Boron- and Nitrogen-Codoped Diamond Electrodes for the Improved Reactivity of Electrochemical CO2 Reduction Reaction

We investigated the electrochemical CO2 reduction reaction (CO2RR) properties of boron- and nitrogen-codoped diamond (BNDD) electrodes. The BNDD electrodes exhibited higher CO2RR performance than boron-doped diamond (BDD) electrodes, indicating that the nitrogen doping can promote CO2RR reactivity. In particular, the faradaic efficiencies of the CO2RR products, obtained at a relatively low negative potential (−2.0 V vs Ag/AgCl) in this study, were significantly higher using BNDD electrodes with high nitrogen-doping levels. At this potential, it should be difficult to generate CO2•– as an initial intermediate of CO2RR; therefore, nitrogen doping promoted the generation of the intermediate through another reaction pathway. Linear sweep voltammetry revealed that nitrogen doping could promote the generation of adsorbed hydrogen atoms on the electrode surface by proton reduction. Thus, we concluded that nitrogen doping promoted the initial step of CO2RR through the adsorption of hydrogen atoms on the electrode surface. In addition, electrolysis using various electrolyte solutions confirmed that the influence of dopants on the BNDD electrode surface was significant for CO2RR, particularly at low overpotentials.