Influence of Expanded Graphite Particle Size on the Properties of Composite Bipolar Plates for Fuel Cell Application

Expanded graphite-based composite bipolar plates are developed from different particle sizes of expanded graphite (EG), which are synthesized by chemical intercalation of natural graphite and sudden expansion at high temperature. The EG is synthesized from different flake sizes of natural graphite and used in the development of composite bipolar plates with novolac phenolic resin as the polymer matrix. It is found that single particle-based (small or big size) EG-resin composite plates do not give the desired properties as per US DOE target at one particular ratio of EG and resin. However, mixed EG particle based composite plates gives the desired mechanical and electrical properties with bulk density between 1.50-1.60 g.cm(-3). The addition of smaller EG particles by 10 wt.% are able to increase the electrical conductivity by similar to 100% without loosing the mechanical properties of bigger EG particle based composite plates. This enhancement is depends upon the accumulation of particles and contact boundaries within the same volume. These EG-based bipolar plates have sufficient power density for use in the polymer electrolyte membrane fuel cell, where air permeability and water absorption is negligible. The lower modulus of bipolar plates attributes that these plates are more flexible and can able to reduce the contact resistance between the components of fuel cell.