Electrocatalytic CO₂ reduction near the theoretical potential in water using Ru complex supported on carbon nanotubes

We successfully developed a highly efficient electrode for CO₂ reduction using a Ru-complex catalyst ([Ru]) supported on carbon paper coated with multi-walled carbon nanotubes (CPCNT/[Ru]). The CPCNT/[Ru] electrode promoted the CO₂ reduction reaction in aqueous solution near the theoretical potential, and produced formate linearly with a current density of greater than 0.9 mA cm^-2 at -0.15 V (versus RHE) for at least 24 h. Due to the outstandingly low overpotential, a monolithic tablet-shaped photo-device was realized by coupling the CPCNT/[Ru] catalyst with amorphous SiGe-jn as a light absorber and IrO _x as a water oxidation catalyst, and the device produced formate from CO₂ and water in a single-compartment reactor. The nanotubes enhanced the rate for CO₂ reduction at [Ru], and accordingly a solar-to-chemical conversion efficiency of 4.3% for formate production was achieved when the CO₂ reduction and H₂O oxidation sites had the same area.