Study On The Effect Of Polyaniline Modified Nitrogen-Doped Carbon Carriers On The Performance Of Platinum-Cobalt Oxygen Reduction Catalysts

Proton exchange membrane fuel cell（PEMFC）has been widely concerned for its advantages of cleanliness,high energy conversion efficiency and low temperature start-up.However,commercialization of PEMFC technology is limited by problems such as the slow kinetics of cathode oxygen reduction reactions and the high cost of catalysts.At present,carbon supported platinum-based nanoparticles（NPs）are widely used as catalysts for anode and cathode in PEMFC.However,the existing carbon supported platinum-based catalysts have some problems,such as insufficient utilization of Pt,easy removal of active component,poor corrosion resistance and low activity.Therefore,improving the activity and stability of the required catalyst and minimizing the platinum load is central to reducing the commercial cost of PEMFC.In this thesis,the enhanced physicochemical properties of carbon carriers have been achieved through nitrogen doping and structural modulation.Thus,the key factors such as electronic structure,particle size and dispersity of PtCo nanoparticles could be adjusted to improve the catalytic activity and durability of PtCo alloy catalysts.The following contents are included:（1）Core-shell nitrogen doped carbon carrier:In order to improve the oxygen reduction performance of carbon-loaded PtCo catalyst,a core-shell nitrogen-doped carbon carrier（C@NC）was prepared.The carrier was prepared by carbonizing polyaniline-coated carbon black.An efficient oxygen reduction catalyst（PtCo/C@NC）was obtained by impregnation reduction method by loading PtCo alloy on C@NC.The carrier not only has the advantages of excellent carbon black conductivity and high specific surface area,but also the nitrogen-containing carbon shell could evenly disperse the metal NPs and protect the carbon carrier from direct exposure to corrosive environment,which further effectively improves the stability of the catalyst.Under acidic conditions,the mass activity（MA）of PtCo/C@NC-700(0.53 A mg _Pt^-1)was 4.8 times that of JM Pt/C(0.11 A mg _Pt^-1).After 10000 potential cycles,the MA loss of PtCo/C@NC-700 was 19%,much lower than that of JM Pt/C（36%）.（2）Porous nitrogen doped carbon carrier:In order to improve the nitrogen content and porosity of nitrogen-doped carbon carrier,nitrogen-doped carbon carrier was prepared by carbonizing polyaniline with in-situ doping method,and then the porous nitrogen-doped carbon carrier（PNC）was obtained by etching it with KOH.KOH activation improves the specific surface area and porosity of the nitrogen-doped carbon carrier,which promotes the dispersion of PtCo NPs and the transfer of electrons and mass.At the same time,the content of high pyridinic nitrogen and oxygen-containing functional groups in PNC-2 not only increases the nucleation site of PtCo NPs,but also improves the utilization rate of Pt,thus increasing the electrochemically active surface area（ECSA）of PtCo/PNC-2.The stability of PtCo/PNC-2 is improved by enhancing the interaction between PNC-2 and PtCo NPs.In electrochemical characterization,PtCo/PNC-2 had the largest ECSA(129.2 m² g _Pt^-1)and the lowest Tafel slope(65.7 mV dec^-1)than JM Pt/C(88.5 m² g _Pt^-1,100.4 mV dec^-1).After 10000cycles,the MA loss of PtCo/PNC-2（17%）was lower than that of PtCo/NC（28%）without porous support.（3）Graphitized porous nitrogen-doped carbon carrier:In order to balance the defects and graphitization degree of porous nitrogen-doped carbon carrier and simplify the preparation process,the graphitized porous nitrogen-doped carbon carrier（NC-I）was prepared.NC-I was prepared by adding iodine in the carbonization process of polyaniline.The presence of iodine improves the graphitization degree of the nitrogen-doped carbon material,thus improving the conductivity and corrosion resistance of the carrier.At the same time,the content of graphite nitrogen in the nitrogen-doped carbon material was increased（2.07 at.%）,and the oxygen reduction activity of the catalyst was improved.The MA(0.48 A mg _Pt^-1)and specific activity(0.70 mA cm _Pt^-2)of PtCo/NC-1I were significantly improved by electrochemical activity test.After stability test,the MA of PtCo/NC-1I decreased by 19%,which was lower than that of JM Pt/C（36%）.TEM characterization and chronocurrent testing indicated that NC-1I maintained the structural stability of PtCo/NC-1I by enhancing the interaction with PtCo NPs and improving its corrosion resistance.