Electrochemical Behavior of the Ce 4+ / Ce 3+ Couple in the Novel Ce - V Redox Flow Cell

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1127-T01-03

Electrochemical Behavior of the Ce4+ / Ce3+ Couple in the Novel Ce - V Redox Flow Cell Yang Liu1, Xi Xia2 1 2

Département de chimie, Université de Montréal, Montréal, QC, H3C 3J7, Canada Institute of Applied Chemistry, Xinjiang University, Urumqi, Xinjiang, 830046, China

ABSTRACT A novel Ce4+/Ce3+– V2+/V3+ redox flow cell has been investigated. It was composed of the Ce /Ce3+ couple, which replaced the V5+/V4+ couple of the all-vanadium redox flow cell, and the V2+/V3+ couple. The normal potential and the kinetic parameters for anodic oxidation of Ce3+ and cathodic reduction of Ce4+ were measured. The results showed that the surface of platinum electrode was fully covered with type I oxide that inhibited the reduction of Ce4+. The reversibility of the Ce4+/Ce3+ couple improved with the increase of H2SO4 concentration, but both higher energy efficiency and coulombic efficiency were observed in 0.5 mol/dm3 H2SO4 solution. Different electrochemically active substances were found to exist at various state of charge (SOC) and the reversibility of the Ce4+/Ce3+ couple at the carbon electrode was found to be superior to platinum electrode. Periodic charge-discharge measurements were conducted under constant current and constant load with the proposed Ce-V redox flow cell. The results indicated that the coulombic efficiency remained around 90% and the discharge voltage stabilized between 1.5 and 1.2 V. But as the cycle numbers increased, the discharge capacity declined a bit and a better result might be expected by improving the separator materials and increase the concentration of electro-active materials. By comparison with the existing Fe-Cr, Fe-Ti and all-vanadium redox flow cell, the Ce-V system has a higher open-circuit voltage (OCV). And results from this preliminary study suggest that the novel Ce-V redox flow cell is a promising energy storage system and is worthy of further studies. 4+

INTRODUCTION A redox flow battery or redox flow cell is a type of rechargeable battery in which a positive and a negative electrolyte containing dissolved electro-active materials flow through a battery or cell that can convert chemical energy to electricity. As shown in scheme 1 for the allvanadium redox flow cell, the electro-active positive electrolyte V5+ (VO2+) and the negative electrolyte V2+ are stored externally, generally in tanks, and are usually pumped into the cells [1]. As a result, redox flow cell can be rapidly recharged by simply replacing the positive and negative electrolytes, just as refilling the fuel tanks for vehicles, while at the same time recovering the discharged electroactive materials for re-energization. Based on the structural characteristics of redox flow cell, it has the following advantages: 1) simple electrode reaction, all the electoactive materials have relatively high solubility, therefore all the electrochemical reactions take place in the solution and there is not complex solid-phase reactions as in other battery systems; 2) long life cycle, the theoretical life cycle is unlimit

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