Revealing the roles of light and heat for enhanced interfacial charge transfer in photocatalytic conversion of methanol to formaldehyde coupled with hydrogen evolution

Abstract

Photothermal catalytic methanol (CH₃OH) dehydrogenation is a sustainable pathway for the co-production of hydrogen (H₂) and formaldehyde (HCHO) under mild reaction conditions. However, this process is hindered by the inefficient interfacial electron transfer at the semiconductor–cocatalyst (SC) interface, which is exacerbated by charge leakage. Using TiO₂ as a model, we systematically investigated the individual effects of irradiation intensity, wavelegth, and temperature on interfacial electron-transfer dynamics. Our findings reveal that increasing the photon flux at a constant temperature effectively reduces the SC barrier and accelerates the electron-transfer kinetics, with little impact on the overall charge-transfer duration. Although short-wavelength light exhibits limited penetration in aqueous media, reducing the wavelength enhances SC interfacial electron-transfer. Conversely, raising the temperature under a fixed photon flux not only lowers the SC barrier but also markedly shortens the total charge transfer time. To address the temperature-induced charge leakage, Sn was doped into the TiO₂ lattice. The optimised Pt/3% Sn–TiO₂ catalyst, employed in a fixed-bed reactor designed to overcome poor UV penetration, achieves an H₂ production rate of 82.86 mmol g⁻¹ h⁻¹ under 30 W UV illumination (254 nm) at 80 °C, representing a 4.08-fold enhancement over Pt/TiO₂. In a 20 h stability test, the system maintained average production rates of 88.12 mmol g⁻¹ h⁻¹ for H₂ and 84.13 mmol g⁻¹ h⁻¹ for HCHO, achieving an apparent quantum efficiency (AQY) of 40.02%. Under 320 W UV irradiation, the catalyst sustained 413.5 mmol g⁻¹ h⁻¹ H₂ generation over 6 h with an AQY of 25.16%. This work presents a promising strategy for designing high-performance catalysts by enhancing SC interfacial electron transfer, thereby significantly improving the photothermal catalytic efficiency.