Electrochemical nitrate reduction reaction (NO3RR) has great potential for simultaneously achieving nitrate-rich wastewater treatment and ammonia (NH3) synthesis. Given that the NO3RR process encompasses distinct steps of deoxygenation and hydrogenation, the active sites of most catalysts frequently demonstrate similar adsorption behavior. In this work, the second-shell iodine-doped modified cobalt single atoms (I-CoN4) and cobalt atomic clusters (Co AC) anchored on nitrogen-doped carbon (Co SAAC/INC) are synthesized through a mild etching synchronization doping strategy. In the neutral electrolyte, Co SAAC/INC exhibits a high NH3 yield rate of 18.64 mg h–1 mgcat–1 at −0.7 V versus reversible hydrogen electrode (vs RHE) and a satisfactory FE of 97.2% at −0.6 V vs RHE. Combining in situ electrochemical Fourier infrared spectroscopy, online differential electrochemical mass spectrometry, confirmatory experiments, and density functional theory calculations demonstrates that second-shell iodine heteroatom doping effectively regulates the electronic structure of CoN4 site and induced the favorable adsorption from H2O/*H to NO3–, while the adjacent Co AC site accelerates the dissociation of H2O and provides abundant active hydrogen (Hads) for the subsequent hydrogenation step, thus constructing the tandem catalytic sites with I-CoN4 site to promote NO3RR. Furthermore, the Zn-NO3– battery with Co SAAC/INC as the cathode shows high power density (15.41 mW cm–2) and excellent NH3 synthesis efficiency, while simultaneously achieving NO3– pollutant removal, NH3 synthesis, and energy supply. This work not only clarifies the transformation of the NO3RR mechanism induced by heteroatom doping but also provides insights into the construction of the tandem catalytic sites.
Cui et al. (Thu,) studied this question.