| Fuel cell is a kind of energy conversion device that directly converts chemical energy in fuel into electric energy.It performs several advantages such as high energy conversion ratio,long working life and quick start-up.For polymer electrolyte membrane fuel cell?PEMFC?,improving the working conditions to intermediate temperature?100-600??has attracted much attention because of the possibility of using non-precious metal catalysts,simple water management system,and good catalyst corrosion resistance,etc.The developments of electrolyte materials with high conductivity,good thermal stability and high mechanical strength are of significant importance to the commercialization of intermediate temperature fuel cells.On the other hand,lowering the working temperature of solid oxide fuel cells?SOFC?to intermediate temperature?500-750??could decrease the cost of manufacturing and operating and benefit its industry application.This also relies on the developments of novel electrolytes with high conductivity in intermediate temperature.Graphene oxide?GO?has high specific surface areas,good water retention,oxygen-containing groups on the surface,which could provide more jumping sites for ion transport under low humidity conditions.This dissertation focus on the developments of composite electrolytes containing GO for high temperature PEMFC and low temperature SOFC,and the fabrication of Pt coated graphene as electrode catalysis for PEMFC.The major research results are listed below:SnP2O7 and GO were prepared by solid state reaction and Hummers method,respectively.Then SnP2O7/GO composite electrolytes were prepared by adding 5 wt%graphene oxide into SnP2O7.The results show that the SnP2O7 synthesized has cubic phase structure and the addition of GO can improve the relative density of the SnP2O7/GO electrolytes.The SnP2O7/GO composite has conductivity of 7.6×10-3 S cm-11 at 225?,which is 2.5 times higher than that of pure SnP2O7 electrolyte,and the composite electrolytes have lower conduction activation energy.At 225?,fuel cells with SnP2O7/GO electrolyte exhibit a power density of 18 mWcm-2,which is about 3times higher(5 mW cm-2)than that of fuel cells with pure SnP2O7 electrolyte.Furthermore,the SnP2O7/GO composite electrolyte exhibits better fuel cell performance under dry atmospheres.Mesoporous SnP2O7 with cubic phase structure was prepared by template method.Then GO was added into the mesoporous SnP2O7 to form mesoporous SnP2O7/GO composite electrolytes.According to the results of BET analysis,the pore size distribution of mesoporous SnP2O7 ranges from 1 to 7 nm,and the average value is about 4 nm,while the average pore size in the non-mesoporous SnP2O7 is 75 nm.At220?,the conductivity of the mesoporous SnP2O7/GO composite electrolyte,mesoporous SnP2O7 and non-mesoporous SnP2O7 is 0.017,0015 and 0.0029 Scm-1respectively,and their corresponding conduction active energy is 20.8,25.6 and 33.8kJ mol-1,respectively.Power density of fuel cells based on the mesoporous SnP2O7/GO composite electrolyte reaches 17 mWcm-2,which is higher than that with the mesoporous SnP2O7 electrolyte(12 mWcm-2)and that with the non-mesoporous SnP2O7 electrolyte(4 mWcm-2),indicating that the mesoporous structure effectively improves the transport of protons in the electrolytes,and GO could improve the conductivity of the electrolyte as well.The Keggin structure CsxH3-xPMo12O40 was synthesized by wetting chemical method and CsxH3-xPMo12O40/GO?20:1?composite electrolyte was also fabricated.EDS results indicate that GO distributes uniformly in the CsxH3-xPMo12O400 electrolyte.The CsxH3-xPMo12O40 and CsxH3-xPMo12O40/GO electrolytes all show good thermal stability at high temperature.And the addition of GO could further improve the thermal stability at 700-800?.The conductivity of CsxH3-xPMo12O40/GO reaches1.7×10-3 Scm-1 at 280?,which is much higher than that of pure CsxH3-xPMo12O40(1.7×10-3 Scm-1).And the conduction activation energy of the CsxH3-xPMo12O40/GO electrolyte is 47.7 kJ mol-1,while which of the CsxH3-xPMo12O400 is 69.6 kJ mol-1.All of these indicate that GO could decrease the proton diffusion energy barrier in CsxH3-xPMo12O40,and CsxH3-xPMo12O40/GO composite electrolyte is a potential high-temperature proton exchange membrane material.Bi2O3/GO composite electrolyte was prepared by mechanically mixing Bi2O3 and Go powders.The sintered density of the Bi2O3 samples were enhanced with smaller grain size due to GO addition,and GO could provide more oxygen ion transport channels in the composite electrolytes.Oxygen ion conductivity of the Bi2O3/GO composite electrolytes reaches 4.16×10-3 S cm-1 at 500?,which is higher than the pristine Bi2O3 electrolyte.Bending strength of the Bi2O3/GO composite electrolyte is16.24 MPa,which is higher than that of 14.19 MPa of pristine Bi2O3.Pt/rGO catalyst was prepared by ethylene glycol reflux reduction.The graphene oxide was completely reduced into graphene and the Pt particles were uniformly loaded on the surface of GO.The particle size of Pt nanoparticles was about 5-10 nm.The graphene-based catalysts have higher specific surface areas and better catalytic activity in cyclic voltammetry test. |
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