Evaluation of a Non-Aqueous Vanadium Redox Flow Battery Using a Deep Eutectic Solvent and Graphene-Modified Carbon Electrodes via Electrophoretic Deposition

Abstract

Common issues aqueous-based vanadium redox flow batteries (VRFBs) face include low cell voltage due to water electrolysis side reactions and highly corrosive and environmentally unfriendly electrolytes (3 to 5 M sulfuric acid). Therefore, this investigation looks into the comparison of a highly conductive ionic liquid with a well-studied deep eutectic solvent (DES) as electrolytes for non-aqueous VRFBs. The latter solvent gives 50% higher efficiency and capacity utilization than the former. These figures of merit increase by 10% when nitrogen-doped graphene (N-G)-modified carbon papers, via a one-step binder-free electrophoretic deposition process, are used as electrodes. X-ray computed tomography confirms the enhancement of electrochemical surface area of the carbon electrodes due to N-G while electrochemical impedance spectra show the effect of its higher conductivity on improving RFB performance. Finally, potential strategies for the scaling-up of DES-based VRFBs using a simple economical model are also briefly discussed. From this study, it is deduced that more investigations on applying DESs as non-aqueous electrolytes to replace the commonly used acetonitrile may be a positive step forward because DESs are not only cheaper but also safer to handle, far less toxic, non-flammable, and less volatile than acetonitrile.

Reline deep eutectic solvent as a green electrolyte for electrochemical energy storage applications

“…DESs share many characteristics with ILs 30 but their low cost makes them particularly attractive in many applications, including electrolytes for energy devices. Due to their unique properties, despite their extremely high cost, ILs found a wide range of applications in various electrochemical devices including lithium-ion batteries, [31][32][33] fuel cells, 34 dye-sensitized solar cells, 35 etc. Like ILs, DESs were also used in electrochemistry as electrolytes for supercapacitors (SCs) due to their wider electrochemical stability window, which increases the energy density of SCs.…”

Modern practices in electrophoretic deposition to manufacture energy storage electrodes

“…Recently, the EPD of nitrogen‐doped graphene (N‐G) on carbon paper electrodes (CP) has been reported by WMG to enhance the performance of non‐aqueous VRFBs applying deep eutectic solvents (DESs) 113 as well as three different RFCs employing either highly acidic or alkaline electrolytes (Figure 12A). 209 In the first investigation, the DES‐based VRFB was subjected to about 20 cycles to evaluate its temporal fluctuation of efficiencies and utilization 113 . Figure 12B, which was reconstructed from x‐ray tomographic scans, clearly shows the N‐G occupying the porous CP electrode, which was considered responsible for the enhanced improvement of the N‐G/CP electrode in comparison to the pristine CP electrodes in the DES‐based VRFB.…”

Deep eutectics and analogues as electrolytes in batteries

“…No attempts will be made to cover DES electrolyte applications in supercapacitors, [91][92][93][94][95][96][97][98][99][100][101] dye sensitized solar cells (DSSCs), [102][103][104][105][106] and redox flow batteries. 25,[107][108][109][110][111][112][113][114][115][116][117] Note that, for the reasons explained above, we will include all eutectic mixtures, regardless of the solid or liquid state at above-ambient temperatures of the constituents in their pure states, and of whether a deviation from ideality has been demonstrated. Solid and semi-solid electrolytes based on DES and polymer or selfassembling molecules will not be reviewed, but briefly mentioned in the outlook section.…”