Use of Mixed Methanesulfonic Acid/Sulfuric Acid as Positive Supporting Electrolyte in Zn-Ce Redox Flow Batter

Abstract

The effect of different positive supporting electrolytes on the performance of a bench-scale Zn-Ce redox flow battery (RFB) has been studied. The effectiveness of mixed methanesulfonic/sulfuric acid, mixed methanesulfonic/nitric acid, and pure methanesulfonic acid has been assessed and compared on the basis of the cyclic voltammetric response for the Ce(III)/Ce(IV) redox couple and galvanic charge-discharge of a bench-scale Zn-Ce RFB. The Ce(III)/Ce(IV) reaction exhibits faster kinetics and the RFB exhibits higher coulombic efficiency and long-term performance over ~40 charge-discharge cycles in the mixed 2 mol/L MSA–0.5 mol/L H2SO4 electrolyte compared to that achieved in the commonly used 4 mol/L MSA electrolyte due to lower H+ crossover and higher Ce(IV) solubility. The coulombic efficiency fade rate in the mixed MSA-H2SO4 electrolyte is 0.55% per cycle over 40 charge-discharge cycles, while the fade rate is 1.26% in the case of 4 mol/L MSA. Furthermore, the positive electrode reaction is no longer the limiting half-cell reaction even at the end of long-term battery charge-discharge operation. This work shows that a mixed MSA–H2SO4 acid electrolyte may be a better option for the positive side of a Zn-Ce RFB as a large-scale energy storage device.

Improving Performance of Hybrid Zn-Ce Redox Flow Battery by Controlling Ion Crossover and Use of Mixed Acid Positive Electrolyte

“…As shown in Figure 1A, the Zn(II) concentration in the negative electrolyte decreases steadily from 1.5 to 0.96 mol/L by the end of 30 cycles, while it increases from 0 to ~0.66 mol/L over the same period in the positive electrolyte. This change is accompanied by a rise of the H + concentration in the negative electrolyte from 1.0 mol/L to ~2.7 mol/L due to transfer from the positive side (Figure 1B), similar to that reported previously [27]. Since these determinations are made at the end of discharge, the Zn(II) concentration measured in the negative electrolyte should ideally remain at 1.5 mol/L from cycle to cycle if no metal is lost from this side of the cell.…”

“…It is not surprising then that these trends can ultimately lead to the complete failure of the battery [16]. in 2/0.5 MA (data obtained in the absence of Zn(II) was originally reported in our previous study [27]) is shown in Figure 3A. The higher coulombic efficiency achieved by switching from the 4 mol/L MSA to 2/0.5 MA supporting electrolyte can be attributed to the reduction in H + 14 concentration difference between the two sides of the membrane, leading to less crossover of H + to the negative electrolyte and lower extent of the irreversible hydrogen evolution side reaction during charge.…”

“…In previous work [27], we found that the leakage of H + from the positive to the negative side over the course of many charge-discharge cycles led to a large increase in the extent of the undesired H2 evolution side reaction during charge and consequently to a steady decay in battery capacity and performance over long-term operation. The crossover of H + from the positive to negative electrolyte has another deleterious effect in eventually causing the precipitation of CeO2 on the positive side since Ce(IV) becomes less soluble as the MSA concentration decreases.…”

“…Typically, when MSA alone has been used as the supporting electrolyte on both sides, the acid concentration is 4 mol/L on the positive side and 1 mol/L on the negative side. In a previous study, we showed that the use of a novel 2 mol/L MSA-0.5 mol/L H2SO4 mixed acid (heretofore denoted as 2/0.5 MA) positive supporting electrolyte with an overall acid concentration of only 3 mol/L, while maintaining 1 mol/L MSA alone as the negative supporting electrolyte, led to a large improvement in the performance of a Zn-Ce RFB from that attained when the positive supporting electrolyte contained 4 mol/L MSA [27]. Another benefit of using this mixed acid positive electrolyte was that CeO2 6 precipitation was not observed to occur even after many galvanostatic charge-discharge cycles, unlike what is always found in the case of the MSA-only electrolyte initially containing 4 mol/L.…”

Methanesulfonic acid (MSA) in clean processes and applications: a tutorial review

“… 171 The use of elevated temperatures is required to boost the sluggish kinetics of the cerium( iv )/cerium( iii ) redox couple. 172 On the other hand, from the point of view of the critically of the materials, the zinc-cerium RFB is advantageous. Zinc and cerium are both earth-abundant elements.…”