An Overview of Carbon Nanomaterials in Solid Acid Fuel Cell Electrodes

Micro- and nanometer sized carbon materials play an important role as components in low and intermediate temperature fuel cell electrodes. Vulcan carbon, active carbon, etc. have been used as catalyst substrates and electronic interconnect materials. As such, they reduce agglomeration of nanoparticulate catalyst and thus increase long-term stability. The catalyst utilization can be also increased significantly by improving the geometrical distribution of the catalyst. Recently, the drive towards ever smaller electrode structures has shifted attention towards carbon nanotubes (CNTs) and graphene. Their excellent electronic conductivity, extremely high specific surface area, and relatively good stability makes them suitable candidates as fuel cell electrode components. Both the catalyst distribution and utilization have been successfully improved, lowering costs and bringing the technology closer to market application. Importantly, numerous studies have recently shown functionalized CNTs and graphene, without precious metals, to be an effective catalyst for the oxygen reduction reaction. Especially nitrogen doped CNTs and graphene flakes show tremendous potential.1 Solid acid fuel cells based on CsH2PO4 as the solid state electrolyte operate at ca. 240°C and are currently performance limited at the cathode. Here, vulcan carbon has been mainly used as an electronic interconnect and catalyst support.2 Recently, carbon nanotubes have been employed, increasing the mass normalized activity of the Pt catalyst up to 61 S/mgPt.3,4 Here we combine the benefits of recent findings and present new fabrication routes based on spraydrying, metal-organic chemical vapor deposition to create highly active, nanostructured composite electrode materials, based on Pt decorated CNTs and graphene. In addition, we evaluate the suitability of surface functionalized carbon nanomaterials as precious metal free catalyst in solid acid fuel cell cathodes. Functionalization includes plasma treatment and electron beam irradiation under controlled atmospheres. Raman and XPS analysis is used before and after electrochemical measurements to evaluate structural and chemical changes. Data from impedance spectroscopy of symmetric electrochemical cells suggest effective electrochemical activity of CNTs and graphene in solid acid fuel cell cathodes.      (1)      Gong, K.; Du, F.; Xia, Z.; Durstock, M.; Dai, L. Science 2009, 323, 760. (2)      Chisholm, C. R. I.; Boysen, D. A.; Papandrew, A. B.; Zecevic, S. K.; Cha, S.; Sasaki, K. A.; Varga, Á.; Giapis, K. P.; Haile, S. M. Interface Magazine 2009, 18, 53. (3)      Varga, Á.; Pfohl, M.; Brunelli, N. A.; Schreier, M.; Giapis, K. P.; Haile, S. M. Physical chemistry chemical physics : PCCP 2013, 15, 15470. (4)      Thoi, V. S.; Usiskin, R. E.; Haile, S. M. Chem. Sci. 2015, 6, 1570.