Development of platinum group metal-free electrocatalysts for oxygen reduction reaction in electrochemical devices

High demand for power generation and the consequent increase of greenhouse gases emissions is one of the most important issues do be overcome to reduce dependence of industry and transportation sector of fossil fuels. In this scenario, fuel cells such as hydrogen-fed anion exchange membrane fuel cells (AEMFCs) are considered promising solutions to decarbonization of the transport sector. The industry sector also requires strategic solutions not only for reducing dependence on fossil fuels for power generation but also efficient treatments of industrial waste. Microbial fuel cells (MFCs) are bioelectrochemical systems which have demonstrated potential application for wastewater treatment and energy recovery. Despite the potential AEMFCs and MFCs, those devices are limited by the sluggish kinetic of oxygen reduction reaction (ORR) at the cathode side of the cell, requiring expensive platinum-group-metal-based (PGM) electrodes. A lot of progress has been made in the development of PGM-free materials to replace Pt/C, the state-of-the art ORR catalysts. Among them, metal-nitrogen-carbon (M-N-C) materials have demonstrated superior performance for Fe-N C based active sites, however, density, accessibility and durability of the active sites still limits their application in a fuel cell environment. In this context, the study carried out in this Ph.D. thesis proposes different synthesis strategies to obtain less expensive materials, with high activity and durability. Imidazole-based molecules, iron-sources and zeolitic imidazolate frameworks precursors were adopted to synthesize high active Fe-N-C catalysts. Insights regarding the performance optimization were achieved combining electrochemical and spectroscopic analysis to investigate chemical surface and catalytic activity towards ORR. Such materials were assembled at the cathode side of energy conversion devices, demonstrating their applicability as Pt/C substitutes with high electrochemical performance and good stability.