Hierarchical NiCo2S4 Nanowire Arrays Supported on Ni Foam: An Efficient and Durable Bifunctional Electrocatalyst for Oxygen and Hydrogen Evolution Reactions

A recent approach for solar-to-hydrogen generation has been water electrolysis using efficient, stable, and inexpensive bifunctional electrocatalysts within strong electrolytes. Herein, the direct growth of 1D NiCo2S4 nanowire (NW) arrays on a 3D Ni foam (NF) is described. This NiCo2S4 NW/NF array functions as an efficient bifunctional electrocatalyst for overall water splitting with excellent activity and stability. The 3D-Ni foam facilitates the directional growth, exposing more active sites of the catalyst for electrochemical reactions at the electrode-electrolyte interface. The binder-free, self-made NiCo2S4 NW/NF electrode delivers a hydrogen production current density of 10 mA cm(-2) at an overpotential of 260 mV for the oxygen evolution reaction and at 210 mV (versus a reversible hydrogen electrode) for the hydrogen evolution reaction in 1 M KOH. This highly active and stable bifunctional electrocatalyst enables the preparation of an alkaline water electrolyzer that could deliver 10 mA cm(-2) under a cell voltage of 1.63 V. Because the nonprecious-metal NiCo2S4 NW/NF foam-based electrodes afford the vigorous and continuous evolution of both H-2 and O-2 at 1.68 V, generated using a solar panel, they appear to be promising water splitting devices for large-scale solar-to-hydrogen generation.