Structure-design and synthesis of nickel-cobalt oxide/sulfide/phosphide composite nanowire arrays for efficient overall water splitting

Abstract

The construction of cost-effective bifunctional electrocatalysts with the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is significant for efficient overall water splitting. Herein, this work demonstrates a novel strategy for the synthesis of nickel-cobalt oxides/sulfides/phosphides composite (denoted as NiCoO–2P/S) nanoarrays on Ni foam. In this method, Ni–Co bimetallic oxide nanowires on Ni foam were partially phosphorized and sulfurized simultaneously in situ to yield Ni–Co oxide/sulfide/phosphide composite. The NiCoO–2P/S arrays have good interfacial effects and display many holes in the nanowires, giving it the advantage of large accessible surfaces on the nanowires and a beneficial for the release of gas bubbles, resulting in an excellent OER performance with a low overpotential ( η ) of 254 mV at 100 mA cm −2 and good HER activity ( η 10 = 143 mV at 10 mA cm −2 ). The electrocatalytic test results demonstrate small Tafel slopes (82 mV dec −1 for HER, 88 mV dec −1 for OER) and the satisfying durability in an alkaline electrolyte, indicating that the HER and OER activity was enhanced by the introduction of the Ni/Co sulfides and phosphides into Ni–Co oxides composite nanowires. Furthermore, the as-prepared NiCoO–2P/S catalyst can be used as both the anode and the cathode simultaneously to realize overall water splitting in the two-electrode electrolyzer. This system can be driven at low cell voltages of 1.50 and 1.68 V to achieve current densities of 10 and 100 mA cm −2 , respectively. This work provides an alternative strategy to prepare high-performance bifunctional electrochemical materials and demonstrates the advantages of Ni–Co oxide/sulfide/phosphide composites for water splitting. • The work demonstrates a novel method for the synthesis of nickel-cobalt oxide/phosphide/sulfide composite arrays. • The nanowires arrays are obtained by a hydrothermal process and one-step in-situ phosphorization and sulfurization. • The HER and OER activity of Ni–Co oxides are enhanced by the introduction of the Ni/Co sulfides and phosphides. • It shows low overpotential and Tafel slopes for HER and OER, and a low cell voltage of 1.50 V for overall water splitting. • It provides an alternative strategy to prepare high-performance bifunctional electrocatalytic materials.