Hierarchical Ni2P/Cr2CTx (MXene) composites with oxidized surface groups as efficient bifunctional electrocatalysts for overall water splitting

Electrocatalysis has the potential to become a more sustainable approach to generate hydrogen as a clean energy source. Developing effective electrocatalysts for water splitting is central to the area of renewable energy. Herein, we performed density functional calculations to predict the electrocatalytic performance of a Ni2P surface and Ni2P/Cr2CO2 (MXene) interface as bifunctional electrocatalysts and clarified the mechanisms of the improvement of the electrocatalytic activity of the Ni2P/Cr2CO2 interface. The optimal overpotential of the Ni2P surface for the oxygen evolution reaction is 0.95 V, and the ideal overpotential of the Ni2P/Cr2CO2 interface for the oxygen evolution reaction is 0.80 V. The Gibbs free energy for the adsorption of atomic hydrogen (G(H*)) on the Ni2P/Cr2CO2 interface can reach -0.09 eV at a suitable hydrogen coverage. The HER processes of both Cr2CO2 and the Ni2P/Cr2CO2 interface follow the Volmer-Heyrovsky mechanism with the activation energy barriers (E-a) of 0.76 eV and 0.68 eV, respectively. The Ni2P/Cr2CO2 interface promotes charge transfer from the Ni atom to O atom, which weakens the interaction between Ni and intermediates and therefore improves the catalytic effect of Ni2P for either the HER or OER. The present results indicate that the hierarchical Ni2P/Cr2CTx composite could be an effective medium for achieving a promising bifunctional electrocatalysis for water splitting.