Preparation Of N,P Doped Carbon Materials Based On Polyaniline And Their Performance In Direct Methanol Fuel Cells

Direct methanol fuel cell（DMFC）with simple structure is an ideal energy conversion device.However,the slow reaction kinetics of anode and cathode requires a large number of catalysts to accelerate the reaction.Platinum-based（Pt/C）precious metal with high cost,limited reserves and poor durability is the most widely used ORR catalyst in DMFC.In recent years,the heteroatom doping carbon materials is expected to replace Pt base metal catalysts for ORR,but impurity atoms doped carbon material synthesis of precursor process is complex and serious environmental pollution,thus simplify the synthetic process and formed morphology of heteroatom doping carbon materials,for the optimization of precursor is a problem to be solved.In recent years,heteroatomic co-doped carbon materials have been proved to be a substitute for Pt-based catalysts,but the synthesis process of heteroatom co-doped carbon materials is complicated.Therefore,simplifying the synthesis process of precursor and forming a co-doped carbon material with a controllable morphology,it is an urgent problem for the optimization of precursors.Polyaniline（PANI）has been widely used in electrocatalyst materials because of its advantages such as simple synthesis process,rich nitrogen element,high electrical conductivity and good electrochemical stability.However,single polyaniline structure is relatively simple,the active site is easy to deactivate during the test process.Graphene materials have attracted much attention in the field of electrocatalyst due to their unique photoelectric and mechanical properties,but intact graphene sheets are unreactable and cannot be used as electrocatalysts for ORR.A varieties of cheap and easily available biomass materials are also good precursor materials,but their electrical conductivity is poor.Based on the above problems,in this paper,it used phytic acid as a dopant to synthesize three-dimensional polyaniline,and composite polyaniline with graphene-based/natural polymers materials,which improved the inactivation of polyaniline,and increase the active site of graphene materials,as well as make up for a lack of the biomass material poor electrical conductivity.In addition,the composite materials would realized the co-doping of nitrogen and phosphorus during the pyrolysis process,and forms a variety of N and P doped carbon materials with controllable morphology at the same time.Moreover,the prepared materials can increase the variety of heteroatom doped carbon catalysts,which is a step closer to the goal of non-noble metal replacing noble metal Pt/C as DMFC electrocatalyst.Specific research contents are as follows:（1）Using phytic acid as a dopant,polyaniline was synthesized by in-situ oxidation.and a series of polyaniline/graphene composites were prepared by adjucted the different proportions of polyaniline.The polyaniline and polyaniline/graphene composites were characterized by SEM,FT-IR and XRD.A series of three dimensional porous graphene co-doped with nitrogen,phosphorus and sulfur（NPS G）were prepared by pyrolysis method using the polyaniline matrix composite as the precursor for ORR catalyst in DMFC.The morphology and structure of carbon materials were characterized by SEM,XRD and XPS,etc.Electrochemical tests showed that when the mass ratio of graphene and aniline was 1:50,the polyaniline-based NPS G₂catalyst exhibited a higher onset potential（1.09 V vs.RHE）than commercial Pt/C,and the catalyst had a four-electron transfer pathway and good methanol tolerance.In addition,the current density of Pt/NPS G₂catalyst for MOR was 2.9 times higher than that of commercial Pt/C catalyst when a series of polyaniline-based NPS G is used as the support for Pt nanoparticles,and the stability of Pt/C catalyst was also better than that of commercial Pt/C catalyst.（2）Based on the optimized content of polyaniline in the previous chapter,the polyaniline/graphene foam composite was synthesized,and the composite was characterized by SEM,FT-IR and XRD.A novel polyaniline-based noble-metal free Fe Ni,nitrogen phosphorus co-doped graphene foam（Fe Ni@NP-GF）was designed by introduced Fe and Ni elements as ORR catalysts.The morphology and structure of the carbon material were characterized by various characterization methods.The influence of Fe Ni alloy doping on the catalytic performance of ORR was investigated.Electrochemical tests showed that compared with the polyaniline catalyst containing only one transition metal（Fe@NP-GF,Ni@NP-GF）and no transition metal（NP-GF）,the prepared Fe Ni alloy doped catalyst（Fe Ni@NP-GF）exhibited a higher half-wave potential（0.74 V vs.RHE）and a higher current density(4.81 m A cm^-2),which can be compared with commercial Pt/C.The catalyst also had better stability and methanol resistance than Pt/C catalyst.In addition,the mass activity of Pt/Fe Ni@NP-GF catalyst for MOR was 1.6 times that of Pt/C catalyst,and the Pt/Fe Ni@NP-GF catalyst had better stability than commercial Pt/C catalyst.（3）The polyaniline/chitosan/silk hydrogel with high nitrogen content was designed with three-dimensional polyaniline as the base material and chitosan and silk macromolecular biomass material with abundant,low cost and nitrogen element as the raw materials.The polyaniline hydrogel was characterized by SEM,FT-IR and XRD.Using the hydrogel as the precursor,a novel porous non-precious metal Ca,N and P co-doped biochar（Ca@NP₆C₄）based on polyaniline was prepared by pyrolysis method.The morphology and structure of the polyaniline based material were characterized by various characterization methods.EDS showed that the content of N in the material is as high as 29.71 wt%,and XPS showed that the main doped configurations of N were pyridine N and graphite N.The ORR catalytic performance of the catalyst was optimized by adjusting the content of silk and polyaniline.Electrochemical tests showed that the Ca@NP₆C₄material exhibited a positive onset potential（0.94 V vs.RHE）,a four-electron transfer process,higher stability and methanol resistance than commercial Pt/C.The catalytic activity of Pt/Ca@NP₆C₄catalyst was 1.6 times that of commercial Pt/C catalyst,and the cycling stability was better than that of Pt/C catalyst.