Reiko Hinogami

Photo-induced CO2 Reduction with GaN Electrode in Aqueous System

CO2 reduction with water and light illumination is realized using a gallium nitride (GaN) photoelectrode in which excited electrons induce CO2 conversion at the counter electrode. For the counter electrode, a copper (Cu) plate was chosen. The low affinity and wide gap of the nitride semiconductor enable us to create an electron–hole pair which has a sufficient energy for both CO2 reduction and water oxidation, in spite of the fact that a high energy for CO2 reduction is required. Within this system, the generation of formic acid (HCOOH) with 3% Faradic efficiency was confirmed by light illumination alone.

Enhanced CO2 reduction capability in an AlGaN/GaN photoelectrode

Light illumination of a gallium nitride photoelectrode creates separate electron-hole pairs that drive water oxidation and CO2 reduction reactions. Here, we show enhanced photocurrent in an AlGaN/GaN device that consists of an unintentionally doped (uid-) AlGaN photoabsorption layer and an n+-GaN electrical-conduction layer. The production rate of formic acid by CO2 conversion in the uid-AlGaN/n+-GaN photoelectrode is about double that in the uid-GaN/n+-GaN device. This improvement is most likely due to the effect of internal bias in the uid-AlGaN layer generated by the polarization effect, which improves electron-hole separation.

CO2 Conversion with Light and Water by GaN Photoelectrode

Light illumination on a photoelectrode creates separate electron and hole pairs that lead to an oxidation and reduction reaction. Here, we show that CO2 reduction by means of water and light is realized by a gallium nitride (GaN) photoelectrode in which excited electrons drive CO2 conversion at the counterelectrode. A copper (Cu) plate was chosen as the counterelectrode. With this system, the generation of formic acid (HCOOH) with 9% Faradic efficiency was confirmed by light illumination alone with the help of NiO co-catalysts.

Highly efficient photochemical HCOOH production from CO2 and water using an inorganic system

We have constructed a system that uses solar energy to react CO2 with water to generate formic acid (HCOOH) at an energy conversion efficiency of 0.15%. It consists of an AlGaN/GaN anode photoelectrode and indium (In) cathode that are electrically connected outside of the reactor cell. High energy conversion efficiency is realized due to a high quantum efficiency of 28% at 300 nm, attributable to efficient electron-hole separation in the semiconductors heterostructure. The efficiency is close to that of natural photosynthesis in plants, and what is more, the reaction product (HCOOH) can be used as a renewable energy source.