Electrochemical reduction of nitrate on boron-doped diamond electrodes: Effects of surface termination and boron-doping level

This study is among the first to systematically study the electrochemical reduction of nitrate on boron-doped diamond (BDD) films with different surface terminations and boron-doping levels. The highest nitrate reduction efficiency was 48% and the highest selectivity in the production of nitrogen gas was 44.5%, which were achieved using a BDD electrode with a hydrogen-terminated surface and a B/C ratio of 1.0%. C–H bonds served as the anchor points for attracting NO3− anions close to the electrode surface, and thus accelerating the formation of NO3−(ads). Compared to oxygen termination, hydrogen-terminated BDD exhibited higher electrochemical reactivity for reducing nitrate, resulting from the formation of shallow acceptor states and small interfacial band bending. The hydrophobicity of the hydrogen-terminated BDD inhibited water electrolysis and the subsequent adsorption of atomic hydrogen, leading to increased selectivity in the production of nitrogen gas. A BDD electrode with a boron-doping level of 1.0% increased the density of acceptor states, thereby enhancing the conductivity and promoting the formation of C–H bonds after the cathodic reduction pretreatment leading to the direct reduction of nitrate. [Display omitted] •The surface termination and boron-doping level play major roles in nitrate reduction.•Hydrogen termination benefits the formation of NO3−(ads).•Hydrogen-terminated surfaces have higher electrochemical reactivity with nitrate.•BDD with a B/C ratio of 1% promotes the formation of C–H bonds thus enhancing nitrate reduction.