Various metal (Fe, Mo, V, Co)-doped Ni2P nanowire arrays as overall water splitting electrocatalysts and their applications in unassisted solar hydrogen production with STH 14 %

The direct growth of metal phosphide (MP) nanowires (NWs) on porous electrodes is a promising approach for developing efficient water splitting catalysts with enhanced activity and catalytic surface area. In this study, various metal (Fe, Mo, V, Co)-doped Ni2P (NiMP) NWs are synthesized on nickel foam by applying a simple two-step process: cation exchange and phosphorization. The prepared NiMP NWs are electrochemically tested as hydrogen/oxygen evolution reaction (HER/OER) catalysts under alkaline conditions. The NiMP NWs show highly enhanced OER activities compared to Ni2P NWs. Especially, Fe-doped Ni2P (NiFeP) NWs exhibit the best OER performance with a remarkably low overpotential of 279 mV for 100 mA cm−2 current generation and a Tafel slope of 34 mV dec−1. In HER activity, Mo-doped Ni2P (NiMoP) NWs show a high performance with a low overpotential of 68 mV for generating 10 mA cm−2 and a Tafel slope of 87 mV dec−1. Density functional theory (DFT) calculations are additionally performed to study the metal doping effects on Ni2P HER/OER activities. The calculation results show a high consistency with the experimental catalytic activity results. Overall water splitting (OWS) combining NiMoP/NiFeP as the HER/OER electrodes requires a low potential of 1.57 V to produce a current density of 10 mA cm−2. Finally, assembling our OWS electrodes with a tandem perovskite photovoltaic cell completes an unassisted photovoltaic-electrochemical (PV-EC) system that generates a high solar-to-hydrogen (STH) conversion efficiency of 14 %.