Efficient Nitrate Reduction over Novel Covalent Ag-Salophen Polymer-Derived "Vein-Leaf-Apple"-like Ag@Carbon...

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.