Shuichi Shinagawa

Tandem photo-electrode of InGaN with two Si p-n junctions for CO2 conversion to HCOOH with the efficiency greater than biological photosynthesis

We report on a highly improved CO2 to HCOOH conversion system using a tandem photo-electrode (TPE) of InGaN and two Si p-n junctions. To improve its efficiency, narrow-band-gap InGaN was applied as the photo-absorption layer. In the TPE structure, the current matching between GaN-based photo-absorption layer and two Si p-n junctions is crucial for the improvement of the efficiency. The energy conversion efficiency for HCOOH production reached 0.97%, which is greater than average of global biological photosynthetic one.

Wireless InGaN–Si/Pt device for photo-electrochemical water splitting

We demonstrate a wireless device comprising a gallium nitride (GaN)–silicon-based photo-electrode, and a platinum cathode. Compared with conventional two-electrode photo-electrochemical systems, this wireless monolithic device showed potential for a wider range of applications, and reduced the resistance losses resulting from the wiring and aqueous solution. The efficiency was improved when the electrolyte was changed from KHCO3 to NaOH because water oxidation capability of the surface of the GaN was enhanced. A wider solar spectrum wavelength range was exploited by adopting InGaN as a photo-absorption layer; the improved efficiency for hydrogen generation was 0.90%.