Engineering a Triphasic\nCo(OH)F/Co–S/CeO<sub>2</sub> Nanostructure Interface for Promoting\nHydrazine-Assisted\nOverall Water Splitting

Synthesizing bifunctional electrocatalysts capable of\nconcurrently\naccelerating the kinetics of both hydrogen evolution reaction (HER)\nand hydrazine oxidation reaction (HzOR) remains a formidable hurdle\nwith academic research. Herein, a nanoneedle-like electrocatalyst\nwith a triphasic nanointerface, consisting of crystalline Co(OH)F,\namorphous Co–S, and crystalline CeO<sub>2</sub>, was synthesized\non nickel foam (NF) (Co(OH)F/Co–S/CeO<sub>2</sub>/NF) through\nan integrated hydrothermal–sulfidation–deposition strategy.\nCo(OH)F/Co–S/CeO<sub>2</sub>/NF not only possessed abundant\nactive sites but also minimized charge-transfer resistance and optimized\nelectron distribution across interfaces, thus significantly accelerating\nreaction kinetics. Then, it demonstrated an overpotential of 153 mV\nfor the HER and a low potential of 80 mV for the HzOR at 10 mA cm<sup>–2</sup>, respectively. Employing Co(OH)F/Co–S/CeO<sub>2</sub>/NF as a bifunctional catalytic electrode, an impressively\nlow cell voltage of 0.20 V was sufficient to achieve a flow of 10\nmA cm<sup>–2</sup> during hydrazine-assisted overall water\nsplitting. Density functional theory calculations elucidated that\nthe superior performance of Co(OH)F/Co–S/CeO<sub>2</sub>/NF\nfor both HER and HzOR was originated from the balanced hydrogen adsorption\nenergy (Δ<i>G</i><sub>H*</sub>) during the HER process\nand the altered rate-limiting step with a relatively low energy barrier\nin HzOR. This research offers valuable insights into the development\nof sophisticated bifunctional electrocatalysts, significantly advancing\nlarge-scale deployment of energy-conserving H<sub>2</sub> production\ntechnologies.