Controlled synthesis of M (M = Cr, Cu, Zn and Fe)-NiCoP hybrid materials as environmentally friendly catalyst for seawater splitting

The consumption of non-renewable resources has determined that the exploration and utilization of pollution free energy has been a hot research subject in the near future. Electrocatalytic water decomposition to produce hydrogen and oxygen, which is a pollution-free method, is likely to become a key project to solve energy shortages. In this study, NiCo-MOF precursor was synthesized through a one-step hydrothermal process, followed by phosphating treatment in a tube furnace to generate Cu-NiCoP catalyst with aggregated nanoblocks, as well as Zn-NiCoP catalyst with aggregated nanosheets and nanoneedles. The prepared catalysts exhibit high activity in hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and overall water decomposition in the electrolysis cell. The overpotential of Cu-NiCoP sample is only 250 mV at 10 mA cm-2 for OER, while the overpotential of Zn-NiCoP is only 150 mV at 10 mA cm-2 for HER. The composed electrolysis cell can achieve a current density of 10 mA cm-2 with only 1.68 V, and has superior durability. It is worth noting that the catalysts were also tested in seawater environment. By comparing the performance in KOH and seawater environments, it was found that the performance of the catalysts would decrease in seawater environment. During the stability test, it was found that the impurities in seawater would corrode the catalyst itself, and the performance would stabilize after a period of reaction. Density functional theory (DFT) demonstrates that the Zn-NiCoP electrode presents optimal hydrogen Gibbs frees energy, thus speeding up the reaction kinetics. In summary, our work demonstrates that the doping of transition metal phosphides with metal elements has great potential and proposes novel views and directions for electrochemical seawater splitting.