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 (0001 j ) 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 H 2 O 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.

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