Optimization of Perovskite Oxide/Carbon Composites for Oxygen Reduction Reaction in Alkaline Media
Authors: Dzara Michael J. , Joghee Prabhuram , Christ Jason M , Ngo Chilan , Cadigan Christopher A. , Batson Tim , Richards Ryan M. , O'Hayre Ryan , Pylypenko Svitlana 
Published: February 2020

Non-precious metal catalysts (NPMCs) for the oxygen reduction reaction (ORR) present an opportunity to improve the industrial feasibility of low temperature fuel cells by replacing expensive precious metal catalysts. However, improvements in performance of NPMCs are needed before they can realize widespread commercial adoption. Since the catalyst is projected to be the largest single contributor to the overall cost of the fuel cell, this area has seen heavy research activity. Many NPMC chemistries have been studied for the ORR in alkaline media, with perovskite oxides (of the form ABO3) being of particular interest due to the large variety of possible compositions that form perovskite structures, and the ability to tune material properties through doping of the A and B sites.1 Optimization of the bulk and surface chemistry to maximize intrinsic catalytic activity is of major importance to drive the development of perovskite oxide NPMCs. Synthesis strategies that balance surface chemistry and surface area optimization are necessary to improve the active site density while maintaining high catalytic activity. In addition, formation of effective perovskite oxide/carbon composites is essential to catalyze the ORR by a 2 step, 4 electron (2 per step) mechanism.2

This work focuses on the development of high performance perovskite/carbon composites by tuning surface chemistry, surface area, and optimizing the ratio of perovskite oxide to carbon. Through an aerogel synthesis process, a high surface area Ca0.9La0.1Al0.1Mn0.9O3-
δ perovskite oxide catalyst was produced. Calcination temperature was varied between 500 and 1000C to study the interplay between phase purity and the catalyst surface area. Rotating disk electrode (RDE) studies showed that the optimum balance between phase, purity, surface composition and surface area is obtained using calcination at 800C. Rotating ring disk electrode studies (RRDE) were used to evaluate the effect of perovskite oxide to carbon ratio with further investigations in membrane electrode assemblies (MEAs) also demonstrating a significant impact on the performance (Figure 1). Additional improvements in performance were realized by varying the catalyst loading and using carbon functionalized with nitrogen.
References
1. Hardin, W. G., Mefford, J. T., Slanac, D. A., Patel, B. B., Wang, X., Dai, S., … Stevenson, K. J. (2014). Tuning the electrocatalytic activity of perovskites through active site variation and support interactions. Chemistry of Materials, 26(11), 3368–3376. http://doi.org/10.1021/cm403785q
2. Poux, T., Napolskiy, F. S., Dintzer, T., Kéranguéven, G., Istomin, S. Y., Tsirlina, G. A., … Savinova, E. R. (2012). Dual role of carbon in the catalytic layers of perovskite/carbon composites for the electrocatalytic oxygen reduction reaction. Catalysis Today, 189(1), 83–92. http://doi.org/10.1016/j.cattod.2012.04.046

Figure 1