Efficient electrocatalysts for nitrate reduction reaction (NO3--RR) that could selectively transfer nitrate into harmless nitrogen are required for water-denitrification treatment. The most widely used electrodes for NO3--RR including noble metals, transition metals, and their alloys still face many challenges such as lower selectivity and efficiency, high cost, and easy corrosion properties. Metallic Ag with acceptable cost possesses strong corrosion resistance in electrolysis, but its activity is often incompetent for NO3--RR. In this work, Ag nanoparticles with a lower loading content (1.99 wt %) on a nitrogen-doped carbon support was successfully used as the robust electrocatalyst for NO3--RR in a Cl--free neutral solution. This Ag@carbon catalyst exhibited an impressive electrochemical performance for NO3--RR, with a NO3--N conversion yield of 53% and a N2-N selectivity of 97% at a low electrolysis overpotential (-0.29 V vs RHE). In particular, the prepared Ag@carbon showed better stability and no secondary Ag ion pollution in electrolysis. Its impressive electrocatalytic performance was attributed to the unique "vein-leaf-apple"-like Ag@carbon structures, prepared by thermal conversion of Ag-salophen polymers@CNTs. CNTs served as veins to enhance the electron transportation in electrocatalysts. Salophen polymer-derived mesoporous N-doped carbon plates acted as leaves to concentrate NO3- from the electrolyte. Like apples on trees, Ag nanoparticles of about 10-20 nm highly dispersed on carbons selectively converted NO3--N into N2-N. It opens up a cost-acceptable and corrosion-resistant Ag-less electrocatalytic pathway for NO3--RR, and the special "vein-leaf-apple"-like Ag@carbon structure could enhance the electrolytic efficiency and N2-N selectivity for NO3--RR.
Keywords: Ag nanoparticles; electrocatalyst; nitrate reduction reaction; nitrogen-doped carbon; salophen polymer.