High energy efficiency and energy density, together with rapid refuelling capability, render fuel cells highly attractive for portable power generation. Accordingly, polymer-electrolyte direct-methanol fuel cells are of increasing interest as possible alternatives to Li ion batteries. However, such fuel cells face several design challenges and cannot operate with hydrocarbon fuels of higher energy density. Solid-oxide fuel cells (SOFCs) enable direct use of higher hydrocarbons, but have not been seriously considered for portable applications because of thermal management difficulties at small scales, slow start-up and poor thermal cyclability. Here we demonstrate a thermally self-sustaining micro-SOFC stack with high power output and rapid start-up by using single chamber operation on propane fuel. The catalytic oxidation reactions supply sufficient thermal energy to maintain the fuel cells at 500–600 °C. A power output of ~350 mW (at 1.0 V) was obtained from a device with a total cathode area of only 1.42 cm^2.

http://server.ihim.uran.ru/files/info/solid-oxide.pdf

A thermally self-sustained micro solid-oxide fuel-cell stack with high power density

This work is focused on the comparative analysis of electrochemical and transport properties in the major families of cathode and anode compositions for intermediate-temperature solid oxide fuel cells (SOFCs) and materials science-related factors affecting electrode performance. The first part presents a brief overview of the electrochemical and chemical reactions in SOFCs, specific rate-determining steps of the electrode processes, solid oxide electrolyte ceramics, and effects of partial oxygen ionic and electronic conductivities in the SOFC components. The aspects associated with materials compatibility, thermal expansion, stability, and electrocatalytic behavior are also briefly discussed. Primary attention is centered on the experimental data and approaches reported during the last 10–15 years, reflecting the main challenges in the field of materials development for the ceramic fuel cells.

Electrode materials and reaction mechanisms in solid oxide fuel cells: a brief review

Nasicons (sodium super ion conductors) are a class of solid electrolytes. Their structure, compositional diversity, evolution, and applications are reviewed. A wide range of materials is considered based on crystalline and glassy Nasicon compositions.

A wide-ranging review on Nasicon type materials

The question whether $\mathrm{La}\mathrm{Mn}{\mathrm{O}}_{3}$ accepts doping with tetravalent cations such as cerium and thus allows the preparation of electron-doped mixed-valent lanthanum manganites has been discussed controversially so far. Against the background of this problem, we present a comparative x-ray photoemission (XPS) study of epitaxial ${\mathrm{La}}_{0.7}{\mathrm{Ce}}_{0.3}\mathrm{Mn}{\mathrm{O}}_{3}$ (LCeMO) and ${\mathrm{La}}_{0.7}{\mathrm{Ca}}_{0.3}\mathrm{Mn}{\mathrm{O}}_{3}$ (LCMO) thin films. We focus on the exchange splitting of the Mn $3s$ core level peak, which is a direct indicator of the Mn valence and allows us to quantify the Mn valence in the outermost $3\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ of the films. We demonstrate that, depending on the oxygen content, the Mn valence can be tuned between a mixed ${\mathrm{Mn}}^{3+∕4+}$ state and a mixed ${\mathrm{Mn}}^{2+∕3+}$ state in both the LCeMO and the LCMO film. The oxygen content was varied by heating in ultrahigh vacuum for deoxygenation and in an oxygen atmosphere for reoxidation. In the LCeMO film, the deoxygenation not only changes the Mn valence, but also the Ce valence is driven from the $4+$ towards the $3+$ state.

XPS investigation of Mn valence in lanthanum manganite thin films under variation of oxygen content

A surface perspective on self-diffusion in rutile TiO2

Single-chamber cells of two different types have been operated between 700 and 800°C in various methane-air mixtures. These cells are made mostly of conventional materials for solid oxide fuel cells (SOFCs), strontium-doped lanthanum manganite, yttria-stabilized zirconia (YSZ), and Ni-YSZ cermet. One type is electrolyte-supported, while the other represents a state-of-the-art fabrication for anode-supported cells. The anode-supported cells operate in a narrower range of methane-air ratios, but offer remarkable maximum specific powers, 360 and 285 mW/cm 2 at 800 and 700°C, respectively. Some theoretical considerations about the actual operation of these cells are also provided.

Operating Conditions of a Single-Chamber SOFC

Single-chamber solid oxide fuel cell (SOFC) experiments have been carried out at temperatures below 900°C with methane-air mixtures. Our study confirms previous results obtained by Hibino and co-workers with conventional materials like for the cathode and a NiO-yttria-stabilized zirconia (YSZ) cermet for the anode. In addition, special attention has been paid both to the gas flow and to the actual operating temperatures. Platinum meshes and wires upon the electrodes would greatly influence their actual operating temperature and they have been systematically avoided for the working cells within this study. © 2004 The Electrochemical Society. All rights reserved.

Evaluation of the Actual Working Temperature of A Single-Chamber SOFC

The phase stability of La0.5Sr0.5CoO3-δ

Pulsed laser deposition of superionic ceramic thin films: deposition and applications in electrochemistry

La0.5Sr0.5MnO3 thin films were deposited onto sapphire substrates by means of the pulsed-laser deposition technique. These films were characterized by several techniques including x-ray diffraction, Rutherford backscattering spectrometry, energy-dispersive x-ray, atomic-force microscopy, scanning electron microscopy, and x-ray photoelectron spectroscopy (XPS). The cation ratios are the same in the deposited films as in the target. However, strontium segregation occurs at the film surface with an enrichment in this element compared to Mn and La, as shown by XPS. In addition, a clear correlation between the three different contributions which compose the O(1s) XPS signal and the Sr, La, and Mn surface concentrations has been established. Annealing the films at a sufficiently high-temperature produces the same crystal structure as in the target.

François Morin

Papers

Operating Conditions of a Single-Chamber SOFC

Evaluation of the Actual Working Temperature of A Single-Chamber SOFC

The phase stability of La0.5Sr0.5CoO3-δ

Pulsed laser deposition of superionic ceramic thin films: deposition and applications in electrochemistry

Chemical and structural characterization of La0.5Sr0.5MnO3 thin films prepared by pulsed-laser deposition