Abstract:

Owing to the increasingly serious environmental problems, there is an urgent need for clean energy with a high energy density and low carbon emissions. As such, electrocatalytic water decomposition has attracted significant interest as an efficient hydrogen production method. The electrolysis of water has two important half-reactions: the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER). Among these two reactions, OER is considered to be the crucial and rate-determining step due to its slower kinetic process and higher overpotential compared to HER. Although noble metal oxides such as IrO₂ and RuO₂ have excellent OER properties under alkaline conditions, their high cost and scarcity limit their commercial application. Therefore, it is of significant interest to develop alternative OER electrodes with excellent catalytic activity, extremely low overpotential, high durability, and low cost. Ni₂P has attracted interest as an electrocatalyst and has improved activity after combination with a cocatalyst. The improved activity is due to heterojunction formation changing the electronic structure and charge transport at the active site. To this end, a novel highly efficient Cu₃P/Ni₂P heterojunction catalyst has been successfully constructed, in which Cu₃P functions solely as a cocatalyst to enhance the electrocatalytic activity by regulating the electron transfer and surface reconstruction of Ni₂P. Consequently, Cu₃P/Ni₂P exhibits superior OER activity and has an ultra-low overpotential of 213 mV at a current density of 10 mA·cm⁻² and a small Tafel slope of 62 mV·dec⁻¹ in 1 mol·L⁻¹ KOH. Additionally, this peculiar self-supporting electrode possesses excellent electrochemical stability and long-term durability at a current density of 10 mA·cm⁻² in an alkaline medium. Through a combination of experimental results and theoretical calculations, it has been shown that the Cu₃P cocatalyst effectively tailors the electronic structure of the Ni center. This results in charge redistribution and a lower reaction energy barrier, thereby significantly improving the OER catalytic activity. In addition, the abundant grain boundaries and lattice distortions induced by the Cu₃P cocatalyst promote surface reconstruction to form Ni₅O(OH)₉, providing an efficient active site for OER. This work constructed a novel heterojunction electrocatalyst by introducing a cocatalyst, offering an avenue for the optimization of the electrocatalytic performance of transition metal phosphide.

Key words: Phosphide, Heterojunction, Cocatalyst, Surface reconstruction, Oxygen evolution reaction