Unveiling the Accelerated Water Electrolysis Kinetics of Heterostructural Iron‐Cobalt‐Nickel Sulfides by Probing into Crystalline/Amorphous Interfaces in Stepwise Catalytic Reactions

Abstract Amorphization and crystalline grain boundary engineering are adopted separately in improving the catalytic kinetics for water electrolysis. Yet, the synergistic effect and advance in the cooperated form of crystalline/amorphous interfaces (CAI) have rarely been elucidated insightfully. Herein, a trimetallic FeCo(NiS 2 ) 4 catalyst with numerous CAI (FeCo(NiS 2 ) 4 ‐C/A) is presented, which shows highly efficient catalytic activity toward both hydrogen and oxygen evolution reactions (HER and OER). Density functional theory (DFT) studies reveal that CAI plays a significant role in accelerating water electrolysis kinetics, in which Co atoms on the CAI of FeCo(NiS 2 ) 4 ‐C/A catalyst exhibit the optimal binding energy of 0.002 eV for H atoms in HER while it also has the lowest reaction barrier of 1.40 eV for the key step of OER. H 2 O molecules are inclined to be absorbed on the interfacial Ni atoms based on DFT calculations. As a result, the heterostructural CAI‐containing catalyst shows a low overpotential of 82 and 230 mV for HER and OER, respectively. As a bifunctional catalyst, it delivers a current density of 10 mA cm −2 at a low cell voltage of 1.51 V, which enables it a noble candidate as metal‐based catalysts for water splitting. This work explores the role of CAI in accelerating the HER and OER kinetics for water electrolysis, which sheds light on the development of efficient, stable, and economical water electrolysis systems by facile interface‐engineering implantations.