Direct Electrosynthesis of Selective Transition-Metal Chalcogenides as Functional Catalysts with a Tunable Activity for Efficient Water Electrolysis

Transition-metal chalcogenides (TMCs) are cheap and abundant and have recently been demonstrated as promising electrocatalysts for sustainable and efficient water electrolysis. The existing TMC synthesizing methods are limited by difficulties in precise composition control and complexities in synthetic parameters, highlighting the need for a facile and viable strategy for direct synthesis of TMCs on conducting substrates. Here, we report a generalized approach for direct synthesis of a variety of high-efficient, robust TMCs and stoichiometric composition-controlled TMC catalysts on conducting three-dimensional porous substrates via an anion-assisted electrochemical deposition technique. Using this strategy, 10 different types of TMC electrocatalysts were designed and synthesized using representative transition-metal elements (Co, Fe, Mo, Ni, and W) and chalcogen elements (S and Se). In particular, NiS and FeSe exhibited excellent activity with overpotentials of 83 and 171 mV to reach a current density of 10 mA cm-2 in HER and OER, respectively. In addition, control over the stoichiometric composition was also demonstrated by adjusting the ratio of binary chalcogen anions, in turn allowing for the modification of catalytic properties. Furthermore, a water electrolysis cell with the NiS cathode and FeSe anode showed remarkable overall water splitting performance with a cell voltage of 1.52 V at 10 mA cm-2 and superior long-term stability for 100 h even at a high current density (100 mA cm-2), which was a significantly higher performance in comparison with the other reported TMC-based cells and the benchmark noble Pt/C∥IrO2 cell.