Solvent-assisted phase modification of Ni[sbnd]P material to boost electrocatalytic water splitting and charge storage capacity

Abstract

Due to their redox features, Fe/Ni-phosphides and phosphates could be utilized as multi-functional electrode materials for hydrogen and oxygen evolution processes (HER and OER) and supercapacitors, however, regulation in their geometry and electrical structure for further performance improvement is still challenging. Herein, we developed a solvent-assisted approach to modify the NiP material's phase, growing Ni2P, Ni12P5, and Ni(PO3)2 cross-linked nanosheets on Ni-foam using the same precursor and different solvents. When compared to Ni2P and Ni12P5, the Ni(PO3)2 sample showed outstanding activity and endurance towards HER (134 mV overpotential@10 mA/cm2 and 112 mV/dec Tafel value) and OER (342 mV overpotential@10 mA/cm2 and 78 mV/dec Tafel value), respectively. Moreover, the specific capacitance of the Ni(PO3)2 electrode was found to be 4366 (at 10 mV/s) and 7582 mF/cm2 (at 1 mA/cm2). Theoretical calculations showed that the density of states and its distribution across the Fermi level increased in the order of Ni2P < Ni12P5 < Ni(PO3)2 which improved their conductivity and electronic properties, benefiting electrocatalytic HER and OER activity and the charge-storing capacity of Ni(PO3)2.