The Effects on the Electric Performance and Durability of CCM Catalyst Layer from Hydrophobic Agglomerant
|School||Wuhan University of Technology|
|Course||Materials Physics and Chemistry|
|Keywords||Proton exchange membrane fuel cell Catalyst layer Agglomerant Porous structure Durability|
Catalyst Coated Membrane (CCM), as the key part of the Proton Exchange Membrane Fuel Cell (PEMFC), is composed of a proton exchange membrane and two catalyst layers. Catalyst layer (CL) is mainly consisted of Pt/C catalyst and agglomerant (Nafion resin/PTFE resin), CL is the location of the electrochemical reaction in membrane electrode.The CL structure and fabrication technology can not only affect the performance of PEMFC, but also affect on reducing cost, improving power density and energy density, and accelerating the commercialization of PEMFC. At present, a main issue on hydrophilic CL of CCM is electrode-flooding. Analysis has showed that adjusting the hydrophobicity-hydrophilicity of CL can effectively alleviate electrode-flooding. In this paper, CLs of CCM were prepared by using special emulsion technique, hydrophobic-hydrophilic adjustable CLs were made by adding different content of PTFE to hydrophilic CL (wt%, Pt/C:Nafion:PTFE= 3:1:1/3). The test of contact angle, Scanning electron microscopy (SEM), pore-size distribution and porosity, single cell performance, cyclic voltammetry, Electrochemical impedance spectra (EIS), accelerated H2O2/Fe2+ -system experiment, and desiccation-moisture experiment, were used to characterize the hydrophobicity, pore structure, electric performance and durability of different CLs. In this research, conclusions had been summarized as followings:(1) In this paper, a new method of emulsion technique were invented to prepare hydrophobic-hydrophilic adjustable CLs of CCM.(2) Along with the increased content of PTFE in CLs, the hydrophobicity and the drainage capacity of CLs were improved. As a result, the electric performance of CLs with the high current density were improved. But excessive PTFE in CLs would reduce the electric performance of CLs in low current density. Comprehensive conclusion was drawn that the best components of CCM catalyst layers was No.5 sample, which was consisted of Pt/C, Nafion and PTFE with a weigt ratio of 3:1:1/3.(3) By adding PTFE to CLs, the porosity of CLs were evidently improved, and three-peak shaped pore distribution were formed in CLs.(4) The durability of CCM catalyst layers were remarkably improved by adding PTFE to CLs. The reason is that the viscidity and stability of PTFE are better than that of Nafion. Furthermore, heat treatment operating in the preparation process of hydrophobic CLs can improve the stability of Nafion.