CaFe 2 O 4 (p-type) and ZnO (n-type) electrodes were prepared for photoelectrochemical hydrogen production from water. The CaFe 2 O 4 electrode showed photo-reduction current in 0.1 M NaOH aqueous solution at potentials more negative than + 0.31 V vs. Ag/AgCl, while ZnO showed photo-oxidation at potentials more positive than - 0.71 V vs. Ag/AgCl. Connecting the both electrodes under UV-light illumination, the open-circuit voltage between the electrodes was 0.82 V, and hydrogen gas was generated from the side of the CaFe 2 O 4 electrode without applying an external voltage. The gas generation continued for 4 days at least. In addition, the hydrogen was generated even under a reverse bias ( - 0.1 V) vs. CaFe 2 O 4 electrode.
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