Crystalline Multi-Metal Nanosheets Array with Enriched Oxygen Vacancies as Efficient and Stable Bifunctional Electrocatalysts for Water Splitting Muhammad Imran Abdullah Asima Hameed Tuoping Hu Ning Zhang Mingming Ma 10.1021/acsaem.9b01944.s001 https://acs.figshare.com/articles/journal_contribution/Crystalline_Multi-Metal_Nanosheets_Array_with_Enriched_Oxygen_Vacancies_as_Efficient_and_Stable_Bifunctional_Electrocatalysts_for_Water_Splitting/10354613 The electrolysis of water on a large scale for hydrogen production needs low cost, efficient, and stable electrocatalysts for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Herein, we report the synthesis of a crystalline multimetal (Co, Ni, Fe) nanosheets array (NSA) enriched with oxygen vacancies by a simple electrosynthesis method, which can serve as efficient and stable electrocatalysts for both OER and HER. The oxygen vacancies are generated by electro-oxidation or electro-reduction of CoFeNiSe precursor via the replacement of selenium by oxygen. For HER, as synthesized CoFeNi-NSA achieved a 400 mA cm<sup>–2</sup> current density at a low overpotential of −211 mV. For OER, CoFeNi-NSA was in situ oxidized to form CoFeNiO-NSA, which achieved a 400 mA cm<sup>–2</sup> current density at a low overpotential of 270 mV. The activities of CoFeNi-NSA and CoFeNiO-NSA remained stable after 150 h HER or OER test at high current densities, showing higher activity and stability than noble-metal electrocatalysts Pt/C and IrO<sub>2</sub>, respectively. The electrolytic cell of CoFeNiO-NSA∥CoFeNi-NSA can achieve a high current density of 400 mA cm<sup>–2</sup> at a moderate voltage of 1.98 V. During a long-term water splitting test, the voltage of the electrolytic cell remained stable at 1.76 V for 150 h at a current density of 120 mA cm<sup>–2</sup>, indicating that these catalysts have both high activity and stability for OER and HER reactions. 2019-11-19 17:06:03 vacancy voltage water splitting test density stability hydrogen evolution reaction electrocatalyst cm oxygen evolution reaction mA overpotential CoFeNiO-NSA OER oxygen vacancies CoFeNi-NSA NSA Crystalline Multi-Metal Nanosheets Array 150 h HER Stable Bifunctional Electrocatalysts Enriched Oxygen Vacancies mV