Voltammetry analysis of Cu-Fe based bimetallic organic framework and its derived oxide for electrochemical energy storage application

Bimetallic oxides derived from metal organic frameworks have been found to exhibit enhanced charge storage capacity in comparison to individual metal oxides due to the presence of multiple oxidation states, crystalline structure and porous morphology. In this research work, copper (Cu), iron (Fe) based bimetallic metal organic framework (Cu-Fe-BTC) and its derived bimetallic oxide (Cu-Fe-O) is synthesized using microwave assisted solvothermal synthesis followed by systematic calcination procedure in nitrogen-air environment. Their electrochemical mechanism has been analyzed using cyclic voltammetry (CV) in potential window of +0.00 V to +0.55 V vs SCE. The electrochemical process for both Cu-Fe-BTC and Cu-Fe-O is found to be diffusion controlled. For region 1 (scan rate < 40 mV s(-1)), Cu-Fe-BTC and Cu-Fe-O demonstrate faster charge storage response, whereas response becomes slower in region 2 (scan rate > 40 mVs(-1)). The peak current density obtained in CV for Cu-Fe-O is found to be significantly larger than Cu-Fe-BTC and the peak separation for Cu-Fe-O is also comparatively smaller than Cu-Fe-BTC. Moreover, the standard rate constant (k(0)) and diffusion coefficient (D) for Cu-Fe-O is comprehensively greater than that of Cu-Fe-BTC. The reason ascribed for the improved kinetics in Cu-Fe-O is due to less concentration of surface adsorbed OH in Cu-Fe-O, thereby allows more incoming OH- ions to participate in charge transfer reaction. Also, the electrochemical energy storage performance of Cu-Fe-O is found to be higher than Cu-Fe-BTC. This research work provides a comprehensive insight towards the determination of electrochemical kinetics and charge storage mechanism using voltammetric analysis which is seldomly addressed in the literature.