Construction of 3D porous MXene-based multiple heterojunction catalyst for efficient water oxidation reaction at high current density

The rational construction of efficient and stable noble-metal-free oxygen evolution reaction (OER) electrocatalysts that work under a industrial-level current density in alkaline environments are urgently needed and challenging. Here we propose a Ti₃C₂T_x MXene-based synthetic method for constructing Co₂P/Ti₃C₂T_x, Fe₂P/Ti₃C₂T_x and Co₂P/Fe₂P multiple heterojunctions (labeled as CoFe-P@MXene) by using strong electrostatic adsorption-electrodeposition-low temperature phosphorization. The obtained CoFe-P@MXene possesses abundant three-dimensional porous structures and inherits the high conductivity of MXene. Experiment results and density functional theory calculations indicate that the formation of multi-heterojunctions between transition metal phosphides and Ti₃C₂T_x MXene can modulate the electronic structure of active sites Co and Fe, alter the d-band center, and thereby optimize the adsorption energy of oxygen-containing intermediates on the active sites. Additionally, the excellent nanoporous structure constructed promotes the penetration of the electrolyte and the release of the product. Thus, The CoFe-P@MXene-based electrocatalyst exhibits excellent OER catalytic performance at both low current densities and industrial-scale current densities, with remarkable low overpotentials of 215 mV at 20 mA cm⁻² and 328 mV at 1000 mA cm⁻² in 1 M KOH solution, respectively. Furthermore, it exhibits good stability, capable of operating stably for 100 h at a current density of 100 mA cm⁻². This work highlights the promising application of MXene-based electrocatalyst with multiple heterojunctional structure for industrial-scale water splitting.