Electrochemical CO₂ reduction on sub-microcrystalline boron-doped diamond electrodes

Boron-doped diamond (BDD) electrodes are being increasingly investigated for application to electrochemical CO₂ reduction. Previous, studies have mainly focused on microcrystalline (MC) BDD electrodes. In our study, we present an analysis of electrochemical CO₂ reduction using sub-microcrystalline (SMC) BDD electrodes with different boron doping concentrations (0.28%, 0.11% and 0.03%). Unlike the microcrystalline case, these synthetic SMC BDD films with high sp²-bonded carbon do not show a boron-concentration dependence in terms of the activity of CO₂ reduction to form formic acid (HCOOH). All the electrodes enabled efficient CO₂ reduction at close to the maximum Faradaic efficiency for HCOOH in the range of 70% to 80%. From our observations, it is suggested that the sp²-bonded carbon should be crucial for the CO₂ reduction. The results are hoped to enable a relaxation on the restrictions on the use of BDD electrodes towards industrial CO₂ reduction application.