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)₃S₂ nanosheet arrays supported on NiFe foam (NFF), whose production can be easily scaled up to meter size per batch operation. The (Ni, Fe)₃S₂/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)₃S₂ 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)₃S₂ nanosheets totally transform into γ-(Fe, Ni)OOH as active catalytic phase for OER. As a consequence, the (Ni, Fe)₃S₂/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.