Advanced Inorganic Materials for Solid Oxide Fuel Cells

Abstract

PC-SOFC -Proton conducting solid oxide fuel cell IT-SOFC -Intermediate temperature solid oxide fuel cell IntroductionFuel cells are widely regarded as a next generation technology that will contribute to reductions in emissions of gases responsible for climate change such as CO 2 . There are several modifications to the basic concept of a fuel cell that allow operation over a wide variety of temperatures and with differing fuels. One of the most promising types of fuel cell for large scale power generation and combined heat and power applications is the solid oxide fuel cell (SOFC). The solid oxide fuel cell offers many advantages over conventional combustion-based power generation technologies and has been the subject of intensive investigation for many years. As with all other fuel cells the SOFC is an electrochemical energy conversion device that converts the chemical energy contained within a fuel (for example, H 2 ) to useful electrical energy through an electrochemical oxidation process. Using the simplest fuel as an example the overall chemical reaction occurring is: To achieve this overall reaction it is essential that we consider the basic components of the fuel cell. A SOFC consists of three ceramic functional components (anode "fuel side", cathode "air side" and electrolyte) plus an electrical interconnect that is either ceramic or metallic depending upon the operating environment. These 4 components are referred to as the fuel cell and to achieve suitable power outputs these individual cells are connected to form a fuel cell stack. Schematics of two alternative designs of a single fuel cell are shown in Figure 1.At the anode the fuel is oxidised with the oxidant (oxygen) reduced at the cathode.These two components are separated by a gas tight electrolyte membrane that is a pure ionic conductor, transporting the oxide ion species from the cathode to the fuel side. This process releases electrons to an external circuit, providing the useful electrical power. These reactions are summarised as:cathode reaction Evidently these electrode reactions are significantly more complex than shown in equations 1.1. and 1.2 and fuller discussions of the proposed fuel oxidation and oxygen reduction electrode reactions are given in [1][2][3][4].It is therefore clear that in a solid oxide fuel cell there are many processes that require optimised materials, and consequently the SOFC is a complex solid state device. As a summary, it is essential that the electrolyte is a gas tight, pure ionic conductor stable over a wide pO 2 range (>10 -24 atm). Anodes have to possess stability in reducing conditions with both high ionic and electronic conductivity, and chemical compatibility with the electrolyte material. Similar properties are required for the cathode with the exception that stability is now in oxidising environments.Additionally the cathode has to be catalytically active towards oxygen reduction, which is often a rate limiting process, particularly at lower temperatures of operation (<650 o C). These are demanding pr...

A Brief Description of High Temperature Solid Oxide Fuel Cell’s Operation, Materials, Design, Fabrication Technologies and Performance

“…Metal, ceramics or their composites are widely used for the construction of these components. Different criteria are required for each material in order to operate in multiple capacities [4][5][6][7][8][9][10][11][12][14][15][16][17][18][19][34][35][36]. Different materials used in different SOFC components along with their requirements are discussed below.…”

The influence of the reducing conditions on the final microstructure and performance of nickel-yttria stabilized zirconia cermets

“…However, it presents some drawbacks including those associated with thermal cycling, redox stability due to the significant volume changes upon oxidation of Ni to NiO and thus affecting the mechanical integrity of the cell, as well as sulphur deposition or coking when 3 carbon rich fuel streams are used [5,6]. In recent years, several efforts are being performed in order to elucidate the redox-cycling problem [7][8][9][10][11][12].…”

Performance of La2–xSrxCo0.5Ni0.5O4±δ as an Oxygen Electrode for Solid Oxide Reversible Cells

“…One of the major problems in SOFCs, particularly at intermediate temperatures (IT), is the large cathode overpotential during operation [1,2]. Up to 60% of voltage loss in anode-supported SOFCs can occur at the cathode due to polarization losses associated with the oxygen reduction reaction [3].…”

“…The overall conductivity at elevated temperatures has been reported as greater than 100 S cm -1 [22] and the material has potential in applications as the oxygen electrode in both SOFC and SOEC modes of operation. 2 .4H 2 O, as described in [22]. In this study, dense electrolyte pellets were fabricated using 10Sc1CeSZ (10% Sc 2 O 3 and 1%CeO 2 doped ZrO 2 ) powder (Fuel Cell Materials Inc).…”