Optimization Ionomer Distribution on Porous Carbon Catalyst Support to Commercialize Low Pt Loaded PEMFCS

Abstract

One of the major drawbacks towards PEMFC (polymer exchange membrane fuel cell) commercialization is the high amount of platinum needed at the cathodic electrode, due to the inherent slow kinetics of the oxygen reduction reaction. It has been widely known that the reduction of the Pt loading at the cathodic electrode leads to significant voltage losses. The origin of which has been correlated to electrode structure, ionomer distribution, type of catalyst support, and location of the Pt particles on the carbon support. A recent study by Orfanidi et al showed that by introducing positively charged nitrogen groups into the carbon structure lead to a more homogeneous distribution of the ionomer, which results in higher performance even at low Pt loaded electrodes [1]. In the present study, a series of different N-functionalized Ketjenblack are synthesized and fully characterized to investigate their use as support material for Pt based electrodes. Pre-oxidized Ketjenblack was heat treated in ammonia at different temperatures [2] followed by Pt precipitation via an ethylenglycol method. This new type of catalyst significantly reduces the additional mass transport resistance and report an unprecedented high coverage of the ionomer over the high surface area carbon supports, especially under dry operating conditions, in addition to high stability under voltage cycling. Those enhanced transport behaviors are deduced to local transport phenomena in the porous carbon structure and we give a tailoring approach for such a carbon material within this work. Our catalyst presents significant advantages as it facilitates manufacturing processes of the electrodes, due to the columbic interaction between the ionomer and the –NHx groups on carbon support, ensuring homogeneous ionomer distribution. This work sheds light into the effect of the different N based groups towards better understanding of the interaction of ionomer with the carbon support. Our concept can be transferred to other kinds of partially amorphous carbon and is not limited to Pt as an active material. Introduction of such a modification step in the production line of electrocatalysts paves the way for PEMFC commercialization in automotive applications, due to enhancement in mass transport and stability. Literature [1] A. Orfanidi, P. Madkikar, H.A. El-Sayed, G.S. Harzer , T. Kratky, H.A. Gasteiger, Journal of the Electrochemical Society 2017, 164, F418-F26. [2] K.F. Ortega, R. Arrigo, B. Frank, R. Schlöten, A. Trunschke, Chemistry of Materials 2016, 28, 6826-6839.