Carbon fiber confined mixed Ni-based crystal phases with interfacial charge redistribution induced by high bond polarity for electrochemical urea-assisted hydrogen generation

Abstract

Interfacial electronic structure modulation of nickel-based electrocatalysts is significant in boosting energy-conversion-relevant urea oxidation reaction (UOR). Herein, porous carbon nanofibers confined mixed Ni-based crystal phases of Ni₂P and NiF₂ are developed via fluorination and phosphorization of Ni coated carbon nanofiber (Ni₂P/NiF₂/PCNF), which possess sufficient mesoporous and optimized Gibbs adsorption free energy by mixed phase-induced charge redistribution. This novel system further reduces the reaction energy barrier and improves the reaction activity by addressing the challenges of low intrinsic activity, difficulty in active site formation, and insufficient synergism. A considerably high current density of 254.29 mA cm⁻² is reached at 1.54 V versus reversible hydrogen electrode on a glass carbon electrode, and the cell voltage requires 1.39 V to get 10 mA cm⁻² in hydrogen generation, with very good stability, about 190 mV less than that of the traditional water electrolysis. The facile active phase formation and high charge transfer ability induced by asymmetric charge redistribution are found in the interface, where the urea molecules tend to bond with Ni atoms on the surface of heterojunction, and the rate-determining step is changed from CO₂ desorption to the fourth H-atom deprotonation. The work reveals a novel catalyst system by interfacial charge redistribution induced by high bond polarity for energy-relevant catalysis reactions.