Molten salt-derived Co-intercalated TiS2/MXene heterostructure for boosting alkaline overall water splitting

Fluoride-free one-step molten-salt synthesis of Co-TiS 2 /Ti 3 C 2 T x heterojunction. • In situ growth of Co-TiS 2 on Ti 3 C 2 T x MXene modulates electronic structure. • Co-TiS 2 /Ti 3 C 2 T x catalyst exhibits enhanced HER and OER performance. • In situ synchrotron FTIR and DFT reveal boosted catalytic mechanisms. Two-dimensional MXenes have emerged as versatile platforms for electrocatalysis due to their tunable surface chemistry and layered structures. However, the intrinsic activity of MXenes is limited by their vulnerability in oxidizing and alkaline environments. Herein, we report a one-step molten-salt topochemical transformation that simultaneously tailors MXene surface terminations and constructs an in situ Co-TiS 2 /MXene heterointerface. This method effectively disperses hexagonal Co-TiS 2 nanoparticles, increases the exposure of active sites, and prevents the oxidation and aggregation of Ti 3 C 2 T x , significantly enhancing the overall water splitting performance. The incorporation of S promotes the transformation of the Ti 3 C 2 T x to the Co-TiS 2 derivative, modulates the electronic structure, and is predicted by DFT calculation to provide more favorable adsorption energies of reaction intermediates. Combined experimental characterization, including X-ray absorption spectroscopy, high-resolution transmission electron microscopy, and in situ synchrotron-based Fourier-transform infrared spectroscopy, together with density functional theory calculations, reveals that the MXene-derived Co-TiS 2 stabilizes the Co atoms, facilitating both hydrogen and oxygen evolution reactions. Consequently, the Co-TiS 2 /Ti 3 C 2 T x (T x  = S, Cl, O) catalyst exhibits enhanced bifunctional activity in 1 M KOH, with lower overpotentials and excellent stability than pristine Ti 3 C 2 T x MXene. This study highlights the potential of surface-engineered MXenes and their derivatives for the rational design of highly efficient electrocatalysts and provides insight into the role of surface terminations in tuning structure and catalytic performance.