Proton infiltration of phosphosilicate glass-electrolytes for intermediate temperature fuel cell
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Proton infiltration of phosphosilicate glass-electrolytes for intermediate temperature fuel cell Yusuke Daiko, Takeshi Yamada, Atsushi Mineshige and Tetsuo Yazawa Department of Materials Science and Chemistry, University of Hyogo, 2167 Shosha, Himeji, 671-2280
ABSTRACT A fast proton conducting glass with proton transport number tH = 1 was successfully prepared by using conventional melting method. In-situ FTIR (Fourier transform infrared) measurements under hydrogen atmosphere, temperature of 300°C and applying 1 V between Pt electrodes were carried out in order to monitor the proton concentration. The electrode reaction on Pt in these conditions is similar to that under intermediate-temperature fuel cell operation. It was found from the in-situ FTIR measurements that the absorbance around 2900 cm-1 increases clearly after applying 1 V, whereas no significant change was observed around 3400 cm-1. Proton infiltration into the glass is discussed based on the in-situ FTIR and impedance results.
INTRODUCTION Fuel cells have attracted much attention as a clean power generator with small amount of CO2 emission. Solid oxide fuel cells (SOFCs) show high energy conversion efficiency, and heatwaste can be also utilized as a cogeneration system. Pt catalyst is not required for both anode and cathode reactions owing to their high operation temperature. However, operation temperature around 750°C for SOFC is relatively very high, and high-temperature materials are required for all the fuel cell components, resulting into increase the fabrication cost. In addition, thermal expansion mismatch between electrode and electrolyte, and also diffusion of some elements in electrode to electrolyte cause a degradation of fuel cell output power density. This has promoted a great interest in developing a new electrolyte with high proton or oxygen conductivity in intermediate temperature (300 - 600 °C).1-3
. Figure 1 Schematic illustration of spinodal-type phase separation for the phosphosilicate glass, and FTIR spectrum for the as-deposited glass.
Recently, we successfully prepared a high proton conducting phosphosilicate glass with proton transport number tH = 1 around 400-500°C.4 This glass shows a typical spinodal-type phase separation as shown in Fig. 1. Fuel cell operation was also confirmed using Pt sputtered electrodes at that temperature range. In general, protons are observed as OH groups in glasses.5,6 The concentration of protons (OH groups) in glasses prepared by the melting method is generally very low because of the very high preparation temperature, e.g. 1600°C. The reason why it was suggested that proton cannot move through glasses.7 Doremus et al. reported that mobility of Na+ ion is more than 10,000 times higher than that of H+ for some silicate glasses.8 Similarly, our glass has almost no OH groups at the as-prepared stage (Fig. 1). On the other hand, continuous fuel cell operation can also be observed at 500°C. It is thus strongly required to clarify which proton can move throughout the phosphosilicate glass during f
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