Development and characterization of nanostructured catalysts

The aim of this thesis work is focused on the development and characterization of nanostructured catalysts, in order to exploit them in two different reactions: the Oxygen Reduction Reaction (ORR) and the CO2 Reduction Reaction (CO2RR). The objective of this research is to find economical and ecological materials that could replace platinum as catalyst of the two reactions, while maintaining comparable performance. Considering the ORR, the study is concentrated on the manganese oxide family (MnxOy), structured in the form of nanofibers by electrospinning technique and subsequent thermal treatment. The aim is to demonstrate that the MnxOy nanofibers own all the necessary properties, e.g. cheapness, efficiency and environmental-friendliness, revealing themselves as promising and innovative structures as catalysts for ORR. This material is studied in terms of morphology, composition and electrochemical activity by varying the final calcination temperature of the nanofibers. Thanks to this study, it is possible to describe the thermal evolution of the catalyst, comparing the electrochemical performance to a precise nanostructure and crystalline composition. The ceramic nanofibers, in fact, catalyze efficiently the ORR, granting a cheaper and more eco-friendly material than platinum, which is the most used today in energy production devices, as Microbial Fuel Cells (MFCs). The MnxOy catalyst is also coupled with a conductive substrate in an MFC device, revealing its capability of successfully reduce oxygen after the direct integration onto the electrode, without changing its catalytic performance. Considering the CO2RR, the attention is focused on the titanium dioxide nanotubes (TiO2 NTs) and copper oxide nanofibers (CuxO NWs) -based catalysts. Vertically oriented TiO2 NTs are obtained by anodic oxidation of a titanium foil and studied, by their own, in terms of morphology and composition. Further they are coupled with a copper and a copper oxide layers, characterizing the electrochemical properties, catalytic performance and selectivity toward CO2RR. As a competitive alternative to TiO2 NTs, CuxO NWs are obtained by thermally oxidizing the copper foils at different temperatures and characterizing them in terms of morphology, composition catalytic activity and selectivity, analyzing both the liquid and gaseous byproducts. Lastly, the CuxO NWs are coupled with and titanium dioxide upper layer, exploiting the same in characterizations of the former substrate in order to be comparable. All the studied substrate show some catalytic activity toward CO2 reduction, but the highest efficiency is associated to the CuxO NWs, revealing formation of byproducts both in liquid and in gaseous form.