Preparation Of Platinum Nanowire Catalytic Layer And Its Effect On The Performance Of Proton Exchange Membrane Fuel Cells

With the serious environmental pollution and the shortage of fossil energy,the development and utilization of renewable and sustainable energy has received more and more attention.The proton exchange membrane fuel cell is a device that directly converts chemical energy into electrical energy by chemical reaction at the electrode.It has the advantages of high energy density,low working temperature,fast startup,and environmental protection,and has broad application prospects.High performance and low cost are the development direction.Cathodes require high Pt loading to catalyze slow and rate-limiting oxygen reduction reactions,which are major factors limiting their development.At present,the zero-dimensional structure and high surface area of commercial Pt/C are prone to agglomeration and particle growth leading to a decrease in activity.The one-dimensional structure of Pt nanowires has inherent structural features,such as anisotropy of high-activity crystal planes and preferential exposure,which is the most promising method for reducing the Pt content and increasing the catalytic activity.The research of this work is mainly focused on improving the cathode Pt nanowire catalytic layer structure and improving the Pt utilization rate and battery performance.In this paper,the Pt nano wires were in-situ grown on the substrate by wet chemical method to prepare a gradient Pt nanowire catalytic layer.Membrane electrodes were then prepared by CCS method for testing and characterization.The effects of different conditions on the growth and distribution of Pt nano wires were analyzed,and the mechanism of the influence of catalytic layer structure on the performance of single cells was discussed.The main research xwork carried out:(1)The effects of reducing agent concentration and reaction temperature on the morphology and distribution of Pt nanowires on carbon substrates were studied,and the distribution of Pt nanowires in the catalytic layer was improved.The concentration of the reducing agent mainly affects the length of the Pt nanowire,and the reaction temperature mainly af-fects the diameter of the Pt nanowire.Optimal performance was obtained at the formic acid concentration of 0.372 M and the temperature of 20℃.The self-made catalyst with a Pt loading of 0.3 mg cm-2 had a power density of about 13.9%higher at 0.6 V than the commercial Pt/C catalyst of the same conditions.(2)The Pt particle seed is introduced into the matrix to obtain a mixed substrate,and the nanowire having a controlled size and distribution is obtained by a seed-mediated method,thereby improving the utilization of platinum while shortening the reduction time.The effect of Pt seed distribution on the growth of nano wires in Pt/C and carbon mixed matrix was investigated.By maintaining a constant Pt seed content,the Pt/C species and carbon content were varied to adjust the distribution of seeds in the carbon and matrix.The Pt nanowire catalytic layer obtained using 20 wt%Pt/C and having a carbon content of 0.15 mg cm-2 has the best performance.The self-made catalytic layer with a Pt loading of 0.255 mg cm-2 had a power density of about 25%higher at 0.6 V than a commercial Pt/C loaded with 0.3 mg cm-2.(3)The effect of Nafion content in the mixed substrate and the Nafion loading on the surface of the catalytic layer was investigated.The optimum performance was obtained with a Nafion content of 20 wt%in the mixed substrate and a surface spray loading of 0.10 mg cm-2.The self-made catalytic layer with a Pt loading of 0.255 mg cm-2 obtained a power density at 0.6 V that is about 25%higher than the commercial Pt/C with a Pt loading of 0.3 mg cm-2 and about 30%higher at 0.4V.The performance of the self-made catalytic layer was further improved in the high current density region,indicating that the mass transfer performance was further improved.