Development of carbon aerogels as Fe-N-C catalyst in high temperature polymer electrolyte membrane fuel cell (HT PEMFC)

Abstract

The high-temperature (HT) polymer electrolyte membrane fuel cell (PEMFC) typically requires platinum catalysts with high amounts of platinum of up to 1 mgPt cm-2 for the anode and cathode, as the adsorption of phosphates leaking from the phosphoric acid electrolyte leads to poisoning of the catalyst. A promising and cost-effective alternative to the commonly used expensive platinum group metals in PEMFCs are the precious metal-free Fe-N-C catalysts. The cost reduction should lead to further commercialization of the PEMFC [1]. One challenge of Fe-N-C catalysts is the lower volumetric activity of Fe-N-Cs compared to Pt/C. Therefore, thicker catalyst layers are required, which can lead to a limitation in mass transport. To address this challenge, highly porous carbon aerogels (CA) are considered as promising materials for the incorporation of Fe-Nx sites. Carbon aerogels, first introduced by Richard Pekala in 1989 [3], are three-dimensional, open porous solid materials produced via carbonization of organic aerogels based on e.g. resorcinol-formaldehyde, phenol-formaldehyde or melamine-formaldehyde polymers. Unique properties of CAs such as well-controlled porosity and pore size, large specific surface area about 500-2000 m²/g, high electrical conductivity, and low envelope density make them promising material for application in adsorption, catalysis, supercapacitors [4], fuel cells or as a cathode host in metal-sulfur cells [5]. Their remarkable electrical conductivity is one of the key factors for electrochemical applications. The incorporation of iron and nitrogen in the structure using simple and scalable methods leads to enhanced oxygen reduction reaction activity. The open-porous network with adjustable microstructure allows high electrolyte access to the active sites. The collaboration of the two DLR institutes for materials research (WF) and engineering thermodynamics (TT) enables the development of novel carbon aerogels with adapted microstructure for incorporation of Fe-N-C. The first results on the development of a suitable microstructure by optimizing the synthesis route and incorporation of Fe-N-Cs are shown within this presentation.