Electrochemical Denitrification by a Recyclable Nanoporous Co3o4/Co Cathode: Rapid Recovery and Selective Catalysis

Cathodic aging and fouling have been the main obstacles to electrochemical denitrification in engineering applications. In this research, a recyclable nanoporous Co3O4/Co cathode was prepared via anodization for nitrate reduction. Throughout the recovery process, cobalt in the inactive catalyst could be recycled on the substrate and regrow the new Co3O4 layer. The structure of the Co3O4 catalyst was a truncated octahedron, which mainly contained Co2+ ions at the surface. Density functional theory calculations confirmed the free energy of -0.89eV was thermodynamically favorable for the bonding between the O atom in NO3- ions and the Co atom in Co3O4 and Co2+ ions played the role of “electron porter” for electron transfer through a redox circle Co2+–Co3+–Co2+. Meanwhile, two energy barriers (*NH2NO to *N2 and *N2 to N2) of 0.83 eV and 1.17 eV respectively resulted in worse N2 selectivity of 9.84% and better NH3 selectivity of 90.02%. The kinetic model of NH4+-N in the presence of Cl- was modified as exponential decay for the actual wastewater treatment. After 3h, nearly 78% of TN and 93% of NO3- were removed, which fitted well with the predictive value. This anodization-based strategy displayed a huge advantage in long-run cost because no extra reagent was required to regenerate cathodes and also provided a new paradigm for electrode sustainability.