Hydrogen evolution on halogenated MXenes via surface termination engineering: a data-informed computational and experimental strategy

Abstract

Surface termination engineering in two-dimensional (2D) MXenes offers a transformative approach to tune electrocatalytic performance, particularly for the hydrogen evolution reaction (HER). While oxygen- and fluorine-terminated MXenes have dominated catalytic studies, the overlooked potential of other halogen terminations and non-metal surface doping offers a crucial frontier for designing next-generation electrocatalysts. Here, we combine first-principles simulation-guided experiments and data-driven structure–electronic property–reactivity correlations to systematically boost the catalytic performance of halogen-terminated Ti₃C₂ MXenes for the HER. Ti₃C₂Cl₂ demonstrates optimal hydrogen adsorption energetics, as predicted computationally and confirmed experimentally through its superior catalytic current density (25.8 mA cm⁻²vs. 7.8 mA cm⁻² at −0.9 V vs. RHE) to F-terminated analogs. We explore non-metal substitution on Cl-terminated MXenes, revealing that ternary Ti₃C₂(Cl, O, T′)₂ (T′ = N, S, Se) surfaces achieve a near-thermoneutral Gibbs free energy change (ΔG_H = −0.05 to −0.1 eV), with activity following T′ = N > S > Se. These computational predictions are further validated experimentally by synthesizing N- and S-doped Ti₃C₂(Cl, O, T′)₂ systems. The N-functionalized variant exhibits the most dramatically enhanced hydrogen evolution, in perfect agreement with in silico findings. The non-parametric structure–property–reactivity correlation mapping identifies that the catalytically active site-Ti bond length and localized charge at the active site are the key descriptors for designing efficient MXene-based catalysts for the HER. These findings emphasize the potential of termination engineering to precisely control the surface chemistry of MXenes, unlocking a new paradigm of high-efficiency, noble-metal-free electrocatalysts for sustainable hydrogen production.