Study On Composition And Performance Of Membrane Electrode For Proton Exchange Membrane Fuel Cells

The proton exchange membrane fuel cell (PEMFC) is a highly attractivepower source for mobile and stationary applications due to its high power densityat lower temperatures and its compact design. At present, a large amount of workhas been devoted to reduce the material costs of PEMFCs to achieve theirwidespread application, including the method of preparing Pt catalyst with a largespecific surface area to minimize the amount (and cost) of Pt required for a givenlevel of activity.This paper presents a detailed study of the impregnation-reduction methodfor the preparation of Supported Pt/C catalysts;TEM results showed that Pt/Ccatalyst with a higher dispersion and a very narrow size distribution (2.6³.8nm)of Pt metal particles was achieved. XRD analysis showed that Pt-Pt neighboringdistances of the three Pt crystal faces were reduced, which is favorable for thedissociative adsorption of oxygen and also for the increase of the catalyticactivity of Pt/C catalysts. The electrochemical characteristics of the Pt/C catalystswere evaluated from voltage -current density curves of the MEA. The resultshows that the electrocatalytic activity of the Pt/C catalysts prepared in the workis better than that of Johnson Mattey Pt/C catalyst.Two kinds of new pore-forming agents, NH4HCO3 and (NH₄)₂SO₄, werestudied in this paper. The results showed that the electrochemical performance ofMEA with suitable amount of NH4HCO3 additive was improved obviously for airand oxygen operations. The cell voltage of MEA with suitable amount of(NH₄)₂SO₄ additive was increased at large current densities for air operations.The pore structure of the catalyst layer in a MEA was investigated by theenvironmental scanning electron microscopy (ESEM) method, and themeasurement results showed that higher porosities were obtained in the catalystlayer with the two additives. This was of benefit to enhance the mass transfer ofoxidants and utilization of catalysts.The technique of preparing MEA with Nafion1135 membrane has also beenstudied in this paper, the structure of gas diffusion layer (GDL) has been designedand optimized, when carbon content in GDL is 3mg/cm², MEA exhibits the bestperformance. The primary study showed that MEA with GDL has capability ofadjusting water, and the highest power density achieved to 0.66W/cm², while thetemperature of reaction gas is 25℃.