Automotive composite fuel cell bipolar plates: Hydrogen permeation concerns

Abstract

At present proton exchange membrane (PEM) performance levels and fuel cell stack operating conditions, require a plate area specific resistance of less than 30 m ohm cm 2 and a plate thickness of less than 2 mm are required to meet the vehicular volumetric power density target (>2 kW l −1). Unfortunately, it is difficult to meet these targets, and simultaneously obtain good mechanical properties and low through-thickness hydrogen permeation rates when using polymeric plate materials. Polymers are brittle at the high conductive filler concentrations (e.g. >50 v/o graphite) required for high conductivity, and are more likely to generate high convection-driven H 2 permeation rates at a high graphite loading and at a thin plate thickness. As a result, high scrap rates are realized during plate manufacturing and stacking operations, and excessive permeation rates are anticipated in pressurized stacks. This study addresses H 2 permeation concerns associated with using thin, highly-filled composite plates, and investigates factors affecting permeation such as plate temperature, thickness, graphite loading, and aging.