Oriented Electronic Structure Design Of Cobalt-based Catalyst For Efficient Ammonia Electrosynthesis From Nitrate And Synchronous Ammonia Recovery

Ammonia is vital to the industrial processes.Currently,the ammonia fertilizer products mainly originate from the Haber-Bosch process that fixes N₂ with H₂ to produce ammonia（NH₃）.But such an instrumental industry consumes approximately2%of the global supply of energy to sustain the harsh reaction condition,which accounts for around 1%of total emissions of the greenhouse gas.Unlike N₂ with inert bond(941 k J·mol^-1),nitrate（NO₃^-）,a common pollutant in wastewater,has relatively low binding energy(204 k J·mol^-1),which promises much better reaction kinetics for NH₃ production.Therefore,upcycling wasted NO₃^-into value NH₃（NRA）fertilizers under ambient condition does not only hold the great premise to relieve energy crisis,but also help address environmental concerns.In view of this,based on the DFT calculation,a defect-engineered Ti O₂ nanotube array cathode（Co-BTNA）was directionally designed and fabricated for NRA in a divided electrolysis cell.The doped cobalt and oxygen vacancy defects in the Co-BTNA synergistically facilitated the electrons transfer to NO₃^-with high selectivity of NH₃,while the OVs defects increased the formation barrier of N₂ and the Co defects suppressed the desorption of*NO/*NO₂,thereby boosting the production of NH₃at a low energy barrier（0.43 e V）.The combined results of physicochemical and electrochemical characterizations demonstrated that adding OVs and Co defects could effectively improve the activity and selectivity of TNA for NRA.Meanwhile,the acid anolyte produced via the electrochemical half-reaction at anode was used to trap NH₃for（NH₄）₂SO₄production.At a current density of 18 m A·cm^-2,100%of NO₃^-removal efficiency,93.0%of NH₃ selectivity and 50%of faraday efficiency were achieved with NH₃recovery rate of 182.25 g-（NH₄）₂SO₄·d^-1·g_cat^-1 at energy consumption of 27.1k Wh·kg^-1（NH₄）₂SO₄.In addition,aiming at the shortcoming of low faraday efficiency of Co-BTNA catalyst,the cobalt phosphide catalyst was further optimized by using DFT calculation to improve the atomic hydrogen（*H）adsorption activity.DFT calculations demonstrated that phosphating and the doping of iron can effectively improve the reaction activity to NO₃^-and optimize the activation energy required for the adsorption of*H,which further regulate the reaction path and inhibit the production of N₂,thus improving the production of NH₃.Fe-doped Co phosphide（Fe-Co₅P/NF）nanowires were further prepared by hydrothermal and low temperature phosphating method.The reduction performance of Fe-Co₅P/NF was improved in a full range as opposed to Co-BTNA,with selectivity and faraday efficiency were up to 95%.Eventually,by combining the paired electrolysis and membrane abstraction,100%of NO₃^-removal and NH₃ recovery efficiency were achieved with NH₃recovery rate of 7.27 g-（NH₄）₂SO₄·d^-1·cm^-2 at energy consumption of 19.05 k Wh·kg^-1（NH₄）₂SO₄.In summary,based on the density functional theory,the cobalt-based oxides and phosphide catalysts were designed for NRA by combining the theory and experiment.Besides,paired electrolysis and membrane abstraction were combined to realize synchronous NO₃^-conversion to NH₃ and upcycling into（NH₄）₂SO₄ without the addition of acid/alkali,which provides a more sustainable way for the green recovery of nitrogen resources in wastewater treatment process.