Multi-interfacial engineering of an interlinked Ni2P–MoP heterojunction to modulate the electronic structure for efficient overall water splitting

Abstract

Exploring efficient and cost-efficient bifunctional electrocatalysts is crucial for H₂ production via overall water splitting. Multi-interface engineering is a promising strategy to overcome the intrinsic activity limitation of electrocatalysts by the ensemble effect and electron effect but it is challenging. Herein, we elaborately designed and synthesized a multi-interface-coupled heterojunction composed of Ni₂P and MoP encapsulated by N-doped carbon (Ni₂P–MoP@NC), which possesses an adjustable electronic structure based on “d-electron complementation” to achieve effective HER and OER catalysis. A post-synthetic modification strategy anchoring Ni²⁺ ions on the phosphomolybdic acid (PMo₁₂)-organic supramolecular via the multiple linkages of organic ligands is proposed, which ensures the construction of multiple hetero-interfaces electrocatalyst by means of the natural quasi-interfaces of {PMo₁₂-organic ligand-Ni}. The organic ligands also play a crucial role in the size control of Ni₂P–MoP nanoparticles (ca. 7 nm). Experimental characterization combined with theoretical calculations reveal that the heterojunction triggers the electron redistribution, thereby facilitating water dissociation and optimizing H* adsorption energy to boost the HER, and balancing the adsorption energies of oxygenated intermediates to lower the thermodynamic barrier for the OER. Consequently, Ni₂P–MoP@NC exhibits excellent HER and OER activity with low overpotentials of 69 and 249 mV at 10 mA cm⁻² in alkaline media. The alkali-electrolyzer assembled by Ni₂P–MoP@NC requires a low voltage of 1.54 V to achieve 10 mA cm⁻² with good durability. This work proposes a new route to design various multi-touch heterojunctions constructed using other early and late transition metals.