Ag2Se. h, Temperature-dependent electrical conductivity for CoSe2 and Ag2Se-CoSe2, respectively. i, UPS spectra of the CoSe2, Ag2Se and Ag2Se-CoSe2.","description":"","filename":"2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-39890/v1/2.jpg"},{"id":1567442,"identity":"488a46f2-8654-4606-aab6-82cf5e414ada","added_by":"auto","created_at":"2020-07-15 16:11:36","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":95334,"visible":true,"origin":"","legend":"Electrocatalytic OER Performances of Ag2Se-CoSe2. a, OER polarization curves of different studied catalysts. Catalyst loading: 0.2 mg cm-2. Sweep rate: 2 mV s-1. b, Tafel plots of different catalysts derived from a. c, d, Exchange current density versus Ag2Se-CoSe2 interface length (c) and Ag2Se area coverage (d). Insets in c and d schematically represent the Ag2Se-CoSe2 interface (red dotted line) and Ag2Se area (red coverage), respectively. The exchange current density exhibits a linear dependence on the Ag2Se-CoSe2 interface length and a volcano-shaped dependence on Ag2Se area coverage. Exchange current densities are extracted from the Tafel plot (Supplementary Fig. 20). The Ag2Se-CoSe2 interface length and Ag2Se area coverage were calculated by using Digital Micrograph analysis (Supplementary Figs. 21 and 22). Error bars are based on the standard deviation of three independent measurements. e, GC-measured O2 amounts at different time intervals, which agree well with the theoretical values, suggesting a device Faradaic efficiency of ~100%. f, Comparison of the anodic energy efficiency of the Ir/C, CoSe2, Ag2Se-CoSe2 and NiFe-LDH catalysts.","description":"","filename":"3.jpg","url":"https://assets-eu.researchsquare.com/files/rs-39890/v1/3.jpg"},{"id":1567443,"identity":"4f8deeaa-11f7-43e5-b97e-fc30fb45ac50","added_by":"auto","created_at":"2020-07-15 16:11:36","extension":"jpg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":186272,"visible":true,"origin":"","legend":"Spectroscopic studies of Ag2Se-CoSe2 before and after OER. a, Valence band edge spectra of Ag2Se, Ag2Se-CoSe2 and CoSe2 catalysts, respectively. b, c, Co K-edge XANES and corresponding k3-weighted Fourier transforms spectra for CoSe2, CoOOH, Ag2Se-CoSe2 before and after OER, respectively. d, Corresponding wavelet transforms of k3-weighted EXAFS spectra of Co K-edge. e, Ag 3d XPS spectra of Ag2Se-CoSe2 before and after OER test. f, XPS spectra of CoSe2 and Ag2Se-CoSe2 before and after OER in Se 3d region. g, Se K-edge XANES for Ag2Se-CoSe2 before and after OER. h, Schematic of the unique surface-reconstruction feature of the Ag2Se-CoSe2 catalyst, showing that the Ag2Se-CoSe2 interface is robust without surface self-reconstruction during OER process. ","description":"","filename":"4.jpg","url":"https://assets-eu.researchsquare.com/files/rs-39890/v1/4.jpg"},{"id":1567444,"identity":"ca39b63a-64d1-4285-9624-a3a6ef242f66","added_by":"auto","created_at":"2020-07-15 16:11:36","extension":"jpg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":98147,"visible":true,"origin":"","legend":"DFT calculations and enhancement mechanism. a, Gibbs free energy change diagrams of the OER process on the CoSe2 (black line) and Ag2Se-CoSe2 (red line) surface models (both terminated with OH groups). b, Three-dimensional electron density difference on the Ag2Se-CoSe2 interface. The cyan and yellow contours represent electron density depressions and accumulations, respectively. c, Calculated density of states (DOS) of CoSe2 and Ag2Se-CoSe2 with the Fermi level aligned at 0 eV. Blue and red dashed line located at the d-band center of CoSe2 and Ag2Se-CoSe2, respectively. d, Temperature-programmed O2 desorption analyses for CoSe2 and Ag2Se-CoSe2 catalysts, respectively.","description":"","filename":"5.jpg","url":"https://assets-eu.researchsquare.com/files/rs-39890/v1/5.jpg"},{"id":15667832,"identity":"2b1f44aa-96e1-4813-9655-bc1568ea50b6","added_by":"auto","created_at":"2021-11-18 13:45:11","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":783318,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-39890/v1/b9b1436b-0256-4095-baa5-6b6784633316.pdf"},{"id":1567446,"identity":"9a092a08-dfc9-422e-9119-1230a76d0e61","added_by":"auto","created_at":"2020-07-15 16:11:37","extension":"pdf","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":16348621,"visible":true,"origin":"","legend":"Supplementary Information","description":"","filename":"SITuringtypecatalyst.pdf","url":"https://assets-eu.researchsquare.com/files/rs-39890/v1/SITuringtypecatalyst.pdf"},{"id":1567447,"identity":"a8f04876-76e9-4d9e-9855-9a4e1aef567b","added_by":"auto","created_at":"2020-07-15 16:11:37","extension":"pdf","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":111208,"visible":true,"origin":"","legend":"","description":"","filename":"Formulas.pdf","url":"https://assets-eu.researchsquare.com/files/rs-39890/v1/Formulas.pdf"}],"financialInterests":"There is \u003cb\u003eNO\u003c/b\u003e Competing Interest.","formattedTitle":"\u003cp\u003eAn efficient Turing-type Ag\u003csub\u003e2\u003c/sub\u003eSe-CoSe\u003csub\u003e2 \u003c/sub\u003emulti-interfacial oxygen-evolving electrocatalyst\u003c/p\u003e","fulltext":[{"header":"Introduction","content":"\u003cp\u003eAlmost seven decades ago, Alan Turing predicted the chemical reaction-diffusion model, in which a pair of activator and inhibitor can interact and self-regulate to form spatiotemporal stationary patterns\u003csup\u003e1\u003c/sup\u003e. This reaction-diffusion model has become a classic mechanism for morphogenesis in biological\u003csup\u003e2,3\u003c/sup\u003e (\u003cem\u003ee.g.\u003c/em\u003e, skin patterns of the pufferfish; Fig. 1a) and chemical systems\u003csup\u003e4\u003c/sup\u003e. In experiments on chemical systems, previous research has led to stationary Turing patterns occurred in the chlorite-iodide-malonic acid\u003csup\u003e5-7\u003c/sup\u003e (CIMA) and the Belousov-Zhabotinsky\u003csup\u003e8,9\u003c/sup\u003e (BZ) reactions. Later, a number of two- and three-dimensional Turing structures was investigated in chemical\u003csup\u003e10,11\u003c/sup\u003e and living systems\u003csup\u003e12,13\u003c/sup\u003e. Very recently, Tan and co-workers reported the preparation of a Turing-type polyamide membrane, which shows markedly enhanced water-salt separation performance compared to the conventional desalination membranes\u003csup\u003e14\u003c/sup\u003e.\u003c/p\u003e\n\u003cp\u003eCreating Turing structures in chemical systems currently remains a huge challenge. The difficulty comes from the necessary requirement that the reaction-diffusion process should evolve far from thermodynamic equilibrium\u003csup\u003e1,15,16\u003c/sup\u003e, in which the inhibitors have a higher diffusion coefficient than the activators, leading to short-range activation and long-range inhibition\u003csup\u003e17\u003c/sup\u003e (Fig. 1b). Nevertheless, in homogeneous media, most chemical reactions involve small molecules with similar or inappropriately differing diffusion coefficients\u003csup\u003e18,19\u003c/sup\u003e. Such difficulty can, in principle, be overcome by introducing an unreactive reagent that reversibly binds the activator species, thus causing suitable differences in the diffusion coefficients\u003csup\u003e6,7,14\u003c/sup\u003e. This has been demonstrated \u003cem\u003evia\u003c/em\u003e coupling starch or polyvinyl alcohol with triiodide (activator) in the CIMA reaction\u003csup\u003e7\u003c/sup\u003e. Although considerable progress, there is no observation of stationary Turing patterns in inorganic solid nanomaterials has been reported thus far.\u003c/p\u003e\n\u003cp\u003eHere, we report the first experimental demonstration of Turing-type silver selenide (Ag\u003csub\u003e2\u003c/sub\u003eSe) nanostructures that patterned on cobalt diselenide (CoSe\u003csub\u003e2\u003c/sub\u003e) nanobelts by reacting Ag\u003csup\u003e+\u003c/sup\u003e ions with previously synthesized CoSe\u003csub\u003e2 \u003c/sub\u003e(ref. 20) in a diethylenetriamine (DETA)-deionized water (DIW) binary solution at room temperature. The conversion from CoSe\u003csub\u003e2\u003c/sub\u003e to Ag\u003csub\u003e2\u003c/sub\u003eSe is a thermodynamic driving process\u003csup\u003e21,22\u003c/sup\u003e, in which the low-mobility CoSe\u003csub\u003e2\u003c/sub\u003e is the activator and the fast-diffusing Ag\u003csup\u003e+\u003c/sup\u003e ions are the inhibitor\u003csup\u003e23\u003c/sup\u003e, thus resulting in a diffusion-driven instability and forming Turing structures. The resultant new material possesses rich Turing-type Ag\u003csub\u003e2\u003c/sub\u003eSe-CoSe\u003csub\u003e2\u003c/sub\u003e interfaces, which manifest excellent activity for electrocatalytic oxygen evolution reaction (OER). Moreover, we show the high robustness of the Turing-type Ag\u003csub\u003e2\u003c/sub\u003eSe nanostructures under harsh OER process. The observed OER performances can be attributed to the large number of Turing interfaces, which are experimentally and computationally confirmed as more favorable sites for the adsorption of oxygen-containing OER intermediates.\u0026nbsp; \u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u003c/p\u003e"},{"header":"Results","content":"\u003cp\u003e\u003cstrong\u003eSynthesis and characterization of Turing-type Ag\u003csub\u003e2\u003c/sub\u003eSe-CoSe\u003csub\u003e2\u003c/sub\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eStationary Turing patterns have been widely observed in living systems\u003csup\u003e12,13,15\u003c/sup\u003e, such as \u003cem\u003ediodon holocanthus\u003c/em\u003e (commonly known as the pufferfish; Fig. 1a). The striped patterns in the pufferfish inspired that a high density of interfaces are likely created when Turing structure can be made in inorganic materials. Chemical transformation of one inorganic solid to another by atom exchange in solution is generally considered as a reaction-diffusion process\u003csup\u003e24\u003c/sup\u003e. This transformation, also known as ion-exchange reaction, has previously been used to pattern solids on nanoscale, leading to new materials with higher compositional and structural complexity\u003csup\u003e25\u003c/sup\u003e. We hypothesize here that cation exchange may offer the ability to generate a Turing pattern once the diffusion coefficients of two cations are appropriately different.\u003c/p\u003e\n\u003cp\u003eWe want to react CoSe\u003csub\u003e2\u003c/sub\u003e nanobelts with Ag\u003csup\u003e+\u003c/sup\u003e ions to produce Ag\u003csub\u003e2\u003c/sub\u003eSe, considering that the conversion to Ag\u003csub\u003e2\u003c/sub\u003eSe is thermodynamically favored with a driving force of around -1000 kJ mol\u003csup\u003e-1\u003c/sup\u003e in the bulk\u003csup\u003e26\u003c/sup\u003e. The previously developed CoSe\u003csub\u003e2\u003c/sub\u003e nanobelts\u003csup\u003e20\u003c/sup\u003e (Supplementary Fig. 1) are the material of choice because they can provide adequate surface regions for the development of Turing structures. In a typical synthesis, the as-synthesized CoSe\u003csub\u003e2\u003c/sub\u003e nanobelts were dispersed in a mixture of DETA and DIW (2/1, v/v) under vigorous stirring. After completely dispersing, AgNO\u003csub\u003e3\u003c/sub\u003e was added and the reaction solution was continuously stirred at room temperature for 4 hours. In this system, CoSe\u003csub\u003e2\u003c/sub\u003e is the activator, and AgNO\u003csub\u003e3\u003c/sub\u003e is the inhibitor (Fig. 1b). The reaction starts when the fast-diffusing Ag\u003csup\u003e+\u003c/sup\u003e comes to the CoSe\u003csub\u003e2\u003c/sub\u003e surface and replaces Co\u003csup\u003e2+\u003c/sup\u003e ions in the solid phase. Because the markedly lower diffusion of Co\u003csup\u003e2+\u003c/sup\u003e, this activator initially replaced by the locally available Ag\u003csup\u003e+\u003c/sup\u003e inhibitor. As the reaction proceeds, more Co\u003csup\u003e2+\u003c/sup\u003e activator diffuses to exchange with nearby inhibitor, and eventually a Turing-type Ag\u003csub\u003e2\u003c/sub\u003eSe pattern forms across the surface of the CoSe\u003csub\u003e2\u003c/sub\u003e nanobelts (Fig. 1c). We note that the diffusion coefficient of Ag\u003csup\u003e+\u003c/sup\u003e ions is ~10\u003csup\u003e-5\u003c/sup\u003e cm\u003csup\u003e2\u003c/sup\u003e s\u003csup\u003e-1 \u003c/sup\u003e(ref. 23), orders of magnitude higher than that of Co\u003csup\u003e2+\u003c/sup\u003e ions in CoSe\u003csub\u003e2\u003c/sub\u003e. Such differences in the diffusion coefficients of the two species thus meet the requirement of activator/inhibiotr-mediated patterning, which result in the unusual Turing structures (Fig. 1c).\u003c/p\u003e\n\u003cp\u003eWe examined the surface morphology of the as-synthesized sample by scanning electron microscopy (SEM), which shows regular striped patterns over the entire CoSe\u003csub\u003e2\u003c/sub\u003e support (Fig. 2a, Supplementary Fig. 2). Transmission electron microscopy (TEM; Fig. 2b) and scanning TEM (STEM; Fig. 2c) studies reveal that very refined and interconnected Ag\u003csub\u003e2\u003c/sub\u003eSe networks grew on CoSe\u003csub\u003e2\u003c/sub\u003e, forming the nanoscale Turing-type structures. To visualize the Ag\u003csub\u003e2\u003c/sub\u003eSe-CoSe\u003csub\u003e2\u003c/sub\u003e interfacial structure, we performed high-angle annular dark-field STEM (HAADF-STEM). Figure 2d validates the formation of distinct solid-state interface with the contrast mainly from the difference in atomic number between Ag\u003csub\u003e2\u003c/sub\u003eSe and CoSe\u003csub\u003e2\u003c/sub\u003e (Supplementary Fig. 3). The dashed circles in Figure 2d highlight different lattice configurations, and their corresponding fast Fourier transform (FFT) patterns feature cubic CoSe\u003csub\u003e2\u003c/sub\u003e (Fig. 2e) and orthorhombic Ag\u003csub\u003e2\u003c/sub\u003eSe (Fig. 2f), respectively. Energy-dispersive X-ray spectrum (EDX) elemental mappings further evidence that Ag\u003csub\u003e2\u003c/sub\u003eSe developed on the CoSe\u003csub\u003e2\u003c/sub\u003e support, where Ag appears only in the Turing-patterned regions (Supplementary Figs. 4, 5). Additionally, our X-ray diffraction (XRD; Supplementary Fig. 6a) measurements confirm the combination of cubic CoSe\u003csub\u003e2\u003c/sub\u003e (JCPDS 09-0234) and orthorhombic Ag\u003csub\u003e2\u003c/sub\u003eSe (JCPDS 24-1041) phases, consistent with the Raman results (Supplementary Fig. 6b). \u0026nbsp;\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eWe carried out a series of control experiments to explore the formation of Turing-type Ag\u003csub\u003e2\u003c/sub\u003eSe-CoSe\u003csub\u003e2\u003c/sub\u003e structure. Despite cation exchange is commonly prohibited at room temperature in the bulk phase, results show that our reaction happened at room temperature with a fast rate. This phenomenon could be ascribed to the reduced reaction barrier in nanosized materials\u003csup\u003e27\u003c/sup\u003e, as well as the favorable thermodynamic driving force for forming Ag\u003csub\u003e2\u003c/sub\u003eSe (ref. 26). We tracked the evolution of the Turing structures as a function of reaction time (Supplementary Figs. 7, 8). The diffusion-driven instability allowed this Turing structures to develop well at mere 1 h; markedly prolonging the reaction time to 12 h resulted in a hollowed-out structure. Moreover, the concentration of AgNO\u003csub\u003e3\u003c/sub\u003e appears to be also critical (Supplementary Figs.9-11). At low Ag\u003csup\u003e+\u003c/sup\u003e concentration, the transformation reaction initiated only at the edges of CoSe\u003csub\u003e2\u003c/sub\u003e nanobelts where the Co\u003csup\u003e2+\u003c/sup\u003e diffusion is easier because of the energy minimization. The addition of excess Ag\u003csup\u003e+\u003c/sup\u003e would cause the formation of over-carved material. Our experiments thus reveal that reacting 7.84 mmol L\u003csup\u003e-1\u003c/sup\u003e AgNO\u003csub\u003e3\u003c/sub\u003e with CoSe\u003csub\u003e2\u003c/sub\u003e at room temperature for 4 h yields the optimal Turing-type Ag\u003csub\u003e2\u003c/sub\u003eSe-CoSe\u003csub\u003e2\u003c/sub\u003e structure.\u003c/p\u003e\n\u003cp\u003eWe investigated the physicochemical properties of the novel Turing-type Ag\u003csub\u003e2\u003c/sub\u003eSe-CoSe\u003csub\u003e2\u003c/sub\u003e material by multiple characterization techniques. Differential scanning calorimetry (DSC) in Figure 2g exhibits a pair of endothermic (located at 417 K) and exothermal (located at 360 K) peaks for the Ag\u003csub\u003e2\u003c/sub\u003eSe-CoSe\u003csub\u003e2\u003c/sub\u003e, which could be the result of a phase transition from low-temperature cubic to high-temperature superionic phase of Ag\u003csub\u003e2\u003c/sub\u003eSe (ref. 28) (Insets in Fig. 2g). This superionic conducting phase transition of Ag\u003csub\u003e2\u003c/sub\u003eSe-CoSe\u003csub\u003e2\u003c/sub\u003e thus hints at potentially high cation mobility of the new structure\u003csup\u003e29\u003c/sup\u003e. Electrical conductivity tests as a function of temperature reveal consistently higher conductivity of the Ag\u003csub\u003e2\u003c/sub\u003eSe-CoSe\u003csub\u003e2\u003c/sub\u003e than that of metallic CoSe\u003csub\u003e2\u003c/sub\u003e (Fig. 2h). Such conductivity enhancement suggests that the Turing-type Ag\u003csub\u003e2\u003c/sub\u003eSe-CoSe\u003csub\u003e2\u0026shy;\u003c/sub\u003e interfaces facilitate electron transfer. Moreover, we performed the work function measurement of Ag\u003csub\u003e2\u003c/sub\u003eSe, CoSe\u003csub\u003e2\u003c/sub\u003e, and Ag\u003csub\u003e2\u003c/sub\u003eSe-CoSe\u003csub\u003e2\u003c/sub\u003e by ultraviolet photoelectron spectroscopy (UPS; Fig. 2i). The results show a lower work function of 3.73 eV for Ag\u003csub\u003e2\u003c/sub\u003eSe-CoSe\u003csub\u003e2\u003c/sub\u003e, versus 3.93 eV for CoSe\u003csub\u003e2\u003c/sub\u003e and 4.24 eV for Ag\u003csub\u003e2\u003c/sub\u003eSe, indicating a modulated electronic structure of Ag\u003csub\u003e2\u003c/sub\u003eSe-CoSe\u003csub\u003e2\u003c/sub\u003e that permit an easier electron transfer, in line with conductivity results\u003csup\u003e30\u003c/sup\u003e.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eOER performance of Turing-type Ag\u003csub\u003e2\u003c/sub\u003eSe-CoSe\u003csub\u003e2\u003c/sub\u003e\u003c/strong\u003e \u003cstrong\u003ecatalyst\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe boosted electron transfer property of Ag\u003csub\u003e2\u003c/sub\u003eSe-CoSe\u003csub\u003e2\u003c/sub\u003e prompted us to explore this new structure for negotiating the sluggish OER catalysis, considering that decent OER activities have been observed previously on CoSe\u003csub\u003e2\u003c/sub\u003e-based catalysts\u003csup\u003e31-34\u003c/sup\u003e. We compared the OER activity of our Turing-type Ag\u003csub\u003e2\u003c/sub\u003eSe-CoSe\u003csub\u003e2\u003c/sub\u003e catalyst with that of four references CoSe\u003csub\u003e2\u003c/sub\u003e, Ag\u003csub\u003e2\u003c/sub\u003eSe, NiFe LDH, and 20 wt% Ir/C catalysts. Rotating disk electrode (RDE) measurements in O\u003csub\u003e2\u003c/sub\u003e-saturated 0.1 M KOH exhibit that Ag\u003csub\u003e2\u003c/sub\u003eSe-CoSe\u003csub\u003e2\u003c/sub\u003e needs an overpotential of mere 221 mV at 10 mA cm\u003csup\u003e-2\u003c/sup\u003e, which increased to 399 mV for CoSe\u003csub\u003e2\u003c/sub\u003e, 350 mV for NiFe LDH, and 393 mV for Ir/C (Fig. 3a). By sharp contrast, Ag\u003csub\u003e2\u003c/sub\u003eSe itself affects negligible OER activity. Tafel analysis (Fig. 3b) yields a slope of 52, 175, 66 and 101 mV decade\u003csup\u003e-1\u003c/sup\u003e for Ag\u003csub\u003e2\u003c/sub\u003eSe-CoSe\u003csub\u003e2\u003c/sub\u003e, CoSe\u003csub\u003e2\u003c/sub\u003e, NiFe LDH and Ir/C catalyst, respectively. A considerably smaller slope achieved in Ag\u003csub\u003e2\u003c/sub\u003eSe-CoSe\u003csub\u003e2\u003c/sub\u003e implies markedly enhanced kinetics for OER. We also conducted electrochemical impedance spectroscopy (EIS) at 340 mV overpotential to probe the charge transfer resistance (\u003cem\u003eR\u003c/em\u003e\u003csub\u003ect\u003c/sub\u003e) for these catalysts. Our measurements (Supplementary Fig. 12) exhibit that the \u003cem\u003eR\u003c/em\u003e\u003csub\u003ect\u003c/sub\u003e of Ag\u003csub\u003e2\u003c/sub\u003eSe-CoSe\u003csub\u003e2\u003c/sub\u003e is ~13 ohms, versus ~41, 18573, 30, 148 ohms for CoSe\u003csub\u003e2\u003c/sub\u003e, Ag\u003csub\u003e2\u003c/sub\u003eSe, NiFe LDH and Ir/C catalyst, respectively. The smaller \u003cem\u003eR\u003c/em\u003e\u003csub\u003ect\u003c/sub\u003e for Ag\u003csub\u003e2\u003c/sub\u003eSe-CoSe\u003csub\u003e2\u003c/sub\u003e suggests an improved charge transfer between the catalyst surface and sorbates (\u003cem\u003ee.g.\u003c/em\u003e, O\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e2-\u003c/sup\u003e and O\u003csup\u003e2-\u003c/sup\u003e) in the OER process\u003csup\u003e35\u003c/sup\u003e. This result agrees well with our double-layer capacitance (\u003cem\u003eC\u003c/em\u003e\u003csub\u003edl\u003c/sub\u003e) measurements (Supplementary Figs. 13) that give the largest \u003cem\u003eC\u003c/em\u003e\u003csub\u003edl\u003c/sub\u003e value for Ag\u003csub\u003e2\u003c/sub\u003eSe-CoSe\u003csub\u003e2\u003c/sub\u003e, which also matches with our conductivity and work function results that Ag\u003csub\u003e2\u003c/sub\u003eSe-CoSe\u003csub\u003e2\u003c/sub\u003e allows more favorable electron transfer.\u003c/p\u003e\n\u003cp\u003eWe systematically assessed the OER performances of the Ag\u003csub\u003e2\u003c/sub\u003eSe-CoSe\u003csub\u003e2\u003c/sub\u003e catalysts that synthesized at different reaction times and Ag\u003csup\u003e+\u003c/sup\u003e concentrations, results of which we show in Supplementary Figures 14 to 16. We uncovered that Ag\u003csub\u003e2\u003c/sub\u003eSe-CoSe\u003csub\u003e2\u003c/sub\u003e with unique Turing-type structure gives the optimal catalytic property, so the rich Turing interfaces aforementioned could be responsible for the superior OER activity. We also underscore that the performance gained from the RDE testing here ranks among the superb for the OER electrocatalysts reported previously (Supplementary Fig. 17). Besides activity, the Ag\u003csub\u003e2\u003c/sub\u003eSe-CoSe\u003csub\u003e2\u003c/sub\u003e catalyst also exhibits excellent operating stability (Supplementary Figs. 18 and 19). For example, our multistep chronopotentiometry recorded at 10, 30 and 50 mA cm\u003csup\u003e-2\u003c/sup\u003e reveals mere a small decay over 70 h of continuous electrolysis (Supplementary Fig. 19).\u003c/p\u003e\n\u003cp\u003eTo verify the hypothesis that Turing-type Ag\u003csub\u003e2\u003c/sub\u003eSe-CoSe\u003csub\u003e2\u003c/sub\u003e interfaces are more OER active sites, we plotted the exchange current density (\u003cem\u003ej\u003c/em\u003e\u003csub\u003e0\u003c/sub\u003e; the most inherent measure of OER activity\u003csup\u003e36,37\u003c/sup\u003e) of each sample versus the Ag\u003csub\u003e2\u003c/sub\u003eSe interface length and the Ag\u003csub\u003e2\u003c/sub\u003eSe covered area (Figs. 3c and d, Supplementary Figs. 20-22), respectively. We find that the \u003cem\u003ej\u003c/em\u003e\u003csub\u003e0 \u003c/sub\u003eincreases linearly as the interface length is increased (Fig. 3c). When plotting versus the Ag\u003csub\u003e2\u003c/sub\u003eSe covered area, a volcano-shaped dependence of the \u003cem\u003ej\u003c/em\u003e\u003csub\u003e0\u003c/sub\u003e was obtained (Fig. 3d), further revealing that the reaction rate is directly proportional to the amount of interface sites. These results thus elucidate that the OER reaction takes place more energetically at the Ag\u003csub\u003e2\u003c/sub\u003eSe-CoSe\u003csub\u003e2\u003c/sub\u003e interfaces.\u003c/p\u003e\n\u003cp\u003eWe used gas chromatography (GC) to detect and quantify the O\u003csub\u003e2\u003c/sub\u003e product evolved from the Ag\u003csub\u003e2\u003c/sub\u003eSe-CoSe\u003csub\u003e2\u003c/sub\u003e-docerated carbon paper electrode at 10 mA cm\u003csup\u003e-2\u003c/sup\u003e. The measured O\u003csub\u003e2\u003c/sub\u003e gas perfectly matches with the theoretical value, corresponding to a Faradaic efficiency of ~100% (Fig. 3e). As a result, we achieved a high anodic energy efficiency up to 84.5%, which far exceeds that of CoSe\u003csub\u003e2\u003c/sub\u003e (73.7%) and also compares favorably to 76.2% for NiFe LDH and 74.4% for Ir/C catalyst (Fig. 3f), respectively.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eSpectroscopic studies of the Turing-type Ag\u003csub\u003e2\u003c/sub\u003eSe-CoSe\u003csub\u003e2\u003c/sub\u003e catalyst\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eWe now study the impact of Ag\u003csub\u003e2\u003c/sub\u003eSe-CoSe\u003csub\u003e2\u003c/sub\u003e interfaces on the electronic structure and catalytic character by using diverse spectroscopic techniques. Prior reports have demonstrated that orthorhombic Ag\u003csub\u003e2\u003c/sub\u003eSe contains Ag (1) occurring in tetrahedral coordination and Ag (2) in triangular coordination\u003csup\u003e38\u003c/sup\u003e (Supplementary Fig. 23). Our valence band spectrum of Ag\u003csub\u003e2\u003c/sub\u003eSe reveals two intensive features at 5.31 and 6.15 eV (Fig. 4a), originating from Ag (1) 5\u003cem\u003ed\u003c/em\u003e and Ag (2) 5\u003cem\u003ed\u003c/em\u003e states\u003csup\u003e39\u003c/sup\u003e, respectively. When forming interfaces with CoSe\u003csub\u003e2\u003c/sub\u003e, a large negative shift (~190 mV) of the Ag (1) 5\u003cem\u003ed\u003c/em\u003e state is observed, whereas the Ag (2) 5\u003cem\u003ed\u003c/em\u003e feature is undisturbed. This result suggests that Ag\u003csup\u003e+\u003c/sup\u003e coordinates tetrahedrally with Se\u003csup\u003e2-\u003c/sup\u003e at the novel Turing-type interfaces (Supplementary Fig. 24).\u003c/p\u003e\n\u003cp\u003eFigure 4b presents the Co K-edge X-ray absorption near-edge structure (XANES), which shows that the absorption edge of Ag\u003csub\u003e2\u003c/sub\u003eSe-CoSe\u003csub\u003e2 \u003c/sub\u003eis shifted to a lower energy versus CoSe\u003csub\u003e2\u003c/sub\u003e because of charge transfer from Ag\u003csub\u003e2\u003c/sub\u003eSe to Co (Supplementary Fig. 25)\u003csup\u003e40\u003c/sup\u003e. Extended X-ray absorption fine structure (EXAFS) spectra (Fig. 4c) of Ag\u003csub\u003e2\u003c/sub\u003eSe-CoSe\u003csub\u003e2\u003c/sub\u003e and CoSe\u003csub\u003e2\u003c/sub\u003e are similar, both showing a peak at ~2.04 \u0026Aring; that ascribed to Co-Se (ref. 33). After OER, two distinct peaks appear in EXAFS spectra: the former at 1.47 \u0026Aring; is due to Co-O, and the latter 2.40 \u0026Aring; is attributed to Co-Co, indicating the formation of CoOOH because of surface self-reconstruction of Ag\u003csub\u003e2\u003c/sub\u003eSe-CoSe\u003csub\u003e2\u003c/sub\u003e catalyst during OER (ref. 41). Intriguingly, the peak at 2.04 \u0026Aring;, characteristic of CoSe\u003csub\u003e2\u003c/sub\u003e, is still observed after OER (Fig. 4c). By contrast, single CoSe\u003csub\u003e2\u003c/sub\u003e undergoes a complete surface self-reconstruction to form CoOOH after OER (Supplementary Fig. 26). The EXAFS wavelet transform (Fig. 4d) analyses－a technique that can discriminate the backscattering atoms－further verify that Co-Se bond (~ 7.82 \u0026Aring;\u003csup\u003e-1\u003c/sup\u003e in \u003cem\u003ek\u003c/em\u003e space) remains in Ag\u003csub\u003e2\u003c/sub\u003eSe-CoSe\u003csub\u003e2\u003c/sub\u003e after OER.\u003c/p\u003e\n\u003cp\u003eUnexpectedly, our Ag 3\u003cem\u003ed\u003c/em\u003e X-ray photoelectron spectroscopy (XPS) analysis (Fig. 4e) reveals that the Ag valence state is unaltered after we performed OER on Ag\u003csub\u003e2\u003c/sub\u003eSe-CoSe\u003csub\u003e2\u003c/sub\u003e catalyst at a 221 mV overpotential (10 mA cm\u003csup\u003e-2\u003c/sup\u003e) for 12 h. Moreover, the signal from Ag-Se bond (at 54.2 eV)\u003csup\u003e42\u003c/sup\u003e in Se 3\u003cem\u003ed\u003c/em\u003e (Fig. 4f, Supplementary Fig. 27) further supports that Ag\u003csub\u003e2\u003c/sub\u003eSe phase survives after OER, agreeing with Se K-edge XANES results (Fig. 4g, Supplementary Fig. 28). By contrast, only oxidized Se species\u003csup\u003e43\u003c/sup\u003e were detected from single CoSe\u003csub\u003e2\u003c/sub\u003e catalyst after OER (Fig. 4f), suggesting a complete surface self-reconstruction to CoOOH.\u003c/p\u003e\n\u003cp\u003eOn the basis of above results, we become clear about the nature at the Turing-type Ag\u003csub\u003e2\u003c/sub\u003eSe-CoSe\u003csub\u003e2\u003c/sub\u003e interfaces. In the reaction-diffusion system, Ag\u003csup\u003e+\u003c/sup\u003e ions replace the Co\u003csup\u003e2+\u003c/sup\u003e ions in CoSe\u003csub\u003e2\u003c/sub\u003e nanobelts and tetrahedrally coordinates with Se\u003csup\u003e2-\u003c/sup\u003e, creating Turing-type Ag\u003csub\u003e2\u003c/sub\u003eSe-CoSe\u003csub\u003e2\u003c/sub\u003e interfaces where the \u003cem\u003ee\u003c/em\u003e\u003csub\u003eg\u003c/sub\u003e filling of adjacent Co cations is increased. This hence causes a near-unity \u003cem\u003ee\u003c/em\u003e\u003csub\u003eg\u003c/sub\u003e occupancy of surface Co cations, leading to enhanced OER activity\u003csup\u003e40,44\u003c/sup\u003e. Moreover, such interfaces also show extreme structural robustness against harsh OER corrosion (Fig. 4h).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eDensity functional theory calculations\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eTo better understand the catalytic nature of the Ag\u003csub\u003e2\u003c/sub\u003eSe-CoSe\u003csub\u003e2\u003c/sub\u003e interfaces, we carried out density functional theory (DFT) calculations. On the basis of experimental characterizations above, we created the Ag\u003csub\u003e2\u003c/sub\u003eSe-CoSe\u003csub\u003e2\u003c/sub\u003e model by bridging Ag\u003csub\u003e2\u003c/sub\u003eSe (112) and CoSe\u003csub\u003e2\u003c/sub\u003e (210) surfaces; regions remote to the interface were replaced with CoOOH to represent the catalyst during OER (Supplementary Figs. 29, 30). Detailed reaction-pathway calculations (Fig. 5a) reveal that the desorption of *OOH to generate O\u003csub\u003e2\u003c/sub\u003e on CoSe\u003csub\u003e2\u003c/sub\u003e (210) is kinetically hindered because of the high barrier of 2.976 eV. On the interface sites, the rate-determining *OOH intermediate is reduced by 0.904 eV, which gives a weaker *OOH adsorption, consistent with our Bader charge analysis\u003csup\u003e45\u003c/sup\u003e (Supplementary Fig. 31). DFT calculations further predict that the Co-O bond length increases from 1.79 to 1.84 \u0026Aring; on the Ag\u003csub\u003e2\u003c/sub\u003eSe-CoSe\u003csub\u003e2\u003c/sub\u003e interface (Supplementary Fig. 32), which explains the weaker *OOH adsorption on Ag\u003csub\u003e2\u003c/sub\u003eSe-CoSe\u003csub\u003e2\u003c/sub\u003e interface relative to CoSe\u003csub\u003e2\u003c/sub\u003e.\u003c/p\u003e\n\u003cp\u003eA plot of the electron density difference (Fig. 5b) displays that the donation of electrons from the Ag\u003csub\u003e2\u003c/sub\u003eSe to nearby Co sites occurs at the interface, which permits \u003cem\u003ee\u003c/em\u003e\u003csub\u003eg\u003c/sub\u003e-orbital occupancy of Co closer to unity and thus enhanced OER activity\u003csup\u003e40,44\u003c/sup\u003e, matching well with our XANES measurements. Moreover, the calculated projected density of states (PDOS; Fig. 5c) shows that the \u003cem\u003ed\u003c/em\u003e-band center of Co atom in Ag\u003csub\u003e2\u003c/sub\u003eSe-CoSe\u003csub\u003e2\u003c/sub\u003e deviates more from the Fermi level than that of single CoSe\u003csub\u003e2\u003c/sub\u003e (210), further evidencing the weak binding of *OOH intermediate on the Ag\u003csub\u003e2\u003c/sub\u003eSe-CoSe\u003csub\u003e2\u003c/sub\u003e interfaces\u003csup\u003e46\u003c/sup\u003e.\u003c/p\u003e\n\u003cp\u003eLastly, to examine the O\u003csub\u003e2\u003c/sub\u003e binding abilities of Ag\u003csub\u003e2\u003c/sub\u003eSe-CoSe\u003csub\u003e2\u003c/sub\u003e and CoSe\u003csub\u003e2\u003c/sub\u003e catalysts, we performed the temperature-programmed desorption analysis. Figure 5d shows that Ag\u003csub\u003e2\u003c/sub\u003eSe-CoSe\u003csub\u003e2\u003c/sub\u003e gives a lower O\u003csub\u003e2\u003c/sub\u003e onset desorption temperature of 111 \u003csup\u003eo\u003c/sup\u003eC versus single CoSe\u003csub\u003e2\u003c/sub\u003e (195 \u003csup\u003eo\u003c/sup\u003eC), which we consider to benefit the rate-determining *OOH desorption step for improved O\u003csub\u003e2\u003c/sub\u003e release. Thus, our results, both experimentally and computationally, have demonstrated that the Turing-type Ag\u003csub\u003e2\u003c/sub\u003eSe-CoSe\u003csub\u003e2\u003c/sub\u003e interfaces are more energetically favored to catalyze the OER.\u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eChemical Turing patterns in inorganic nanomaterials have not yet been reported. Here we demonstrate that Turing-driven morphogenesis occurs in a cation exchange process, which was originated from the appropriate differences between the diffusion coefficients of Ag\u003csup\u003e+\u003c/sup\u003e and Co\u003csup\u003e2+\u003c/sup\u003e (diffused from CoSe\u003csub\u003e2\u003c/sub\u003e), creating stationary Ag\u003csub\u003e2\u003c/sub\u003eSe Turing patterns on CoSe\u003csub\u003e2\u003c/sub\u003e nanobelts. The obtained new material comprises abundant Turing-structured Ag\u003csub\u003e2\u003c/sub\u003eSe-CoSe\u003csub\u003e2\u003c/sub\u003e interfaces, which enable excellent OER electrocatalytic activity and stability in alkaline electrolyte. Our work opens the possibility of producing stationary reaction-diffusion patterns in inorganic solids that would not otherwise have such structures. Furthermore, the unusual engineered interfaces may see application in a wider spectrum of electrocatalytic processes.\u003c/p\u003e"},{"header":"Methods","content":"\u003cp\u003e\u003cstrong\u003eMaterial synthesis\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAll chemicals are of analytical grade and were used as received without further purification.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eSynthesis of CoSe\u003csub\u003e2\u003c/sub\u003e/DETA nanobelts\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe CoSe\u003csub\u003e2\u003c/sub\u003e/DETA nanobelts were synthesized by a hydrothermal method using our previously developed method\u003csup\u003e20\u003c/sup\u003e. Briefly, 0.249 g Co(AC)\u003csub\u003e2\u003c/sub\u003e\u0026sdot;H\u003csub\u003e2\u003c/sub\u003eO and 0.173 g Na\u003csub\u003e2\u003c/sub\u003eSeO\u003csub\u003e3\u003c/sub\u003e were added into a mixed solution (40 ml) with a volume ratio of V\u003csub\u003eDETA\u003c/sub\u003e/V\u003csub\u003eDIW\u003c/sub\u003e = 2:1 (DIW = deionzed water). After stirring for 30 min, the obtained wine solution was transferred into a Teflon-lined autoclave, which was sealed and maintained at 180 \u003csup\u003eo\u003c/sup\u003eC for 17 h. The resulting CoSe\u003csub\u003e2\u003c/sub\u003e nanobelts were carefully washed and dried before use.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eSynthesis of Turing-type Ag\u003csub\u003e2\u003c/sub\u003eSe-CoSe\u003csub\u003e2\u003c/sub\u003e catalyst\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe Turing-type Ag\u003csub\u003e2\u003c/sub\u003eSe-CoSe\u003csub\u003e2\u003c/sub\u003e was prepared through an ion-exchange reaction. Briefly, 20 mg freshly made CoSe\u003csub\u003e2\u003c/sub\u003e nanobelts was added into a mixed solution (15 mL) with a volume ratio of V\u003csub\u003eDETA\u003c/sub\u003e/V\u003csub\u003eDIW\u003c/sub\u003e = 2:1. After completely dispersing, 20 mg AgNO\u003csub\u003e3\u003c/sub\u003e was added and drastically stirring at room temperature for 4 h, the obtained Turing-type Ag\u003csub\u003e2\u003c/sub\u003eSe-CoSe\u003csub\u003e2\u003c/sub\u003e powder was carefully washed and dried before use.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eMaterial\u003c/strong\u003e\u003cstrong\u003e characterizations\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eX-ray powder diffraction (XRD) was obtained from a Philips X\u0026rsquo;Pert Pro Super X-ray diffractometer with Cu K\u0026alpha; radiation (\u0026lambda; = 1.54178 \u0026Aring;). The morphology of the samples was achieved by SEM (Zersss Supra 40) and TEM (Hitachi H7650). The STEM and HAADF images, SAED, and EDX elemental mappings were measured on JEMARM 200F Atomic Resolution Analytical Microscope with an acceleration voltage of 200 kV. Raman spectra were taken on a Raman microscope (Renishaw\u0026reg;) excited with a 514 nm excitation laser. ICP-AES data were investigated by an Optima 7300 DV instrument. Ultraviolet-photoelectron spectroscopy was obtained at the BL11U beamline of National Synchrotron Radiation Laboratory in Hefei, China. The X-ray absorption spectra of Co L-edges were taken on the BL10B beamline of National Synchrotron Radiation Laboratory in Hefei (China). The X-ray absorption spectra of Co and Se K-edges were carried out at the beamline 14W1 of Shanghai synchrotron Radiation Laboratory (China). XPS was performed on an X-ray photoelectron spectrometer (ESCALab MKII) with an X-ray source (Mg K\u0026alpha; \u003cem\u003eh\u0026upsilon;\u003c/em\u003e=1253.6 eV). The O\u003csub\u003e2\u003c/sub\u003e- temperature-programmed desorption analysis (TPD) measurements were taken on AutoChem II 2920. The electrical conductivity measurements were measured by using the standard four probe transport measurement on commercial apparatus of Physical Property Measurement System (Quantum Design, PPMS). Differential scanning calorimetry (DSC) cycling curves were carried out by the NETZSCH DSC Q2000 with a heating/cooling rate of 5 K min\u003csup\u003e\u0026minus;1\u003c/sup\u003e between 273 and 473 K.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eElectrochemical measurements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAll the electrochemical measurements were performed in a standard three-electrode cell at ambient temperature connected to a VSP-300 potentiostat (BioLogic, France). Ag/AgCl (3.5 M KCl) electrode and graphite rod were used as the reference and counter electrodes, respectively. The potentials reported in this work were normalized versus the RHE through a standard RHE calibration (E = E\u003csub\u003e Ag/AgCl\u003c/sub\u003e + 0.97 V). A rotating disk electrode (RDE) with glassy carbon (PINE, 5.00 mm diameter, disk area: 0.196 cm\u003csup\u003e2\u003c/sup\u003e) was used as the working electrode.\u003c/p\u003e\n\u003cp\u003eTo make the working electrodes, 5 mg catalyst powder was dispersed in 1 ml of 1:3 v/v isopropanol/DIW mixture with 20 \u0026mu;L Nafion solution (5 wt%), which was ultrasonicated to yield a homogeneous ink. Then, 8 \u0026mu;L catalyst ink was pipetted onto the glassy carbon disk to ensure the catalyst loading of ~0.2 mg cm\u003csup\u003e-2\u003c/sup\u003e. The fresh electrolytes (0.1 M KOH) were bubbled with pure oxygen for 30 min before measurements. The electrodes were pre-cycled between 0 and 0.8 V vs. Ag/AgCl at a sweep rate of 100 mV s\u003csup\u003e\u0026minus;1\u003c/sup\u003e for 30 cycles until reaching the stable state, then the OER polarization curves were recorded at a sweep rate of 2 mV s\u003csup\u003e-1\u003c/sup\u003e and 1600 r.p.m (to remove the O\u003csub\u003e2\u003c/sub\u003e bubbles formed \u003cem\u003ein situ\u003c/em\u003e) at ambient temperature. The EIS measurement was performed in the same configuration at 340 mV overpotential over a frequency range from 100 KHz to 100 mHz at the amplitude of the sinusoidal voltage of 5 mV. The polarization curves were re-plotted as overpotential (\u003cem\u003e\u0026eta;\u003c/em\u003e) versus log current (log \u003cem\u003ej\u003c/em\u003e) to get Tafel plots to assess the HER kinetics of investigated catalysts. The Tafel slope (\u003cem\u003eb\u003c/em\u003e) can be obtained by fitting the linear portion of the Tafel plots to the Tafel equation ( ). The exchange current density (\u003cem\u003ej\u003c/em\u003e\u003csub\u003e0\u003c/sub\u003e) were calculated from Tafel curves using extrapolation method. The values of mass activity (A mg\u003csup\u003e-1\u003c/sup\u003e) were calculated from the catalyst loading \u003cem\u003em\u003c/em\u003e (0.2 mg cm\u003csup\u003e-2\u003c/sup\u003e) and the current density of 10 mA cm\u003csup\u003e-2\u003c/sup\u003e: mass activity = \u003cem\u003ej\u003c/em\u003e / \u003cem\u003em\u003c/em\u003e.\u003c/p\u003e\n\u003cp\u003eThe Ag\u003csub\u003e2\u003c/sub\u003eSe-CoSe\u003csub\u003e2\u003c/sub\u003e-modified carbon paper (catalyst loading: ~0.20 mg cm\u003csup\u003e\u0026minus;2\u003c/sup\u003e) was used as working electrode to conduct chronopotentiometry experiments. The O\u003csub\u003e2\u003c/sub\u003e product, evolved from the Ag\u003csub\u003e2\u003c/sub\u003eSe-CoSe\u003csub\u003e2\u003c/sub\u003e-docerated carbon paper electrode at 10 mA cm\u003csup\u003e-2\u003c/sup\u003e, was detected and quantified by gas chromatography. The accelerated stability measurements were carried out by potential cycling between 0 and 0.6 V Ag/AgCl at a sweep rate of 100 mV s\u003csup\u003e\u0026minus;1\u003c/sup\u003e. After cycling, the resultant electrode was used for polarization curves with a sweep rate of 2 mV s\u003csup\u003e\u0026minus;1\u003c/sup\u003e. To estimate the double-layer capacitance, cyclic voltammograms were measured at different sweep rates in the potential region of 1.25-1.35 versus RHE at ambient temperature. All the polarization curves were corrected with \u003cem\u003ei\u003c/em\u003eR compensation that resulted from the solution resistance.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAnodic \u003c/strong\u003e\u003cstrong\u003eenergy\u003c/strong\u003e\u003cstrong\u003e efficiency\u003c/strong\u003e\u003cstrong\u003e calculations\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAnodic energy efficiency was calculated via the following formula\u003csup\u003e47\u003c/sup\u003e: (see Formula 1 in the Supplementary Files)\u0026nbsp;\u003c/p\u003e\n\u003cp\u003ewhere E\u003csup\u003e0\u003c/sup\u003e is the equilibrium cell potential for water decomposition (E\u003csup\u003e0\u003c/sup\u003e = 1.23 V). FE is the Faradaic efficiency for H\u003csub\u003e2\u003c/sub\u003eO to O\u003csub\u003e2\u003c/sub\u003e conversion, and \u003cem\u003e\u0026eta;\u003c/em\u003e\u003csub\u003e,an \u003c/sub\u003eis the overpotential at the anode and was measured at 10 mA cm\u003csup\u003e-2 \u003c/sup\u003ein this work.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eDFT calculations\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe overall OER process includes four elementary steps that follow: (see Reactions\u0026nbsp;1-4 in the Supplemental Files)\u003c/p\u003e\n\u003cp\u003eHere, (*) denotes the \u0026ndash;OH terminated CoSe\u003csub\u003e2\u003c/sub\u003e or Ag\u003csub\u003e2\u003c/sub\u003eSe- CoSe\u003csub\u003e2\u003c/sub\u003e surface. We used \u0026ndash;OH groups to replace the unsaturated Se atoms as models to represent the surface hydroxylation of CoSe\u003csub\u003e2\u003c/sub\u003e or Ag\u003csub\u003e2\u003c/sub\u003eSe-CoSe\u003csub\u003e2\u003c/sub\u003e, because the whole structure is well maintained. These are similar to the \u0026ndash;OH groups terminated surface of oxide models\u003csup\u003e48\u003c/sup\u003e. It is more convenient to calculate the thermochemistry of the OER under acidic condition. Following Bajdich \u003cem\u003eet al.\u003c/em\u003e\u003csup\u003e49\u003c/sup\u003e, we consider the following elementary steps: (see\u0026nbsp;Reactions 5-8 in the Supplemental Files)\u003c/p\u003e\n\u003cp\u003eReactions 5-8 are thermodynamically equivalent to reactions 1-4 shown above.\u003c/p\u003e\n\u003cp\u003eThe Gibbs free energy changes are calculated as follows: (see Changes in the Supplemental Files)\u003c/p\u003e\n\u003cp\u003eThe G values are calculated by: (see Formula 2 in the Supplemental Files)\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eE\u003csub\u003eDFT\u003c/sub\u003e is the total energy from the DFT calculation. E\u003csub\u003eZPE\u003c/sub\u003e is the zero-point energy, S is the entropy and T is the temperature (298K). The energy of is got from the energy of \u0026nbsp;using the standard hydrogen electrode (SHE). The bond energy is calculated by: (see Formula 3 in the Supplemental Files)\u003c/p\u003e\n\u003cp\u003eThe density functional theory calculations were performed by Vienna ab initio simulation package (VASP)\u003csup\u003e50\u003c/sup\u003e program with projector augmented wave (PAW) method and the kinetic energy cut off was set to be 500 eV. The convergence criterion for the electronic self-consistent iteration was set to be \u0026nbsp;10\u003csup\u003e-4\u003c/sup\u003e eV. The atomic positions were fully relaxed until the force on each atom is less than 0.02 eV \u0026Aring;\u003csup\u003e-1\u003c/sup\u003e. The Perdew-Burke-Ernzerhof (PBE)\u003csup\u003e51\u003c/sup\u003e generalized gradient approximation (GGA) exchange-correlation functional was used throughout. The slab model of CoSe\u003csub\u003e2\u003c/sub\u003e (210) surface was constructed based on the optimized crystal structure and we selected the right Ag\u003csub\u003e2\u003c/sub\u003eSe cluster anchored on the CoSe\u003csub\u003e2 \u003c/sub\u003e(210) surface. The vacuum layer was set to be 15 \u0026Aring; to ensure the separation between slabs.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgements:\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis work was supported by the funding support from the National Natural Science Foundation of China (Grants 21975237 and 51702312), the National Basic Research Program of China (Grant 2018YFA0702001), the Fundamental Research Funds for the Central Universities (WK2340000076), and the Recruitment Program of Global Youth Experts. This work was partially performed at the USTC Center for Micro and Nanoscale Research and Fabrication.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor Contributions:\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eM.-R.G. conceived and supervised the project. X.-L.Z. and P.-P.Y. performed the experiments, collected and analyzed the data. X.-S.Z. and J.-F.Z. performed XPS and UPS measurements. X.-L.Z., S.-J.H and X.Z. carried out the DFT calculations. T.M., F.-Y.G., Z.-Z.W., Z.-Z.N., Y.-R.Z., X.-X.Y., R.W., Y.D., C.G., L.-P.C. and S.Q. helped with electrochemical data collection and analysis. M.-R.G. and X.-L.Z. co-wrote the manuscript. All authors discussed the results and commented on the manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAdditional information:\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eSupplementary information is available in the online version of the paper. Correspondence and requests for materials should be addressed to M.R.G.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting financial interests:\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare no competing financial interests.\u003c/p\u003e"},{"header":"References","content":"\u003cp\u003e1\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp; Turing, A. M. The chemical basis of morphogenesis. \u003cem\u003ePhil. Trans. R. Soc. Lond. B\u003c/em\u003e \u003cstrong\u003e237\u003c/strong\u003e, 37-72 (1952).\u003c/p\u003e\n\u003cp\u003e2\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp; Meinhardt, H. \u003cem\u003eModels of biological pattern formation\u003c/em\u003e. (Academic Press, 1982).\u003c/p\u003e\n\u003cp\u003e3\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp; Murray, J. 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We report a simple cation exchange approach to produce Turing-type Ag2Se on CoSe2 nanobelts relied on diffusion-driven instability. The resultant Turing-type Ag2Se-CoSe2 material is highly effective to catalyze the oxygen evolution reaction (OER) in alkaline electrolytes with an 84.5% anodic energy efficiency. Electrochemical measurements show that the intrinsic OER activity correlates linearly with the length of Ag2Se-CoSe2 interfaces, determining that such Turing-type interfaces are more active sites for OER. Combing X-ray absorption and computational simulations, we ascribe the excellent OER performance to the optimized adsorption energies for critical oxygen-containing intermediates at the unconventional interfaces. Our work offers opportunities for creating Turing structures in other inorganic nanomaterials with unexplored catalytic abilities.","manuscriptTitle":"An efficient Turing-type Ag2Se-CoSe2 multi-interfacial oxygen-evolving electrocatalyst","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2020-07-15 16:11:33","doi":"10.21203/rs.3.rs-39890/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"2a63959d-15de-4d60-94de-18de8f20bfc9","owner":[],"postedDate":"July 15th, 2020","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[{"id":161121,"name":"Materials Chemistry"},{"id":161122,"name":"Materials Engineering"},{"id":161123,"name":"Catalysis"}],"tags":[],"updatedAt":"2020-12-21T20:35:56+00:00","versionOfRecord":[],"versionCreatedAt":"2020-07-15 16:11:33","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-39890","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-39890","identity":"rs-39890","version":["v1"]},"buildId":"WrCJVZZCHTDjtuVLN7oU0","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}