Coupling TiO2 with Nb carbide-based materials for H2 photoproduction: From 3D carbides to 2D MXenes

• Fluorine-free synthesis of Nb 2 CT x (T= O, OH) MXene using NH 3 and a hydrothermal route. • NbMXene better co-catalyst of TiO 2 anatase than NbMAX or 3D NbC • NbMXene/TiO 2 ensures efficient and stable H 2 photoproduction from ethanol both in gas and liquid phase. • NbMXene/TiO 2 shows the highest lifetime of photogenerated charges from in situ IR. In this work we coupled 3D Nb carbide, ternary layered NbMAX, and 2D NbMXene with TiO 2 , developing new photocatalysts for the renewable H 2 production from ethanol aqueous solutions. A new preparation method of Nb 2 CT x MXene is reported; the hydrothermal method proposed, uses NH 3(aq) and avoids the utilization of hazardous HF or a strong acid and fluoride salts. After thorough characterization of the structural and physico-chemical features of the materials, their photocatalytic performance has been related to their photoelectrochemical properties. Moreover, the interaction of the reactant molecules with the TiO 2 -based composites and their evolution under UV irradiation has been investigated by in situ IR spectroscopy. All composites showed a higher H 2 production rate and a higher lifetime of photogenerated charges (h + /e - ) than TiO 2 . The Nb 2 CT x -containing photocatalyst showed the best H 2 production yield, both in gas and liquid phase, owing to a very efficient transfer of the photogenerated electrons from the TiO 2 conduction band to the MXene phase, decreasing the rate of charge recombination and favoring the H 2 formation. The H 2 production of NbMXene/TiO 2 was more than 3.5 times that of TiO 2 and showed a stable behavior at least up to 7 h with light on/light off cycles.