In the upcoming hydrogen era, it is necessary to implement high operando stability in terms of the polymer electrolyte fuel cell (PEFC) stack. The U.S. Department of Energy (DOE) lifetime targets, which are currently the global leading standards in the fuel cell, are 4,000-8,000 hours and 40,000-80,000 hours for automotive and stationary PEFC systems, respectively [1]. The standard PEFC electrode is hot-pressed in the dry state at higher operating temperatures and pressures (150-210 ℃ and 30-60 bar) which have been reported by several pioneering research groups including Los Alamos National Laboratory [2]. This resulted in an increased interfacial resistance at the Pt-ionomer interfaces, due to excessive heat and pressure applied during the hot-pressing process. In particular, an increased interfacial resistance between the catalyst layer and ionomer membrane adversely affects the cell performance as well as operando stability; it is thus imperial to gain further reduced interfacial resistances while maintaining the operating temperatures and pressures at a much lower level. In this study, we succeeded in transfer 1,5-pentanediol based binary-solvent-mixture (BSM) was used as a wet solvent to perform the wet decal transfer method (WDTM) at lower temperatures and lower pressures of 110 °C and 3 bar. Firstly, to adopt an appropriate BSM for the swelling agent at wet solvent, BSM was dispersed for 1 h through a homogenizer by 1,5-pentanediol concentration and temperature and time were screened to determine the relationship between the solvent and the side chain length. After that, dry state transfer MEA and wet state transfer MEA were transferred at the optimum temperature and pressure, respectively, and it was confirmed that the catalyst layer and the decal catalyst layer of wet state transferred MEA were almost the same thickness through a cross-sectional scanning electron microscope (SEM) image. Herein, we confirmed BSM as a wet solvent for swelling agent improves the mobility of ionomers distributed in the catalyst layer and membrane, and this makes it possible to obtain a very high level of transfer ratio of about 99% at low temperature and low pressure. The pore distribution and porosity in each MEA state were also confirmed through surface SEM images and porosimetry, and the definition between micro-pores and mass transfer resistance was investigated through polarization curves and electrochemical impedance spectroscopy (EIS). In addition, through wet transfer at low temperature and low pressure, the high-frequency resistance (HFR) of the membrane decreased by 5 to 10 mΩ cm², which can be regarded as reduced interfacial resistance between the catalyst layer and the ionomer. Finally, the in-situ EIS was analyzed during the operando stability test during 200 h operation to specify the main cause of reduction in performance decay. Given the significant improvements in the long-term stability, this work may draw an important step towards an advanced manufacture technology for PEFC electrode for stationary applications.

[Reference]

1. A. Kannan, J. Kaczerowski, A. Kabza and J. Scholta, Fuel Cells, 18.3, 287 (2018).

2. M. S. Wilson, J. A. Valerio and S. Gottesfeld, Electrochimica Acta, 40.3, 355 (1995).