Alkaline Water Splitting Enhancement by MOF-Derived Fe–Co–Oxide/Co@NC-mNS Heterostructure: Boosting OER and HER through Defect Engineering and In Situ Oxidation

Introducing defects and in situ topotactic transformation of the electrocatalysts generating heterostructures of mixed-metal oxides(hydroxides) that are highly active for oxygen evolution reaction (OER) in tandem with metals of low hydrogen adsorption barrier for efficient hydrogen evolution reaction (HER) is urgently demanded for boosting the sluggish OER and HER kinetics in alkaline media. Ascertaining that, metal–organic-framework-derived freestanding, defect-rich, and in situ oxidized Fe–Co–O/Co metal@N-doped carbon (Co@NC) mesoporous nanosheet (mNS) heterostructure on Ni foam (Fe–Co–O/Co@NC-mNS/NF) is developed from the in situ oxidation of micropillar-like heterostructured Fe–Co–O/Co@NC/NF precatalyst. The in situ oxidized Fe–Co–O/Co@NC-mNS/NF exhibits excellent bifunctional properties by demanding only low overpotentials of 257 and 112 mV, respectively, for OER and HER at the current density of 10 mA cm⁻², with long-term durability, attributed to the existence of oxygen vacancies, higher specific surface area, increased electrochemical active surface area, and in situ generated new metal (oxyhydr)oxide phases. Further, Fe–Co–O/Co@NC-mNS/NF (+/−) electrolyzer requires only a low cell potential of 1.58 V to derive a current density of 10 mA cm⁻². Thus, the present work opens a new window for boosting the overall alkaline water splitting.