Ce (¢ô) / Ce (¢ó) Redox Properties

The Ce(Ⅳ)/Ce(Ⅲ) redox couple which has a high redox potential (1.61V) comparing with other redox couple is electrochemically promissing for redox flow battery. The electrochemical behavior of the Ce(Ⅳ)/Ce(Ⅲ) redox couple was first investigated systematically. Finally,we worked on how to enhance the reduction kinetics of the electrochemical reaction.The reaction mechanism and the reduction konetics of the Ce(IV)/Ce(III) couple were investigated by means of cyclic voltammetry, polarization curve and impedance spectroscopies, and the correlative kinetics parameters were calculated. The results indicated that Ce(IV)/Ce(III) redox reaction was quasi-reversible. The diffusion coefficient for Ce(Ⅳ) reduction was 1.4×10-6 cm2·s-1 and the standard rate constant was 3.24×10-4 cm·s-1. The influence of reaction temperature, concentration of electrolyte were studied by cyclic voltammetry later and showed the acid concentration of 3mol·L-1 and high temperature are electrochemical favorable for the electro transfer of the Ce(IV)/Ce(III) couple.The effect of electrolyte additives was studied subsequently. Ag+, Cr3+ Co2+, NH4+ was found to improved the redox reaction of Ce(Ⅳ)/Ce(Ⅲ) couple and the diffusion coefficient for Ce(IV) reduction for which were 4.0×10-6 cm2·s-1,3.48×10-6 cm2·s-1,2.85×10-6 cm2·s-1, 2.62×10-6 cm2·s-1, respectively. A 2.20 V of initiative discharge voltage and 65.7% coulombic efficiency after 30 cycles were achived at a current density of 25mA·cm-2, together with the carbon felt surface of 6 cm2, and the voltage gap between the charge and discharge process was lower than 0.4 V.Finally, the influnce of other acids focus on the elctrode reaction of the Ce(Ⅳ)/Ce(Ⅲ) redox couple was analysed in this paper. The reseach included that citric acid, oxalic acid, boric acid accelerated the Ce (Ⅲ) oxidation, and acetic acid promoted the cathodic kinetics of Ce (Ⅳ) reduction. But they all enhanced the discharge voltage platform of the corresponding redox battery.