Temperature-boosted photocatalytic H2 production and charge transfer kinetics on TiO2 under UV and visible light

Abstract

This study investigates the effect of reaction temperature (298–353 K) on photocatalytic H₂ production in bare and platinized TiO₂ (Pt/TiO₂) suspensions containing various organic hole scavengers (EDTA, methanol, and formic acid) under UV (λ > 320 nm) and visible light (λ > 420 nm for ligand-to-metal charge transfer). H₂ production rates are enhanced ∼7.8- and ∼2.5-fold in TiO₂ and Pt/TiO₂ suspensions, respectively, with EDTA under UV by simply elevating the reaction temperature from 298 K to 323 K (ΔT = 25 °C). Such a temperature-boosted increase in H₂ production is always observed, regardless of the TiO₂ crystalline structure (anatase, rutile, and an anatase/rutile mixture), type of hole scavenger, and irradiation wavelength range. It is estimated that approximately 90% of incident photons are utilized in H₂ production, for which the activation energy is 25.5 kJ mol⁻¹. Detailed photoelectrochemical analyses show the positive relationship between reaction temperature and photocurrent generation, with charge carrier mobility and interfacial charge transfer improving at higher temperatures. Other possible factors, such as H₂ solubility and mass transport, play a limited role.