Biomass-derived Defect-rich Crystalline Carbon-based Catalysts Are Used For Oxygen Reduction Reactions

With the continuous development of human society,the demand for energy is also increasing,and the problems of energy depletion and environmental pollution are increasing.The development and utilization of sustainable energy was an effective means to relieve the energy and environmental crises,and it is therefore necessary to develop efficient energy storage and conversion technologies,such as fuel cells and metal-air batteries.Oxygen Reduction Reaction?ORR?has a slow kinetics,which is the control step of fuel cell and metal-air cell,and determines the overall performance of these devices.At present,Pt-based catalysts are considered as the most active ORR catalysts,but Pt-based catalysts are still faced with the problems of resource shortage,high price and poor stability,which is difficult to satisfied the large-scale commercial applications.Therefore,it is very important to develop low-cost and excellent performance non-noble metal-based ORR catalysts.Based on the properties of defect engineering,hetero-atom doping and graphite-carbon materials,we designed and synthesized the defective graphite carbon nanosheets materials with excellent ORR catalytic activity by use biomass as carbon source,its application in the field of zinc-air battery was also explored.The main research contents of this paper are as follows:1.Using cellulose extracted from coconut shell as carbon source,the B,N-doped defective carbon entangled Fe₃C nanoparticles?D-BNGFe-2-900?composites was synthesized by carbonization,N doping and fabrication of defects.In the synthesis,the usage of iron species could effectively prevent the formation of BN covalent bond,benefits to maximize the ORR activity.Moreover,nanocarbon coated Fe₃C nanoparticles avoid the dissolution Fe₃C nanoparticles in electrochemical measurements and improve the stability of the catalyst.The D-BNGFe-2-900 has excellent ORR electrocatalytic properties due to the synergistic effect of N doping,Fe₃C nanoparticles and defect sites.Primary ZABs was assembled by using D-BNGFe-2-900 as the air-electrode,which deliver a high discharge capacity of 769 m Ah g_Zn^-1 at 10 m A cm^-2and discharge continuously for 96 h.2.The N-doped defective porous graphite carbon nanosheets materials?D-NPC-3?was synthesized by using cellulose extracted from coconut shell as carbon source,ferric salt as graphitic agent,Zn Cl₂ as activator.During heat treatment,Zn Cl₂ not only as a activating agent and left a lot of pores in the carbon substrate after decomposition,but also inhibited iron aggregation and enhanced conductivity.The large surface area and graphitic carbon are beneficial for the rapid transport of electrons,therefore,D-NPC-3catalyst has better ORR activity and stability than Pt/C.The primary zinc-air battery with D-NPC-3 electrode shows excellent performance with a high discharge capacity of801 m Ah g_Zn^-1 at 10 m A cm^-2and discharge continuously for 95 h.3.Layered double hydroxide?NiFe-LDH?structure was grown on nickel foam and iron foam by hydrothermal method,which present excellent OER catalytic activity and samples were denoted as NiFe-LDH@CF and NiFe-LDH@FF.Two composite electrodes for D-BNGFe-2-900||NiFe-LDH@CF and D-NPC-3||NiFe-LDH@FF were synthesized by coated the front synthetic D-BNGFe-2-900 and D-NPC-3 on the two self-supporting materials,respectively.Using two composite electrodes to assemble rechargeable Zn-air batteries?ZABs?with high power density and stable rechargeable performance.Furthermore,the assembly of all-solid-state ZABs demonstrates the mechanical flexibility and wearable of the material.Two of such ZABs connected in series are shown to successfully drive a splitting water device,shows advanced concept of efficient energy conversion from chemical energy to electric energy and clean fuel gas?H₂?.The method realizes the application of two catalysts in the field of ZABs.