CO2 reduction by visible-light-induced photoemission from heavily N-doped diamond nano-layer

Abstract

While realizing carbon neutrality is an urgent priority, diamond materials with negative electron affinity (NEA) are considered productive sources of solvated electrons, which can help efficiently reduce CO2 in potential green chemistry applications. Recently, CO2 was photocatalytically reduced into CO by solvated electrons using commonly used H-terminated diamond with NEA under deep ultraviolet light irradiation. However, CO2 has never been reduced under visible-light irradiation, would be more practicable in the living environment, because of the wide band gap afforded by diamonds. In this study, electrons excited by visible light in heavily N-doped surface nano-layer of diamond platelets are emitted through the H-terminated surface with NEA toward a CO2-saturated aqueous solution, successfully reducing CO2 into CO. To this end, the B-doped p-type diamond films are grown by chemical vapor deposition on initial seed layers of detonation-synthesized nanodiamonds (DNDs). This approach allows incorporating the abundantly available N atoms in the DNDs into the surface nano-layer on the diamond platelets, resulting in the formation of an electron-excitation nano-layer having ≥1021 N atoms/cm3 and associated defects absorbing visible light. These results pave the way toward a new, energy-efficient technology for CO2 reduction with strong implications for achieving a carbon-negative society.