Study On The Preparation Of Meas With Low-platinum-loading And Self-humidification For Proton Exchange Membranes Fuel Cell

Fuel cells can directly, efficiently and eco-friendly convert chemical energy of fuel intoelectrical energy. Among of them, proton exchange membrane fuel cells （PEMFCs） areconsidered to be one type of the most promising clean energy conversion technologies in the21st century since they are highly competitive in the aspects of power density and operatingtemperature. PEMFCs are particularly suitable for transportation applications since they areenvironmental friendly and are able to start up quickly, and their modular features also makeit matches the needs of different power requirements in the occasions of household,communication and other stationary applications. Despite the basically matured keytechnologies of PEMFCs, the commercialization of them is still greatly hindered by the highcost and complexity of the system. Membrane electrode assembly （MEA）, as the keycomponent of PEMFC, not only has a great influence on PEMFC performance, but also isvery important for simplifying the device, reducing cost and speeding up thecommercialization process. It is required that MEA not only has reliable performance andreasonable price, but also has a wide operating range in order to adapt different harshenvironmental conditions. Based on these considerations, the research work on the MEA hasbeen focusing on two aspects, one is to develop low or ultra-low platinum loading MEA, andthe other is to explore self-humidification MEA, which can make it possible for PEMFCs tobe adapted to the harsh environmental conditions, especially in the absence of external or lowhumidity.To reduce the cost of PEMFCs, improve the cell performance and the applicability ofMEA in the absence of external or low humidity, in this thesis, the preparation of MEA withlow platinum loading and self-humidification ability has been investigated extensively basedon the previous works in our group.Firstly, we prepared a high performance MEA with low platinum loading, the effects ofpreparation methods of MEA catalyst layer, the composition optimization of catalyst slurryand the aftertreatment technique on the performance have been investigated. With theoptimized conditions, the low platinum loadings MEA, with0.2mg Pt/cm²at cathode sideand0.1mg Pt/cm²on the anode side, achievd the high density of ca.700mA cm^-2at0.7 V. Meanwhile, the effects of operation conditions of the single cell on the performance ofMEA also have been investigated, and some important information about the relationshipbetween the single cell operating conditions and the performance of low-platinum-loadingMEA.Secondly, we successfully developed a novel self-humidification Pt/RuO₂-SiO₂/C anodecomposite catalyst, based on our group’s study about developing a novel self-humidifyingMEA with Pt/SiO₂/C anode composite catalyst，which could improve the performance ofPEMFC operating at low humidity conditions. The characteristics of the composite catalystswere investigated by XRD, TEM and contact angle measurements. Compared to thecommercial JM Pt/C and Pt/SiO₂/C catalyst, the Pt/RuO₂-SiO₂/C catalyst with3wt.%RuO₂shows better dispersion, higher activity and hydrophility. Single cell tests showed that theMEA with3wt.%RuO₂in the composite catalyst achieved best performance withouthummudification. A long term self-humidification test for the MEA was proceesed withoutany external gas humidification at the cell temperature of50℃, the results showed that thecurrent density maintained at700mA cm^-2（at0.6V） after48hours, just with a smallattenuation.Thirdly, we also developed anovel self-humidification MEA by using aPWA/Nafion/PTFE composite membrane. The influence of the PWA content in the compositemembrane on the MEA performance was investigated by single cell tests and EIS analysis.The results showed that the best self-humidification performance could be obtained for theMEA with a composite membrane of3wt.%PWA. The current density of the MEA could behigh up to500mA cm^-2（at0.6V） after constant pressure discharge for6hours without anyexternal gas humidification at the cell temperature of50℃, indicating the good selfhumudification of the membrane. Furthmore, we also investigated the self-humidificationperformance of MEA using another SiO₂/PWA/Nafion/PTFE composite membranes with5wt.%PWA and5wt.%SiO₂, and made a comparison with PWA/Nafion/PTFE compositemembranes contain5wt.%PWA. The experimental results showed that both of the two MEAhad almost the same performance in the presence of external gas humidification. However,without any external gas humidification at the cell temperature of50℃, the former oneachieved a current density of600mA cm^-2at working-voltage of0.6V, while the later one only provided500mA cm^-2.