Highly efficient oxygen evolution from CoS/CNT nanocomposites via a one-step electrochemical deposition and dissolution method.

The oxygen evolution reaction (OER) has been viewed as a critical step in electrochemical energy conversion and storage devices. However, searching for cheap and efficient OER electrocatalysts still remains an urgent task. Herein, we develop a new strategy involving a one-step electrochemical deposition and dissolution method to fabricate hydrophilic porous CoS/carbon nanotube (CNT) composites (CNT-CoS). X-ray photoelectron spectroscopy and near-edge X-ray absorption fine structure spectroscopy measurements confirm the formation of hydrophilic groups on the surface of the porous CoS during electrochemical oxidation. Our design holds several advantages. The electricity conductivity of CoS is increased by introducing CNTs as a conductive substrate. The porous nanostructures of CoS increase its surface area, and provide paths to promote charge and reactant transfer. The active edge sites modified with hydrophilic groups can increase the content of electrolyte-electrode contact points, increasing the intrinsic catalytic performance of CoS. These factors allow CNT-CoS to achieve a low onset potential of 1.33 V vs. RHE, a stable current density (j) of 10 mA cm at an overpotential of 290 mV, and excellent stability under alkaline conditions compared to that of IrO. The comprehensive performance of the CNT-CoS electrocatalyst is comparable to or better than that of any reported noble metal-free OER catalyst, even RuO and IrO. This facile synthesis strategy involving synchronous electrochemical deposition and dissolution should be easily adapted for large-scale water electrolysis.