A New Pathway for CO₂ Reduction Relying on the Self-Activation Mechanism of Boron-Doped Diamond Cathode

By means of an initial electrochemical carbon dioxide reduction reaction (eCO₂RR), both the reaction current and Faradaic efficiency of the eCO₂RR on boron-doped diamond (BDD) electrodes were significantly improved. Here, this effect is referred to as the self-activation of BDD. Generally, the generation of carbon dioxide radical anions (CO₂ ^•-) is the most recognized pathway leading to the formation of hydrocarbons and oxygenated products. However, the self-activation process enabled the eCO₂RR to take place at a low potential, that is, a low energy, where CO₂ ^•- is hardly produced. In this work, we found that unidentate carbonate and carboxylic groups were identified as intermediates during self-activation. Increasing the amount of these intermediates via the self-activation process enhances the performance of eCO₂RR. We further evaluated this effect in long-term experiments using a CO₂ electrolyzer for formic acid production and found that the electrical-to-chemical energy conversion efficiency reached 50.2% after the BDD self-activation process.