Carbon Aerogel Based Thin Electrodes for Zero‐Gap all Vanadium Redox Flow Batteries – Quantifying the Factors Leading to Optimum Performance

Direct growth of resorcinol−formaldehyde carbon aerogels (CAGs) on carbon paper electrodes was achieved using a new approach. Materials with variations in density, mesoporosity and microporosity were prepared. Microstructural properties of the resultant thin electrodes are shown to directly influence performance in zero‐gap redox flow battery (RFB). BET analysis shows a total surface area between 643 to 931 m2 g−1. Deposition of only ≈15 wt.% CAG on the carbon electrode leads to a 320‐fold increase in electrochemical surface area. Analysis of the results saw a strong positive correlation of RFB performance with surface area. The best performing electrodes had a good balance between microporous and external surface area, and on the macroscopic scale had sufficiently large pores to allow efficient electrolyte permeation. The poorest performing electrodes which had the highest surface area, also had poor macroscopic porosity leading to large mass transport and solution resistance losses. The best performing electrodes were tested in a zero‐gap setup using polarization curves, showing a 25 % increase in power density at 100 mA cm−2 and a peak power density of 706 mW cm−2 at 1 V using thin electrodes. Carbon Aerogels Porosity Optimisation: Different synthetic conditions for the growth of carbon aerogels (CAGs) over a carbon paper electrode were explored, in order to understand the performance in a thin electrode Zero‐Gap all Vanadium Redox Flow Battery. To understand the performance of the electrodes prepared, polarization curves and galvanostatic charge/discharge experiments were performed. As a result, the best performing electrode prepared, shows a very high volumetric power density and electrolyte utilisation.