Impact of Clamping Force Distribution on Loss Processes in a Segmented PEMFC

Abstract

The operation of large-scale polymer electrolyte membrane fuel cells (PEMFC) inevitably leads to significant spatial gradients along the gas channels. Depending on the local operating conditions, the physicochemical processes and thus also the resistances in the cell vary, which in turn determine the local performance. In addition, design parameters such as the spatial clamping force distribution have a significant influence on the ohmic contact resistance and the compression of the porous layers and thus the diffusion resistance. Thereby, the influences of these factors on the corresponding resistances are opposite to each other, resulting in conflicting objectives.To enable an optimization of the operating strategy and the component design, a quantification of the local resistances and their dependencies is essential.This requires a measurement setup that allows the precise adjustment of the operating conditions and contact pressure along the gas channel, as well as a measurement and analysis method that identifies and quantifies the locally occurring processes.For this purpose, we are applying electrochemical impedance spectroscopy (EIS) on a segmented cell. In this cell the local clamping force is individually adjusted and continuously measured for each segment enabling measurements at constant clamping force as well as selectable clamping force distributions. The local performance limiting loss processes within the cell are separated by the distribution of relaxation times (DRT) and quantified by a physico-chemical meaningful transmission line model (TLM) as a function of local operating conditions and clamping force [1, 2, 3].In this contribution an experimental analysis of the ohmic, charge transfer and diffusion resistances will be presented. The impact of contact pressure distribution and operating conditions on resistances and their distribution along the gas channels will be discussed. Furthermore, it is demonstrated how the performance can be optimized by adjusting the contact pressure distribution along the gas channel.1. H. Schichlein et al., J. Appl. Electrochem. 32, pp. 875-882 (2002).2. E. Ivers-Tiffée et al., J. Ceram. Soc. Japan 125, pp. 193-201 (2017).3. M. Heinzmann et al., J. Power Sources 558, 232540 (2023).