Vacancy-rich heterogeneous MnCo₂O_4.5@NiS electrocatalyst for highly efficient overall water splitting

Alkaline water electrolysis is regarded as a promising technology for sustainable energy conversion. Spinel oxides have attracted considerable attention as potential catalysts because of their diverse metal valence states. However, achieving the required current densities at low voltages is a challenge due to its limited active sites and suboptimal electron transport. In this study, we present a novel bifunctional catalyst composed of MnCo₂O_4.5 nanoneedles grown on NiS nanosheets for water electrolysis. Remarkably, MnCo₂O_4.5@NiS demonstrates exceptional catalytic activity, requiring 187 and 288 mV to achieve a current density of 100 mA cm^-2 for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), respectively. The impressive performance of MnCo₂O_4.5@NiS is demonstrated by the lower value of voltage 1.44 V needed to deliver the current density of 10 mA cm^-2, which outperformed the 1.66 V required for a commercial Pt/C||RuO₂ system. Detailed structure analysis and density functional theory (DFT) calculations reveal that the MnCo₂O_4.5@NiS heterostructure enhances electron transfer at the interface, promotes the formation of oxygen vacancies and tunes the electronic structures of Mn and Co. These findings underscore the potential of MnCo₂O_4.5@NiS as an efficient and cost-effective electrocatalyst for hydrogen production.