WO₃/Nb₂CT_<i>x</i> MXene 2D–2D heterojunction as a high performance photoanode for photoelectrochemical water splitting

Photoelectrochemical (PEC) water splitting plays a key role in the production of green hydrogen, which is a sustainable energy source and non-exploitative to the environment. Therefore, the development of efficient photocatalysts is essential for enabling green hydrogen generation. In this work, the synergistic effect between tungsten oxide (WO₃) and Nb₂CT _<i>x</i> (MXene) was explored for PEC water oxidation, and a composite catalyst was prepared using a hydrothermal and sonication approach to obtain a 2D/2D WO₃/Nb₂CT _<i>x</i> heterojunction. WO₃ is a promising photocatalyst owing to its optimal band gap, stability, and cost-effectiveness, but its efficiency is hindered by poor charge transfer, rapid recombination, and weak visible light absorption. Integrating Nb₂CT _<i>x</i> , a highly conductive MXene, enhances charge separation, reduces electron-hole recombination, and strengthens photocatalytic activity. This synergy increases the number of catalytic sites, improves visible light absorption, and stabilizes WO₃, leading to a more efficient and durable material for solar energy conversion and water splitting. The Tauc plot of the composite shows a slightly lower bandgap (2.56 eV) than that of pristine WO₃ (2.74 eV), while the charge separation efficiency of the composite is confirmed by its lower photoluminescence intensity than that of pristine WO₃. Among the synthesized catalysts, WO₃@Nb₂C3 showed improved PEC-OER activity by attaining a photocurrent density of 4.71 mA cm^-2 at 1.23 V <i>vs.</i> RHE compared to the pristine WO₃ that attained a photocurrent density of 2.15 mA cm^-2 at the same potential. This strategy appears promising for designing catalysts for PEC water oxidation in a solar-driven hydrogen-powered future.