Enhanced performance and durability of composite bipolar plate with surface modification of cactus-like carbon nanofibers

To sufficiently improve the electrical conductivity of composite bipolar plates is crucial for their application in fuel cells and redox flow batteries. Eliminating the resin-rich layer on the surface of composite bipolar plates turns to be an effective approach. In this work, graphite/resin composite bipolar plates with advanced performance and durability are obtained after surface treatment with cactus-like carbon nanofibers which grow from the catalyst cores and stretch out to form cactus-like structures. Morphology and structure of the carbon nanofibers, as well as the morphology, electrical conductivity, electrochemical properties and charge-discharge performance of the bipolar plates in a vanadium redox flow battery (VRFB) are investigated. Results show that surface treatment with graphitized cactus-like carbon nanofibers significantly enhance the conductivity of the composite plates which reaches as high as 198.7 S cm⁻¹, and the area specific resistance can be reduced to 25.4 mΩ cm². The VRFB single cell with the modified bipolar plate exhibits very high energy efficiency of 86.28%, at 100 mA cm⁻², and shows excellent durability in charge-discharge cycling test. With the superior properties above, composite bipolar plates after surface treatment with cactus-like carbon nanofibers are promising candidates for VRFBs.