Sulfur Vacancy-Engineered Mn-Ni3S2@FeS Heterostructure for Efficient Alkaline Water/Seawater Splitting

Designing exceptional activity and durable noble-metal-free electrocatalysts for freshwater/seawater splitting remains an ongoing challenge for the practical deployment of the hydrogen economy. In this study, a heterostructured Mn-doped Ni3S2@FeS electrocatalyst on Ni foam with S-vacancies (Mn-Ni3S2@FeS) is prepared. Benefiting from the synergistic merits of the heterostructure, heteroatom doping, and the abundance of sulfur vacancies induced by Mn doping, Mn-Ni3S2@FeS drives the OER and HER with remarkable efficiency, necessitating exceptionally low overpotentials of 141 and 235 mV (OER) as well as 124 and 205 mV (HER) to achieve 10 and 100 mA cm–2, respectively. More importantly, Mn enhances the electronic conductivity of Ni3S2@FeS and triggers accelerated catalyst reconstruction, spawning the actual active phases of Mn-NiFeOOH for OER. Moreover, Mn-Ni3S2@FeS acts as a premier bifunctional catalyst capable of driving overall water and seawater splitting at impressively low cell voltages of merely 1.46 and 1.48 V to reach 10 mA cm–2, respectively, along with stable seawater electrolysis over 100 h at 500 mA cm–2. Density functional theory (DFT) simulations unveil that the coupling of Mn doping with S vacancies synergistically tailors the localized electronic configuration and optimizes the adsorption free energies of reactive intermediates, thus accelerating the intrinsic reaction kinetics for HER and OER. This study combines multiple synergistic strategies, offering valuable design insights for developing efficient catalysts for sustainable hydrogen generation.