Application Research Of Porous Carbon Nanofiber In Membrane Electrode Assembly Of Proton Exchange Membrane Fuel Cell

Under the background of environmental problems and energy crisis,the demand for renewable clean energy is increasing.Proton exchange membrane fuel cell（PEMFC）,as an outstanding representative of clean energy,has attracted continuous attention of researchers due to its high energy conversion efficiency and zero pollution emissions.The most costly membrane electrode（MEA）in PEMFC is hindered by the use of precious metal platinum（Pt）to catalyze the oxygen reduction reaction（ORR）with high overpotential and slow kinetic process.At the same time,the carrier carbon black used by the commercial catalyst Pt/C will corrode during the long-term operation of the PEMFC,resulting in a decrease in the efficiency of the active sites on the carrier.This has also become one of the problems that PEMFC must solve.Therefore,the research and development of economic,efficient and stable new catalysts are of great significance for the promotion and development of PEMFC.The application of carbon nanofiber materials in electrocatalysis has been widely studied.This article focuses on the composite or doping of porous carbon nanofibers,which are used as carriers to support precious metals and alloys.As ORR catalysts,their performance are studied.In addition,we also studied porous carbon nanofiber as a microporous layer（MPL）material in MEA,and studied the impact of its unique structural properties on the overall performance of MEA.The details are as follows:（1）.Porous carbon nanofibers（PCNF）and carbon black（CB）were combined as a composite carrier（PCNF-CB）,and precious metal platinum was supported on the composite carrier by ethylene glycol reduction method to prepare Pt/PCNF-CB catalyst.SEM and TEM tests showed that the composite carrier exhibits excellent dispersibility when the CB ratio is 30%.The electrocatalytic activity and stability of Pt/PCNF-CB catalyst and commercial Pt/C catalyst were studied using cyclic voltammetry（CV）and linear scanning voltammetry（LSV）.The results showed that Pt/PCNF-CB-30%not only exhibits better catalytic activity,but also has a higher initial potential and mass specific activity（MA）.After 2000 accelerated potential cycles,the electrochemically active surface area（ECSA）of Pt/PCNF-CB-30%remained 68%,the half-wave potential lost 24 m V,while the ECSA of commercial Pt/C retained 43%and the half-wave potential dropped by 94 m V.The single-cell test results confirmed that the maximum power density of the MEA composed of Pt/PCNF-CB-30%as the cathode catalyst is almost twice that of the MEA composed of the Pt/C catalyst.Compared to commercial Pt/C catalysts,Pt/PCNF-CB-30%showed better stability and single-cell performance,proving its potential application value as a fuel cell cathode catalyst.（2）.During the preparation process of electrospinning,Ca CO₃ was added as the second pore-forming agent,porous carbon nanofiber PCNF（Ca CO₃）was obtained through spinning,pre-oxidation and carbonization process.PCNF（Ca CO₃）was characterized by SEM,BET and other tests.The SEM results showed that the pore of PCNF（Ca CO₃）obtained by adding Ca CO₃ were mainly distributed inside the fiber,and the pores of PCNF without Ca CO₃ were mainly distributed on the surface of the fiber.The BET data showed that when the amount of Ca CO₃ added is 1%,the specific surface area of PCNF（Ca CO₃-1%）reached 169.7 m² g^-1,which is an increase of 25.7%compared to the PCNF 135.0 m² g^-1.Electrochemical tests showed that the initial potential of Pt/PCNF（Ca CO₃-1%）in the LSV curve is 0.93 V,which is an increase of30 m V and 20 m V than Pt/PCNF and commercial Pt/C.The half-wave potential was increased by 37 m V and 26 m V,respectively.After 1000 cycles of testing,the Pt/PCNF（Ca CO₃-1%）catalyst exhibited better stability than the commercial Pt/C catalyst.In addition,the membrane electrode（MEA）prepared with PCNF（Ca CO₃-1%）as the microporous layer material showed much higher maxium power density than the MEA with carbon black as the microporous layer material.（3）.The post-treatment method was used to dope the PCNF with nitrogen,that is,the high-temperature carbonized PCNF and 2-aminothiazole were blended and calcined,and the nitrogen element was introduced into the PCNF through the heat treatment method.Tests such as SEM and XPS found that when the mass ratio of nitrogen-containing precursor to PCNF is 1:20,and the heat treatment temperature is 900℃,the obtained N-PCNF（1:20-900）not only retained the porous fiber structure,but the content of pyridine N in the N content was higher.Pt/N-PCNF catalysts were prepared by supporting platinum nanoparticles on this carrier.Electrochemical tests showed that the half-wave potential of Pt/N-PCNF（1:20-900）is 0.760 V,which is 30 m V higher than that of commercial Pt/C catalyst,showing better ORR catalytic performance.Pt NW/N-PCNF（1:20-900）catalyst loaded with platinum nanowires prepared by using N-PCNF（1:20-900）as the carrier and through template-free method showed better ORR activity in the CV and LSV results compared to commercial Pt/C and Pt/N-PCNF（1:20-900）.（4）.Porous carbon nanofiber（PCNF）was prepared by electrospinning and subsequent heat treatment,and the microporous layer of the membrane electrode was constructed by this.Unlike the carbon black particles as a microporous layer showed a close-packed structure,the microporous layer structure built by PCNF was loose and presented a three-dimensional continuous structure.The single cell test of the membrane electrode showed that when the cathode catalyst loading/anode catalyst loading is 0.5mg cm^-2/0.25mg cm^-2,the maximum power density（70.0m W/cm²）of the membrane electrode with porous carbon nanofiber as the microporous layer（MPL-PCNF）is much higher than that（58.1m W/cm²）of the membrane electrode with carbon black as microporous layer（MPL-CB）membrane electrode,and the maximum power density of the membrane electrode without a microporous layer（Ref）structure was only（27.7m W/cm²）,and under the conditions of multiple different electrode loadings,they all showed the same trend.It proved that porous carbon nanofiber have obvious advantages as a microporous layer material.（5）.Pt Fe alloy nanoparticles were loaded on porous carbon nanofiber（PCNF）via one-step modified glycol reduction method by adjusting solution p H.On the surface of PCNF,Pt Fe alloy nanoparticle can be uniformly dispersed with a narrow particle size distribution.The catalyst Pt_4.8Fe/PCNF prepared in p H=7 solution with PCNF as carbon support exhibited better ORR performance,which shows even 18m V higher onset potential than that of commercial catalyst Pt/C.Moreover,comparable durability was also obtained through ADT test after 2000 cycles.The excellent performance of Pt_4.8Fe/PCNF catalyst may attribute to the structural and electronic effects of transition metal in the Pt Fe alloy.The rough surface and porous structure of PCNF was also supposed to be beneficial for performance improvement.