First-Principles Calculations of Hydrogen Generation Due to Water Splitting on Polar GaN Surfaces

We present the chemical reactions leading to hydrogen gas generation via water splitting on polar GaN surfaces, which can be a significant source of renewable energy. To build an understanding at the atomic level of the activations afforded by the GaN (0001) and (000 (1) over bar) surfaces, we determine the reaction mechanism of hydrogen generation on the polar faces using density functional theory calculations. The calculation results show that the first H splitting from water can occur with ground-state electronic structures; the barriers of H2O splitting are 0.10 and 0.34 eV on the Ga-face and the N-face, respectively. However, the second H splitting requires huge energies of 1.42 and 1.73 eV, respectively, on the Ga-face and the N-face. Although the polar GaN surface can catalyze the first hydrogen splitting from water, we suggest that photoexcitation should be necessary for the second splitting.