Synthesis And Electrochemical Performance Investigation Of Electrocatalysts For Direct Methanol Fuel Cells

Due to its high energy conversion efficiency, low pollution, wide fuel sources, etc.,direct methanol fuel cell(DMFC) is becoming a hotspot research in new energy domain. However, the current major bottleneck for DMFC in its commercial development mainly includes:(1) The widely used precious metal platinum(Pt) causes high cost of the electrocatalysts;(2) As cathode electrocatalyst, the low electrochemical activity and low tolerance to crossover effect for alcohol molecules decrease the catalytic performance. Therefore, it is the focus in DMFC research that looking for the electrocatalysts with low-cost, high activity and long stability. In this paper, the preparation of various catalysts such as nitrogen-doped graphene scrolls(NG), Pt nanoparticles/nitrogen-doped graphene nanohybrid scrolls(Pt NPs/N-GNSs),Pt Ru nanoparticles/nitrogen doped mesoporous carbons(Pt Ru/NMPCs),nitrogen-doped hollow carbon sphere(N-HCS), Pt nanoparticles/nitrogen doped hollow carbon sphere(Pt/N-HCS) and Pt nanoparticles/carbonized chitosan@carbon nanotubes(Pt/C-Chitosan@CNTs) were investigated, and the resulting materials were utilized as the anode or cathode electrocatalysts in DMFC research.(1) The series of nitrogen-doped graphene scrolls(NG) were fabricated by the ultrasonic cavitation assisted hydrogen implosion method using GO and poly(diallyldimethylammonium chloride)(PDDA) as precursor and nitrogen source,respectively. The characterization analysis results from TEM, XPS, FTIR, XRD and Raman showed that the nitrogen doped speices, reduction degree and curly/folded structure of NG can be changed with various ultrasonic power. Furthermore, the electrocatalytic investigations by CV and LSV methods in alkaline media indicated that NG-700 prepared under ultrasonic power(700 W) possess much better ORR activity through four-electron pathway similar to the comerical Pt/C(E-TEK),long-term stability and higher resistance to the methanol crossover, which have the high reduction degree, pyridinic/graphitic type enriched nitrogen doped properties and the scrolled morphology.(2) Using GO and poly(diallyldimethylammonium chloride)(PDDA) as precursor and nitrogen source, respectively, Pt NPs/nitrogen-doped graphene scrolls(Pt NPs/N-GNSs) were fabricated by the ultrasonic cavitation assisted hydrogen implosion method. The series analysis results from TEM, XPS and FTIR showed that PtNPs/N-GNSs have the scrolling structure, high reduction degree and nitrogen-doped properties. Additionally, the electrocatalytic investigations for methanol oxidation indicated that Pt NPs/N-GNS possess much better electrochemical performance and longer stability than Pt NPs/PDDA-RGO.(3) The homogeneous nitrogen-doped hollow carbon spheres(N-HCS) were obtained through hydrothermal, carbonization and etching treatment of PPy/Si O2 composites, which were prepared by polymerization of pyrrole(Py) to form polypyrrole(PPy) on nano-Si O2 spheres surface using ammonium persulfate((NH4)2S2O8) as the oxidant. The series analysis results from SEM, TEM, XPS, XRD and BET showed that N-HCS possess not only high surface area(759 m2·g-1), large diameter(370 nm), thick hollow carbon sphere wall(15 nm) but also pyridinic/graphitic type enriched nitrogen doped properties. Furthermore, the electrocatalytic investigations by CV and LSV methods in alkaline media indicated that N-HCS possess much better ORR activity through four-electron pathway and higher resistance to the methanol crossover.(4) Using N-HCS as supporting material, Pt/N-HCS nanohybrids were fabricated via a microwaveassisted reduction process in ethylene glycol. The series test results from SEM, TEM, XRD, EDS, ICP-AES, XPS showed that Pt NPs with small particle size(2.64 nm) were uniformly deposited on the N-HCS surface, the mass ratio of Pt in Pt/N-HCS was 18.76%. Moreover, the electrocatalytic investigations for methanol oxidation indicated that Pt/N-HCS possess much better electrochemical performance and longer stability than the commercial Pt/C(E-TEK).(5) Nitrogen doped mesoporous carbons(NMPCs) were prepared by direct carbonization of zeolitic imidazolate framework-8(ZIF-8) without acid etching treatment. The series analysis results from SEM, TEM, XPS, BET and XRD showed that NMPCs possess not only high surface area(1960 m2·g-1), large pore volume(1.16cm3·g-1), small pore size distribution(~ 3.6 nm) but also polyhedral morphology and nitrogen doped properties. Moreover, Pt Ru NPs with small particle size are uniformly dispersed on the NMPCs surface via a microwave assisted reduction process in ethylene glycol, and the as prepared Pt Ru/NMPCs nanohybrids were used as electrocatalysts for methanol oxidation, and the results showed that Pt Ru/NMPCs possess much better electrochemical performance and longer stability than the commercial Pt Ru/C(E-TEK). Kinetic study further confirmed that Pt Ru/NMPCs for methanol electrooxidation is controlled by the diffusion process of methanol.(6) Pt/C-Chitosan@CNTs nanohybrids were prepared by hydrothermal reduction of Pt Cl62- and carbonization of chitosan-functionalized CNTs(Chitosan@CNTs),respectively. The characterization analysis results from TEM, XPS, FTIR, XRD and Raman showed that Pt NPs with small particle size(1.39±0.2 nm) were uniformly deposited on the carbonized-Chitosan@CNTs surface, the mass ratios of Pt in Pt/C-Chitosan@CNTs was 19.46%. Additionally, the electrocatalytic investigations for methanol oxidation revealed that Pt/C-Chitosan@CNTs possess much better electrochemical performance and longer stability.