Automotive composite fuel cell bipolar plates: Hydrogen permeation concerns

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 cm2 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 H2 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 H2 permeation concerns associated with using thin, highly-filled composite plates, and investigates factors affecting permeation such as plate temperature, thickness, graphite loading, and aging.