(Invited) Development of Photocatalytic and Photoelectrochemical CO2 Reduction System

Morphology controlled brookite TiO 2 nanorod having brookite phase was developed. Exposed crystal surfaces play different roles such as oxidation and reduction, respectively. These properties are a great advantageous for multi-electron reaction such as CO 2 reduction. We also investigated the co-catalysts loading effects for improving CO 2 reduction. The maim product for CO 2 reduction was methanol The photocatalytic activates of brookite TiO 2 nanorods loaded with Ag or Rh were about 10 times higher than that of brookite TiO 2 without co-catalysts loading. The apparent quantum efficiency of the reaction reached to about 3 % under UV light. We had also developed g-C 3 N 4 /WO 3 nanocomposite photocatalysts for CO 2 reduction to generate methanol, CO, CH 4 , and formic acid under visible light Among the several kinds of products, methanol was obtained as a main product. Co-catalysts loading effect such as Ag, Au had been also investigated. The reaction mechanism was investigated by using double beam pohtoacoustic spectroscopy. Several kinds of photoelectrochemical systems for CO 2 reduction by using B-doped g-C 3 N 4 , CuCrO 2 , Cu 3 Nb 2 O 8 photocatalysts electrodes had been developed in order to separate the products such as CO, methanol, etc.. The photocurrent responses for CO 2 reduction using the g-C 3 N 4 electrodes improved by Boron doping and co-catalysts coating such as Au, Ag, Rh etc on the surface of the electrodes. The main product of this photoelectronchemical system was ethanol. The photocurrent responses of CuCrO 2 and Cu 3 Nb 2 O 8 electrodes were about 10-30 times higher than that of the Boron doped g-C 3 N 4 coted with Rh photoelectrode. The detailed discussion of these results will be presented at the presentation. We had also developed CZTS (Cu 2 ZnSnS 4 ) photoelectrode covered by ZnS, CdS or In 2 S 3 for CO 2 reduction. ZnS, CdS or In 2 S 3 played a role for an electron correction layer and protection layer. The photocurrent response for H + reduction and CO 2 reduction was drastically improved by covering CdS or In 2 S 3 thin layer. Faraday efficiency of H 2 , CO evolution and HCOOH generation are about 60, 1.5, and 2.5 %, respectively. The effects of CdS, In 2 S 3 , and metals co-catalyst loading will be discussed.