Plasmon-induced charge separation (PICS) occurs at the interface between plasmonic nanostructures of gold, silver, or copper and a semiconductor such as titanium oxide.^1-3 PICS involves energetically uphill transfer of electrons (or holes) from the plasmonic nanostructure to the semiconductor, so that the active carriers are retained in the semiconductor for a certain period of time and used for electrochemical reduction (or oxidation). We reported PICS for the first time more than 10 years ago^1-3 and studied its mechanisms^1-6 and applications^2,3 including photocatalysis. We have reported oxidation of alcohols and aldehydes by PICS,¹ and recently worked on photocatalytic reduction of water to hydrogen based on PICS at gold nanoparticle/titanium oxide systems.

We coated an indium-tin oxide transparent electrode with a titanium oxide thin film. We deposited a hexagonal array of small plasmonic gold nanoparticles on the titanium oxide film, followed by deposition of cocatalysts such as platinum nanoparticles. This working electrode was connected with a counter electrode such as a platinum wire and those electrodes were immersed in an electrolyte solution containing an electron donor such as methanol. The working electrode was irradiated with visible light, and hydrogen was evolved at the counter electrode even without bias voltage application, although the hydrogen evolution rate was enhanced when a bias voltage was applied. We will report optimization of the cocatalyst systems.

1. Y. Tian and T. Tatsuma, J. Am. Chem. Soc., 127, 7632 (2005).

2 . T. Tatsuma, Bull. Chem. Soc. Jpn., 86, 1 (2013) [account].

3. T. Tatsuma, H. Nishi, and T. Ishida, Chem. Sci., in press (doi: 10.1039/C7SC00031F) [review].

4. E. Kazuma and T. Tatsuma, Adv. Mater. Interfaces, 1, 1400066 (2014).

5. H. Nishi and T. Tatsuma, Angew. Chem. Int. Ed., 55, 10771 (2016).

6. K. Saito, I. Tanabe, and T. Tatsuma, J. Phys. Chem. Lett., 7, 4363 (2016).