A photoelectrochemical (PEC) cell composed of an Al‐doped La5Ti2Cu0.9Ag0.1S5O7 (Al‐LTCA) photocathode and a BaTaO2N (BTON) photoanode was employed for overall water splitting. The surface of the Al‐LTCA photocathode was modified first with CdS by a chemical bath treatment (CBT) and subsequently with TiO2 and Pt (to form Pt/TiO2/CBT‐CdS/Al‐LTCA). The modified photocathode Pt/TiO2/CBT‐CdS/Al‐LTCA showed a significantly enhanced photocurrent for the PEC hydrogen evolution reaction in strongly alkaline aqueous phosphate solutions. This enhancement was attributed to surface stabilization by TiO2 and to the enhanced charge separation caused by the formation of a p–n junction at the CBT‐CdS/Al‐LTCA interface. The BTON photoanode surface modified with Co and Ir species (Ir/Co/BTON) showed a lower onset potential than that of a Co‐loaded BTON photoanode for the PEC oxygen evolution reaction. A PEC cell incorporating the Pt/TiO2/CBT‐CdS/Al‐LTCA photocathode and the Ir/Co/BTON photoanode exhibited stoichiometric H2 and O2 generation. The solar‐to‐hydrogen energy conversion efficiency of this PEC cell was found to be 0.14 % following a minute of simulated sunlight irradiation.

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Zinc telluride (ZnTe)-based photocathodes with appropriate modifications showed incident-photon-to-current conversion efficiencies (IPCEs) higher than 30% at 420–520 nm, reached 40% IPCE at 460 nm, and were not zero up to 710 nm because of photoexcitation related to the intermediate-band. ZnTe films were prepared by productive close-spaced sublimation. After surface modification with CdS and Pt, the photocathode showed clear cathodic photoresponse in the phosphate buffer solution. The modulation of substrate temperature, incorporation of Cu, and further surface modification with very thin Mo and Ti layers significantly enhanced cathodic photocurrent which contributes to hydrogen evolution from water. Through the measurement of IPCEs, photoelectrochemical hydrogen evolution from water utilizing photoexcitation related to the intermediate-band was first confirmed. The photocathode showed advantageous durability under simulated sunlight: during irradiation of about 50 min, the stabilized photocurrent slightly decreased from 1.6 mA cm−2 to 1.5 mA cm−2.

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