The Synthesis Of Non-platinum Electrocatalysts Based On Biomass-derived Carbon For Oxygen Reduction Reaction

As a new generation of green energy device,Fuel Celsl（FCs）need to overcome the kinetic process of slow oxygen reduction reaction（ORR）to complete the high-efficiency conversion of electric energy.Hence,the application of catalyst is the core to the development of FCs.In general,noble Pt-based nanomaterials are the most representative materials in the field of catalysis.However,in order to break the barriers to commercialization and reduce the commercial cost of FCs,it is still the goal of many researchers to find low-cost and efficient non-Pt catalysts.The emergence of advanced carbon nanomaterials significantly promote the progress of FCs,and it is reported that the modification of carbon can improve the intrinsic properties of the materials.However,the large-scale production and applications of carbon materials are still limited due to their high cost and complex preparation process.Biomass is an environmentally friendly,economically feasible and abundant natural resource,which has drawn wide attention for its potential as a carbon precursor.The unique pore structure inherent in biomass provides a broad research space,especially in the field of catalytic materials.Among this field,the porous structure is an effective way to promote the transport of reactants and electrons.Based on above,this paper prepared different heteroatom-doped biomass-derived carbon materials.Through a series of physical property characterization,microstructure characterization and electrochemical tests,we investigate the influence of their morphology and composition on the ORR catalytic performance.This paper has carried out the following work:（1）Using the fallen plum blossoms as a carbon source,through KOH activation,the pore structure of material is completed during carbonization process,and then mixed with the nitrogen-rich melamine precursor to prepare plum blossom-derived nitrogen（N）-doped porous carbon materials（PBCs）.The material has a fold structure,and the abundant hierarchical pores are distributed on honeycomb-like sheets.The N-doped porous PBC-A materials are dominated by pyridine N and graphite N,with the content of 39.68%and 32.94%,respectively.The specific surface area of the PBC-A via KOH activation is as high as 2118.9 m² g^–1.Electrochemical performance of PBC-A catalysts show that the onset potential and half-wave potential are 0.91 V and 0.82 V（vs.RHE）,respectively,which are comparable to those of the commercial Pt/C.And it has better methanol resistance and stability than those of commercial Pt/C.（2）Ammonium persulfate（（NH₄）₂S₂O₈）is mixed with plum blossom powder.Among them,（NH₄）₂S₂O₈ will volatile and slightly explosive during high pyrolyzed temperature.It can be used as an auxiliary agent for the formation of porous structure and provide both N and sulfur（S）sources for carbon materials,relazing simple synthesis of N and S co-doped porous carbon nanosheets（NSCs）.By adjusting the pyrolysis temperature,we found that the NSC-900 material prepared at 900°C is dominated by highly active N（79.5%）and active S（76.1%）.The addition of S element can increase more catalytic sites.In alkaline conditions,NSC-900 catalyst possess a half-wave potential of 0.84 V（vs.RHE）,which is only 10 m V behind commercial Pt/C,and the onset potential of 0.96 V surpasses commercial Pt/C,exhibiting better ORR performance than monadic N-doped carbon.（3）During the synthesis,the fallen plum blossom and iron chloride hexahydrate（Fe Cl₃·6H₂O）were used as C and Fe precursors,respectively.Graphitic carbon nitride（g-C₃N₄）can provide sufficient N sources.The Fe,N co-doped porous carbon material（Fe-N-C-T）was prepared by precisely adjusting the hydrothermal and carbonization temperature.Among them,Fe-N-C-900samples are obtained at 180°C hydrothermal reaction and 900°C pyrolysis temperature,forming more rich pore structure on the layer.The introduction of g-C₃N₄ increase the specific surface area of Fe-N-C-900 to 489.22 m² g^–1,the N content in this sample reached 4.1%,and the Fe–N bonding is the active sites in favor of the reaction in catalytic process.Fe-N-C-900 catalyst possesses the best ORR performance,the onset potential and half-wave potential are further increased to 0.99 V and 0.89 V（vs.RHE）,which exceed commercial Pt/C.Moreover,Fe-N-C-900 exhibits a maximum power density of 164.3 m W cm^–2 in zinc-air battery.