Synthesis Of Hydrogel-derived Carbon-based Nanomaterials And Electrochemical Catalytic Performance For Nitrate Reduction To Ammonia

Ammonia,as a crucial industrial chemical,has been widely used in pharmaceuticals,fertilizers,and energy carriers.Recently,the energy-intensive Haber-Bosch(H-B)process via the conversion of atmospheric nitrogen and hydrogen under high temperature and pressure conditions produces about 176 million tons of industrial NH3 per year.Although the H-B process has improved the chemical industry,it consumes 2%of global energy resources and emits 1%CO2 per year,which is detrimental to green and sustainable development.In recent years,many researchers have paid considerable attention to the development of environmentfriendly technologies for ammonia synthesis.However,it is essential to design the catalyst for electrocatalytic ammonia synthesis.The works are illustrated as follows:(1)Synthesis of copper single cluster catalysts and electrocatalytic performance of nitrate reduction to ammoniaIn this section,single Cu cluster catalysts(Cu SCCs)of supramolecular crosslinked polypyrrole hydrogels were successfully prepared to efficiently synthesize ammonia from nitrate.At-0.5 V vs.RHE,the maximum faraday efficiency of Cu SCCs was ca.96%and the yield is 1.99 mgNH3 h-1 cm-2.Density functional theory(DFT)calculations revealed SCCs endowed with metal-substrate and metal-metal interactions improved the dynamic energy for nitrate and corresponding intermediates to enhance the nitrate-to-ammonia conversion.This section provides a synthesis strategy for aerogel-based catalysts in electrocatalytic reactions via special clusters with strong metal-substrate and metal-metal interactions.(2)Synthesis of nitrogen-doped free-metal catalysts and electrocatalytic performance of nitrate reduction to ammoniaIn this section,nitrogen-doped free-metal carbon catalysts with the species and contents of regulating nitrogen moieties were successfully prepared for the efficient nitrate reduction to ammonia.The results showed the graphite nitrogen moiety played an important role in the performance of nitrate to ammonia.N-C-1000 exhibited the maximum faraday efficiency of 95%and yield of 1.33 mgNH3 h-1 cm-2 at-0.7 V vs.RHE.The theoretical calculations showed that the graphite nitrogen moiety with the strong adsorption of nitrate and optimal reaction path enhanced the performance of nitrate reduction to ammonia.This section provides an understanding of the internal mechanism of nitrogen-doped carbon catalysts used in nitrate reduction to ammonia,which contributes to the design of advanced free-metal electrocatalysts.