Laser-perforated carbon paper electrodes for improved mass-transport in high power density vanadium redox flow batteries

• Laser-perforated carbon paper electrodes are tested in vanadium flow batteries.
• Effects of perforation size, spatial density, and flow rate are investigated.
• Power density of perforated electrodes is improved (30%) compared to raw electrodes.
• Performance improvement is attributed to the enhanced electrolyte accessibility.

In this study, we demonstrate up to 30% increase in power density of carbon paper electrodes for vanadium redox flow batteries (VRFB) by introducing perforations into the structure of electrodes. A CO2 laser was used to generate holes ranging from 171 to 421 μm diameter, and hole densities from 96.8 to 649.8 holes cm−2. Perforation of the carbon paper electrodes was observed to improve cell performance in the activation region due to thermal treatment of the area around the perforations. Results also demonstrate improved mass transport, resulting in enhanced peak power and limiting current density. However, excessive perforation of the electrode yielded a decrease in performance due to reduced available surface area. A 30% increase in peak power density (478 mW cm−2) was observed for the laser perforated electrode with 234 μm diameter holes and 352.8 holes cm−2 (1764 holes per 5 cm2 electrode), despite a 15% decrease in total surface area compared to the raw un-perforated electrode. Additionally, the effect of perforation on VRFB performance was studied at different flow rates (up to 120 mL min−1) for the optimized electrode architecture. A maximum power density of 543 mW cm−2 was achieved at 120 mL min−1.