Noble Metal-Free Co9S8 and NiS Composite Nanosheets for Enhanced Electrocatalytic Oxygen Evolution Reaction

The electrocatalytic oxygen evolution reaction (OER) is an important factor affecting the efficiency of many energy systems, such as hydrogen production from water. However, there are still some problems with the electrocatalytic OER, for example, high overpotential and sluggish kinetics. Herein, we prepare 15 nm-thick two-dimensional (2D) composite nanosheets containing Co 9 S 8 and NiS on nickel foam. In the electrocatalytic OER, the overpotential at 50 mA cm –2 of the composite nanosheets is 253 mV, with a Tafel slope of 43 mV dec –1 . The electrocatalytic efficiency of the composite nanosheets is much better, as compared with the pure Co 9 S 8, pure NiS, and conventional IrO 2 catalysts. The 2D composite nanosheets are flexible for electron transfer to trigger water splitting, thus enhancing the efficiency of the composite nanosheets in the electrocatalytic OER. Besides, theoretical calculations imply that the Co 9 S 8 –NiS interface on the composite nanosheets is the active site for the adsorption and splitting of the water molecules and promotes the transfer of the electrons from both Co 9 S 8 and NiS to the water molecule. This also favors for improving the efficiency of the composite nanosheets in the electrocatalytic OER. The results of the present work are beneficial for developing efficient noble metal-free catalysts for electrocatalysis.