Effect of doping level on the electrochemical reduction of CO₂ on boron-doped diamond electrodes

Boron-doped diamond (BDD) electrodes have been applied on the electrochemical reduction of CO₂. Although boron doping level can strongly affect the electrochemical properties of BDD electrodes, there are, so far, no reports about the effect of doping level on the electrochemical reduction of CO₂ using BDD electrodes. Here, we investigated the relationship between boron content of BDD electrodes and the products of CO₂ reduction. We prepared five kinds of BDD electrodes with various boron contents (0.01%, 0.1%, 0.5%, 1%, and 2%). The highest faradaic efficiency for producing formic acid was achieved by using a BDD electrode with the boron content of 0.1%, and the faradaic efficiency for hydrogen evolution increased with increasing boron content due to narrower potential window of BDD with higher boron content. On the other hand, the faradaic efficiency for producing CO, which was a side product, slightly increased with increasing boron content. This trend suggested that the adsorbability of CO₂ and its intermediates could be altered by controlling boron content. The research opens new insights for design and control of boron-doped diamond for the electrochemical reduction of CO₂.