Room‐Temperature, Meter‐Scale Synthesis of Heazlewoodite‐Based Nanoarray Electrodes for Alkaline Water Electrolysis

Abstract Alkaline water electrolysis is among the most promising technologies to massively produce green hydrogen. Developing highly‐active and durable electrodes to catalyze the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER) is of primary importance. Here a facile, room‐temperature synthetic route is presented to access heazlewoodite phase (Ni, Fe) 3 S 2 nanosheet arrays supported on NiFe foam (NFF), whose production can be easily scaled up to meter size per batch operation. The (Ni, Fe) 3 S 2 /NFF electrode can serve as a high‐performance electrocatalyst for both HER and OER in alkaline media, and remains highly stable for over 1000 h at 100 mA cm −2 current densities. When working as HER electrocatalyst, (Ni, Fe) 3 S 2 is confirmed as catalytic phase that provides a high density of efficient active sites (e.g., Ni─Ni and Ni─Fe bridge sites). During electrochemical OER testing, (Ni, Fe) 3 S 2 nanosheets totally transform into γ ‐(Fe, Ni)OOH as active catalytic phase for OER. As a consequence, the (Ni, Fe) 3 S 2 /NFF can be used to integrate into an alkaline electrolyzer as both the cathode and anode, and to give an excellent catalytic performance (600 mA cm −2 @1.93 V), which is better than the alkaline electrolyzer based on commercial Raney Ni electrodes.