Synthesis of Ir Nanoparticles As Promoters for the Stabilization of Fenc-Catalysts Under Ssc Conditions

Abstract

Fuel cells are promising devices for implementation in automotive propulsion. While the standard operation seems feasible, during start-up and shutdown high potentials occur on the cathodic site induced by the reverse current mode. In consequence, the carbon oxidation reaction (COR) occurs and limits the lifetime of PEMFCs. One approach suppressing carbon corrosion is the introduction of small amounts of an oxygen evolution reaction (OER) catalyst, as e.g. iridium. In our recent work we showed that in relative manner the durability was improved, however, the initial performance was less compared to the non-modified FeNC catalyst.[1 ] These NP had been prepared by a polyol approach.[2 ] However, capping agents (CA) could eventually still be present in these systems, blocking the particles in their performance.Herein, we present our results using an alternative surfactant free synthesis of Ir nanoparticles, adapted from literature,[3 ] that are then used for the modification of an FeNC catalysts. The performance of the newly prepared FeNC+Ir vs the FeNC+Ir+CA reference was evaluated employing accelerated stress tests mimicking the start-up and shut down conditions in RDE and PEMFC. It is shown that with this new approach the amount of NP on the surface can be better controlled. Beside the electrochemical testing structural characterization by X-ray-diffraction, thermogravimetric analysis and transmission-electron-microscopy was performed.It will be shown that by surfactant free synthesis Ir nanoparticles with high purity can be obtained. Due to the higher purity, an improvement of the OER activity can be achieved with the same Ir loading. In the RDE, an improvement in stability was observed by loading an FeNC catalyst with Ir nanoparticles. However, under fuel cell conditions, no improvement in stability was observed by loading Ir nanoparticles onto a FeNC catalyst.List of references[1] Prössl, C., Kübler, M., Paul, S., Ni, L., Kinkelin, S. J., Heppe, N., Eberhardt, K., Geppert, C., Jaegermann, W., Stark, R. W., Bron, M. & Kramm, U. I. (2022). Impact of Ir modification on the durability of FeNC catalysts under start-up and shutdown cycle conditions. Journal of Materials Chemistry A, 10(11), 6038-6053.[2] Prössl, C., Kübler, M., Nowroozi, M. A., Paul, S., Clemens, O., & Kramm, U. I. (2021). Investigation of the thermal removal steps of capping agents in the synthesis of bimetallic iridium-based catalysts for the ethanol oxidation reaction. Physical Chemistry Chemical Physics, 23(1), 563-573.[3] Bizzotto, F., Quinson, J., Schröder, J., Zana, A., & Arenz, M. (2021). Surfactant-free colloidal strategies for highly dispersed and active supported IrO2 catalysts: Synthesis and performance evaluation for the oxygen evolution reaction. Journal of catalysis, 401, 54-62.