Novel carbon nanomaterials for the direct methanol fuel cell electrodes

Direct methanol fuel cells (DMFC) are great candidates for portable power source applications. However, the sluggish reaction kinetics are key challenges in DMFC technology. The state-of-the-art electrocatalysts are Pt-based catalysts supported on carbon black. However, the high price of Pt, corrosion of carbon support and Pt degradation are the main problems. In this thesis, carbon nanomaterials, namely few-walled carbon nanotubes (FWCNTs) and graphitized nanofibers (GNFs) were used as catalyst supports in the search for stable and durable catalysts. PtRu nanocatalysts with similar particle size and composition were synthesized and deposited on FWCNTs and GNFs. The electrochemical activities for methanol oxidation were compared with that of PtRu-carbon black in acidic conditions. The half-cell electrochemical measurements revealed higher activity with PtRu-GNFs and PtRu-FWCNTs. Later, the electrocatalysts were tested in macro- and micro-DMFC. The results revealed the significant influence of the catalyst support, inomer contect, electrode structure, preparation method, as well as the fuel cell architecture on the performance of a specific electrode material. The results also highlighted the necessity of electrode composition optimization when applying new materials at the electrodes, in order to achieve the best activity and durability for a certain electrocatalyst. A special effort was also done to achieve Pt-free electrocatalysts with high activity for the oxygen reduction reaction (ORR) by introducing nitrogen heteroatoms in carbon nanomaterials, namely FWCNTs and graphite nanoplatelets (GNPs). N-FWCNTs exhibited remarkable electrocatalytic activity for ORR in alkaline media, despite their very low nitrogen content (~0.5 at.%). N-FWCNTs performed on par or better than a commercial Pt-C at the cathode of an alkaline DMFC. The N-GNPs exhibited enhanced electrocatalytic activity for ORR compared to pristine GNPs in alkaline media. The results indicated that N-doped carbon nanomaterials could be promising alternatives to their Pt counterparts to reduce fuel cell costs. However, further investigations are necessary to ascertain the real active sites in order to design more efficient and durable ORR electrocatalysts