Effect of Electrode and Electrolyte Modification on the Performance of One‐Chamber Solid Oxide Fuel Cell

Abstract

One-chamber solid oxide fuel cells (SOFCs) working in mixtures of methane and air have been studied extensively, 1-6 because of the advantages of the direct use of hydrocarbons such as methane as fuel gas without a reformer and the simpler cell structure compared to that of a conventional fuel cell. For instance, this cell can easily be stacked using staggered anodes and cathodes on one side of the electrolyte, 3,7-9 thus the ohmic resistance of the cell can be decreased by reducing the distance between anode and cathode rather than by using thin electrolytes as done in conventional SOFCs. The working principle of this cell is based on the difference in catalytic activity between Pt and Au electrodes for the partial oxidation of CH 4 to form H 2 and CO at high temperatures, as shown in Eq. 1which is active for the Pt electrode and relatively inactive for the Au electrode, thus resulting in the formation of electromotive force (emf) between the two electrodes. Presently, the electrolyte materials investigated in the one-chamber cell include mixed ionic (H ϩ and O 2Ϫ ) conductors such as BaCeO 3 -based ceramics 3,4 and an oxygen ion conductor such as yttria-stabilized zirconia (YSZ), as widely used in conventional SOFCs. It was reported that a power density of up to 0.17 W cm Ϫ2 was generated at 950ЊC for a one-chamber cell using BaCe 0.8 Y 0.2 O 3Ϫ␣ as electrolyte. 4 However, it was found that the BaCeO 3 -based ceramic electrolyte would react with CO 2 , a product of the cell, to form BaCO 3 at the surface of the electrolyte and consequently degrade cell performances. 10 The emf of a one-chamber cell using YSZ as electrolyte will decrease with time. Moreover, the power density is very low due to the large polarization characteristics of both Au and Pt electrodes. 5,6 It was suggested by comparison with the good performance of Au and Pt electrodes on BaCeO 3 -based electrolyte, which exhibits partial electronic conduction, 2,4 that electronic conduction at the electrolyte surface may play a role by increasing the length of the threephase boundaries where electrode reactions take place, leading to a decrease in electrode polarization. As a result, investigations have sought to improve the polarization characteristics of Au and Pt electrodes by using TiO 2 -doped or Pr 6 O 11 -coated YSZ electrolytes 5,6 in which electronic conduction (n-type or p-type) was expected to be present.In this work, Au and Pt electrodes were modified by incorporating oxides with cations of different valence. The valence change or electron hopping mechanism in the oxide additives was expected to provide some electrocatalysis of the electrode reactions. Experimental results showing improved discharge characteristics of electrodes and electrolyte with added MnO 2 and the corresponding microstructures of the electrolyte/electrodes interfaces are reported, and the possible effects of MnO 2 in the electrodes and the electrolyte are discussed in this paper. ExperimentalThe structure of the one-chamber fuel cell is illustrated in Fig. 1a. The dis...

Single-Chamber Solid Oxide Fuel Cell Technology—From Its Origins to Today’s State of the Art

“…In [114], both Pt and Au electrodes were doped with MnO 2 leading to a decrease in electrode overpotentials and reaction resistance. For an optimized composition of 15 wt% MnO 2 -Pt and 20 wt% MnO 2 -Au on a YSZ electrolyte, an OCV of 0.62 V and a maximum current density of 160 mA·cm…”

Electrodeposition of a Au-Dy2O3 Composite Solid Oxide Fuel Cell Catalyst from Eutectic Urea/Choline Chloride Ionic Liquid

“…The counter electrode (CE) was a graphite rod with an exposed area of 3 cm 2 . A Au wire was chosen as the quasi-reference electrode (QRE), as customary in the literature and successfully tested in our own laboratory [18,31].…”

“…In this way an oxide with controlled nanometric structure, more suited for electrocatalytic work can be achieved. We used a gold matrix in order to devise a model system aiming at singling out the specific catalytic properties of finely dispersed dysprosium oxide, according to cognate SOFC literature discussing dispersed MnO 2 catalyst in a Au matrix [17,18]. Of course, it is relatively straightforward to replace Au with another metal that can be electrodeposited from the same solvent, such as Ni, if the target of the research is to fabricate a better performing catalyst for direct application.…”

Single‐Chamber Fuel Cells

“…For a Pt cathode and Au anode, the performance could be enhanced with various electrolyte materials, and a maximum power of 170 mW cm −2 at 950 • C was obtained with a Pt|BaCe 0.8 Y 0.2 O 3−α |Au cell [50]. YSZ electrolytes doped with TiO 2 , Tb 4 O 7 , and Pr 6 O 11 [49,51], MnO 2 -doped Pt, and Au electrodes [52] were also investigated before turning to cells composed of conventional SOFC materials [53]. OCVs of about 1 V and power densities of several hundred milliwatts per square centimeter can be obtained with these cells at high and intermediate operating temperatures [4], and operation at temperatures below 450 • C becomes possible by using the heat released from the fuel reactions [25].…”