Thermal Acceleration of Electron Migration in Gallium Oxide Photocatalysts

In the photocatalytic steam reforming of methane (CH 4 + 2H 2 O → 4H 2 + CO 2 ) over gallium oxide (β-Ga 2 O 3 ), 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 Ga 2 O 3, 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 Ga 2 O 3 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 Ga 2 O 3 and at the metal−semiconductor junction between the metal cocatalyst and Ga 2 O 3 .