Boron-doped diamond semiconductor electrodes: Efficient photoelectrochemical CO 2 reduction through surface modification

Competitive hydrogen evolution and multiple proton-coupled electron transfer reactions limit photoelectrochemical CO reduction in aqueous electrolyte. Here, oxygen-terminated lightly boron-doped diamond (BDD ) thin films were synthesized as a semiconductor electron source to accelerate CO reduction. However, BDD alone could not stabilize the intermediates of CO reduction, yielding a negligible amount of reduction products. Silver nanoparticles were then deposited on BDD because of their selective electrochemical CO reduction ability. Excellent selectivity (estimated CO:H mass ratio of 318:1) and recyclability (stable for five cycles of 3 h each) for photoelectrochemical CO reduction were obtained for the optimum silver nanoparticle-modified BDD electrode at -1.1 V vs. RHE under 222-nm irradiation. The high efficiency and stability of this catalyst are ascribed to the in situ photoactivation of the BDD surface during the photoelectrochemical reaction. The present work reveals the potential of BDD as a high-energy electron source for use with co-catalysts in photochemical conversion.