A New Pathway for CO(2) Reduction Relying on the Self-Activation Mechanism of Boron-Doped Diamond Cathode

[Image: see text] By means of an initial electrochemical carbon dioxide reduction reaction (eCO(2)RR), both the reaction current and Faradaic efficiency of the eCO(2)RR 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 (CO(2)(•–)) is the most recognized pathway leading to the formation of hydrocarbons and oxygenated products. However, the self-activation process enabled the eCO(2)RR to take place at a low potential, that is, a low energy, where CO(2)(•–) 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 eCO(2)RR. We further evaluated this effect in long-term experiments using a CO(2) electrolyzer for formic acid production and found that the electrical-to-chemical energy conversion efficiency reached 50.2% after the BDD self-activation process.