Preparation Of Chitosan-based Nitrogen-doped Carbon Aerogel Catalyst And Its Electrocatalytic Oxygen Reduction/hydrogen Evolution Reaction Performanc

Zinc-air batteries（ZABs）are regarded as a new generation of potential energy storage and conversion equipment due to its advantages of high energy density,small size and no pollution.However,the slow kinetics of cathodic oxygen reduction（ORR）in Zinc-air batteries are still the first problem to be solved by researchers.In addition,hydrogen has a very high specific energy density and absolute pollution-free,which makes it an incomparable advantage in various alternative energy sources.Among them,electrocatalytic hydrogen evolution reaction（HER）has become an important technology to promote sustainable development of hydrogen energy.Whether in ORR or HER process,finding low-cost electrocatalyst products with high activity and high durability is the key to achieve large-scale application and alleviate the problem of energy shortage.However,most of commercial electrocatalysts use precious metals,and the disadvantages of high cost and scarcity hinder their development and application in the future.In this paper,we provide a simple and scalable method for the preparation of metal/nitrogen-doped carbon aerogel to replace precious metals and reduce platinum content,that is,chitosan complexes with metal ions using a unique molecular structure.It provides a new idea for the preparation of other metal carbides or low content noble metal/nitrogen doped carbon aerogel catalysts.The specific research contents are as follows:（1）Transition metal carbides/nitrogen-doped carbon aerogels（TMCs/NCA）,including Fe₃C/NCA,Mo₃C₂/NCA and Fe₃C-MO₂C/NCA,were prepared by electrostatic interaction between amino protonated chitosan molecules and metal complex anions.Among them,Fe₃C/NCA composites were pyrolyzed at 1000℃to obtain Fe₃C/NCA-1000composites with graphite nitrogen and carbon defects,or Fe₃C/NCA-NH₃ composites with high nitrogen content were obtained by secondary nitrogen doping treatment,both of which had ORR activity similar to that of commercial Pt/C.The Fe₃C/NCA-1000 and Fe₃C/NCA-NH₃ assembled ZABs show excellent performance with power densities of 200 mW cm^-2and 250 m W cm^-2,respectively.Finally,the density functional theory（DFT）calculation showed that the presence of graphite nitrogen,pyridine nitrogen and carbon defects in the carbon framework effectively reduced the ORR reaction free energy of Fe₃C,thus improving the ORR reaction activity,and further proved that the doping of nitrogen and the construction of carbon defects promoted the ORR activity of the catalyst.（2）Low platinum/nitrogen doped carbon aerogel（Chi-Pt/NCA）was prepared by electrostatic interaction between chitosan molecules protonated with amino groups as carbon and nitrogen sources.Among them,Chi-Pt/NCA was pyrolysed at 1000℃to obtain Chi-Pt/NCA-1000 composites containing carbon defects,which had ORR activity similar to that of commercial Pt/C.In addition,the power density of ZABs assembled from Chi-Pt/NCA-1000 reaches 205 m W cm^-2.Meanwhile,Chi-Pt/NCA and Chi-Pt/NCA-1000composites also have excellent HER catalytic activity.In particular,Chi-Pt/NCA-1000 has a high catalytic activity of 1.00 A mg _Pt^-1 and maintains a high stability of 95.7%after 15 h of operation.