Novel materials for oxygen reduction reaction

The 21st century is characterised by the rush to tackle climate change by resorting to sustainable development. When it comes to energy, new technological opportunities have been ceased, including the promising fuel cell, an electrochemical device that offers a clean and environmentally friendly alternative to conventional combustion engines. Their use could revolutionise several sectors, from transport to stationary power generation. However, for them to spread on a large scale, several difficulties must be overcome, including the development of an efficient, selective catalyst without rare materials that facilitates the oxygen reduction reaction (ORR) and enables good cell performance and durability. The ORR occurs at the cathode of the fuel cell and is regarded as the rate-determining step due to its sluggish kinetics. Traditionally, this electrochemical reduction reaction of oxygen to water has been supported by catalysts based on noble metals, such as platinum, due to their strong catalytic activity. However, their high cost, limited availability and vulnerability to poisoning promote the search for viable alternative catalysts that can provide comparable or superior performance. This thesis aims to give an overview of the development of catalysts for the oxygen reduction reaction and to present the potential opportunities offered by Fe/N/C-based catalysts. In particular, the work carried out can be divided into several stages: template synthesis and subsequent preparation of the Fe-N-C catalytic material by impregnation and pyrolysis, chemical-physical characterisation and electrochemical performance analysis. The idea behind the coordination of iron with nitrogen is dictated by the atomic disposition which brings the material to characteristics emulating the active sites found in heme-enzymes and moreover alters the structure of iron d-band, leading it to electrochemical characteristics resembling those of noble metals, but at a considerably more affordable cost that could allow the development on a large scale. In this work, a Fe-N-C catalyst with mesoporous structure was synthesized. The structural and morphological characterizations reveal the co-presence of Fe and N without crystalline Fe species. Moreover, a high BET surface area and large pore volume are observed. The electrochemical measurements disclose that the sample exhibits remarkable electrocatalytic performances for ORR.