Atomically Dispersed Ni–N Sites on N -Doped Carbon for Electrochemical Nitrite Detection

Excessive nitrite (NO2–) ion discharge threatens aquatic ecosystems and human health, causing conditions such as methemoglobinemia and facilitating the formation of carcinogenic N-nitrosamines under acidic gastric conditions. These risks underscore the urgent need for sensitive and reliable monitoring of NO2– ion in water. Herein, we report a highly efficient electrocatalyst based on atomically dispersed Ni embedded in a covalent imine polymer (CIP) derived nitrogen-doped carbon matrix (Ni–N–SAC) for NO2– ion detection. The Ni–N–SAC-modified glassy carbon electrode (GCE) delivers exceptional sensing performance, exhibiting a wide linear range of 10–10000 μM with a limit of detection of 1.1 μM and a limit of quantification of 3.6 μM. The sensor delivers normalized sensitivities of 18.0 and 26.0 μA mM–1 cm–2 across low and high-concentration regimes, respectively. It also demonstrates outstanding selectivity, reproducibility, and successful application in real water and processed cheese samples. Density Functional Theory (DFT) calculations attribute the enhanced sensing performance to the NiN4 coordination environment, which promotes NO2– ion adsorption and electron transfer compared to NiCN3 and NiC4. These findings, along with XAS studies, emphasize the crucial role of electronic metal–support interactions (EMSI) influenced by first-shell coordination in nickel single-atoms in electrochemical detection of NO2– ions.