Homogeneous electron transfer reactions of the Cu(II) complexes of 5,10,15,20-tetraphenylporphyrin (TPP) and 2,3,7,8,12,13,17,18-octaethylporphyrin (OEP) with various oxidizing reagents were spectrophotometrically investigated in acetonitrile. The reaction products were confirmed to be the pi-cation radicals of the corresponding Cu(II)-porphyrin complexes on the basis of the electronic spectra and the redox potentials of the complexes. The rate of the electron transfer reaction between the Cu(II)-porphyrin complex and solvated Cu(2+) was determined as a function of the water concentration under the pseudo first-order conditions where Cu(2+) is in large excess over the Cu(II)-porphyrin complex. The decrease in the pseudo first-order rate constant with increasing the water concentration was attributed to the stepwise displacement of acetonitrile in [Cu(AN)(6)](2+)(AN = acetonitrile) by water, and it was concluded that only the Cu(2+) species fully solvated by acetonitrile, [Cu(AN)(6)](2+), possesses sufficiently high redox potential for the oxidation of Cu(ii)-OEP and Cu(ii)-TPP. The reactions of the Cu(II)-porphyrin complexes with other oxidizing reagents such as [Ni(tacn)(2)](3+)(tacn = 1,4,7-triazacyclononane) and [Ru(bpy)(3)](3+)(bpy = 2,2'-bipyridine) were too fast to be followed by a conventional stopped-flow technique. Marcus cross relation for the outer-sphere electron transfer reaction was used to estimate the rate constants of the electron self-exchange reaction between Cu(II)-porphyrin and its pi-cation radical: log(k/M(-1) s(-1))= 9.5 +/- 0.5 for TPP and log(k/M(-1) s(-1))= 11.1 +/- 0.5 for OEP at 25.0 degrees C. Such large electron self-exchange rate constants are typical for the porphyrin-centered redox reactions for which very small inner- and outer-sphere reorganization energies are required.

Doped Bi-based oxides were investigated as potential anode materials for direct hydrocarbon solid oxide fuel cells ͑SOFCs͒ at intermediate temperatures. (Bi 2 O 3 ) 0.85 (Ta 2 O 5 ) 0.15 met this criterion most successfully. A fraction of Bi 2 O 3 in this material was reduced to BiO and Bi metal under fuel conditions, which yielded high conductivities ͑Ͻ1 S cm Ϫ1 ͒ based on oxide ions and electrons above 500°C. Carbon deposition was successfully prevented when butane was used as the fuel below 800°C. The catalytic activities for hydrocarbon oxidation were high enough to promote the complete oxidation of butane during cell operation. These abilities provided an enhanced anode performance with increasing temperature from 600 to 750°C, and the resulting polarization resistance reached 1.4 ⍀ cm 2 at 750°C. Solid oxide fuel cells ͑SOFCs͒ can convert hydrocarbon fuels directly to electrical power with high efficiency, which provides a portable and economical system. 1,2 However, the most commonly used Ni/yttria-stabilized zirconia ͑YSZ͒ cermet anodes are not optimized for small-scale SOFC systems. Such a system must be regularly stopped and restarted for maintenance, which causes a serious volume change upon redox cycling of the Ni component. Moreover, these anodes are not well suited for use with hydrocarbon fuels because these promote their cracking. Recently, LaCrO 3 -based perovskite oxides have been considered alternative anodes. 3-8 These materials are p-type semiconductors in reducing atmospheres and can avoid carbon deposition successfully. Nonetheless, since the LaCrO 3 -based anodes are not as good electrocatalysts as the Ni/ YSZ-cermet anodes, the polarization resistances are large, especially at intermediate temperatures, unless catalysts such as Ni are doped into the B-site of LaCrO 3 .In this study, we attempted to use doped Bi-based oxides as potential anode materials for small-scale SOFC systems. These materials are readily reduced in reducing atmospheres at elevated temperatures, 9,10 which results in electronic conduction enough to provide the electrical path under fuel conditions. Many doped Bibased oxides also show high catalytic properties for hydrocarbon oxidation. 11 These abilities would offer suitable performance for operation on hydrocarbon fuels. A similar concept was proposed by Steele et al. in the 1990s, 12 but still has not been substantiated ͑al-though bismuth oxide-based catalysts such as Bi 2 Ru 2 O 7 and Bi 3 Ru 3 O 11 have been investigated as cathodes for oxygen sensors͒. 13 ExperimentalDifferent doped Bi-based oxides were investigated as anodes ͑see Table I͒, where Ce 0.9 Gd 0.1 O 1.95 ͑GDC͒ ͑14 mm diam, 0.75 mm thick͒, Sm 0.5 Sr 0.5 CoO 3 ͑0.5 cm 2 area͒, and Pt ͑ca. 0.2 cm 2 area͒ were used as the electrolyte, the counter and reference electrodes, respectively. The preparation and treatment of the latter three materials were described in detail elsewhere. 14,15 The anodes were synthesized as follows. The desired amounts of Bi 2 O 3 and M x O y (M ϭ Mo, W, Ba, Y, Yb, Gd, Er, Nb, ...