Adjustable composition of self-supported amorphous Ni–Fe–P nanosheet decorated NiP microspheres for efficient and stable overall alkaline freshwater/seawater splitting

Abstract

Developing highly efficient and robust nonprecious metal-based electrocatalysts for overall fresh/sea water electrolysis for hydrogen production remains a major challenge for the hydrogen economy. In this study, a novel approach utilizing a one-step rapid electrodeposition technique was employed to fabricate amorphous bimetallic nickel–iron–phosphorus (NiFeP) nanosheets with tunable compositions on nickel phosphorus (NiP) microspheres. The unique amorphous structure and the capability to adjust the composition of the NiFeP nanosheets were crucial for enhancing the electronic structure and increasing the number of active sites on the catalyst. The seamless integration and self-supporting nature of the NiFeP/NiP on nickel foam significantly enhanced mass transport and minimized electrical resistance during the electrocatalytic process. Moreover, the superior corrosion resistance of the amorphous NiFeP/NiP contributed to its outstanding stability over prolonged periods. When optimized, the NiFeP/NiP with 25% iron content demonstrated low overpotentials of 241.8 and 273.7 mV for the OER at current densities of 10 and 100 mA cm⁻², respectively, in alkaline freshwater. Additionally, NiFeP/NiP with 10% iron content exhibited low overpotentials of 69.5 and 127.6 mV for the hydrogen evolution reaction (HER) at the same current densities in the same medium. In alkaline seawater, the optimized configurations for OER and HER showed overpotentials at corresponding current densities, further confirming the catalysts’ efficiency under varying conditions. When employed in an electrolyzer for splitting alkaline freshwater or seawater, the combination of NiFeP/NiP electrodes with 10% and 25% iron content operated at remarkably low voltages of 1.55 and 1.62 V to achieve a current density of 10 mA cm⁻², respectively. This performance was stable over 500 hours, surpassing that of nearly all previously reported non-noble metal electrocatalysts and even the benchmark platinum/carbon and ruthenium dioxide coupled electrodes for both freshwater and seawater electrolysis. This research introduces a straightforward and expedient method for crafting non-noble metal electrocatalysts with modifiable composition and electronic modulation, yielding highly active and durable catalysts for alkaline water splitting.