Core-shell cobalt-iron silicide electrocatalysts with enhanced bifunctional performance in hydrogen and oxygen evolution reactions.

To satisfy the growing demand for green energy, hydrogen production through water electrolysis has emerged as a promising approach, making the design and synthesis of efficient and durable bifunctional electrocatalysts both critical and challenging for the advancement of hydrogen energy. In this study, we synthesized core-shell structured bifunctional transition metal silicide electrocatalysts using a magnesium thermal reduction method. During the exothermic reduction, a silicon oxide (SiO) shell was formed, coating the active centers of the silicide and providing a protective core-shell structure. The overpotentials of oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) of bimetallic cobalt iron silicide (CFS-2, Co: Fe = 1:1) catalyst in 1 M KOH at 10 mA cm were 291 mV and 242 mV, respectively, with Tafel slopes of 65 and 164 mV dec, which were superior to single metal electrocatalysts of cobalt silicide (CS) and iron silicide (FS). The core-shell structure, with a metal silicide core and a passivating silica shell, enhances electron transfer while preventing silicon leaching and improving catalyst stability. Remarkably, after continuous operation for 24 h at a fixed current density of 10 mA cm, it remained stable at 1.66 V. This work represents the first successful synthesis of cobalt-iron bimetallic silicide catalysts for overall water splitting, demonstrating their significant potential for electrocatalytic applications and promoting the broader use of silicides in hydrogen production.