Towards the Reduction of Pt Loading in High Temperature Proton Exchange Membrane Fuel Cells - Effect of Fe-N-C in Pt-Alloy Cathodes.

Pt poisoning by phosphate in high temperature proton exchange membrane fuel cells (HT-PEMFC) leads to loadings up to 1 mgPt cm-2 per electrode of costly materials. While cheaper Fe-N-C catalysts are unaffected by phosphate deactivation and contribute to the catalysis of the oxygen reduction reaction, their volumetric activity is substantially lower. In this study, the effect of Pt-loading reduced hybrid cathodes for HT-PEMFC is investigated using commercial Celtec®-P-based assembling. A promising effect of Fe-N-C incorporation in terms of acid attraction and activity retention is found. A longer activation (230 h, 0.3 A cm-2 ) for the hybrid membrane electrode assembly (MEA) is necessary, due to the slower acid distribution within Fe-N-Cs. This study shows the potential of Pt-content reduction by up to 25 % compared to standard MEA using hybrid electrodes. Moreover, important insights for future strategies of cell activation are revealed for these hybrid MEAs.

Relevant Properties of Carbon Support Materials in Successful Fe-N-C Synthesis for the Oxygen Reduction Reaction: Study of Carbon Blacks and Biomass-Based Carbons.

Fe-N-C materials are promising non-precious metal catalysts for the oxygen reduction reaction in fuel cells and batteries. However, during the synthesis of these materials less active Fe-containing nanoparticles are formed in many cases which lead to a decrease in electrochemical activity and stability. In this study, we reveal the significant properties of the carbon support required for the successful incorporation of Fe-N-related active sites. The impact of two carbon blacks and two activated biomass-based carbons on the Fe-N-C synthesis is investigated and crucial support properties are identified. Carbon supports having low portions of amorphous carbon, moderate surface areas (>800 m2/g) and mesopores result in the successful incorporation of Fe and N on an atomic level and improved oxygen reduction reaction (ORR) activity. A low surface area and especially amorphous parts of the carbon promote the formation of metallic iron species covered by a graphitic layer. In contrast, highly microporous systems with amorphous carbon provoke the formation of less active iron carbides and carbon nanotubes. Overall, a phosphoric acid activated biomass is revealed as novel and sustainable carbon support for the formation of Fe-Nx sites. Overall, this study provides valuable and significant information for the future development of novel and sustainable carbon supports for Fe-N-C catalysts.