Evaluation of carbon composite materials for the negative electrode in the zinc–cerium redox flow cell

An investigation into the suitability of three carbon composites as substrates for the negative electrode in the zinc–cerium redox flow cell has been carried out. The composite electrodes examined comprised the use of polyvinylidene fluoride (PVDF) and high density polyethylene (HDPE) as binders for the carbon and the third was a graphite foil electrode of ∼1 mm thickness. The zinc deposition process was carried out in a methane sulfonic acid (MSA) electrolyte at 60 °C and nucleation studies revealed the growth of the deposits to be instantaneous in this medium. Galvanostatic charge/discharge cycles were performed in order to test the performance of these composite materials under a variety of operating conditions. For all the materials, the highest charge/discharge coulombic efficiencies (∼95%) were found for the highest discharge current densities (200 mA cm−2) employed in the study but this falls as the charge period is increased. The effect of solution flow velocity is however less clear. Prolonged zinc charging–discharging cycling on the composite materials revealed that whereas the PVDF-based electrode exhibited no loss in efficiency with cycling (>250), a drastic reduction was observed for the HDPE-based and graphite foil electrodes beyond 70 cycles and this was accompanied by the physical deterioration in the electrode surface.