| Proton exchange membrane(PEM)fuel cell has become a promising electrochemical energy conversion device because of its high reliability,rapid response and low pollutant emission.However,the extensive commercialization of PME fuel cells urgently needs further performance improvement and cost reduction.As a place for transporting reactants and removing products,the structure of bipolar plate(BP)flow field has an important impact on gas transportation and water management in fuel cell.A well-designed flow field can effectively and timely remove the liquid water produced in the fuel cell,greatly improve the concentration of reactants at the three-phase interface of the catalyst layer,and improve the overall output performance of the fuel cell.However,there are still many deficiencies in the experimental research of bipolar plate flow field,especially for the water management of flow field,it is difficult to evaluate by experimental means.Therefore,this paper adopts the current density scanning method to evaluate the flow field water management by testing the dynamic change of fuel cell current density distribution.On this basis,combined with the simulation method,the water management characteristics of the flow field with baffle are studied.The specific research contents are as follows:(1)Experimental verification of water flooding diagnosis method: through experiments,the current density scanning method is applied to the water flooding diagnosis of fuel cell,and combined with electrochemical AC impedance spectroscopy,the feasibility of current density scanning method in water flooding diagnosis is verified.On this basis,the variation laws of total current,voltage and current density with time in serpentine flow field under constant current and constant voltage modes are studied.The results show that this method can monitor the flooding state in real time and quantify the impact of local flooding on fuel cells.(2)Simulation of trapezoid baffle flow field: This paper proposes an improved method of adding trapezoid baffle in parallel flow channel,and studies and compares the performance differences between parallel flow field and trapezoid baffle flow field based on three-dimensional multiphase flow fuel cell model.Through the detailed analysis of the output performance of the two flow fields,the gas flow rate in the flow channel,the liquid water content in the diffusion layer and the reactant concentration distribution in the catalyst layer,the advantages of the flow field improvement method are verified,and the mechanism of trapezoid baffle flow field to improve the performance of fuel cell is expounded.(3)Experimental study on trapezoid baffle flow field: in order to comprehensively evaluate the actual state of the whole flow field plate during operation,graphite bipolar plates with parallel flow field and trapezoid baffle flow field were processed respectively.Combined with the output performance of fuel cell,inlet and outlet pressure drop of flow field and current density distribution,the effects of trapezoid baffles with different heights on fuel cell performance improvement and water management were compared and studied.Based on this experiment,a flow field optimization method of arranging trapezoid baffles in different regions is proposed,which not only ensures good water management performance,but also improves the net output power of fuel cell. |
PDF Full Text Request