CoNi₂S₄ Nanosheets on Carbon Cloth Using a Deep Eutectic Solvent Strategy as Bifunctional Catalysts for Water/Simulated Seawater Electrolysis

Designing and developing low-cost, high-efficiency catalysts to reduce the overpotential and improve the efficiency of hydrogen energy conversion are current research hotspots. In this work, CoNi2S4 nanosheets on carbon cloth (CoNi2S4/CC) were prepared to use one-step pyrolysis of the deep eutectic solvent (DES) precursor. It is feasible to cover carbon cloth evenly with DES due to its intense adherence and liquid conditions at ambient temperature. The CoNi2S4 nanosheet's coupling a CC substrate increases the electron transport efficiency and prevents the catalyst from agglomeration and corrosion during catalytic processes. Self-supported CoNi2S4/CC exhibited excellent hydrogen evolution reaction (155 mV at 50 mA cm(-2) and 30 mV at 10 mA cm(-2)) and oxygen evolution reaction (372 mV at 100 mA cm(-2) and 153 mV at 10 mA cm(-2)) activities. Serving as a bifunctional catalyst, CoNi2S4/CC requires cell voltages of only 1.42 and 1.86 V to achieve 10 mA cm(-2) and 100 mA cm(-2) current density, respectively, in overall water splitting in 1.0 M KOH, exhibiting extraordinary durability. Moreover, CoNi2S4/CC exhibits excellent overall water-splitting activity in simulated seawater, which significantly advances the development of seawater electrolysis.