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The effect of phosphate additive on the positive electrolyte stability of vanadium redox flow battery 被引量:2
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作者 Fengyu Tian Lei Wang Chang-Sheng Wang 《Journal of Energy Chemistry》 SCIE EI CAS CSCD 2018年第5期1376-1380,共5页
The electrolyte is one of the most important components of vanadium redox flow battery (VRFB). and its stability and solubility determines the energy density of a VRFB. The performance of current positive elec- trol... The electrolyte is one of the most important components of vanadium redox flow battery (VRFB). and its stability and solubility determines the energy density of a VRFB. The performance of current positive elec- trolyte is limited by the low stability of VO2+ at a higher temperature. Phosphate is proved to be a very effective additive to improve the stability of VO2+. Even though, the stabilizing mechanism is still not clear, which hinders the further development of VRFBs. In this paper, to clarify the effect of phosphate additive on the positive electrolyte stability, the hydration structures of VO2+ cations and the reaction mechanisms of precipitation with or without phosphate in the supporting electrolyte of H_2SO_4 solutions were investigated in detail based on calculations of electronic structure. The stable configurations of com- plexes were optimized at the B3LYP/6-311 + G(d,p) level of theory. The zero-point energies and Gibbs free energies for these complexes were further evaluated at the B3LYP/aug-cc-pVTZ level of theory. It shows that a structure of [VO_2(H_2O)_2]+ surrounded by water molecules in H2S04 solution can be formed at the room temperature. With the temperature rises, [VO_2(H_2O)_2]+ will lose a proton and form the interme- diate of VO(OH)_3, and the further dehydration among VO(OH)_3 molecules will create the precipitate of V_2O_5. When H_3PO_4 was added into electrolytes, the V-O-P bond-containing neutral compound could be formed through interaction between VO(OH)_3 and H_3PO_4, and the activation energy of forming the V-O-P bond-containing neutral compound is about 7 kcal tool-1 lower than that of the VO(OH)_3 dehydration, which could avoid the precipitation of V_2O_5 and improve the electrolyte stability. 展开更多
关键词 all vanadium redox flow battery Phosphate additive Density functional theory Transition state Reaction mechanism
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Optimized the vanadium electrolyte with sulfate-phosphoric mixed acids to enhance the stable operation at high-temperature
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作者 Ling Ge Tao Liu +1 位作者 Yimin Zhang Hong Liu 《Frontiers of Chemical Science and Engineering》 SCIE EI CSCD 2024年第2期13-26,共14页
Herein, the influence of the concentration design and comprehensive performance of the sulfate-phosphoric mixed acid system electrolyte is investigated to realize an electrolyte that maintains high energy density and ... Herein, the influence of the concentration design and comprehensive performance of the sulfate-phosphoric mixed acid system electrolyte is investigated to realize an electrolyte that maintains high energy density and stable operation at high temperatures. Static stability tests have shown that VOPO4 precipitation occurs only with vanadium(V) electrolyte. The concentration of vanadium ion of 2.0–2.2 mol·L^(–1), phosphoric acid of 0.10–0.15 mol·L^(–1), and sulfuric acid of 2.5–3.0 mol·L^(–1) are suitable for a vanadium redox flow battery in the temperature range from –20 to 50 ℃. The equations for predicting the viscosity and conductivity of electrolytes are obtained by the response surface method. The optimized electrolyte overcomes precipitation generation. It has 2.8 times higher energy density than the non-phosphate electrolyte, and a coulomb efficiency of 94.0% at 50 ℃. The sulfate-phosphoric mixed acid system electrolyte promotes the electrode reaction process, increases the current density, and reduces the resistance. This work systematically optimizes the concentrations of composition of positive and negative vanadium electrolytes with mixed sulfate-phosphoric acid. It provides a basis for the different valence states and comprehensive properties of sulfate-phosphoric mixed acid system vanadium electrolytes under extreme environments, guiding engineering applications. 展开更多
关键词 all vanadium redox flow battery mixed-acid vanadium electrolyte concentration optimization response surface methodology high-temperature stability
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