Study On Low Platinum Loading GDE And Stability Diagnosis Of HT-PEMFC

It's a trend to elevate the operate temperature of polymer electrolyte membrane fuel cell?PEMFC?to meet some technical challenges at low temperatures,such as low toleranc of carbon monoxide,complex hydrothermal manage system,low thermal value,etc.High temperature PEMFC based on phosphoric acid?H₃PO₄?doped polybenzimidazole?PBI?membrane is so far the most successful andidate in this field.However,the low efficiency of oxygen reduction reaction?ORR?in HT-PEMFC system results in the use of high amount of Pt catalyst,which greatly increased its cost and became a serious obstacle to its practical application.Therefore,it is of great significance to improve catalyst utilization efficiency,thereby reducing the use of Pt while simultaneously maintaining the superior fuel cell performance,to promot the commercialization of HT-PEMFC.In this thesis,the research and development of novel structural gas diffusion electrode?GDE?for HT-PEMFC were carried out to improve electrode reaction efficiency and reducing Pt loading.At the same time,the diagnostic method of the performance degradation of HT-PEMFC was preliminarily studied.Firstly,an attempt to lower the Pt loading and higer the performance for HT-PEMFC is made by combinating the microporous layer?MPL?-free electrode structure design with low Pt content catalyst,by which high Pt utilization and minimum mass transfer resistance can be simultaneously maintained.The results show that the electrode Pt loading can be lowered to 0.2 mg cm^-2 by this strategy but it still demonstrates a maximum Pt-specific performance of 1.6 W mg _Pt^-1 and an area-specific power density of 0.32 W cm^-2,which is a considerable improvement on developing HT-PEMFC with low Pt loading.There is a tradeoff between reducing Pt loading and increasing Pt utilization to maintain a superior catalyst layer?CL?quality,then ensuring that the fuel cell performance is fit for practical applications.Then,a novel GDE with dual-CL was made based on the difference in the degree of electrochemical reaction with the electrode of HT-PEMFC,the inner and outer layer of which used varies Pt content catalyst and binder ratio,in order to get higher Pt utilization and better interface combination of GDE/CL/polymer electrolyte membrane?PEM?.Theeffect of dual ratio on the modified CL structure on the performance of fuel cell was investigated.It is verified that the single cell with dual-CL structured GDE possesses high performance due to the decreased charge transfer resistance and the increased electrochemical surface area than that of conventional GDE with the same Pt loading,which further confirmed by the electrochemical impedance spectroscopy and cyclic voltammograms of single cell.Moreover,the modified GDE showed the highest power density of 338.26 mW cm^-2 at H₂/Air streams compared with others,and higher performance is expected to be achieved by further tuning the CL properties.Finally,we proposed an in-situ low-invasive technique of electrochemical impedance spectroscopy?EIS?,to investigate the stability of HT-PEMFC,which is suitable for judging the possible mechanism of performance degradation during short-term operation The results from the study suggests that a high cell performance decay rate cannot be directly attributed to materials degradation,especially in a short-term steady-state operation.In contrast,the change of Tafel slope could be seen as a clear indicator to determine the extent of catalyst degradation of HT-PEMFC,no matter which test protocol was applied.Postanalysis of Transmission Electron Microscopy?TEM?on the catalysts before and after tests further confirmed the main mechanism for the performance losses of the HT-PEMFC underwent two test protocols,while acid loss and membrane degradation were negligible during the short-term tests.