Photothermally boosted water splitting electrocatalysis by broadband solar harvesting nickel phosphide within a quasi-MOF

Abstract

The thermal field effect effectively boosts water splitting electrocatalysis by lowering activation energy barriers and accelerating sluggish kinetics. Solar-powered light-to-heat conversion of photothermal materials enabling desirable surface heat localization satisfies the integration of in situ heating to supply an additional energy source to promote electrocatalytic reactions. Based on these concepts, we herein report a robust photothermal–electrocatalytic water splitting system based on broadband solar harvesting nickel phosphide (Ni₂P) within a heat-insulating quasi-Ni-BDC-MOF. Benefiting from the controllable thermal treatment for partial deligandation and synchronous phosphorization, the highly dispersed ultrafine Ni₂P nanoparticles are spatially confined within quasi-Ni-BDC-MOF nanosheets, ensuring the effective utilization of local heat assisted by heat-insulating quasi-Ni-BDC-MOF to suppress heat loss. The resulting black Ni₂P@quasi-Ni-BDC exhibits an ultrasensitive and stable light-to-heat response under simulated solar light illumination. By coupling with this excellent photothermal performance, Ni₂P@quasi-Ni-BDC under full spectrum light illumination demonstrates the ultralow overpotentials of 246 and 218 mV to deliver 100 mA cm⁻² current density for oxygen and hydrogen evolution reactions and shows negligible degradation over operating for 50 h and excellent recyclability under several repeated on–off cycles. This performance compares favorably with those of previously reported electrocatalysts working at large currents and outperforms those of most of the photothermal electrocatalysts for water splitting.