Photocatalytic Activation of Water and Methane over Modified Gallium Oxide for Hydrogen Production

Abstract

Ga2O3 photocatalysts showed a high and stable activity for the photocatalytic steam reforming of methane (PSRM; 2H2O(g) + CH4 → 4H2 + CO2) around room temperature. The activity was much influenced by the cocatalyst and the crystal structure of Ga2O3; the highest activity was obtained over Pt-loaded β-type Ga2O3 with specific surface area of 10−20 m2 g−1. The addition of metal cations into the bulk and/or on the surface of Ga2O3 was also effective to improve the photocatalytic activity; metal cations having both a smaller oxidation number than that of Ga3+ and a similar ionic radius to that of Ga3+, such as Mg2+ and Zn2+, were effective as the dopant into the bulk of β-Ga2O3, while cations of the aluminum group such as In3+ and Al3+ were effective as the surface additives. When we compared the activity for the PSRM with those for the water decomposition (WD; H2O → H2 + 1/2O2) and the methane decomposition (MD; CH4 → x/2H2 + CH4−x), it was revealed that the improvement of the bulk processes would mainly influence the water activation while that of the surface processes would affect the methane activation.