In-Situ Construction of Hexagonal-Star-Shaped Mnco2s4@Mos2 Boosting Overall Water Splitting Performance at Large-Current-Density: Compositional-Electronic Regulation, Functions, and Mechanisms

Abstract

It remains to be challenging to develop bifunctional catalysts for overall water splitting (OWS) with high activity and durability at large current density. In an attempt to overcome this bottleneck, unique MnCo2S4 hexagonal stars covered with MoS2 nanosheets were in-situ grown on nickel foam (NF) to obtain  MnCo2S4@MoS2/NF heterostructure with optimized composition and local electronic structure in this work. When employed as a bifunctional catalyst, it only needs low overpotentials of 208 and 332 mV in 6.0 M KOH to drive 1000 mA cm-2 with small Tafel slopes of 56.8 and 75.6 mV dec-1 for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), respectively. In addition, MnCo2S4@MoS2/NF showed remarkable stability in simulated industrial conditions, operating stably for 50 hours at 1000 mA cm-2 without any attenuation for HER/OER. Thus, the MnCo2S4@MoS2/NF can function as a bifunctional electrocatalyst for OWS, only requiring 1.795 V to afford 1000 mA cm-2 with splendid stability. The improved performance is ascribed to dual electric and compositional regulation, which endow MnCo2S4@MoS2/NF with rich active sites and heterointerfaces, thereby promoting electron transfer and boosting the reaction kinetic. Furthermore, density functional theory (DFT) calculations reveal that the construction of heterostructure can help regulate intrinsic electronic structure, resulting in accelerated reaction kinetics. This work provides a reasonable and meaningful method for boosting industrial green hydrogen production.

Keywords: bifunctional catalyst, overall water splitting, MnCo2S4@MoS2/NF, Heterogeneous structure, Regulation, High current density