SYNTHESIS AND CHARACTERISATION OF NOVEL CATALYTIC MATERIALS FOR THE OXYGEN REDUCTION REACTION

The oxygen reduction reaction (ORR) is the semi-reaction that occurs at the cathode in technologies like the polymer electrolyte membrane fuel cells (PEMFCs). These devices are notable for their high efficiency in converting chemical energy to electricity, compact design, and potential for near-zero emissions, making them essential for clean energy production. However, the current state-of-the-art electrocatalysts for PEMFCs predominantly rely on platinum (Pt/C), which poses significant barriers to widespread commercialisation due to platinum’s limited availability, high cost, and high volatility. Consequently, developing novel, more affordable catalysts with improved activity and enhanced durability represents a relevant research focus in PEMFC technology. Among the most promising alternatives are non-precious-metal “M-N-C” catalysts, which incorporate metal ions (such as Fe, Co, etc.) within a nitrogen-doped mesoporous carbon support. The active sites offered for the ORR are the metal ions, which coordinate with defects and/or nitrogen moieties linked to the carbon structure. Meanwhile, the porous carbon functions both as a support and as an electrical conductor. Among the diverse synthesis methods, the sacrificial support method (SSM) is particularly notable for its simplicity and effectiveness. The aim of this thesis is to investigate the influence of different mesoporous silica templates on the final morphological and electrocatalytic properties of the resulting catalysts, as well as to assess the impact of varying nanocasting approaches on samples derived from the same silica template. Six catalysts have been synthesised, three from different silica sources and three with variations in impregnation steps and conditions. All carbon based catalysts were produced by high temperature pyrolysis, followed both by acid and alkali etching steps. Additionally, in the attempt of improving the physical and catalytic properties of the samples, they were subjected to a second round of pyrolysis. The synthesised samples were characterised using physicochemical methods, revealing varying degrees of crystallinity, high specific surface area, and different pore structures depending on the choice of the silica and the impregnation steps followed. These samples were subsequently tested for ORR using a rotating ring-disk electrode (RRDE) in both acid and alkaline electrolyte solutions, highlighting the crucial role of the starting silica hard template. The cited samples exhibited high catalytic activity, making their use as cathodic catalysts in PEMFC very promising.