8:00 PM - EN05.05.05
High Catalytic Activity towards ORR on Iron/Carbon Nanostructures in Fuel Cells for Space Applications
Armando Pena-Duarte1,S.H. Vijapur2,T.D. Hall2,S. Snyder2,E.J. Taylor2,Jeffrey Sweterlitsch3,Carlos Cabrera1
University of Puerto Rico1,Faraday Technology Inc2,NASA/Johnson Space Center3
Fuel cells are promising candidates for clean energy conversion for terrestrial and space applications such as human space travels, which require several technological developments that support the energy-efficient production and preservation of closed systems in microgravity spaceship environments . The overpotential required for the Oxygen Reduction Reaction (ORR) is the main electrochemical factor that diminish practical application of fuel cells . ORR in aqueous solutions occurs mainly by two pathways: the direct four-electron reduction pathway from O2 to H2O, and the two-electron reduction pathway from O2 to hydrogen peroxide (H2O2). In fuel cell processes, the four-electron direct pathway is highly preferred. The two-electron reduction pathway is used in industry for H2O2 production . Carbon nanostructures (Nanocarbons), such as Vulcan and carbon nano-onions (CNOs), have been previously used as catalyst due to high stability and surface area, high electrical conductivity, and mesoporous structure. Studies have revealed that carbon nanostructures and metal-carbon structures show catalytic activity in ORR [5,6]. Rotating disk slurry electrodeposition technique (RoDSE), as electrodeposition process without high temperatures, hazardous compounds, and nor energetic procedures, has been used to deposit metal nanoparticles on carbon to prepare a hybrid catalyst in powder form, . Accordingly, in order to evaluate the ORR essential role in fuel cells in microgravity conditions and space applications, iron nanoparticles supported on Nanocarbons (FeNanocarbons) were synthesized and characterized by RoDSE. The structural properties of the FeNanocarbons were investigated using X-ray diffraction, Raman spectroscopy, scanning electron microscopy, induced coupled plasma, and X-ray photoelectron spectroscopy. FeNanocarbons electrochemical characterization revealed higher performance than Nanocarbons, due to Fe nanoparticle enhances the electronic conductivity and specific capacitance. An analysis of the rotating disk electrode (RDE) technique data was done to evaluate the ORR kinetics, including n-values which are related to the mechanism of oxidation, at the FeNanocarbons, using the Koutechy-Levich (K-L) equation. ORR over FeNanocarbons and Nanocarbons was evaluated in O2 saturated 0.1 M KOH, by a scan rate of 10 mV/s at different rotation rates: 800, 1200, 1600, 2000, and 2400 rpm. Initial fuel cell tests at 6V, utilizing oxygen and RO water, showed that Fe/Nanocarbons and Nanocarbons can generate 0.055 and 0.025 w/w% peroxide concentration, respectively. The system output current was 0.38 amps for Fe/Nanocarbons and 0.25 amps for Nanocarbons. These results suggested that Nanocarbons performs high selectivity toward a two-electron pathway reduction process, whereas Fe/Nanocarbons catalyzes a four-electron route. Therefore, our approach would be promising to control of four- or two-electrons route kinetics of ORR in fuel cells for space technologies, by the nanocarbon source and metal-nanocarbon configurations. References:  NASA Strategic Plan, 2018, at: https://www.nasa.gov/sites/default/files/atoms/files/nasa_2018_strategic_plan.pdf.  J. K. Nørskov, J. Rossmeisl, A. Logadottir and L. Lindqvist. J. Phys. Chem. B, 108 (46), 17886–17892, 2004.  Song, C,; Zhang, J. Electrocatalytic ORR in PEM fuel cell electrocatalysts and catalyst layers. Springer; 2008, 89-134.  F. Hennrich, C. Chan, V. Moore, M. Rolandi, and M. O’Connell, “The element carbon,” in Carbon Nanotubes Properties and Applications, M. J. O’Connell, Ed., Taylor & Francis, Boca Raton, Fla, USA, 2006.  Xing W, Qiao SZ, Ding RG, Li F, Lu GQ, Yan ZF..Carbon, 44(2):216–24, 2006.  Frédéric Haschéa, Mehtap Oezaslan, Peter Strasser, Tim-Patrick Fellinger. Journal of Energy Chemistry 25, 251-257, 2016.  D. Santiago, G. G. Rodriguez-Calero, H. Rivera, D. A. Tryk, M. A. Scibioh, and C. R. Cabrera, J. Electrochem. Soc., 157(12), F189 (2010).