Constructing Nickel Phosphate Polymorph Heterojunctions by In Situ Cr-Induced Structural Transition for Enhanced Bifunctional Electrochemical Water Splitting

The engineering of polymorph heterojunctions is an essential approach for improving the catalytic kinetics for water electrolysis. Yet, efficient tailoring tactics with component regulation and optimization in the microenvironment are highly desired but a huge challenge. Herein, the design and construction of a kind of nickel phosphide polymorph heterojunction (Ni2P/Ni3P) by an in situ Cr-induced structural transition method is presented, which needs overpotentials of only 108 and 270 mV to reach 10 mA cm(-2) for the hydrogen evolution reactions (HER) and oxygen evolution reactions (OER), respectively. It exhibits superior bifunctional activity for overall water splitting, which reaches a current density of 10 mA cm(-2) at a cell voltage of 1.56 V. The above current density is 9.1 times higher than that of the Pt/C@NF(-)//RuO2@NF(+) pair at the same cell voltage. The in situ induced phase transition approach is beneficial for Cr-Ni2P/Ni3P@NF with strong interfacial coupling and more active sites constructed by the amorphous region, which optimize the d-band center of the electrocatalyst and lead to charge redistribution at the interfaces of Ni2P/Ni3P, regulating the adsorption of H* and OOH* intermediation. This work provides inspiration for optimizing the catalytic activity through the engineering of polymorph heterojunctions by in situ metal-induced structural transition for bifunctional transition metal compound electrocatalysts.