Metal–organic complexes as redox candidates for carbon based pseudo-capacitors

Abstract

We present metal–organic complexes as a new type of redox active materials for pseudo-capacitors. The adsorption of three iron complexes with different sizes of aromatic ligands on activated carbon electrodes and the consequent electrode structure and composition were studied by gas-adsorption measurements, UV-vis spectroscopy, thermal gravimetric analysis (TGA), electron microscopy and inductively coupled plasma-atomic emission (ICP-AE) spectroscopy. The electrochemical performance of these composite electrodes was studied by cyclic voltammetry and galvanostatic measurements. The high specific capacitance was measured with composite activated carbon electrodes containing ferrocene (143 F g⁻¹) in neutral aqueous solutions or ferroin (315 F g⁻¹) in non-aqueous solutions. The latter systems exhibit a 370% gain in capacity due to the adsorption of the redox compound on the surface of the activated carbon electrodes. These systems demonstrated very good stability during more than 12 000 cycles and also exhibited high rate capability.