Photocatalytic Synthesis of CdS(core)-CdSe(shell) Quantum Dots with a Heteroepitaxial Junction on TiO2 : Photoelectrochemical Hydrogen Generation from Water

Kaoru Kitazono; Ryo Akashi; Keigo Fujiwara; Atsunobu Akita; Shin-Ichi Naya; Musashi Fujishima; Hiroaki Tada

doi:10.1002/cphc.201700708

Photocatalytic Synthesis of CdS(core)-CdSe(shell) Quantum Dots with a Heteroepitaxial Junction on TiO₂ : Photoelectrochemical Hydrogen Generation from Water

Chemphyschem. 2017 Oct 19;18(20):2840-2845. doi: 10.1002/cphc.201700708. Epub 2017 Aug 28.

Authors

Kaoru Kitazono¹, Ryo Akashi¹, Keigo Fujiwara¹, Atsunobu Akita¹, Shin-Ichi Naya², Musashi Fujishima¹, Hiroaki Tada^{1

2}

Affiliations

¹ Graduate School of Science and Engineering, Kindai University, 3-4-1, Kowakae, Higashi-Osaka, Osaka, 577-8502, Japan.
² Environmental Research Laboratory, Kindai University, 3-4-1, Kowakae, Higashi-Osaka, Osaka, 577-8502, Japan.

PMID: 28833927
DOI: 10.1002/cphc.201700708

Abstract

A major challenge in chemistry for the synthesis of hetero-nanostructures is to build up atomically commensurate interfaces for smooth interfacial charge transfer. Photodeposition of CdSe on a CdS-preloaded mesoporous TiO₂ nanocrystalline film yields CdS(core)-CdSe(shell) quantum dots (CdS@CdSe/mp-TiO₂ ) with a heteroepitaxial nanojunction at 298 K. Two-electrode quantum-dot-sensitized photoelectrochemical (QD-SPEC) cells with the structure photoanode |0.25 M Na₂ S, 0.35 M Na₂ SO₃ (solvent=water)| cathode were fabricated. The CdS@CdSe QD-SPEC cell affords a solar-to-current efficiency (STCE) of 0.03 % without external bias under illumination of simulated sunlight (λ>430 nm, AM 1.5, one sun). By applying 0.1 V between the electrodes, the STCE increases up to 0.048 %, far surpassing the CdS/mp-TiO₂ and CdSe/mp-TiO₂ photoanode cells. The CdS-CdSe interfacial analysis by high-resolution transmission electron microscopy and the band energy analysis taking the size quantization and the electrolyte effect indicate that the excellent performance of the CdS@CdSe/mp-TiO₂ photoanode originates from the effective charge separation due to the cascade-like band edge alignment and the heteroepitaxial junction between CdS and CdSe QDs. In addition, high surface coverage of TiO₂ with QDs can contribute to the reduction in the loss of the electron transport from TiO₂ to the electron collecting electrode.

Keywords: epitaxial junctions; hydrogen evolution; photoelectrochemical cell; quantum dots; water splitting.