(599c) Nanostructured Composite Intermediate-Temperature Solid Acid Fuel Cells Fabricated By Needleless Electrospinning

Fuel cells are the most efficient technology available today for the conversion of chemical energy into electricity. A new and promising fuel cell technology is the solid acid fuel cells (SAFCs), offering unique possibilities as a result of their intermediate-temperature region of fuel cells (100â??300 °C). Their state of the art solid electrolyte, CsH₂PO₄ (CDP) is a solid acid compound with a superprotonic phase transition around 240 °C [1]. Under a dry condition the dehydration of CDP proceeds to form polymerization at temperatures above 200 °C, and CDP transforms into CsPO₃ [2]. Development of the catalytic performance can enable this type of fuel cell to be among the leading fuel cells on todayâ??s market.

Due to the pure ionic conducting nature of the electrolyte, the electrochemical reactions occur at the so-called triple phase boundaries, between the catalyst, electrolyte and the gas phase. Because of the triple phase, decreasing just the size of the catalyst does not increase the electrochemical reaction rates. However, in case the size of the electrolyte is also decreased, the electrochemical reaction rate is higher at the triple phase boundary resulting in increased power density of the fuel cell [1].

Needleless electrospinning technique was employed to fabricate nanostructured SAFC electrodes from CDP/CsPO₃-polymer solutions. Nanostructured CDP composite has the advantage of increased catalytic surface due to the large surface area. Needleless electrospinning is an inexpensive technique for producing nanostructured fuel cells at industrial scales. Instead of the commonly used nozzle, the needleless design employs a rotating drum immersed in a solution bath. Multiple Taylor cones form on the drum electrode surface resulting in rapid deposition of nanofibers over large areas. By applying CsPO₃ solutions, the phosphate groups form a chain, increasing the viscosity of the solution. This enables electrospinning with negligible amounts of polymers. The fibers produced from the solutions have diameters between 30 nm â?? 300 nm depending on the initial solution concentration, substrate temperature, and applied voltage. The deposition area is over 100 cm² and the deposition rate is up to 2 g/hr in the laboratory scale setup. Electrochemical characterization of the nano-composite electrodes, performed by A.C. impedance spectroscopy of symmetric cells under humidified hydrogen, confirmed the high activity of the electrospun nanocomposite electrodes. Fuel cell results using electrospun nanofibers from CsPO₃ solutions demonstrate that a 0.86 V cell voltage can be obtained at a current density of 50 mA/cm², which is ~10% higher than what can obtained using state-of-the-art techniques.

[1] C. R. Chisholm, D. A. Boysen, A. B. Papandrew, S. K. Zecevic, S. Cha, S., K. A. Sasaki, Á. Varga, K. P. Giapis, S. M. Haile, Interface, 2009, 18, 53-59.

[2] Y. Taninouchi, T. Uda, Y. Awakura, A. Ikeda, S.M. Haile J. Mater. Chem., 2007, 17, 3182.