Heterointerfacial Engineering of cerium fluoride-confined molybdenum nitride for overall water splitting

Abstract

The pursuit of highly efficient, pollution-free hydrogen generation using bifunctional electrocatalysts composed of rare-earth and non-noble metals is of paramount importance. However, this remains a formidable challenge in Mo-derived catalysts due to agglomeration and strong Mo–H binding. Herein, a bifunctional CeF₃@Mo₂N heterostructure has been designed, which exhibits excellent HER and OER activities with low overpotentials of 195 and 311 mV, and corresponding Tafel slopes of 101 and 107 mV dec⁻¹, respectively. The remarkable synergistic effect between CeF₃ and Mo₂N increases the catalytically active surface area, exposing abundant active sites, enhancing porosity, and ensuring intimate contact between CeF₃@Mo₂N and the NF. This interaction regulates the electronic redistribution around the Mo sites, resulting in enhanced catalytic performance. Mechanistic investigations imply that the built-in electric field (BIEF) at the Schottky interface narrows the band gap of CeF₃@Mo₂N, thereby improving the charge transport during electrolysis. Upon formation of the Schottky interface between CeF₃ and Mo₂N phases, both the conduction band (CB) and valence band (VB) of the CeF₃ phase bend downward due to the metal–semiconductor (M–S) effect. The enhanced *OH adsorption on CeF₃@Mo₂N was further verified by Laviron analysis. The reaction kinetics were examined via impedance analysis, revealing a very low activation energy after CeF₃ coupling, as supported by the Arrhenius plot. The higher rate constant extracted from the Trumpet curve for CeF₃@Mo₂N indicates rapid formation of O₂ bubbles. Additionally, CeF₃@Mo₂N exhibits a low potential of 1.48 V at 10 mA cm⁻² for the (CH₂OH)₂ oxidation reaction (EGOR), along with high stability and faradaic efficiency, surpassing many state-of-the-art electrocatalysts. The alkaline, solar-driven electrolyzer using CeF₃@Mo₂N^(+,−) requires only 1.59 V, indicating strong potential for practical applications.