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The discovery of more efficient and stable catalysts for oxygen evolution reaction (OER) is vital in improving the efficiency of renewable energy generation devices. Given the large numbers of possible binary and ternary metal oxide OER catalysts, high-throughput methods are necessary to accelerate the rate of discovery. Herein, Mn-based spinel oxide, Fe10 Co40 Mn50 O, is identified for the first time using high-throughput methods demonstrating remarkable catalytic activity (overpotential of 310 mV on fluorine-doped tin oxide (FTO) substrate and 237 mV on Ni foam at 10 mA cm-2 ). Using a combination of soft X-ray absorption spectroscopy and electrochemical measurements, the high catalytic activity is attributed to 1) the formation of multiple active sites in different geometric sites, tetrahedral and octahedral sites; and 2) the formation of active oxyhydroxide phase due to the strong interaction of Co2+ and Fe3+ . Structural and surface characterizations after OER show preservation of Fe10 Co40 Mn50 O surface structure highlighting its durability against irreversible redox damage on the catalytic surface. This work demonstrates the use of a high-throughput approach for the rapid identification of a new catalyst, provides a deeper understanding of catalyst design, and addresses the urgent need for a better and stable catalyst to target greener fuel. Ministry of Education (MOE) National Research Foundation (NRF) This research was partially supported by grants from the National Research Foundation, Prime Minister’s Office, Singapore, under its Campus of Research Excellence and Technological Enterprise (CREATE) program. This work was partially supported by the Singapore Ministry of Education (MOE2019-T2-1-163), Tier 1 grant (2020-T1-001-147(RG64/20)), Tier 2 grant (MOE T2EP50120-00081), Singapore National Research Foundation-National University of Singapore Postdoc Fellowship, and NUS core SupportC-380-003-003-001.

Hematite is a promising photoanode for solar water splitting by photoelectrochemical (PEC) cells, but its performance is limited by the slow kinetics of water oxidation reaction or oxygen evolution reaction (OER). Surface modification of hematite photoanodes with a suitable water oxidation cocatalyst is a key strategy for improving the kinetics of water oxidation. In this study, a CeOx overlayer is deposited on the surface of the hematite photoanode by a water‐based solution method with ceric ammonium nitrate (CAN) followed by heat treatment. The photocurrent of CeOx‐modified hematite is 3 times higher than that of pristine hematite (at 1.23 V vs. RHE) under AM 1.5G, 1 sun conditions. Through hole‐scavenger measurements, Tafel plot analysis, and electrochemical impedance spectroscopy, it is concluded that CeOx overlayer increases the hole injection efficiency, improves the surface catalytic activity, and enhances charge transfer across the photoanode/electrolyte interface. These observations are attributed to the synergistic effects of Ce3+/Ce4+ redox species in CeOx and the oxygen vacancies. This work elucidates the role of CeOx as an efficient cocatalyst overlayer to improve the OER kinetics of photoanodes. Ministry of Education (MOE) National Research Foundation (NRF) Accepted version This research is partially supported by grants from the National Research Foundation, Prime Min ister’s Office, Sin g ap o re un der its Campus of Research Excellence and Technological Enterprise (CREATE) programme and Ministry of Education (MOE) Tier 2 Project (MOE2016-T2-1-030).