Free‐Standing Multiscale Porous High Entropy NiFeCoZn Alloy as the Highly Active Bifunctional Electrocatalyst for Alkaline Water Splitting

Comprehensive Summary In the endeavor of searching for highly active and stable electrocatalysts toward overall water splitting, high‐entropy‐alloys have been the intense subjects owing to their advanced physicochemical property. The non‐noble metal free‐standing multiscale porous NiFeCoZn high‐entropy‐alloy is in situ constructed on the surface layer of NiZn intermetallic and Ni heterojunction over nickel foam (NiFeCoZn/NiZn‐Ni/NF) by one scalable dealloying protocal to fulfill the outstanding bifunctional electrocatalytic performances toward overall water splitting. Because of the high‐entropy effects and specific hierarchical porous architecture, the as‐made NiFeCoZn/NiZn‐Ni/ NF displays high intrinsic catalytic activities and durability toward both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in alkaline media. In particular, the in‐situ construction of bimodal porous NiFeCoZn high‐entropy‐alloy results in the small overpotentials ( η 1000 = 254/409 mV for HER and OER), low Tafel slopes, and exceptional long‐term catalytic durability for 400 h. Expressively, the electrolyzer constructed with NiFeCoZn/NiZn‐Ni/NF as both cathode and anode exhibits a low cell voltage of 1.72 V to deliver the current density of 500 mA·cm –2 for overall water splitting. This work not only provides a facile and scalable protocol for the preparation of self‐supporting high‐entropy‐alloy nanocatalysts but also enlightens the engineering of high performance bifunctional electrocatalysts toward water splitting.