Highly dense (> 94 vol%) oxides, such as zirconia, ceria, and titania, presenting high proton conductivity can be prepared by High-pressure Field Assisted Sintering (HP-FAST) method. The observed protonic conduction is unexpected in this class of oxides and is produced by an interconnected network of open nanoporosity deriving from the fast sintering procedure.
The resulting conductivity values are much higher than those of liquid water, indicating a significant increase in the charge carriers concentration. At higher temperatures (up to 450 °C), unexpected proton conduction is still present, thanks to the persistence of hydroxyl groups, derived from water chemisorption, which still produce protons by ionization. The phenomenon is strongly dependent on grain size, and not explicable by simple geometric brick-layer models, suggesting that the enhanced ionization could rely on space charge region effects.
Uncovering the mechanism of low-temperature protonic conduction in highly dense nanostructured metal oxides opens the possibility to exploit the application of simple ceramic electrolytes in proton exchange fuel cells, overcoming the drawbacks related to the use of polymeric membranes.
Related publications:
Tredici, Ilenia G., Filippo Maglia, Chiara Ferrara, Piercarlo Mustarelli, and Umberto Anselmi-Tamburini. “Mechanism of Low-Temperature Protonic Conductivity in Bulk, High-Density, Nanometric Titanium Oxide.” Advanced Functional Materials 24, no. 32 (2014): 5137–46.
lia, Filippo, Ilenia G. Tredici, Giorgio Spinolo, and Umberto Anselmi-Tamburini. “Low Temperature Proton Conduction in Bulk Nanometric TiO2 Prepared by High-Pressure Field Assisted Sintering.” JOURNAL OF MATERIALS RESEARCH 27, no. 15 (2012): 1975–81.
Chiodelli, Gaetano, Filippo Maglia, Umberto Anselmi-Tamburini, and Zuhair A. Munir. “Characterization of Low Temperature Protonic Conductivity in Bulk Nanocrystalline Fully Stabilized Zirconia.” Solid State Ionics 180, no. 4–5 (2009): 297–301.
Kim, Sangtae, Umberto Anselmi-Tamburini, Hee Jung Park, Manfred Martin, and Zuhair A. Munir. “Unprecedented Room-Temperature Electrical Power Generation Using Nanoscale Fluorite-Structured Oxide Electrolytes.” Advanced Materials (Weinheim, Germany) 20, no. 3 (2008): 556–59.
Anselmi-Tamburini, Umberto, Filippo Maglia, Gaetano Chiodelli, Pietro Riello, Stefania Bucella, and Zuhair A. Munir. “Enhanced Low-Temperature Protonic Conductivity in Fully Dense Nanometric Cubic Zirconia.” Applied Physics Letters 89, no. 16 (2006): 163116/1–163116/3.