Laser-Perforated Carbon Paper Electrodes for High-Power Vanadium Redox Flow Batteries

Abstract

Recently, there has been considerable effort to increase the power density and lower the cost of vanadium flow battery (VRFB) systems via new system architectures and optimized electrode materials. To date, research on electrodes has primarily focused on improving the surface area, surface chemistry, pore size distribution and resistivity of the material to improve the reaction kinetics, mass transport ability and the areal series resistance (ASR).While carbon felt materials have been conventionally used, the recent push for higher power densities has required the application of new electrode materials.Carbon paper was proposed by Aaron et al. as high-performance VRFB electrode material [1]. This material has a reduced thickness and high active surface area, as compared to carbon felt, which reduces the ASR and overpotential, and significantly improves the current- and power density. In their study, the authors demonstrated a VRFB with a peak power of 557 mW cm-2 . Liu et al. further improved the performance of a VRFB with no-gap architecture by thermal pre-treatment of carbon paper electrodes in air [2]. The thermal treatment showed a 16% improvement in power density compared to the raw material.Although carbon paper electrodes exhibit significantly higher power density than carbon felt electrodes, they have a significantly lower porosity and reduced pore size. As a result, mass transport is expected to be problematic in these materials. To address these limitations, we utilized a procedure similar to Manahan et al. [3] by introducing laser perforations to facilitate the transport of reactants within this type of electrodes. A CO2 laser was employed to cut different hole patterns in SGL 10AA carbon paper. Specifically, the hole diameter and hole density (number of holes per electrode) were varied in order to better understand the tradeoffs between improved mass transport and reduced surface area in these materials. It was found that a 30% improvement in power density (as compared to non-perforated electrode) was achieved through optimization of the perforation pattern. Interestingly, this condition corresponds to a loss of 15% of the original surface area due to laser perforation. The results of this study highlight the fact that by proper tailoring the transport pathways in the electrode structure, it is possible to achieve significantly higher power density with a low surface area electrode material.