Surface Modification of NiCo2O4 Nanowires using Organic Ligands for Overall Water Splitting

Bifunctional electrocatalysts in alkaline media play an important role in the hydrogen evolution reaction ( HER) and oxygen evolution reaction (OER), owing to the considerable influence of water splitting in the green energy sector. Herein, we present surface-modified NiCo2O4 nanowires (NWs) with rich defects as a highly efficient overall water splitting electrocatalyst in alkaline media, where the surface modification is accomplished using organic ligands. X-ray photoelectron spectroscopy reveals that the increase in the Co2+/Co3+ ratio is responsible for the excellent bifunctional electrocatalytic performance of the surface- modified NiCo2O4 NWs. As expected, benefiting from the organic ligand-dominated surface modification, the optimized NiCo2O4 NWs can display an overpotential of only 83 mV for the HER and 280 mV for the OER, with a current density of 10 mA(.)cm(-2) in 1.0 mol(.)L(-1) KOH solution. More importantly, the NiCo2O4 NWs surface-modified using organic ligands exhibit outstanding performance for overall water splitting, with a voltage of 2.1 V and current density of 100 mA(.)cm(-2), and also maintain their activity for at least 15 h. The present work highlights the importance of increasing the content of Co2+ in the spinel structure of NiCo2O4 NWs for enhancing their performance in overall water splitting.