| Proton exchange membrane(PEM)fuel cell is a kind of hydrogen energy through electrochemical reaction into electrical energy device,with the advantages of low pollution,low noise,high efficiency,easy operation,etc.,known as the fourth generation power generation technology.High-temperature proton exchange membrane fuel cell(HT-PEMFC),in which operating temperature is about 180?,is one of the proton exchange membrane fuel cell,it can reduce the poisoning of CO and other impurities,also can simplify the cell water management issues.But the toxic impurities in fuel will still cause poisoning to the cell.Electrode electrochemical reaction is the most important factor of HT-PEMFC characteristics.A large number of literatures have studied the electrode electrochemical reaction materials and the basic process by experimental method.However,the process and path of oxygen reduction reaction in the cathode of proton exchange membrane fuel cell are still less.In this thesis,the influence of toxic impurities in fuel on cell electrode impedance and the cathode oxygen reduction reaction path and reaction mechanism were studied by simulation and experiment,which provided the basis for further study and future application of HT-PEMFC.The history,characteristics and classification of fuel cells was summarized in this thesis,the structure and key components of HT-PEMFCs was introduced,and the working principle and research progress of HT-PEMFC was emphatically expounded.According to the performance characteristics of PEM fuel cell,a fuel cell test system was established.The hardware components,software components,operation steps and test methods of the test system were introduced.In the thesis,the HT-PEMFC monomer was assembled.The voltammetry and AC impedance characteristics of the HT-PEMFC were tested by using the fuel cell test system.The effects of NH3,humidification temperature and cell temperature on fuel cell performance and AC impedance spectrum were analyzed.At the equivalent circuit method was used to study the AC impedance spectrum of HT-PEMFC.The equivalent circuit and equivalent impedance components in HT-PEMFC were obtained.The effect of NH3,humidification temperature and cell temperature on the impedance of equivalent components in the fuel cell was analyzed.By analyzing the test results,it was found that the influence of NH3 in fuel on the performance of the cell gradually decreased with the increase of inlet temperature.When the cell was humidified,the poisoning effect of NH3 on the cell was slightly less than that when the cell was not humidified.With the increase of cell temperature,poisoning of the cell performance by the NH3 in the fuel gradually decreased.According to the principle of molecular dynamics,the molecular mathematical model of oxygen reaction mechanism under the catalysis of oxygen was established based on the density functional theory and the first principle.Materials Studio software was used to establish the Pt(1 1 1)surface,Pd(1 1 1)surface and oxygen molecule model of HT-PEMFC cathode catalyst.The adsorption of cathodic oxygen molecules on the Pt(1 1 1)and Pd(1 1 1)catalysts of HT-PEM fuel cells at different temperatures and the reaction of four hydrogen ions with oxygen molecules on the two catalyst surfaces was simulated respectively.The variation of energy,bond length,bond angle,reaction particle velocity and reaction particle distribution of the two catalysts were analyzed.By analyzing the data obtained by simulation,it was found that the bond length and bond angle of the water molecules of the reaction product were consistent with the actual measured values.The results show that the model and simulation methods established in the thesis were effective.The adsorption time of oxygen molecules to the catalyst layer is the longest,which is the control step of the whole reaction process.The time required for the bond length to reach equilibrium in each reaction is less than the time required for the bond angle to reach equilibrium. |
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