Investigation on the Structure Evolution Mechanism of the Catalyst Layer During the Hot-Pressing Process

Abstract:

The fabricating process of polymer electrolyte fuel cell membrane electrode assembly significantly affects its power generation performance， particularly the hot-pressing process. However， the internal structure evolution mechanism of the catalyst layer （CL） during the hot-pressing period is not fully understood. Therefore， the effect of the hot-pressing temperature and the treatment time on the CL structure variations is investigated in this study， utilizing orthogonal experiments， characterization， and performance analysis. Based on the scanning electron microscope data， the compressed behavior of the pore structure in the CL can been observed after the hot-pressing treatment and increasing the hot-pressing temperature and the treatment time can deteriorate this compressed effect， which is consistent with the pore diameter analysis. In addition， the secondary pores are mainly compressed. These phenomena illustrate the soften behavior of the ionomer in the CL above the glass transition temperature. Furthermore， the electrical performance analysis demonstrates the mass transfer resistance significantly increments due to the hot-pressing treatment and the mass transfer resistance increment of the CL hot-pressed at 160 ℃ for 9min is the most significant， which is 2.77 folds more than that of the CL prepared by direct spraying method and it is the result of the compressed pore structure in the CL. This study provides more sights into comprehending the effect of the ionomer thermal response behavior in the CL on the structure evolution process of the CL， and offers theoretical support for the critical parameter optimization of the hot-pressing procedure.

Key words:polymer electrolyte fuel cell;hot-press process;catalyst layer (CL);ionomer;glass transition temperature