| Proton exchange membrane fuel cell(PEMFC)has attracted widespread attention for its advantages including high power density,quick start and so on.However,for the sluggish kinetics and high overpotential of oxygen reduction reaction(ORR)in the cathode,the expensive metai catalysts such as Pt group catalysts have long been adopted in PEMFC,making its cost expensive and limiting its commercial application.Recently,there are three main ways to reduce the amount of Pt in ORR.One of them is optimizing the preparation technology of Pt-based catalyst layer to obtain the cathodic catalyst layer with low Pt load and uniform distribution.The second one is taking advantages of alloying effect to increase the utilization rate of Pt.The third one is adopting cheap and efficient Pt-free catalysts in PEMFCs to thoroughly solve the problems of limited resource and high price of Pt.In this paper,the three ways above to reduce the amount of Pt in cathode catalyst layer were all explored.Firstly,high-activity Fe/N/C catalyst basing on the m-Phenylenediamine was prepared according to the previous way of our group.The in-plane structure design of cathodic catalyst layer was carried out for the problem of oxygen mass transfer in the catalyst layer with heavy load of Fe/N/C catalyst using laser etching to make follow channels in the catalyst layer to improve the mass transfer performance.High cell performance was obtained when the preparation of membrane electrode for Pt/C catalyst fuel ceil was investigated and optimized.On tlhis basis,the application of high activity PtCu alloy catalyst in PEMFC was preliminarily explored.The main results are as follows:(1)Although proton conductivity increased as the amount of Nafion increased in Fe/N/C cathode catalyst layer,mass transfer polarization increased rapidly.The gas diffusion channels with different depth and spacing were etched on the catalyst layer by laser etching.The mass transfer polarization in large current area was effectively alleviated by optimizing the laser etching parameters and channel size.The maximum power was able to reach 628 mW·cm-2.(2)Fine performance of fuel cell was obtained after the preparation technology of Pt-based catalyst fuel cells were explored and optimized,including Nafion content,volume ratio of isopropanol to water in catalyst slurry,different methods of preparation of catalyst layer,thermal pressure condition and thickness of gaskets used in single cell assembly.The maximum power density was close to 1600 mW·cm-2 when commercial 60%Pt/C catalyst was used in cathode.Carbon carrier helpd to disperse platinum catalyst,avoid agglomeration,improve the porosity of catalytic layer,and promote mass transfer.However,too high content of carbon carrier could increase the thickness of catalyst layer and reduce mass transfer performance.The hydrophobicity of carbon carrier was also an important factor.When the hydrophobicity was too strong,the catalyst layer as well as the proton exchange membrane couldn't be fully wetted so that the proton conduction resistance was high.Poor hydrophobicity lead to water flooding in the catalyst layer,which sharply reduced mass transfer performance.For PtCu octahedron catalyst of 5?7nm,the hydrophobicity of carbon carrier had an important influence on the cell performance.The best cell performance was obtained through proper hydrophobic functional group grafting of common carbon black.In this paper,the application of Pt-free catalysts and Pt-based catalysts in PEMFC were explored.Anew method using laser etching for constructing gas transfer channels in catalyst layer,especially the thick Pt-free catalyst layer,was presented through optimization of structure design and process parameters of the catalyst layer.The method was proved to be creative and promising as the gas transfer speed had been improved effectively. |
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