Ternary Phase Diagram-Facilitated Rapid Screening of Double

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Ternary phase diagram-facilitated rapid screening of double perovskites as electrocatalysts for the oxygen evolution reaction Hainan Sun, Zhiwei Hu, Xiaomin Xu, Juan He, Jie Dai, Hong-Ji Lin, TingShan Chan, Chien-Te Chen, Liu Hao Tjeng, Wei Zhou, and Zongping Shao Chem. Mater., Just Accepted Manuscript • DOI: 10.1021/acs.chemmater.9b02261 • Publication Date (Web): 22 Jul 2019 Downloaded from pubs.acs.org on July 22, 2019

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Chemistry of Materials

Ternary phase diagram-facilitated rapid screening of double perovskites as electrocatalysts for the oxygen evolution reaction Hainan Suna, Zhiwei Hub, Xiaomin Xuc, Juan Hea, Jie Daia, Hong-Ji Lind, Ting-Shan Chand, Chien-Te Chend, Liu Hao Tjengb, Wei Zhoua,*, and Zongping Shaoa,c,* a

State Key Laboratory of Materials-Oriented Chemical Engineering, College of Chemical Engineering, Nanjing Tech University, Nanjing 211816, P. R. China

b

Max-Planck-Institute for Chemical Physical of Solids, Nöthnitzer Street 40, Dresden 01187, Germany

c

WA School of Mines: Minerals, Energy and Chemical Engineering (WASM-MECE), Curtin University, Perth, Western Australia, 6845 Australia

d

National Synchrotron Radiation Research Center, 101 Hsin-Ann Road, Hsinchu 30076, Taiwan

*Corresponding author: E-mail addresses: [email protected] (Wei Zhou) [email protected] (Zongping Shao) Abstract: The development of cost-effective non-noble metal electrocatalysts for the oxygen evolution reaction (OER) is of paramount importance for sustainable technologies. Efficient screening strategies for electrocatalysts can greatly increase the commercialization speed of these advanced technologies. Here, ternary phase diagrams with large-scale tuning and designated-scale tuning strategies are applied for the first time to provide a new method for screening perovskite oxide-based electrocatalysts for OERs. Specifically, the family of double perovskites (Sr2Fe1.5-x-yCoxNiyMo0.5O6-, 0  x, y  1.5) was utilized to understand the role of transition metals in perovskite oxides. Ternary phase diagrams can facilitate a rapid screening process, provide a straightforward relationship between phase structures and catalytic activities, and help to confirm the effects of various combinations of transition metals on the OER activity. The Fe-Co system (Sr2Fe1.5-xCoxMo0.5O6-δ) improves the catalytic activities, as demonstrated by the reduced Tafel slope and enhanced stability, while the Fe-Ni system (Sr2Fe1.5-yNiyMo0.5O6-δ) improves the surface kinetic properties of the OER, as demonstrated by its reduced overpotential. Significantly, the Co, Ni and Fe ternary phase systems can serve as the synergistic coactive sites (Sr2Fe1.5-x-yCoxNiyMo0.5O6-δ) to 1 / 23

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catalyse the OER, resulting in an improved overall OER performance. This systematic study not only demonstrates a new strategy to allow the rapid screening of double perovskite OER catalysts based on large-scale tuning and designated-scale tuning strategies, but, more importantly, also provides an insightful understanding of the use of multi-transition metal-based double perovskites for catalysis of the OER. 1. Introduction The diminishing of fossil energy resources and increasing demand for alternative energy sources necessitate the development of efficient and alternative energy-storage devices.1,2 The production of hydrogen through electricity-driven water splitting, which includes two half reactions, namely, the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER), has received much attention as green energy in the past few decades.3 Compared with that of the HER, the kinetics of the OER are slow, thus leading to a large overpotential.4,5 Therefore, the development of highly efficient OER electrocatalysts to expedite the reaction is warranted. The current state-of-the-art OER electrocatalysts are noble metal oxides, which possess high OER activity. However, their widespread application is impeded by their high cost and scarcity.6 At the forefront of OER research, tremendous efforts have been made to develop non-precious metal catalysts. The earth-abundant 3d transition metals (3d-TM) are considered promising candidates for the replacement of precious catalysts, due to their high activity, low cost, and robust stability. Specifically, extensive research has been conducted on Fe-/Co-/Ni-based materials such as spinel-type oxides, (oxy)hydroxides, transition-metal nitrides, and perovskite oxides as potential OER electrocatalysts.7-11 Perovskites with the general formula ABO3- (single perovskite), where A is an alkaline or alkaline-earth cation and B is a transition metal cation, such as 3d-TM (e.g., Mn, Fe, Co, Ni and Cu), 4d transition metals (e.g., Mo, Nb, and Pd) and 5d transition metals (e.g., Hf, Ta, and W), are an important family of materials that are active towards the OER.12 Benefiting from the considerable possible substitutions at both the A and B sites, perovskites show great flexibility with regard to the tailoring and tuning of their physicochemical properties, resulting in a more general composition of (A1-xAx’)(B1-yBy’)O3-.13 The double perovskites (A2BB’O6-), which constitute a subclass of perovskite materials, are even more promising electrocatalysts for OER because of their unique physicochemical properties compared to single perovskites.14,15 The 3d-TMs are the main active sites 2 / 23


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for the OER for both single and double perovskites. Importantly, mixed-metal systems are efficient electrocatalysts for OER and exhibit dramatically enhanced catalytic activities.16-19 Duan et al. reported an increase in OER activity as a result of doping LaCoO3 with 10 wt. % Fe. Density function theory (DFT) calculations verified that the improved OER performance was due to the enhanced Co 3d-O 2p covalency.16 In another case, PrBa0.85Ca0.15MnFeO5+δ, a cation-ordered double perovskite oxide, exhibited remarkable OER performance, which was attributed to the presence of an Fe dopant that endowed the B-site cation with an optimal eg filling.17 This synergistic effect between multiple transition metals has been seen in various kinds of electrocatalysts, such as Co-Fe (oxy)hydroxides,20 Co-Fe oxides,21 and Co-Ni phosphides.22 Additionally, in the area of lithium ion battery development (LIB), the three-component layer-structured LiNixCoyMnzO2 (0 ≤ x, y, z1) is a potential candidate to replace the single-component LiCoO2 as a cathode material, due to its high discharge capacity and low cost.23,24 A high content of Ni, Mn, and Co enhances the capacity, structural stability, and rate performance, respectively. Importantly, the synergistic effect created by the three transition elements in this structure contributes to the significantly improved electrochemical properties.23 Previous studies have been conducted to obtain a deeper understanding of the synergistic effect of transition metals, which are present in the forms of alloys (e.g., quaternary FeCoNiMn alloy),25 metal phosphides (e.g., FeCoNiP),26 or transition metal oxides (e.g., (Ni-Fe-Co-Ce)Ox).27 However, little has been reported on the systematic study of the multi-transition metal composition of perovskite oxides, especially for double perovskite oxides. The double perovskite oxide Sr2Fe1.5Mo0.5O6- (SF1.5M), which is a mixed ionic and electronic conductor, is chemically stable and catalytically active functions as the anode/cathode for solid oxide fuel cells.28,29 Mo-based materials (e.g., MoS2, MoO2, and MoP) are usually beneficial for HER30 and Fe-based perovskite oxides traditionally have poor activity and unfavorable durability for OER.4,10,11,31 Thus, SF1.5M is not expected as an outstanding OER electrocatalyst, In this work, we replace the B-site of Fe in SF1.5M by OER-active elements (Co and Ni) to comprehensively improve the OER catalytic activity. As a proof-of-concept, we utilize ternary phase diagrams to conduct a systematic investigation on improving the OER performance of the double perovskite SF1.5M system by a combined tuning of the compositional transition metals with both large-scale tuning (Sr2Fe1.5-x-yCoxNiyMo0.5O6-, 0x, y1.5) and designated-scale tuning (Sr2Fe1.5-x-yCoxNiyMo0.5O6-, 0x, y0.5) and illustrate the critical role of each transition metal in enhancing the OER.32-34 In the 3 / 23



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Fe, Co, Ni-based multi-metal framework, Fe is required to maintain the double perovskite structure. The Fe-Co system (Sr2Fe1.5-xCoxMo0.5O6-δ) improves the catalytic activities, as suggested by the reduced Tafel slope and enhanced stability, while the Fe-Ni system (Sr2Fe1.5-yNiyMo0.5O6-δ) enhances the surface kinetic properties of the OER, which is improved by the reduced overpotential. Significantly, the Co, Ni and Fe ternary phase system can serve as the synergistic coactive sites (Sr2Fe1.5-x-yCoxNiyMo0.5O6-δ) to catalyse the OER, and this ternary phase system can overcome the drawbacks of each of the binary combinations, resulting in an improved overall OER performance. This systematic study not only demonstrates a new strategy to allow the rapid screening of double perovskite OER catalysts based on large-scale tuning and designated-scale tuning, but, more importantly, also provides an insightful understanding of the use of multi-transition metal-based double perovskites for catalysis of the OER. 2. Results and Discussion

Figure 1. (a) The ternary phase diagram of the large-scale tuning with an internal value of 0.375 (25%). The specific phase information about the ternary phase diagram of the large-scale tuning powders, including (b) the edge of Fe/Co with the composition Sr2Fe1.5-xCoxMo0.5O6- (x=0.375, 0.75, 1.125, and 1.5), (c) the edge of Fe/Ni with the composition Sr2Fe1.5-xNixMo0.5O6- (x=0.375, 0.75, 1.125, and 1.5), (d) the edge of Ni/Co with the composition Sr2Ni1.5-xCoxMo0.5O6- (x=0.375, 0.75, 1.125, and 1.5), (e) the edge of Fe/Co/Ni with the composition Sr2Fe1.5-x-yCoxNiyMo0.5O6- (x=0.375, y=0.75; x=0.75, y=0.375; x=0.375, y=0.375). We first conducted a large-scale tuning of double perovskite catalysts based on the ternary phase diagram in Figure 1a, which, with an internal value of 0.375 (25%) for each edge, allows a 4 / 23


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systematic investigation into 15 different double perovskites spanning 4 different compositional combinations of Fe/Co, Fe/Ni, Ni/Co, and Fe/Co/Ni. Considering that perovskites are known to show phase-dependent OER activity,35 we analysed the phase structures of these double perovskite compositions by X-ray diffraction (XRD). For the edge of Fe/Co, an almost pure perovskite phase was observed, except for that of Sr2Co1.5Mo0.5O6-δ (SC1.5M) with a secondary phase indexed to SrCoO2.52 (Figure 1b and Figure S1a). For the edge of Fe/Ni, a pure phase was only achieved at a limited Ni-doping level, i.e., Sr2Fe1.125Ni0.375Mo0.5O6-δ (SFN0.375M) (Figure 1c and Figure S1b), and an additional phase of NiMoO4 increased with the increasing replacement of Fe by Ni. The phase structure formation for the edges of Fe/Co and Fe/Ni agreed with previous reports.28,29 In contrast, for the edge of Ni/Co, it was difficult to obtain a pure phase without the presence of Fe, indicative of the critical role that Fe plays in stabilizing the double perovskite backbone structure (Figure 1d). The important role of Fe was further supported by the observation on the edge of Fe/Co/Ni (Figure 1e). Goldschmidt tolerance (t) has been used for decades to predict the crystal structures of perovskite materials.36 A stable cubic structure is formed in perovskites with a t range of 0.9-1.0. The concept of the tolerance factor can also be applied to double perovskites (A2B1-xBx’’B’O6), in which the tolerance factor is defined as t =

rA + rO rB(1 ― x) √2( 2

+

rB x ′′ 2

+

rB ′ 2

(rA, rB, rB', rB'', + rO)

and rO are the ionic radii of the respective ions).37 Since Co cations have ionic radii that are similar to that of Fe3+ (0.65 Å for Co2+ and 0.63 Å for Co3+ versus 0.645 Å for Fe3+), whereas the Ni cation has a much larger ionic radius (0.72 Å for Ni2+),29, 38-40 the Sr2Fe1-xCoxMo0.5O6-δ series are expected to better maintain double perovskite structures compared with those of the Sr2Fe1-xNixMo0.5O6-δ series. Specifically, the t values of SF1.5M was estimated to be 0.991 (~1.0) and the incorporated Ni essentially reduced the tolerance factor relative to the parent perovskite oxide, while the introduced Co maintained its cubic structure well.

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Figure 2. OER performance of different kinds of electrocatalysts measured in 0.1 M KOH. (a) The onset overpotentials. (b) The overpotentials corresponding to a current density of 10 mA cm-2. (c) Tafel slopes. The OER catalytic activity of the catalysts in this study was tested in a standard three-electrode configuration using a rotating disk electrode (RDE) in an O2-saturated KOH aqueous alkaline solution (0.1 M) (Figure S2). The onset overpotential (), overpotential corresponding to 10 mA cm-2 (10) and Tafel slope, which are crucial parameters and can offer more insightful information about the mechanism of the electrochemical reaction, were utilized to fairly evaluate the performance of the electrocatalysts.41 Of note, the onset overpotential is generally obtained at the point where the current density is 0.3 mA cm-2 from LSV curves.4,42,43Similar to the analysis of the XRD data, we also give a summary of the functions of the introduced Co and Ni. For the edge of Fe/Ni, although their OER performances differed greatly, the combination of Fe/Ni reduced the  and 10 sharply (Figure 2a and Figure 2b). Considering SFN1.125M, for example, its  reached 154 mV, which 6 / 23


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exceeds even that of iridium oxide (IrO2, 240 mV),44 demonstrating that the synergistic effect of Fe/Ni greatly enhanced the OER activities. Furthermore, the OER kinetics was evaluated using the Tafel slopes (Figure 2c). The electrocatalysts with a combination of Fe and Co exhibited the lowest Tafel slopes (~ 80 mV dec-1), demonstrating the facile kinetics of the OER with the series of Fe-Co. In addition, the ternary oxides that contained Fe, Co, and Ni in the B-site also possessed small Tafel slopes (~ 85 mV dec-1). Notably, the Tafel slopes of all the studied catalysts (Figure 1a) were in the range of 60-120 mV dec-1, suggesting that the rate-limiting step of the OER is the chemical adsorption of OH-.45 For the edge of Ni/Co, the parameters η, η10, and the Tafel slope, indicated that the electrocatalysts showed unsatisfactory OER performance, demonstrating the crucial role a pure perovskite phase structure plays in the OER electrocatalysis. The ternary Fe/Co/Ni samples exhibited a favourable activity due to the effects of Fe/Co and Fe/Ni (Figure 2a-c). For example, SFC0.75N0.375M showed an outstanding OER performance of η (259 mV), η10 (400 mV), and Tafel slope (84 mV dec-1), surpassing those of all the other compositions. In addition to the OER catalytic activity, the durability is an important parameter for the assessment of the catalytic efficiency. Figure S3 shows the LSV curves at different scans for the large-scale-tuned catalysts. Although only the first several scans are given, we can establish knowledge about the durability tendencies of various combinations of Fe, Co, and Ni. The curves were reduced with the consecutive linear sweeping for the samples of Fe/Ni. However, restricted by the limited scans, we have not gained a better understanding of the reasons for the large differences in the durability among the various edges, which will be discussed in detail below.

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Figure 3. (a) A summary of the phase structure of the ternary phase diagram by large-scale tuning, (b) the ternary phase diagram of the designated-scale tuning with an internal value of 0.125. The specific phase information about the ternary phase diagram of the designated-scale tuning powders, including (c) the edge of Fe/Co-2 with the composition Sr2Fe1.5-xCoxMo0.5O6- (x=0.125, 0.25, 0.375, and 0.5), (d) the edge of Fe/Ni-2 with the composition Sr2Fe1.5-xNixMo0.5O6- (x=0.125, 0.25, 0.375, and 0.5), (e) the edge of Fe/Co/Ni-2.1 with the composition Sr2FeNi0.5-xCoxMo0.5O6- (x=0.125, 0.25, 0.375, and 0.5), and (f) the edge of Fe/Co/Ni-2.2 with the composition Sr2Fe1.5-x-yCoxNiyMo0.5O6- (x=0.25, y=0.125; x=0.125, y=0.25; x=0.125, y=0.125). In the discussion above, attention was mainly given to the doping ability of SF1.5M. The backbone structure of the perovskite was based on the optimal concentration of Fe. If Fe was doped to a large extent by Ni or Co, a pure perovskite phase was not sustainable. We therefore made a distinction between the multi-phase, the complicated phase and the single phase for the large-scale tuning catalysts (Figure 3a). Taking various factors into consideration, including phase structure, OER catalytic activity, and durability, we narrowed the range by limiting the minimum concentration 8 / 23


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of Fe to 50% (relative to B-site concentration), and the ternary phase diagram of the designated-scale tuning with an internal value of 0.125 is presented in Figure 3b. Because there are many electrocatalysts in this diagram, several representative catalysts were selected from each edge, including SF1.5M, SFC0.375M, SFN0.25M, SFC0.25N0.125M, and SFC0.125N0.125M. The crystal structures of the selected electrocatalysts were determined by XRD together with the refinement results by the Rietveld method (Figure S4 and Table S1), and all these samples exhibited a pure cubic structure (space group Fm-3m, PDF#97-009-6223) without any impurity phase detected. High-resolution transmission electron microscopy (HR-TEM) characterization was performed to further probe the crystal structure. The HR-TEM images show a high crystallinity with clear lattice fringes (Figure S5). For example, the fast Fourier transform (FFT) analysis of SFN0.25M revealed a lattice spacing of 0.274 nm, corresponding to the (220) lattice plane, further confirming the cubic structure of SFN0.25M, which agrees with the Rietveld refinement. This result is also consistent with the previous literature.29

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Figure 4. The parameters (a) onset overpotential, (b) intrinsic activity (mA cm-2oxide) at an overpotential of 400 mV, and (c) η10 of the designated-scale tuning catalysts (the black star indicates that the value is too large to illustrate). To visually aid the evaluation of the OER catalytic activity, three parameters, including η, intrinsic 10 / 23


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activity (mA cm-2oxide) at an overpotential of 400 mV, and η10, were replotted in Figure 4 based on the data from the LSV curves (Figure S6). The presence of Ni effectively enhanced the reaction kinetics compared with that of the Fe/Co-2 series. The overpotential of the catalyst SFC0.25N0.125M, reached 250 mV, which compares favourably with the precious metal oxide IrO2 (240 mV) (Figure 4a). Since the intrinsic activity can reveal more information about the OER catalytic activity, the OER currents at an overpotential of 400 mV were normalized to the specific surface areas of the catalysts estimated by N2 sorption measurements (Table S2).46 The SFC0.25N0.125M, SFC0.125N0.375M, and SFC0.375M catalysts delivered a remarkable intrinsic activity of nearly 1.3 mA cm-2oxide, which is approximately 160 times higher than that of the parent oxide SF1.5M (Figure 4b). The value of the 10 metric is too large for SF1.5M, demonstrating its extremely poor OER activity (Figure 4c). By contrast, SFC0.125N0.375M showed the lowest 10 of 370 mV, with a sharp enhancement compared to that of SF1.5M. Notably, among most of the well-tuned catalysts reported here, our materials showed a superior performance to some currently reported high-performance OER electrocatalysts (Table S3). Furthermore, the electrochemical impedance spectroscopy (EIS) measurements were performed to investigate the OER kinetics of the electrode. Figure S7 shows the Nyquist plots, from which the charge transfer resistance of the electrode was obtained. The rate of OER follows the order of SF1.5M

≫

SFN0.25M

≥

SFC0.375M ≈ SFC0.125N0.125M. This result suggests that fast electrode transfer and facile OER kinetics is feasible for the binary and ternary phases.47,48 The operating durability was evaluated by the chronoamperometry method with different fixed current densities, which was reflected by the potential change upon an abrupt change in current density. (Figure S8).49,50 The parent oxide SF1.5M exhibited an abrupt potential increase within several minutes of testing at 5 mA cm-2. In contrast, SFN0.25M showed an apparently enhanced stability during the test and more importantly, SFC0.375 and SFC0.25N0.125M exhibited negligible change, even at the potential needed to afford the high current density of 15 mA cm-2. The chronopotentiometry test was carried out at a constant current density of 5 mA cm-2 to further evaluate the long-term stability.51 The chronoamperometric responses demonstrate the high stability of SFC0.375 and SFC0.125N0.125M, showing a nearly unchanged potential within 20 h (Figure S9). We have discussed the relationship between the phase structure and OER performance and the 11 / 23



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synergistic effect between the various combinations of the 3d TM. A summary can be given based on the ternary phase diagrams of the large-scale tuning and designated-scale tuning. First, a single double perovskite phase is based on the optimal concentration of Fe. Second, a binary combination of Fe and Co can effectively enhance the OER performance with low Tafel slopes, and a binary combination of Fe and Ni has the advantage of reducing the overpotential of the OER process. These conclusions are based on the tremendous attention paid to the fine-tuning of the activity of the transition-metal based double perovskites for the OER in alkaline solution. In addition to tuning the OER activities of the series of double perovskites, it is useful and necessary to thoroughly understand the relationship between the electronic states of the transition metals and the OER performance, which is also instrumental in the design of more efficient OER electrocatalysts. Below, attention is given to the origin of the enhanced OER performance based on the selected electrocatalysts. Consistent with the SEM observations (Figure S10), the selected powders were composed of nanoparticles that were several hundred nanometers in size according to the TEM images (Figure S11). The combustion synthesis method is a facile and attractive approach to obtain homogeneous, unagglomerated, and highly crystalline nanoparticles.52 This method usually produces particles with a smaller size compared to other conventional methods, e.g., the sol-gel process and solid-state reaction route, by which more active sites are exposed. Moreover, partial substitution of Fe by Co and/or Ni does not alter the formation of a pure cubic perovskite phase. Additionally, their morphologies are similar, which is important for comparing their catalytic activities for the same crystal structures and comparable nanoparticle sizes. The water-splitting process includes the OER (anode) and the HER (cathode). The overall efficiency of the process is mainly hindered by the high overpotential for the OER due to its sluggish kinetics. The widely accepted mechanism of the OER in alkaline solution involves four-electron charge-transfer steps, which is also called a single-site mechanism.2,5,11 A series of consecutive reaction intermediates, including HO*, O*, and HOO*, are generated on the active sites at the catalyst surface. The active sites for perovskite materials usually refer to the B-site transition metal cations.11,17,20 A dual-metal-site mechanism was proposed to demonstrate the synergistic effect of multi-elements in catalytic activity.53 In our previous work, we presented a universal strategy that introduces multi-element synergy and builds an ordered structure to improve the OER performance of the perovskite.10 Notably, the optimal combinations of different active sites can provide optimal 12 / 23


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binding to the different reaction intermediates and thus accelerate the OER process. Therefore, the strategy of designing electrocatalysts by ternary phase diagrams in this work is to afford optimal binding. The designed electrocatalysts showed improved kinetics compared to that of parent oxide, as demonstrated by the enhanced rate determining step (chemical adsorption of OH- for HO* formation, Figure 2c).

Figure 5. XAS spectra of (a) Fe-L2,3 edges of SFC0.375M, SFN0.25M, SFC0.125N0.125M, SFC0.125N0.375M, and Fe2O3 (reference). (b) Ni-L2,3 edges of SFN0.25M, SFC0.125N0.125M, SFC0.125N0.375M, and NiO (reference). (c) Mo-L3 edge of SFC0.375M, SFN0.25M, SFC0.125N0.125M, SFC0.125N0.375M, and MoO3 (reference). (d) Co-L2,3 edges of SFC0.375, SFC0.125N0.125M, SFC0.125N0.375M, and CoO (reference). Another important feature of perovskite materials is the existence of oxygen defects (oxygen vacancies). Defect engineering is a widely adopted methodology for tailoring the catalytic activity of many oxides and carbon-based materials.54 The oxygen vacancies (δ) in a perovskite oxide were determined by the charge neutrality requirement.10 Soft X-ray absorption spectroscopy (XAS) at the transition metal L2,3 edges is a very sensitive experimental tool to explore their valence states.55-58 Figure 5a shows the Fe L2,3 XAS spectra of the selected samples. The nearly identical multiplet spectral feature and energy position to those of the Fe3+ reference of Fe2O3 suggests that the oxide state of Fe at the surface was 3+. Trivalence iron is a common existence in the system of spinel oxide 13 / 23



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and perovskite.59-62 We also determined the similar oxidation state of Ni (Ni2+) and Mo (Mo6+) in comparison with NiO as a Ni2+ reference and MoO3 as a Mo6+ reference, respectively (Figure 5b and 5c).63,64 The Co L2,3-edge XAS spectra of SFC0.375M, SFC0.125N0.125M, and SFC0.125N0.375M, as well as CoO, serving as a Co2+ reference are shown in Figure 5d. The Co ion had mainly a 3+ valence state 65-68 in low-spin state 67,68 with a very small 2+ content, evidenced by a minor pre-edge peak at 777.8 eV (fingerprint of Co2+ species). Basically, partial substitution of Fe3+ by Ni2+ (or Co2+) would result in either a shift of the oxidation state of the Fe ions to higher values (Fe3+/Fe4+) or an increase in the content of δ. From the analysis of XAS, we observed that the Fe valence states remained unchanged (Fe3+) upon doping with various kinds of transition metals (Co, Ni and Co/Ni). Thus, the content of δ depended mainly on the content of Ni ions. For the system of Sr2Fe1.5-yNiyMo0.5O6-δ, the δ value increased dramatically with increased Ni doping levels. Previous research suggested that greatly increasing δ led to a significant deterioration in the OER performance.69 The best catalytic activity needed an optimal δ value.70 Furthermore, the much increased δ value had a negative effect on stabilizing the perovskite structure.71,72 Since the Co ion, generally regarded as the OER active site, was mainly in the 3+ state, which was the same as the Fe ion, the Co substitution did not enhance the δ value. Therefore, Sr2Fe1.5-xCoxMo0.5O6-δ had better stability of OER performance than did the Sr2Fe1.5-yNiyMo0.5O6-δ system. However, the introduction of Ni into the ternary phase system further reduced the overpotential. 3. Summary In summary, we reported how ternary phase diagrams can be utilized to achieve a rapid screening of multi-transition metal-based double perovskites with enhanced OER performance. Large-scale tuning and designated-scale tuning strategies were used to gain a comprehensive understanding of the effects of various combinations of transition metal elements in the B-site of double perovskites on the crystal structure, electronic structure and oxygen nonstoichiometry, which are factors of prime significance that determine the activity for the water oxidation reaction. Fe functions to maintain the double perovskite structure, while the combinations of the Fe-Co system (Sr2Fe1.5-xCoxMo0.5O6-δ) can improve the catalytic activities, and the catalysts of the Fe-Ni system (Sr2Fe1.5-yNiyMo0.5O6-δ) can facilitate the surface kinetic properties of OER. The Fe, Co and Ni ternary phase system act as the synergistic coactive sites (Sr2Fe1.5-x-yCoxNiyMo0.5O6-δ) to catalyse the OER activity and overcome the 14 / 23


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drawbacks of each of the binary combinations, resulting in a considerable increase in the OER performance. We expect that this systematic work could shed light on understanding the OER electrocatalysis on multi-transition metal-based perovskite catalysts and expedite the development of efficient catalytic candidates to realize the commercialization of related energy conversion and storage devices. Supporting Information Synthesis of the catalysts, materials characterizations, electrode preparation and electrochemical measurements, XRD patterns, XRD Rietved refinement patterns and results, LSV and CP curves, HRTEM images, SEM images, and surfae area ORICD Hainan Sun

0000-0003-1589-3860

Xiaomin Xu

0000-0002-0067-3331

Jie Dai

0000-0001-9470-5172

Wei Zhou

0000-0003-0322-095X

Zongping Shao

0000-0002-4538-4218

Acknowledgements This work was financially supported by the Jiangsu Natural Science Foundation for Distinguished Young Scholars (No. BK20170043), and National Natural Science Foundation of China (No. 21576135). We acknowledge support from the Max Planck-POSTECH-Hsinchu Center for Complex Phase Materials.

References (1) Chu, S.; Majumdar, A. Opportunities and Challenges for a Sustainable Energy Future. Nature 2012, 488, 294-303. (2) Song, A.; Cao, L.; Yang, W.; Yang, W.; Wang, L.; Ma, Z.; Shao, G. In Situ Construction of Nitrogen-Doped Graphene with Surface-Grown Carbon Nanotubes as a Multifactorial Synergistic Catalyst for Oxygen Reduction. Carbon 2019, 142, 40-50. (3) Zhang, Y.; Rui, K.; Ma, Z.; Sun, W.; Wang, Q.; Wu, P.; Zhang, Q.; Li, D.; Du, M.; Zhang, W.; 15 / 23



Page 16 of 23

Lin, H.; Zhu, J. Cost-Effective Vertical Carbon Nanosheets/Iron-Based Composites as Efficient Electrocatalysts for Water Splitting Reaction. Chem. Mater. 2018, 30, 4762-4769. (4) Suen, N.-T.; Huang, S.-F.; Quan, Q.; Zhang, N.; Xu, Y.-J. Chen, H. M. Electrocatalysis for the Oxygen Evolution Reaction: Recent Development and Future Perspectives. Chem. Soc. Rev. 2017, 46, 337-365. (5) Song, F.; Bai, L.; Moysiadou, A.; Lee, S.; Hu, C.; Liardet, L.; Hu, X. Transition Metal Oxides as Electrocatalysts

for

the

Oxygen

Evolution

Reaction

in

Alkaline

Solutions:

An

Application-Inspired Renaissance. J. Am. Chem. Soc. 2018, 140, 7748-7759. (6) Wang, J.; Cui, W.; Liu, Q.; Xing, Z.; Asiri, A.; Sun, X. Recent Progress in Cobalt-based Heterogeneous Catalysts for Electrochemical Water Splitting. Adv. Mater. 2016, 28, 215-230. (7) Zhou, Y.; Sun, S.; Xi, S.; Duan, Y.; Sritharan, T.; Du, Y.; J.Xu, Z.; Superexchange Effects on Oxygen Reduction Activity of Edge-Sharing [CoxMn1-xO6] Octahedra in Spinel Oxide. Adv. Mater. 2018, 30, 1705407. (8) Song, F.; Xu, X. Exfoliation of Layered Double Hydroxides for Enhanced Oxygen Evolution Catalysis. Nat. Commun. 2014, 5, 4477. (9) Chen, G.; Zhu, Y.; Chen, H. M.; Hu, Z.; Huang, S.-F.; Ma, N.; Dai, J.; Lin, H.-J.; Chen, C.-T.; Zhou, W.; Shao, Z. An Amorphous Nickel-Iron-Based Electrocatalyst with Unusual Local Structures for Ultrafast Oxygen Evolution Reaction. Adv. Mater. 2019, 31, 1900883. (10) Sun, H.; Xu, X.; Hu, Z.; Tjeng, L. H.; Zhao, J.; Zhang, Q.; Lin, H.-J. ; Chen, C.-T.; Chan, T.-S.; Zhou, W.; Shao, Z. Boosting the Oxygen Evolution Reaction Activity of a Perovskite through Introducing Multi-Element Synergy and Building an Ordered Structure. J. Mater. Chem. A 2019, 7, 9924-9932. (11) Han, L.; Dong, S.; Wang, E. Transition-Metal [Co, Ni, and Fe]-Based Electrocatalysts for the Water Oxidation Reaction. Adv. Mater. 2016, 28, 9266-9291. (12) Hwang, J.; Rao, R. R.; Giordano, L.; Katayama, Y.; Yu, Y.; Shao-Horn, Y. Perovskites in Catalysis and Electrocatalysis. Science 2017, 358, 751-756. (13) Sun, H.; Chen, G.; Sunarso, J.; Dai, J.; Zhou, W.; Shao, Z. Molybdenum and Niobium Codoped B-Site-Ordered Double Perovskite Catalyst for Efficient Oxygen Evolution Reaction. ACS Appl. Mater. Interfaces 2018, 10, 16939-16942. (14) Xu, X.; Zhong, Y.; Shao, Z. Double Perovskites in Catalysis, Electrocatalysis, and 16 / 23


Page 17 of 23 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Photo(electro)catalysis. Trends Chem. 2019, 1, 410-424. (15) Tong, Y.; Wu, J.; Chen, P.; Liu, H.; Chu, W.; Wu, C.; Xie, Y. Vibronic Superexchange in Double Perovskite Electrocatalyst for Efficient Electrocatalytic Oxygen Evolution. J. Am. Chem. Soc. 2018, 140, 11165-11169. (16) Duan, Y.; Sun, S.; Xi, S.; Ren, X.; Zhou, Y.; Zhang, G.; Yang, H.; Du, Y.; J.Xu, Z. Tailoring the Co 3d-O 2p Covalency in LaCoO3 by Fe Substitution to Promote Oxygen Evolution Reaction. Chem. Mater. 2017, 29, 10534-10541. (17) Hua, B.; Sun, Y.-F.; Li, M.; Yan, N.; Chen, J.; Zhang, Y.-Q.; Zeng, Y.; Amirkhiz, B.; Luo, J. Stabilizing Double Perovskite for Effective Bifunctional Oxygen Electrocatalysis in Alkaline Conditions. Chem. Mater. 2017, 29, 6228-6237. (18) Xiong, Y.; Yang, Y.; Feng, X.; DiSalvo, F. J.; Abruña, H. D. A Strategy for Increasing the Efficiency of the Oxygen Reduction Reaction in Mn-Doped Cobalt Ferrites. J. Am. Chem. Soc. 2019, 141, 4412-4421. (19) Liu, P.; Yang, S.; Zhang, B.; Yang, H. Defect-Rich Ultrathin Cobalt-Iron Layered Double Hydroxide for Electrochemical Overall Water Splitting. ACS Appl. Mater. Interfaces 2016, 8, 34474-34481. (20) Burker, M. S.; Kast, M. G.; Trotochaud, L.; Smith, A. M.; Boettcher, S. W. Cobalt-iron (Oxy) Hydroxide Oxygen Evolution Electrocatalysts: the Role of Structure and Composition on Activity, Stability, and Mechanism. J. Am. Chem. Soc. 2015, 137, 3638-3648. (21) Kim, B.-J.; Fabbri, E.; Abbott, D. F.; Cheng, X.; Clark, A. H.; Nachtegaa, M.; Borlaf, M.; Castelli, I. E.; Graule, T.; Schmidt, T. J. Functional Role of Fe-doping in Co-based Perovskite Oxide Catalysts for Oxygen Evolution Reaction. J. Am. Chem. Soc. 2019, 141, 5231-5240. (22) Fu, S.; Zhu, C.; Song, J.; Engelhard, M. H.; Li, X.; Du, D.; Lin Y. Highly Ordered Mesoporous Bimetallic Phosphides as Efficient Oxygen Evolution Electrocatalysts. ACS Energy Lett. 2016, 1, 792-796. (23) Jung, S.; Gwon, H.; Hong, J.; Park, K.; Seo, D.; Kim, H.; Hyun, J.; Yang, W.; Kang, K. Understanding the Degradation Mechanisms of LiNi0.5Co0.2Mn0.3O2 Cathode Material in Lithium Ion Batteries. Adv. Energy Mater. 2014, 4, 1300787. (24) Manthiram, A.; Song, B.; Li, W. A Perspective on Nickel-Rich Layered Oxide Cathodes for Lithium-Ion Batteries. Energy Storage Mater. 2017, 6, 125-139. 17 / 23



Page 18 of 23

(25) Gupta, S.; Zhao, S.; Wang, X.; Hwang, S.; Karakalos, S.; Devaguptapu, S. V.; Mukherjee, S.; Su, D.; Hui, X.; Wu, G. Quaternary FeCoNiMn-Based Nanocarbon Electrocatalysts for Bifunctional Oxygen Reduction and Evolution: Promotional Role of Mn Doping in Stabilizing Carbon. ACS Catal. 2017, 7, 8386-8393. (26) Xu, J.; Li, J.; Xiong, D.; Zhang, B.; Liu, Y.; Wu, K.-H.; Amorim, I.; Li, W.; Liu, L. Trends in Activity for the Oxygen Evolution Reaction on Transition Metal (M = Fe, Co, Ni) Phosphide Precatalysts. Chem. Sci. 2018, 9, 3470-3476. (27) Favaro, M.; Drisdell, W.; Marcus, M.; Gregoire, J.; Crumlin, E.; Haber, J.; Yano, J. An Operando Investigation of (Ni-Fe-Co-Ce)Ox System as Highly Efficient Electrocatalyst for Oxygen Evolution Reaction. ACS Catal. 2017, 7, 1248-1258. (28) Pan, X.; Wang, Z.; He, B.; Wang, S.; Wu, X.; Xia, C. Effect of Co Doping on the Electrochemical Properties of Sr2Fe1.5Mo0.5O6 Electrode for Solid Oxide Fuel Cell. Int. J. Hydrogen Energy 2013, 38, 4108-4115. (29) Dai, N.; Feng, J.; Wang, Z.; Jiang, T.; Sun, W.; Qiao, J.; Sun, K. Synthesis and Characterization of B-site Ni-Doped Perovskites Sr2Fe1.5-xNixMo0.5O6-δ (x = 0, 0.05, 0.1, 0.2, 0.4) as Cathodes for SOFCs. J. Mater. Chem. A 2013, 1, 14147-14153. (30) Zhang, X.; Yu, X.; L. Zhang, F. Zhou, Y. Liang, R. Wang, Molybdenum Phosphide/Carbon Nanotube Hybrids as pH-Universal Electrocatalysts for Hydrogen Evolution Reaction. Adv. Funct. Mater. 2018, 28, 1706523. (31) Hona, R. K.; Ramezanipour, F. Remarkable Oxygen-Evolution Activity of a Perovskite Oxide from the Ca2-xSrxFe2O6-δ Series. Angew. Chem. Int. Ed. 2019, 58, 1-5. (32) Smith, R. D.; Prévot, M. S.; Fagan, R. D.; Trudel, S.; Berlinguette, C. P. Water Oxidation Catalysis: Electrocatalytic Response to Metal Stoichiometry in Amorphous Metal Oxide Films Containing Iron, Cobalt, and Nickel. J. Am. Chem. Soc. 2013, 13531, 11580-11586. (33) Cao, X.; Zhang, N.; Chen, Q.; Masud, J.; Zaeem, M. A.; Nath, M. Phase Exploration and Identification of Multinary Transition-Metal Selenides as High-Efficiency Oxygen Evolution Electrocatalysts through Combinatorial Electrodeposition. ACS Catal. 2018, 89, 8273-8289. (34) Cao, X.; Johnson, E.; Nath, M. Expanding Multinary Selenide Based High-Efficiency Oxygen Evolution Electrocatalysts through Combinatorial Electrodeposition: Case Study with Fe-Cu-Co Selenides. ACS Sustainable Chem. Eng. 2019, 710, 9588-9600. 18 / 23


Page 19 of 23 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(35) She, S.; Yu, J.; Tang, W.; Zhu, Y.; Chen, Y.; Sunarso, J.; Zhou, W.; Shao, Z. Systematic Study of Oxygen Evolution Activity and Stability on La1-xSrxFeO3-δ Perovskite Electrocatalysts in Alkaline Media. ACS Appl. Mater. Interfaces 2018, 10, 11715-11721. (36) Li, Z.; Yang, M.; Park, J.; Wei, S.; Berry, J.; Zhu, K. Stabilizing Perovskite Structures by Tuning Tolerance Factor: Formation of Formamidinium and Cesium Lead Iodide Solid-State Alloys. Chem. Mater. 2016, 28, 1, 284-292. (37) Wang, L.; Liu, Q.; Shen, K.; Zhang, Q.; Zhang, L.; Song, B.; Wong, C. A High Quenching Content Red-Emitting Phosphor based on Double Perovskite Host BaLaMgSbO6 for White LEDs. J. Alloys Compd. 2017, 696, 443-449. (38) Wu, S.; Yao, X.; Zhang, L.; Cao, Y.; Zou, W.; Li, L.; Ma, K.; Tang, C.; Gao, F.; Dong, L. Improved Low Temperature NH3-SCR Performance of FeMnTiOx Mixed Oxide with CTAB-Assisted Synthesis. Chem. Commun. 2015, 51, 3470-3473. (39) Hwang, J.-Y.; Yoon, C. S.; Belharouak, L.; Sun, Y.-K. A Comprehensive Study of the Role of Transition Metals in O3-Type Layered Na(NixCoyMnz)O2 (x=1/3, 0.5, 0.6, and 0.8) Cathodes for Sodium-Ion Batteries. J. Mater. Chem. A 2016, 4, 17952-17959. (40) Saffari, F.; Kameli, P.; Rahimi, M.; Ahmadvand, H.; Salamati, H. Effects of Co-Substitution on the Structural and Magnetic Properties of NiCoxFe2-xO4 Ferrite Nanoparticles. Ceram. Int. 2015, 41, 7352-7358. (41) Wei, C.; Rao, R. R.; Peng, J.; Huang, B.; Stephens, I. E. L.; Risch, M.; J.Xu, Z.; Shao-Horn, Y. Recommended Practices and Benchmark Activity for Hydrogen and Oxygen Electrocatalysis in Water Splitting and Fuel Cells. Adv. Mater. 2019, 31, 1806296. (42) Liu, S.; Luo, H.; Li, Y.; Liu, Q.; Luo, J.-L. Structure-Engineered Electrocatalyst Enables Highly Active and Stable Oxygen Evolution Reaction over Layered Perovskite LaSr3Co1.5Fe1.5O10-δ, Nano Energy 2017, 40, 115-121. (43) Sun, H.; He, J.; Hu, Z.; Chen, C.-T.; Zhou, W.; Shao, Z. Multi-Active Sites Derived from a Single/Double Perovskite Hybrid for Highly Efficient Water Oxidation. Electrochimica Acta 2019, 299, 926-932. (44) Zhu, Y.; Zhou, W.; Chen, Z.-G.; Chen, Y.; Su, C.; Tadé, M. O.; Shao, Z. SrNb0.1Co0.7Fe0.2O3-δ Perovskite as a Next-Generation Electrocatalyst for Oxygen Evolution in Alkaline Solution. Angew. Chem. Int. Ed. 2015, 54, 3897-3901. 19 / 23



Page 20 of 23

(45) Wang, H.-Y.; Huang, S.-F.; Chen, H.-Y.; Chan, T.-S.; Chen, H. M.; Liu, B. In Operando Identification of Geometrical-Site-Dependent Water Oxidation Activity of Spinel Co3O4. J. Am. Chem. Soc. 2016, 138, 36-39. (46) Sun, H.; Chen, G.; Zhu, Y.; Liu, B.; Zhou, W.; Shao, Z. B-Site Cation Ordered Double Perovskites as Efficient and Stable Electrocatalysts for Oxygen Evolution Reaction. Chem. Eur. J. 2017, 23, 5722-5728. (47) Wang, Y.; Zhang, Y.; Liu, Z.; Xie, C.; Feng, S.; Liu, D.; Shao, M.; Wang, S. Layered Double Hydroxide Nanosheets with Multiple Vacancies Obtained by Dry Exfoliation as Highly Efficient Oxygen Evolution Electrocatalysts. Angew. Chem. Int. Ed. 2017, 56, 5867-5871. (48) Oh, N. K.; Kim, C.; Lee, J.; Kwon, O.; Choi, Y.; Jung, G. Y.; Lim, H. Y.; Kwak, S. K.; Kim, G.; Park, H. In-Situ Local Phase-Transitioned MoSe2 in La0.5Sr0.5CoO3-δ Heterostructure and Stable Overall Water Electrolysis over 1000 Hours. Nat. Commun, 2019, 10, 1723. (49) X. Lu, C. Zhao, Electrodeposition of Hierarchically Structured Three-Dimensional Nickel-Iron Electrodes for Efficient Oxygen Evolution at High Current Densities. Nat. Commun, 2015, 6, 6616. (50) Z. Qiu, C.-W. Tai, G. A. Niklasson, T. Edvinsson, Direct Observation of Active Catalyst Surface Phases and the Effect of Dynamic Self-Optimization in NiFe-Layered Double Hydroxides for Alkaline Water Splitting. Energy Environ. Sci. 2019, 12, 572-581. (51) J. Kim, O. Gwon, O. Kwon, J. Mahmood, C. Kim, Y. Yang, H. Lee, J. H. Lee, H. Y. Jeong, J.-B. Baek, G. Kim, Synergistic Coupling Derived Cobalt Oxide with Nitrogenated Holey Two-Dimensional Matrix as an Efficient Bifunctional Catalyst for Metal-Air Batteries. ACS Nano 2019, 13, 5502-5512. (52) Manikandan, A.; Kennedy, L. J.; Bououdina, M.; Vijaya, J. J. Synthesis, Optical and Magnetic Properties of Pure and Co-Doped ZnFe2O4 Nanoparticles by Microwave Combustion Method. J Magn Magn Mater, 2014, 349, 249-258. (53) Dai, J.; Zhu, Y.; Chen, Y.; Zhou, W.; Shao, Z. Na0.86Co0.95Fe0.05O2 Layered Oxide As Highly Efficient Water Oxidation Electrocatalyst in Alkaline Media. ACS Appl. Mater. Interfaces 2017, 9, 21587-21592. (54) Zhu, Y.; Liu, X.; Jin, S.; Chen, H.; Lee, W.; Liu, M.; Chen, Y. Anionic Defect Engineering of Transition Metal Oxides for Oxygen Reduction and Evolution Reactions. J. Mater. Chem. A 20 / 23


Page 21 of 23 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


2019, 7, 5875-5897. (55) Chen, C.-T.; Sette, F. High Resolution Soft X-Ray Spectroscopies with the Dragon Beamline. Physica Scripta, 1990, 1990, 119-126. (56) Mitra, C.; Hu, Z. ; Raychaudhuri, P.; Wirth, S.; Csiszar, S. I.; Hsieh, H. H.; Lin, H.-J.; Chen, C.-T.; Tjeng, L. H. Direct Observation of Electron Doping in La0.7Ce0.3MnO3 Using X-Ray Absorption Spectroscopy. Phys. Rev. B 2003, 67, 092404. (57) Burnus, T.; Hu, Z.; Haverkort, M.; Cezar, J.; Flahaut, D.; Hardy, V.; Maignan, A.; Brookes, N.; Tanaka, A.; Hsieh, H.; Lin, H.-J.; Chen, C.-T.; Tjeng, L. H. Valence, Spin, and Orbital State of Co Ions in One-Dimensional : An X-Ray Absorption and Magnetic Circular Dichroism Study. Phys. Rev. B 2006, 74, 245111. (58) Burnus, T.; Hu, Z.; Hsieh, H.; Joly, V. L. J.; Joy, P. A.; Haverkort, M. W.; Wu, H.; Tanaka, A.; Lin, H.-J.; Chen, C.-T.; Tjeng, L. H. Local Electronic Structure and Magnetic Properties of Studied by X-Ray Absorption and Magnetic Circular Dichroism Spectroscopy. Phys. Rev. B 2008, 77, 125124. (59) Kuo, C.-Y.; Hu, Z.; Yang, J.; Liao, S.-C.; Huang, Y.; Vasudevan, R.; Okatan, M.; Jesse, S.; Kalinin, S.; Li, L.; Liu, H.; Lai, C.-H.; Pi, T.; Agrestini, S.; Chen, K.; Ohresser, P.; Tanaka, A.; Tjeng, L. H.; Chu, Y. Single-Domain Multiferroic BiFeO3 Films. Nat. Commun. 2016, 7, 12712. (60) Chang, C.; Hu, Z.; Klein, S.; Liu, X.; Sutarto, R.; Tanaka, A.; Cezar, J.; Brookes, N.; Lin, H.-J.; Hsieh, H.; Chen, C.-T.; Rata, A.; Tjeng, L. H. Dynamic Atomic Reconstruction: How Fe3O4 Thin Films Evade Polar Catastrophe for Epitaxy. Phys. Rev. X 2016, 6, 041011. (61) Zhou, Y.; Sun, S.; Song, J.; Xi, S.; Chen, B.; Du, Y.; Fisher, A. C.; Cheng, F.; Wang, X.; Zhang, H.; J.Xu, Z. Enlarged Co-O Covalency in Octahedral Sites Leading to Highly Efficient Spinel Oxides for Oxygen Evolution Reaction. Adv. Mater. 2018, 30, 1802912. (62) Chen, G.; Hu, Z.; Zhu, Y.; Chen, Z.-G.; Zhong, Y.; Lin, H.-J.; Chen, C.-T.; Tjieng, L. H.; Zhou, W.; Shao, Z. Ultrahigh-Performance Tungsten-Doped Perovskites for the Oxygen Evolution Reaction. J. Mater. Chem. A 2018, 6, 9854-9859. (63) Alders, D.; Tjeng, L. H.; Voogt, F.; Hibma, T.; Sawatzky, G.; Chen, C.-T.; Vogel, J.; Sacchi, M.; Iacobucci, S. Temperature and Thickness Dependence of Magnetic Moments in NiO Epitaxial Films. Phys. Rev. B 1998, 57, 11623. 21 / 23



Page 22 of 23

(64) Haverkort, M.; Csiszar, S.; Hu, Z.; Altieri, S.; Tanaka, A.; Hsieh, H.; Lin, H.-J.; Chen, C.-T.; Hibma, T.; Tjeng, L. H. Magnetic versus Crystal-Field Linear Dichroism in NiO Thin Films. Phys. Rev. B 2004, 69, 020408. (65) Hu, Z.; Wu, H.; Haverkort, M.; Hsieh, H.; Lin, H.-J.; Lorenz, T.; Baier, J.; Reichl, A.; Bonn, I.; Felser, C.; Tanaka, A.; Chen, C.-T.; Tjeng, L. H. Different Look at the Spin State of

Co3+

Ions in a CoO5 Pyramidal Coordination. Phys. Rev. Lett. 2004, 92, 207402. (66) Chen, J.-M.; Chin, Y.-Y.; Valldor, M.; Hu, Z.; Lee, J.-M.; Haw, S.-C.; Hiraoka, N.; Ishii, H.; Pao, C.-W.; Tsuei, K.-D.; Lee, J.-F.; Lin, H.-J.; Jang, L.-Y.; Tanaka, A.; Chen, C.-T.; Tjeng, L. H. A Complete High-to-Low Spin State Transition of Trivalent Cobalt Ion in Octahedral Symmetry in SrCo0.5Ru0.5O3-δ. J. Am. Chem. Soc. 2014, 136, 1514-1519. (67) Haverkort, M.; Hu, Z.; Cezar, J.; Burnus, T.; Hartmann, H.; Reuther, M.; Zobel, C.; Lorenz, T.; Tanaka, A.;. Brookes, N.; Hsieh, H.; Lin, H.-J.; Chen, C.-T.; Tjeng, L. H. Spin State Transition in Studied Using Soft X-ray Absorption Spectroscopy and Magnetic Circular Dichroism. Phys. Rev. Lett. 2006, 97, 176405. (68) Chang, C.; Hu, Z.; Hua, W, Burnus, T.; Hollmann, N.; Benomar, M.; Lorenz, T.; Tanaka, A.; Lin, H.-J.; Hsieh, H.; Chen, C.-T.; Tjeng, L. H. Spin Blockade, Orbital Occupation, and Charge Ordering in La1.5Sr0.5CoO4. Phys. Rev. Lett. 2009, 102, 116401. (69) Miao, X.; Wu, L.; Lin, Y.; Yuan, X.; Zhao, J.; Yan, W.; Zhou, S.; Shi, L. The Role of Oxygen Vacancies in Water Oxidation for Perovskite Cobalt Oxide Electrocatalysts: Are More Better? Chem. Commun. 2019, 55, 1442-1445. (70) Guan, D.; Zhou, J.; Hu, Z.; Zhou, W.; Xu, X.; Zhong, Y.; Liu, B.; Chen, Y.; Xu, M.; Lin, H.-J.; Chen, C.-T.; Wang, J.-Q.; Shao, Z. Searching General Sufficient-and-Necessary Conditions for Ultrafast Hydrogen-Evolving Electrocatalysis. Adv. Funct. Mater. 2019, 29, 1900704. (71) May, K. J.; Carlton, C. E.; Stoerzinger, K. A.; Risch, M.; Suntivich, J.; Lee, Y.-L.; Grimaud, A.; Shao-Horn, Y. Influence of Oxygen Evolution during Water Oxidation on the Surface of Perovskite Oxide Catalysts. J. Phys. Chem. Lett. 2012, 3, 3264-3270. (72) Zhang, Z.; Chen, Y.; Dai, Z.; Tan, S.; Chen, D. Promoting Hydrogen-Evolution Activity and Stability of Perovskite Oxides via Effectively Lattice Doping of Molybdenum. Electrochim. Acta 2019, 312, 128-136. 22 / 23


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Ternary Phase Diagram-Facilitated Rapid Screening of Double

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