Kinetics study of transition metal complexes (Ce–DTPA, Cr–DTPA and V–DTPA) for redox flow battery applications

Electrochemical kinetics of Ce(IV), Cr(III) and V(IV) and their diethylenetriaminepentaacetic acid (DTPA) complexes are studied by electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) on Pt-electrode. Kinetic parameters such as potential, limiting current, transfer coefficient, diffusion coefficients, and rate constants were examined. The EIS results confirm the results from CV and are in good agreement with the obtained experimental data. The Cr–DTPA complex rate constant of 2.1 × 10−4 cm s−1, diffusion coefficient of 1.9 × 10−6 cm2 s−1 and the V–DTPA complex rate constant of 2.2 × 10−4 cm s−1 and diffusion coefficient of 4.9 × 10−4 cm2 s−1 were obtained and compared with the Ce(IV)–DTPA complex. The Ce(IV)–DTPA complex appear to better satisfy the requirement of a suitable electrolyte for RFB applications than Cr(III)–DTPA and V(IV)–DTPA complexes.

Graphical abstractCyclic voltammograms of Ce(IV)–DTPA, Cr(III)–DTPA and V(IV)–DTPA and the electrochemical impedance spectroscopy results with the equivalent circuit diagram.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Kinetics study of Ce–DTPA, Cr–DTPA and V–DTPA complexes were investigated by EIS and CV. ► Electrochemical reversibility, fast kinetics, diffusion control and mass transfer. ► Higher potential and low charge transfer resistance. ► Ce–DTPA complex was the most suitable when compared to Cr–DTPA and V–DTPA complexes.