Abstract
A new flow battery is presented using the abundant and inexpensive active material pairs permanganate/manganate and disulfide/tetrasulfide. A wetted material set is identified for compatibility with the strongly oxidizing manganese couple at ambient and elevated temperatures. Both solutions allow high active material solubility, with cells tested at theoretical energy densities up to 43 Wh l−1 for the ∼1.2 V cell. Full cells built with nickel foam electrodes and sodium-exchanged Nafion 115 membranes deliver a baseline area-specific resistance of 2.7 Ω-cm2. Incorporation of high-surface-area cobalt-coated carbon paper and high-surface-area stainless steel mesh electrodes, and an expanded Nafion 115 membrane delivers cells with 44% lower resistance at 1.6 Ω-cm2. All cells show performance decay over the course of cycling. The Co-decorated carbon paper electrodes provide significant kinetic improvements, shifting electrode performance from non-linear with Ni-foam to linear with a volume-normalized exchange current density value of 3.2 A cm−3. The expanded membrane provides increased conductivity over the 13 mS cm−1 conductivity observed in as-received, sodium-exchanged Nafion 115. Although boiled membranes provide improved conductivity, it is at the cost of decreased Coulombic efficiency and poorer manufacturability. Full cell models suggest that similar cell resistances (1.7 Ω-cm2) should be feasible with as-received Nafion 115 and advanced electrodes.
Highlights
To cite this article: Zhiwei Yang et al 2021 J
The S-Mn redox flow batteries (RFBs) described relies on polysulfide reactions nominally ranging between the disulfide and tetrasulfide species for the negative electrolyte as described in Reaction 1
Negative couples can lead to hydrogen generation as observed with the chromium couple in iron-chrome systems,[23] or strongly positive couples can lead to carbon or membrane oxidation as evidenced with vanadium systems.[24]
Summary
To cite this article: Zhiwei Yang et al 2021 J. The more rapid self-discharge of solutions in contact with the conductive materials must be considered for cells that can deliver high SOC positive electrolytes. Baseline cell performance using Ni foam electrodes.—Porous nickel foam was reported to effectively catalyze the polysulfide redox reaction,[25,26] and can support the permanganate reduction reaction at reasonably high rates.[14] The first polysulfide—permanganate (pS-Mn) flow battery cell is demonstrated using Ni foam as both anode and cathode electrodes and AR-Na N115 as membrane.
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