Thin-film approach for scalability and enhancement of solar hydrogen production with CNT integrated Ce-doped-TiO2 composite in direct sunlight

Abstract

Solar hydrogen production by photocatalysis has long been considered as an important energy option. Whichever photocatalyst succeeds, methods should be available to scale-up in a most sustainable and cost-effective manner, and the present work addresses this specific issue. In the present study, Ce-doped in the TiO₂ lattice (Ce-TiO₂) and the same integrated with CNT (CNT-Ce-TiO₂; (CCT)) composite was synthesized and characterized. Current study demonstrates the synergistic integration of Ce-TiO₂ as a light absorber and charge generator with CNTs as efficient charge separation at heterojunctions as well as charge transporter in a thin-film configuration (lab-scale (4.7 cm²), bench-scale (500 cm²)). Improved H₂ generation under direct sunlight demonstrated in thin film form, than in particulate suspension, is attributed to efficient light absorption, particularly for electron-hole pair separation and their dispersion to redox sites. Additionally, the role of the binder is highlighted for improving H₂ yield and the sustainability of the thin-film form of photocatalyst. ∼200 mg (1 g) CCT coated over 500 cm² (2500 cm²) photocatalyst produced 21.6 mmol/h (102 mmol/h) H₂ in sunlight. Present results provides a proof of concept that the thin film form of photocatalyst displays, at least 10 times, higher H₂ yield than its powder counterpart, depending on the measurement conditions. A non-linear enhancement in H₂ yield with small and large area thin-film indicates complex underlying factors and highlights the scope for further improvements.