Activation of Boron-Doped Diamond Electrodes for Electrochemical CO₂Reduction in a Halogen-free Electrolyte

The electrochemical reduction of carbon dioxide (CO2) has been attracting great interest in these days. In particular, the electrochemical production of formic acid from carbon dioxide in a halogen-free electrolyte is practically important for recently developed applications such as hydrogen carriers and fuel cells. In the present work, we have demonstrated highly selective electrochemical CO2 reduction in a halogen-free electrolyte by an "activation"process which involves an initial electrochemical CO2 reduction reaction at a boron-doped diamond (BDD) electrode. The BDD activation increased the Faradaic efficiency of formic acid from 10 to 90%. A mechanistic study on the BDD activation is presented, which can explain the drastic change of reaction selectivity from the perspective of reducing the energy of electron transfer from the BDD electrode and the mass transport of CO2 molecules to the electrode surface.