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Research Papers

Effect of Phosphate Additive for Thermal Stability in a Vanadium Redox Flow Battery

[+] Author and Article Information
Sun-Hwa Yeon

Energy Storage Laboratory,
Korea Institute of Energy Research,
102, Gajeong-ro, Yuseong,
Daejeon 305-343, South Korea
e-mail: ys93@kier.re.kr

Jae Young So

Energy Storage Laboratory,
Korea Institute of Energy Research,
102, Gajeong-ro, Yuseong,
Daejeon 305-343, South Korea;
Department of Energy Engineering,
Hanyang University,
222, Wangsimni-ro, Seongdong-gu,
Seoul 133-791, South Korea

Jin Hee Yun, Se-Kook Park, Chang-Soo Jin

Energy Storage Laboratory,
Korea Institute of Energy Research,
102, Gajeong-ro, Yuseong,
Daejeon 305-343, South Korea

Kyoung-Hee Shin

Energy Storage Laboratory,
Korea Institute of Energy Research,
102, Gajeong-ro, Yuseong,
Daejeon 305-343, South Korea

Yun Jung Lee

Department of Energy Engineering,
Hanyang University,
222, Wangsimni-ro, Seongdong-gu,
Seoul 133-791, South Korea

1Corresponding author.

Manuscript received July 14, 2017; final manuscript received September 20, 2017; published online October 17, 2017. Assoc. Editor: Kevin Huang.

J. Electrochem. En. Conv. Stor. 14(4), 041007 (Oct 17, 2017) (11 pages) Paper No: JEECS-17-1088; doi: 10.1115/1.4038019 History: Received July 14, 2017; Revised September 20, 2017

Organic/inorganic materials are investigated as additives to improve the stability of a vanadium electrolyte for a vanadium redox flow battery (VRFB) at operating temperatures of 25 °C and 40 °C. Among these materials, the most effective additive is chosen based on the thermal stability and electrochemical performance with a long inhibition time. Through precipitation time and electrochemical measurements, the results show that the best inhibition effect is achieved by adding sodium pyrophosphate dibasic (SPD, H2Na2O7P2) as an additive at a considerably high H2SO4 concentration (3M) electrolyte, indicating an improved redox reversibility and electrochemical activity. Nonflow cell assembled with the SPD additive exhibits larger discharge capacity retentions of 40% than a blank solution with the retentions of 2% at 600 cycles at 40 °C. In the case of flow cell, the capacity retention on the SPD additive shows 55.4%, which is 5.3% higher than the blank solution at 40 °C and 180 cycles. The morphology of the precipitation is investigated by SEM, which exhibits more severe V2O5 precipitation amount on the carbon felt electrode used in the blank electrolyte at 40 °C, which causes larger capacity losses compared to cells assembled with the SPD additive electrolyte.

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References

Figures

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Fig. 1

VRFB flow cell configuration for electrolysis reduction: composition ((A): supporting plate, (B): copper collector, (C): graphite polar plate, (D): manifold (poly propylene), (E): carbon felt, (F): ion exchange membrane (Nafion117)) of unit cell (a) and flow cell state of before (b) and after (c) electrolysis reduction process

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Fig. 2

Precipitation observation of SOC 95% samples prepared by (a) 2M VOSO4·3.5H2O(Wako Co., 99%) +3.0 M H2SO4 (Aldrich 98%) and (b) 2M VOSO4·3.5H2O(Wako Co., 99%) +3.0 M H2SO4 (Aldrich 98%) + 0.1M SPD. The charge conditions for the electrolysis reduction process were a current density of 10 mA/cm2 and a cut-off voltage of 1.57 V for SOC 95%. During the charging process, V(IV) became V(V) through oxidation in the cathode. After pouring the SOC 95% sample in transparent vial under Ar condition, the sample was kept in 40 °C. The precipitation status was observed every 3 h by naked eye.

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Fig. 3

Four expected mechanisms in inhibition effects between the SPD and the vanadium electrolyte

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Fig. 4

Cyclic voltammograms of 2.0 M V(IV)/V(V) in 3.0 M H2SO4 with and without SPD additive at scan rate (a) 5 mV/s and (b) 50 mV/s (50 scans) at 25 °C

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Fig. 5

Charge–discharge curve at first cycle without and with the SPD additives at 25 °C at the current density of 10 mA/cm2

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Fig. 6

Cyclic charge–discharge time curves of non-flow cells without (a) and with SPD additive (b) in 2.0 M V(V) in 3.0 M H2SO4 at 25 °C

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Fig. 7

Charge–discharge curve during the first cycle without and with the SPD additives at 40 °C at the current density of 10 mA/cm2

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Fig. 8

Cyclic charge–discharge time curves of non-flow cells without (a) and with SPD additive (b) in 2.0 M V(V) in 3.0 M H2SO4 at 40 °C

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Fig. 9

SEM micrographs at 10 (a–d) and 80 (e–f) times magnification showing the surfaces of the positive felt (XF-30A) electrode of VRFB before and after 600 galvanic cycles of non-flow cells without (a,c) and with 0.1M SPD additive (b,d) in 2.0 M V(V) in 3.0 M H2SO4 at 25 °C and 40 °C, respectively

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Fig. 10

Cyclic charge–discharge capacity and efficiency curves of flow cells without (a) and with SPD additive (b) in 2.0 M V(V) in 3.0 M H2SO4 at 40 °C

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Fig. 11

Cyclic charge–discharge capacity (a and d) and efficiency curves (b and c) of flow cells without and with SPD additive in 2.0 M V(V) in 3.0 M H2SO4 at 40 °C

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