Drastic Enhancement of Hydrogen Production from Water in Gold–Silver Sulfide Hybrid Quantum Dot-Sensitized Photoelectrochemical Cell through Plasmon–Plasmon–Exciton Coupling

Metal sulfide quantum dot-sensitized photoelectrochemical (QD-SPEC) cells can efficiently and stably produce H2 from water containing S2– ions by acting as an excellent electron donor and an inhibitor of the QD photodissolution. Among the metal sulfides, Ag2S is a promising material for the photosensitizer due to the narrow band gap of ∼1 eV and nontoxicity. However, the performance of Ag2S QD-SPEC cells remains at a low level so far. Here, we report that the use of a hybrid photosensitizer consisting of Ag2S QDs and Au nanoparticles (NPs) for a mesoporous TiO2 photoelectrode drastically enhances the photocurrent. Under optimal conditions, the photon-to-current conversion efficiency at 400 nm reaches 400% of the value for the Ag2S QD-SPEC cell. This striking nanohybridization effect can stem from the plasmon–plasmon–exciton coupling around the interfaces among Au NPs, Ag2S, and TiO2, in addition to the quantum size effect of Ag2S.