Sunao Kamimura

Fabrication of a porous ZnRh2O4 photocathode for photoelectrochemical water splitting under visible light irradiation and a significant effect of surface modification by ZnO necking treatment

A porous ZnRh2O4 electrode was fabricated by an electrophoretic deposition method on a fluorine-doped tin oxide substrate, and photoelectrochemical water splitting under visible light irradiation (λ > 420 nm) was performed. The porous ZnRh2O4 electrode exhibited a cathodic photocurrent under visible light irradiation and an extremely positive onset potential at +1.2 V vs. reversible hydrogen electrode (RHE) in aqueous Na2SO4 solution. ZnO necking treatment, by which effective contact between ZnRh2O4 particles is formed, afforded a significant increase in the photocurrent. The incident photon to current efficiencies (IPCEs) of the ZnRh2O4 and ZnO/ZnRh2O4 photocathodes were calculated to be ca. 8% and ca. 13% at 400 nm, respectively, at 0 V vs. RHE in aqueous Na2SO4 solution. H2 evolution under visible light (λ > 420 nm) was demonstrated using the ZnRh2O4 and ZnO/ZnRh2O4 photocathodes combined with a Pt electrode under an applied bias (0 V vs. RHE).

Platinum and indium sulfide-modified Cu3BiS3 photocathode for photoelectrochemical hydrogen evolution

A polycrystalline Cu3BiS3 film as a photoelectrode was fabricated by an electrodeposition method on a molybdenum-coated glass substrate for photoelectrochemical hydrogen evolution. The Cu3BiS3 film was composed of dense crystallites with thicknesses of ca. 0.65 μm, and the optical bandgap was estimated to be ca. 1.6 eV. Photoelectrochemical characterization revealed that the Cu3BiS3 film was a p-type semiconductor with a flat band potential of ca. +0.1 V (vs. Ag/AgCl at pH 6), which is suitable for water reduction but cannot be used for water oxidation. Deposition of an In2S3 buffer layer, by which effective contact between p-type Cu3BiS3 and n-type In2S3 was formed, resulted in a significant increase in the photocurrent and a large shift of the photocurrent onset to the positive region. H2 evolution under AM 1.5G simulated solar light was demonstrated using the Pt–In2S3/Cu3BiS3 electrode combined with a Pt electrode under an applied bias (0 V vs. RHE).

Improvement of selectivity for CO2 reduction by using Cu2ZnSnS4 electrodes modified with different buffer layers (CdS and In2S3) under visible light irradiation

Cu2ZnSnS4 (CZTS) electrodes modified with different n-type buffer layers (CdS and In2S3) were used as photocathodes for CO2 reduction under visible light irradiation (420 < λ < 800 nm) in aqueous media. Compared to a bare CZTS electrode, CZTS electrodes modified with n-type buffer layers (CdS and In2S3), by which a p–n heterojunction between CZTS and the n-type buffer layer is formed, showed a significant increase in the photocurrent assigned to CO2 reduction. In addition, product selectivity of CO2 reduction was improved by surface modification with an n-type buffer layer: that is, selective CO2 reduction into CO was achieved by using a CdS/CZTS electrode, while HCOOH selectivity was observed over an In2S3/CZTS electrode. In this study, we investigated the photoelectrochemical properties of CZTS electrodes modified with n-type buffer layers (CdS and In2S3) in conjunction with the structural and optical properties, and we investigated their activity for PEC CO2 reduction.

Catalytic Graphitization for Preparation of Porous Carbon Material Derived from Bamboo Precursor and Performance as Electrode of Electrical Double-Layer Capacitor

The combination of addition of Fe (as a catalyst for graphitization) and CO2 activation (a kind of gaseous activation) was applied to prepare a porous carbon material from bamboo powder (a waste product of superheated steam treatment). Regardless of the heat treatment temperature, many macropores were successfully formed after the heating process by removal of Fe compounds. A turbostratic carbon structure was generated in the Fe-added sample heated at 850°C. It was confirmed that the added Fe acted as a template for pore formation. Moreover, it was confirmed that the added Fe acted as a catalyst for graphitization. The resulting electrochemical performance as the electrode of an electrical double-layer capacitor, as demonstrated by cyclic voltammetry, electrochemical impedance spectroscopy, and charge–discharge testing, could be explained based on the graphitization and activation effects. Addition of Fe could affect the electrical properties of carbon material derived from bamboo.