Direct measurement of through-plane thermal conductivity and contact resistance in fuel cell materials

Abstract

An experimental study to determine the through-plane thermal conductivity of dry Nafion ®, various diffusion media, catalyst layer, and the thermal contact resistance between diffusion media and a metal plate as a function of temperature and pressure was performed. Dry Nafion ® thermal conductivity was determined to be 0.16 ± 0.03 W m −1 K −1 at room temperature, which decreases to 0.13 ± 0.02 W m −1 K −1 at 65 °C. Diffusion media thermal conductivity was found to be function of PTFE content and manufacturer, and was 0.48 ± 0.09 W m −1 K −1 for untreated and 0.22 ± 0.04 W m −1 K −1 for 20 wt.% PTFE treated SIGRACET ® diffusion media, respectively. Toray diffusion media thermal conductivity was measured to be 1.80 ± 0.27 W m −1 K −1 at 26 °C and decreases to 1.24 ± 0.19 W m −1 K at 73 °C. The thermal contact resistance between Toray carbon paper and aluminium bronze material was determined to vary from 6.7 × 10 −4 to 2.0 × 10 −4 m 2 K W −1 for an increase in compression pressure from 0.4 to 2.2 MPa. The equivalent thermal conductivity of a 0.5 mg cm −2 platinum loaded catalyst layer was estimated to be 0.27 ± 0.05 W m −1 K −1. A one-dimensional analytical model was also used to estimate the temperature drop in the fuel cell components. A maximum of 3–4 °C temperature drop can be expected for a 200 μm thick SIGRACET ® diffusion media at 1 A cm −2. The thermal properties characterized should be useful to help modelers accurately predict the temperature distribution in a fuel cell.