Engineering CoO/B heterojunction electrocatalysts for boosting electrocatalytic nitrate reduction to ammonia

[Display omitted] •CoO/B heterojunction electrocatalysts comprised with sub-nanometric CoO decorated B nanosheets were synthesized.•The optimized CoO/B-1 nanosheet displays a high FE and NH3 yield of 95.41 % and 29.42 mg h-1 mgcat-1, respectively.•Charge distribution at the interface lowers the formation energy of *NOH, and suppress the HER, leading to high performance. Electrocatalytic nitrate reduction to ammonia represents a one-stone-two-birds approach for mitigating nitrate pollution and large-scale ammonia production. However, due to its multiple-electron process, it faces challenges regarding unsatisfactory Faraday efficiency (FE) and ammonia yield rate. Herein, a novel heterojunction electrocatalyst with sub-nanometric cobaltous oxide (CoO) decorated boron (B) nanosheets for electrocatalytic nitrate reduction (NO3RR) is first presented as an efficient electrocatalyst. The CoO/B heterojunction electrocatalyst exhibits a noteworthy NO3RR performance with an ammonia FE and yield rate of 95.41 % and 29.42 mg h-1 mgcat-1, respectively, in alkaline media at −0.4 V vs. reversible hydrogen electrode (RHE), surpassing CoO and B catalysts. Results demonstrated that the synergistic effect of CoO and B enhances the adsorption and activation of NO3−, lowers the formation energy of *NOH and provides sufficient active hydrogen to facilitate hydrogenation, thereby enhancing NO3RR performance. This work presents a novel approach for constructing cost-effective and high-performance NO3RR heterojunction electrocatalysts.