Rodrigo Della Noce

Abstract:

There has been an explosive growth of research dedicated to new electrochemical energy storage devices in the last decades. Among these devices, redox supercapacitors (SCs) have emerged as very attractive solutions for several applications. These devices are pin pointed as strategic materials in the European Roadmaps for materials enabling low carbon technologies. It is therefore not surprising that although supercapacitors have already encountered their place in the energy storage global market, research efforts continue in order to develop electrode materials that can further enhance SCs energy density, while maintaining a high power density. In this context, SCs electrode materials have been produced by different methods. Electrodeposition has stood out in comparison with many other synthesis routes due to important features such as cost-effectiveness, high quality deposits, production at room temperature (no need of high vacuum), scale-up ability, and easy operating conditions. In this work, we have designed nanostructured porous single and mixed transition metal oxides/hydroxide electrodes, and its composites with carbon nanofoams, for developing high energy density charge storage electrodes for SCs. The electrodes were fabricated by a one-step process, consisting on the electrodeposition of transition metal oxides on stainless steels or on carbon nanofoams. Electrodeposition of manganese, nickel and cobalt oxides/hydroxides was performed from the corresponding salt electrolytes at constant or under pulsed potential. The morphology, chemical composition and phase composition of the electrodeposited electrodes were studied by scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD) and Raman spectroscopy. The electrochemical performance of the electrodes was studied by cyclic voltammetry and chronopotentiometry (charge-discharge cycles) and the specific capacitance of the material was calculated from the experimental data. The variation of capacitance was related to the substrate material and morphology of the electrodeposited oxides and hydroxides. The results demonstrate that the morphology and composition of the metallic transition oxides/hydroxides electrodes and its composites can be tailored by changing the electrodeposition parameters. The results also evidence that it is possible to fabricate charge storage electrodes, displaying specific capacitances 2-4 times above those of the conventional carbon-based double layer capacitors. The composites obtained with carbon nanofoams reveal an increased working potential window, in aqueous electrolytes, up to 2.1 V, thus resulting in electrodes that can be assembled in devices that display enhanced energy density. In conclusion, electrodeposition allows fabricating a new class of advanced electrodes for redox supercapacitors, based on 3D architectures of transition metal oxides/hydroxides and its composites with carbon nanofoams, capable of attaining energy density values much above commercial carbon-based solutions. Keywords: charge storage, supercapacitors, transition metals, carbon nanofoams.