PDF Publication Title:
Text from PDF Page: 013
Energies 2021, 14, 5643 13 of 45 Vanadium-Polyhalide Redox Flow Battery (G2 RFB) RFBs are well known for their long working life and decoupled power and energy. However, one of their major drawbacks is their low energy density, which ultimately limits their commercial application for stationary storage. A possible strategy to increase this parameter is to increase the solubility of the redox species in the solvent and therefore to store more energy in the same volume of electrolyte. Accordingly, it was proposed that a vanadium–halide solution (HBr and HCl) electrolyte could achieve higher solubilities for vanadium ions, the reactions for which are indicated in Equations (1)–(3) [73–75]. Negative Side : Positive Side : Positive Side : 2VCl3+ 2e− 2VCl2 + 2Cl− (1) 2Br−+ Cl− ClBr2− + 2e− (2) Br−+ 2Cl− BrCl2−+ 2e− (3) A typical electrolyte is composed of 7–9 M HBr with 1.5–2 M HCl and 2–3 M vanadium. Due to the higher solubility of vanadium bromide, the volume of the positive half-cell elec- trolyte tank can be severely reduced, leading to an enhanced specific energy of 25–50 Wh kg−1 and an energy density in the range of 35–70 Wh L−1 [77]. Additionally, since a mixed solution of V/HBr/HCl is used in both half-cells, the long-term issues associated with cross-contamination through the membrane are mitigated [77,101,102]. Another interesting feature about this configuration is that since there is no V(IV)/V(V) pair on the positive side, this battery does not suffer from the limited solubility of V5+ at high temperatures, increas- ing the temperature range of operation to 0–50 ◦C [79]. However, the possibility of bromine vapor formation is one of the major drawbacks of this configuration. To minimize this, it is common to use complexing agents such as tetrabutylammonium bromide, polyethylene glycol, N-methyl-N-ethyl morpholinium bromide, and Nmethyl-N-ethyl pyrrolidinium. As consequence, a feature of G2 RFBs is the formation of a second phase composed of the bromine complexing agents during the cell charge step [101–103]. Despite the effort to produce and to screen more efficient components for this technology [77,104], these complexing agents are too expensive and still represent a significant economical barrier. The development of more cost-effective alternatives to prevent the bromine evolution are mandatory for the commercialization of the G2 RFB [101–103]. Mixed Acid Vanadium Redox Flow Battery (G3 RFB) Another way to optimize the solubility of redox species is to use electrolyte additives to thermodynamically increase the solubility threshold and therefore to improve the kinetics, stability, and energy density of redox flow batteries. It is known that vanadium ions V2+, V3+, and VO2+(i.e., V4+) precipitate as its sulfate salts at low temperatures through the exothermal reactions represented by Equations (4)–(6) [4,38,105]: SO2− + V2+ → VSO4 (4) 4 3SO2−+2V3+ →V2(SO) (5) 443 SO2−+VO2+ → VO(SO4) (6) 4 However, VO2+ (i.e., V5+) does not precipitate as a sulphate salt but it reacts with water in an endothermal reaction [4,38,105]: 2VO2+ +H2O → V2O5 +2H+ (7) Therefore, increasing temperature will increase the solubility of vanadium salts but will also shift Equation (7) to the right, reducing the amount of V5+ dissolved. This leads to a tradeoff situation where higher temperatures will favor the solubility of V2+, V3+, and V4+ but will disfavor the solubility of V5+.PDF Image | PNNL Vanadium Redox Flow Battery Stack
PDF Search Title:
PNNL Vanadium Redox Flow Battery StackOriginal File Name Searched:
energies-14-05643-v2.pdfDIY PDF Search: Google It | Yahoo | Bing
Salgenx Redox Flow Battery Technology: Salt water flow battery technology with low cost and great energy density that can be used for power storage and thermal storage. Let us de-risk your production using our license. Our aqueous flow battery is less cost than Tesla Megapack and available faster. Redox flow battery. No membrane needed like with Vanadium, or Bromine. Salgenx flow battery
| CONTACT TEL: 608-238-6001 Email: greg@salgenx.com | RSS | AMP |