Surface Phosphation of 3D NiCo2O4 Nanowires Grown on Ni Foam as an Efficient Bifunctional Catalyst for Water Splitting

Highly efficient, cost-effective and durable electrocatalysts for water splitting are crucial for energy conversion and storage. Transition-metal phosphides have been proven to be efficient catalysts for water splitting. In this paper, surface phosphation of 3D NiCo2O4 nanowires grown on Ni foam (P-NiCo2O4/NF) have been prepared to investigate the effect of surface phosphating on catalyst activity. XRD and XPS results demonstrate that P element has been decorated on the surface of the NiCo2O4 nanowires. The electrochemical results prove that P-NiCo2O4/NF shows better electrochemical performance than pure NiCo2O4/NF as an electrode for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) of water splitting. It achieves a current density of 10 mA cm(2) at an overpotential of 279 mV and 164 mV for OER and HER in 1.0 M KOH electrolyte, respectively. In addition, the P-NiCo2O4/NF parallel to P-NiCo2O4/NF electrode is constructed by employing P-NiCo2O4/NF as both the anode and cathode, it only requires a low 1.68 V of cell voltage to reach the current density of 10 mA cm(-2). Notably, P-NiCo2O4/NF parallel to P-NiCo2O4/NF also exhibits excellent stability for over 30 h-long. These results indicate that surface phosphation is an effective approach to improve the electrochemical performance of NiCo2O4/NF electrode materials.