ABSTRACT The rise in the concentration of anthropogenic nitrogen oxyanions, such as nitrates and nitrites, necessitates the design of efficient nitrate and nitrite reducing electrocatalysts. Herein, we report a detailed computational mechanistic study on a cobalt‐based graphite‐conjugated electrocatalyst GCC‐Co(DIM)Br 2 + (GCC‐Co‐DIM) and its ability to reduce nitrate and nitrite in water. We observed that unlike the molecular CoDIM electrocatalyst, which is active for both nitrate and nitrite reduction, the conjugated congener only reduces nitrite. This is due to a high kinetic barrier associated with the intramolecular electron transfer from the electrocatalyst into the bound nitrate. Our results, however, predict a facile nitrite to NH 3 reduction by the GCC‐Co‐DIM electrocatalyst that proceeds via the amino proton assisted mechanism. Other nitrite reduction pathways (such as ligand‐mediated and hydroxyl transfer) were ruled out due to higher kinetic barriers. The highly exergonic nature of the nitrite to NH 3 potential energy surface suggests a selective reduction to ammonia. This is consistent with our experimentally determined Faradaic efficiencies. In agreement with DFT analysis of the mechanisms, in situ X‐ray spectroscopy has shown that while under catalytic conditions the cobalt ions in both catalysts are reduced to Co(II), the observed reactive intermediates have different structures. Overall, the insights provided by this study can serve as a guide for the design of better electrocatalysts.
Fosu et al. (Fri,) studied this question.