Charge self-regulation of Ti sites in Ti3C2 MXene via rich unsaturated Ti for boosted photocatalytic hydrogen generation

Abstract

Recently, Ti₃C₂ MXene has been widely regarded as an effective cocatalyst to boost the hydrogen-generation activity of photocatalysts due to its high specific area, outstanding electronic conductivity, and flexible adjustability of its terminal groups. However, the basal plane of Ti₃C₂ MXene contains multiple dormant F-terminal groups from F-contained etchants (referred to as Ti₃C₂F_x), resulting in strong H-adsorption affinity of Ti for the limited hydrogen generation rate. To weaken the H-adsorption affinity of Ti, in this paper, a charge self-regulation strategy by increasing the antibonding-orbital occupancy of Ti–H_ads bonds is revealed in rich unsaturated Ti structure in Ti₃C₂F_x (referred to as Ti₃C₂F_x-U). Herein, the Ti₃C₂F_x-U cocatalyst was prepared by an NH₄F-assisted etching method at a controllable temperature and later tightly combined with TiO₂via an ultrasound-assisted method to obtain Ti₃C₂F_x-U/TiO₂. Photocatalytic H₂-evolution results showed that Ti₃C₂F_x-U/TiO₂ has superior H₂-production activity (379 μmol g⁻¹ h⁻¹), which was 27 and 1.82 times higher compared to that of TiO₂ and Ti₃C₂F_x/TiO₂, respectively. Characterizations and DFT calculations demonstrated that unsaturated Ti sites can weaken the atomic H-adsorption ability of Ti by increasing the antibonding-orbital occupancy state in Ti₃C₂F_x-U. This work provides a new idea for tuning the H-adsorption ability of active sites to develop efficient MXene cocatalysts for photocatalytic hydrogen evolution.