Variable-valence ion and heterointerface accelerated electron transfer kinetics of electrochemical water splitting.

Accelerating electron transfer kinetics is an efficient strategy to tackle the sluggish oxygen evolution reaction (OER). Herein, Ni₃Fe_1−xV_x/Ni₃Fe_1−xV_xN heterojunctions were elaborately constructed to demonstrate that the coupling of variable-valence metal doping and nanoalloy/nitride heterointerfaces could optimize the OER performance of antiperovskite nitrides. The spectroscopic results suggested that during OER electrochemical surface reconstruction occurred to form an assembly of a crystalline Ni₃Fe_1−xV_x/Ni₃Fe_1−xV_xN heterojunction core and amorphous NiFeOOH shell (Ni₃Fe_1−xV_x/Ni₃Fe_1−xV_xN@NiFeOOH). The electron transfer from the OER intermediates via the amorphous NiFeOOH shell was efficiently accelerated by the variable-valence V^3+/4+ electron acceptor at the core@shell interface and the heterojunction effect in the Ni₃Fe_1−xV_x/Ni₃Fe_1−xV_xN core. As a result, the oxygen and hydrogen evolution reactions can occur at low overpotentials of 260 mV at 50 mA cm⁻² and 113 mV at 10 mA cm⁻², respectively, affording a low cell voltage of 1.66 V at 10 mA cm⁻² for water splitting in alkaline electrolyte (1.0 M KOH). Our results provide a new attempt at improving water splitting kinetics via the variable-valence ion coupling heterojunction effect. [ABSTRACT FROM AUTHOR]