Reticulated Carbon Electrodes for Improved Charge Transport in Electrochemical Flow Capacitors

Abstract

In this study, we report on an approach to flow cell design that can enable a significantly improved power output (∼10x) for electrochemical flow capacitors (EFCs), even at large flow channel gaps. Reticulated vitreous carbon (RVC) electrodes of various average pore sizes (0.43–2 mm) were integrated into EFC flow cell fixtures with channel gaps of 5 mm. Electrochemical testing under flow conditions showed a 10-fold improvement in the power density with the RVC integration (290 W/m2, 580 W/kg) for the same slurry composition. This improvement was mostly attributed to the presence of a 3D porous electrode insert (i.e., RVC) that shortened the travel distance of the electrons to the current collectors. Pressure drop in the RVC containing cells was also investigated and found to increase up to 30% depending on the pore size. However, this increase was found to be offset by the increase in the channel depth, yielding almost no change in pressure as compared to conventional narrow-gap (>0.75 mm) flow channels. RVCs having an average pore size of 0.55 mm showed the best performance out of all studied cases with improved coulombic efficiency and good specific capacity (85 F/g) under flowing conditions.