Defect Engineering Regulation And Oxygen Reduction Performance Of Carbon-based Materials

In consideration of the increasingly serious energy and environmental crisis,new energy storage and conversion devices are developing rapidly.Fuel cell is regarded as one of the most important electrochemical devices to resolve these crises,due to its excellent sustainability,efficiency and environmental-friendliness.However,its large-scale application is severely limited by the scarce resource,high price and poor durability of precious metal platinum.Metal-free carbon nanomaterials have been widely employed in cathodic oxygen reduction reaction?ORR?of fuel cells because of their controllable structure,outstanding electrical conductivity,electrochemical stability and high specific surface area.The performance optimization of carbon nanomaterials is mainly carried out by means of structural construction,heteroatom doping and defect engineering.In this paper,we systematically explored the action mechanism of defective heteroatom-doped carbon nanomaterials in ORR and their application in zinc-air batteries from the theoretical and experimental viewpoints,through reasonable structural design,defect and heteroatom doping engineering.The main contents are as follows:1.The synergistic effect of defect sites and nitrogen/sulfur dopants on the electrochemical reactivity of carbon materials was researched theoretical simulation,and it was found that the combined action of defects and dopants reduced the band gap,induced the local electro rearrangement of carbon matrix,thus improving the ORR activity.Biomass waste?chicken feather?was selected as the carbon,nitrogen and sulfur sources,which was converted into carbon material through pre-carbonization treatment.The defective N/S-codoped product CF-K-A was obtained after the successional potassium hydroxide and ammonia activation.As a result of the internally connected three-dimensional porous structure,high specific area,defect degree and heteroatom doping amount,CF-K-A showed superb ORR activity and stability,well verifying the theoretical calculation results.Moreover,as the cathodic ORR catalyst,CF-K-A showed a good performance in practical zinc-air batteries.2.The superiority of carbon pentagon?C5?,relative to hexagon?C6?,were predicted by density functional theory calculation.It was found that C5 possessed narrower band gap,larger charge density distribution and better oxygen affinity,which might be the catalytic active sites of ORR.Then we chose fullerenes(C₆₀)with intrinsic pentagons as raw materials.The C5 structure was exposed in the reconstructed carbon-based materials via in situ alkaline etching at high temperature,thus obtaining the pentagon defect-rich carbon nanomaterials?PD-C?.Compared with the similar etching product?D-G?by employing the graphene composed of hexagons as raw material,PD-C with abundant intrinsic pentagon defects exhibited much better activity,reaction mechanism and durability under similar defect degrees,well confirming the theoretical results.Further,the pentagon defect-rich and nitrogen-doped product?PD/N-C?showed a comparable ORR performance to commercial Pt/C catalysts and can employed in practical zinc-air batteries.In addition,these materials also showed decent prospect for the electric double layer capacitors.