Insights into co-removal of trichloroacetic acid and bromate by an electroreduction process: Competitive reaction mechanism and enhanced atomic H* stabilization

Electrocatalytic reduction treatment is a promising method for the abatement of oxyanions and chlorinated disinfection by-products. The atomic hydrogen (H*) produced by electroreduction of protons/water is highly reductive, whose stabilization on the cathode surface is pivotal to improve the catalytic efficacy. Here, we prepared a noble metal-free N-doped graphene-Cu (NG-Cu) foam electrode by chemical vapor deposition method, which exhibited a superior electrocatalytic activity towards the reduction of bromate and trichloroacetic acid (TCAA) with rate constants of 0.319 and 0.271 min-1 at -1.2 V, respectively. Bromate has a much higher affinity for the reaction sites than TCAA, dividing TCAA reduction into two stages controlled by the surface active sites and diffusion, respectively. Electron spin resonance analysis and density functional theory computations suggested that the production and stabilization of H* are strengthened by the heteroatoms-doping, leading to the higher contribution of indirect H* reduction for both bromate and TCAA removal at NG-Cu foam cathode. This work provided a promising strategy for boosting indirect H* reduction for electrocatalytic purification processes without using precious metal catalysts.