A Fully Reversible Water Electrolyzer Cell Made Up from FeCoNi (Oxy)hydroxide Atomic Layers

Renewable electricity powered water electrolysis is a promising solution for the conversion and storage of the intermittent renewable energy resources in the form of hydrogen. Herein, atomically thin FeCoNi ternary (oxy)hydroxide nanosheets (FeCoNi-ATNs) are developed as efficient and robust bifunctional electrocatalysts for the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in 1 m KOH solution (pH = 14). The electrocatalyst shows remarkably high apparent catalytic performance (400 mA cm(-2) at 350 mV for OER and 240 mV for HER) and mass activities at modest overpotentials (1931 A g(-1) at 330 mV for OER; 1819 A g(-1) at 200 mV for HER). Moreover, the OER and HER performance of FeCoNi-ATNs are fully reversible and electrochemically switchable, due to the interconversion attribute of two catalytic states for OER and HER. Using the dual functional properties of this catalyst, a fully reversible water electrolyzer cell is fabricated, exhibiting a robust reversibility between two half reactions in water electrolysis under a high current density (100 mA cm(-1)), which can effectively overcome the stability issues caused by electrode depolarization during frequent power interruptions, an inevitable phenomenon commonly brought about by the usage of intermittent renewable energy supplies.