| Proton exchange membrane fuel cell (PEMFC) has the characteristics of low-temperature operation, and high efficiency. The development of non-precious metal oxygen reduction catalyst is the hotspot of PEMFC research. At present, there are problems of high-cost starting materials, complex preparation route and pollution for important transition metal macrocycle compound oxygen reduction catalysts. We had designed and prepared CoTETA/C oxygen reduction catalysts, and CV test showed that they had good activity for oxygen reduction. However, the preparation of the membrane electrode assembly (MEA) based on our catalysts has not been reported.This thesis reported the preparation process for MEA with Pt/C as cathode & anode catalyst. The preparation of MEA included hot press method and catalyst-coated membranes (CCM) method. The effects of process parameters of hot press MEA (pressing pressure, pressing time and catalyst slurry on the performances of single cell tests) and comparison of the polarization curves of the MEAs prepared by the two methods were studied. The activation method and test conditions of single cell were also investigated.Then the preparation of MEA with CoTETA/C as cathode catalyst was investigated. As to the difference between CoTETA/C and Pt/C, the performances of MEAs with CoTETA/C as cathode catalysts which were made by the traditional hot press method were poor. The new preparation method of MEAs were developed. Recently, carbon nanotubes were widely used as catalyst carrier because of its unique pore structure, pore volume, pore size distribution and surface functional groups which isconducive to the dispersion of the metal. The CoTETA/MWNT catalysts made from multi-walled nanotubes (MWNT) were investigated.Through the above research, this thesis drew the following conclusions:1 The best preparation conditions of MEA by hot press with Pt/C catalyst as catalysts: the catalyst slurry employed isopropyl alcohol as the solvent, pressing pressure was 8 MPa, and pressing time was 45 s. The best optimal conditions of single cell: cell working temperature was 80 oC, the humidification temperature of hydrogen was 95 oC, the humidification temperature of oxygen was 75 oC; The maximum power density of MEA prepared by hot press was 604.3 mW/cm~2, and the maximum power density of MEA prepared by CCM was 700.3 mW/cm~2.2 The best preparation conditions MEA based on CoTETA/C catalyst: pressing pressure was 12 MPa, CoTETA/C catalyst loading was 2 mg/cm~2, the best anode catalyst loading was 0.15 mg Pt/cm~2, mass ratio of CoTETA/C to Nafion was 2:1. Adding a certain proportion of ethylene glycol to the catalyst slurry can improve contact between CoTETA/C and Nafion membrane, and greatly improve the cell performance. The maximum power density of MEA prepared by hot press was 180.9 mW/cm~2, and the maximum power density of MEA prepared by CCM was 218.3 mW/cm~2.3 The electrochemical impedance test of single cell with CoTETA/C catalyst was performed, and the corresponding equivalent circuit was studied. It was found that the increasing of CoTETA/C loading could increase the cell performance at low temperatures, but increasing of the thickness of the catalyst layer also increased the mass transfer resistance and the possibility of flooding. The best single cell test temperature was found to be 60 oC.4 The redox potential of CoTETA/MWNT was 0.004 V lower than that of CoTETA/C, and its oxygen reduction current was 30 mA larger than that of CoTETA/C. Single-cell tests showed that the current density of CoTETA/MWNT was better than that of CoTETA/C. TEM study showed that some elemental Co evenly distributed in the catalyst support MWNT. Heat treatment of the catalyst was very important to oxygen reduction activity, and the catalyst active sites were generated at higher heat temperatures treatment. |
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