Thermal Acceleration of Electron Migration in Gallium Oxide Photocatalysts

In the photocatalytic steam reforming of methane (CH4 + 2H2O → 4H2 + CO2) over gallium oxide (β-Ga2O3), the hydrogen production rate increased with an increase of the reaction temperature before reaching ca. 343 K, and then it became constant. The pseudo-Arrhenius plot for the production rate in the lower temperature range showed a straight line, and the thermal activation energy was typically less than ca. 10 kJ mol−1. The thermal activation energy varied with the irradiation light intensity, the crystallite size of Ga2O3, and the loading of metal cocatalyst. The lower thermal activation energy was given by the higher intensity of the irradiation light, the larger crystallite size of Ga2O3 particles, and the larger particle size of the cocatalyst, whereas the higher one was given by the surface defects and/or the cocatalyst alloying. These facts suggest that the thermal energy would promote the migration of photoexcited carriers both in the bulk of Ga2O3 and at the metal−semiconductor junction between the metal cocatalyst and Ga2O3.