Metal–organic framework-derived sulfide-based bifunctional electrocatalyst for efficient water electrolysis in alkali solutions

Abstract Metal–organic frameworks (MOFs) exhibit ultra-high specific surface areas and tunable porous structures. Thus, they can function as highly efficient electrocatalysts for water-splitting applications. However, the practical application of pristine MOFs is limited by insufficient active sites, sluggish charge transfer kinetics and the constrained activity and selectivity of single metal centers. To address these challenges, we developed a layered iron (Fe)-modified zinc (Zn)-cobalt sulfide (CoS) heterostructure on nickel foam (NF), denoted as Ni–Fe@Zn–CoS/NF, using a three-step synthesis strategy: (i) epitaxial growth of Zn–Co-MOF arrays, (ii) hydrothermal sulfidation and (iii) Fe–Ni electrodeposition. This approach resulted in a sponge-like architecture, which significantly enhanced electrocatalytic performance. The optimized electrocatalyst exhibited exceptional catalytic activity in 1-M KOH, attaining overpotentials of 158 mV for the hydrogen evolution reaction and 214 mV for the oxygen evolution reaction to achieve a current density of 10 mA cm ⁻² . When assembled in a symmetric electrolyzer for overall water splitting, the system achieved a current density of 10 mA cm ⁻² at 1.60 V and retained 95% of its original activity after continuous operation for 20 h. Our study presents a practical and efficient approach for improving the electrocatalytic performance and long-term stability of MOF-derived composite materials, demonstrating significant potential for water electrolysis applications.