Component Engineering of Multiphase Nickel Sulfide-Based Bifunctional Electrocatalysts for Efficient Overall Water Splitting

The development of highly efficient and low-cost bifunctional electrocatalysts for water splitting has become increasingly attractive. So far, the strategies to optimize electrocatalytic performance have mainly focused on enhancing the active sites and regulating the surface structures through doping foreign metal or anions into the composites; however, the internal and external adjustments achieved by tuning the chemical composition and crystalline phases in a material in order to investigate the composition-dependent catalytic activity has generally remained limited. Here, through various in situ composition-dependent nickel sulfides grown while controlling the sulfidation degree, we achieve the precise regulation of nickel sulfides from a single-phase component to multiple-phase components (i.e., two-phase components and three-phase components), further comparing the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) performances. Benefiting from the synergy of an analogous uniform nanoarray structure and excellent intrinsic activation, the as-obtained NixSy-5, with three-phase components, shows low overpotentials at 10 mA cm-2 for HER (148 mV) and OER (111 mV), as well as a low cell voltage of 1.48 V for overall water splitting in alkaline media, which are among the best results ever reported for overall water splitting.