Reversible Solid Oxide Fuel Cell Technology for Green Fuel and Power Production

Abstract

A reversible solid oxide fuel cell (RSOFC) is a device that can operate efficiently in both fuel cell and electrolysis operating modes. Thus, in the fuel cell mode, an RSOFC functions as an SOFC, generating electricity by electrochemical combination of a fuel (hydrogen, hydrocarbons, alcohols, etc.) with air (oxygen in the air). In the electrolysis mode, an RSOFC functions as an electrolyzer (in this case, referred to as a solid oxide electrolysis cell or SOEC), producing hydrogen (from water) or chemicals such as syngas (from mixtures of water and carbon dioxide) when coupled with an energy source (fossil, nuclear, renewable). Figure 1 illustrates the operating principles of the RSOFC. The RSOFC has the following attractive features (demonstrated or potential): compatibility (environmentally compatible with reduced CO 2 emissions in power generation mode), flexibility (fuel flexible and suitable for integration with any type of energy sources), capability (useful for different functions), adaptability (suitable for a variety of applications and adaptable to local energy needs), and affordability (competitive in costs). 1 The RSOFC thus possesses all the desired characteristics to serve as a technology base for green, flexible, and efficient energy systems in the future (Fig. 2).Sustainable energy systems based on the RSOFC for the future is feasible. An example of such a system is shown schematically in Fig. 3. In this system, the RSOFC, operating in the electrolysis mode, uses a renewable energy supply (e.g., solar, wind, hydro) to produce hydrogen (from H 2 O) or syngas (H 2 +CO) (from mixtures of H 2 O and CO 2 ). The chemicals produced can be used to generate power by the same RSOFC operating in the fuel cell mode or can be stored or converted to other chemicals/fuels for subsequent uses. Similarly, the RSOFC can generate power from biomass-derived fuels and the electricity generated can then be used for a variety of power generation applications.The RSOFC is both the SOFC and SOEC incorporated in a single unit. Since the SOEC is the SOFC operated in reverse mode and traditionally derived from the SOFC, the RSOFC being developed is typically based from the more technologically advanced SOFC. Thus, materials for the RSOFC are those commonly used in the SOFC, i.e., yttria stabilized zirconia (YSZ) for the electrolyte, perovskites (such as lanthanum strontium manganese oxide or LSM, lanthanum strontium cobalt iron oxide or LSCF) for the oxygen electrode, nickel/YSZ cermet for the hydrogen electrode and for stacking, conductive oxides (such as lanthanum strontium chromium perovskite or LSC) or stainless steels for the interconnect (depending on the operating temperature). Like the SOFC, the RSOFC operates in the temperature range of 600 o -1000 o C. Specific operating temperature depends on cell/stack designs and selected materials. 2,3 Solid Oxide Fuel Cell TechnologyThe RSOFC is fundamentally and technologically based on SOFC technology. In the past 20 years, the SOFC has received significant attention as a ...

Kinetics of CO/CO2 and H2/H2O reactions at Ni-based and ceria-based solid-oxide-cell electrodes

“…We propose that a higher surface concentration of reaction sites on the ceria nanoparticles in CO/CO 2 respectively (speculated to be so at ambient pressure).…”

“…[1][2][3][4] Furthermore, SOCs can operate with carbonaceous feedstocks (hydrocarbons, CO, CO 2 , etc.) [5][6][7][8] A good physical and chemical understanding of the electrochemical reactions (ERs) that occur in the fuel-electrode, CO 2 , is crucial for addressing performance and lifetime limiting factors as well as for designing new improved electrodes. The reactions take place either at the 3-phase boundary (3PB) between the gas, O 2À conductor and e À conductor, or at the 2-phase boundary (2PB) between the gas and the surface of a mixed ionic and electronic conducting (MIEC) solid, depending on the electrode materials.…”

High steam utilization operation with high current density in solid oxide electrolysis cells

“…In general, SOECs can operate reversibly in both electrolysis and fuel cell modes. 23) To reveal the electrode behavior, the iV curve in fuel cell mode was also measured. Here, the feed rate of the supplied gaseous mixture to the fuel electrode was a sufficiently high value for electrolysis to avoid the depletion of H 2 O at the surface of the fuel electrode.…”

“…This might be a consequence of concentration polarization due to a low water partial pressure, p H2O , compared with hydrogen partial pressure, p H2 , in the supplied fuel. Also, because the oxygen electrode performance at high i in the electrolysis mode is often irreversible to the fuel cell mode, 23) the increase in V in the electrolysis mode might be attributed to the oxygen electrode reaction. Figure 3 shows the impedance spectra for the SOEC at different V in electrolysis mode.…”

“…For electrode polarization, the increase in R 1 and R 2 was considered due to the decreasing performance of the oxygen electrode with increasing i in electrolysis mode. 23) Also, the increasing R 3 indicates that the concentration polarization resistance of the fuel electrode was severely affected i even though H 2 O for electrolysis was supplied in excess. This suggests that reducing the concentration polarization resistance is essential to achieve high U steam and high i operation.…”