Solid Oxide Regenerative Fuel Cells Research Articles

Advanced materials for family of fuel cells: a review of polymer electrolyte membrane

Hydrogen is an important energy carrier and a strong candidate for energy storage. It will be a useful tool for storing intermittent energy sources such as sun. Hydrogen is a versatile energy carrier that can be used to power nearly every end-use energy need. By this work, modeling and controlling of ion transport rate efficiency in proton exchange membrane (PEMFC), alkaline (AFC), direct methanol (DMFC), phosphoric acid (PAFC), direct forming acid (DFAFC), direct carbon fuel cell (DCFC) and molten carbonate fuel cells (MCFC) have been investigated and compared together. Thermodynamic equations have been investigated for those fuel cells in viewpoint of voltage output data. Effects of operating data including temperature (T), pressure (P), proton exchange membrane water content (λ), and proton exchange membrane thickness (d_mem) on the optimal performance of the irreversible fuel cells have been studied. Performance of fuel cells was analyzed via simulating polarization and power curves for a fuel cell operating at various conditions with current densities. SOFC (Solid oxide fuel cell) is usually combined with a dense electrolyte sandwiched via porous cathode and anode and SORFC (Solid oxide regenerative fuel cell) is a subgroup of RFC with solid oxide regenerative fuel cell. SORFC operates at high temperature with high efficiency and it is a suitable system for high temperature electrolysis.

Nano-tailoring of infiltrated catalysts for high-temperature solid oxide regenerative fuel cells

Solid oxide regenerative fuel cells (SORFCs), which perform the dual functions of power generation and energy storage at high temperatures, could offer one of the most efficient and environmentally friendly options for future energy management systems. Although the functionality of SORFC electrodes could be significantly improved by reducing the feature size to the nanoscale, the practical use of nanomaterials has been limited in this area due to losses in stability and controllability with increasing temperature. Here, we demonstrate an advanced infiltration technique that allows nanoscale control of highly active and stable catalysts at elevated temperatures. Homogeneous precipitation in chemical solution, which is induced by urea decomposition, promotes crystallization behavior and regulates precursor redistribution, thus allowing the precise tailoring of the phase purity and geometric properties. Controlling the key characteristics of Sm0.5Sr0.5CoO3 (SSC) nanocatalysts yields an electrode that is very close to the ideal electrode structure identified by our modeling study herein. Consequently, outstanding performance and durability are demonstrated in both fuel cell and electrolysis modes. This work highlights a simple, cost-effective and reproducible way to implement thermally stable nanocomponents in SORFCs, and furthermore, it expands opportunities to effectively exploit nanotechnology in a wide range of high-temperature energy devices.

High Performance Air Electrode for Solid Oxide Regenerative Fuel Cells Fabricated by Infiltration of Nano-Catalysts

A high performance air electrode fabricated by infiltration of highly active nano-catalysts into a porous scaffold is demonstrated for high-temperature solid oxide regenerative fuel cells (SORFCs). The nitrate precursor solution for Sm0.5Sr0.5CoO3 (SSC) catalyst is impregnated into a porous La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) – gadolinia-doped ceria (GDC) composite backbone, and extremely fine SSC nano-particles are uniformly synthesized by in-situ crystallization at the initial stage of SORFC operation via homogeneous nucleation induced by urea decomposition. The SSC nano-catalysts are in the size range of 40-80 nm and stable against coarsening upon the SORFC operation at 750oC. The electrochemical performance is significantly improved by incorporation of SSC nano-catalysts in both power generation and hydrogen production modes. Systematic analysis on the impedance spectra reveals that the surface modification of the air electrode with nano-catalysts remarkably accelerates the chemical surface exchange reactions for both O2 reduction and O2- oxidation, which are the major limiting processes for SORFC performance.

High Performance Air Electrode for Solid Oxide Regenerative Fuel Cells Fabricated by Infiltration of Nano-Catalysts

A high performance air electrode was fabricated by infiltration of nano-catalysts into a porous backbone for high-temperature solid oxide regenerative fuel cells (SORFCs). The Sm0.5Sr0.5CoO3 (SSC) nano-catalysts were uniformly synthesized in a porous La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) – gadolinia-doped ceria (GDC) composite backbone by impregnation of nitrate precursor solution followed by homogeneous nucleation induced by urea decomposition. Significant improvement in the electrochemical performance was achieved in both solid oxide fuel cell (SOFC) and solid oxide electrolysis cell (SOEC) modes.

Electrochemical performance and long-term durability of a 200 W-class solid oxide regenerative fuel cell stack

The electrochemical performance and durability of a 200 W-class solid oxide regenerative fuel cell (SORFC) stack are investigated for cyclic mode-changing and long-term operation. Three unit cells (10 cm × 10 cm), each based on a Ni – yttria-stabilized zirconia (YSZ) fuel electrode, a scandia-stabilized zirconia (ScSZ) electrolyte and a Sr-doped LaCoO3 (LSC) – gadolinia-doped ceria (GDC) air electrode, are used for the stack development. Delamination of the air electrode is suppressed by using a mixed ionic- and electronic-conducting air electrode with no oxygen excess non-stoichiometry, and gas leakage is minimized by using novel glass-ceramic composite sealants. Excellent electrochemical performance is achieved in a single cell level by minimizing the ohmic and electrode polarizations, and the three-cell stack is successfully configured without major performance loss associated with electrical contacts, gas supply or sealing. Stable operation is confirmed at a thermal neutral voltage for 1000 h in the solid oxide electrolysis cell (SOEC) mode, and the periodic change of the operation mode between the solid oxide fuel cell (SOFC) and SOEC is found to accelerate the performance degradation. The effect of cyclic mode-changing on the stability of the SORFC stacks is discussed in detail based on the observations from the post-mortem microstructural analysis.

Challenges in the electrochemical modelling of solid oxide fuel and electrolyser cells

Computational fluid dynamics (CFD) tools for the modelling of solid oxide fuel cells (SOFC), solid oxide electrolyser cells (SOEC) or solid oxide regenerative fuel cells (SORFC) nearly always require a fitting process prior to its application for cell design or optimisation purposes. In this fitting, a set of experimental data is used to guess the value of those parameters of the model that cannot be either modelled or measured experimentally. This is crucially the case of the charge transfer coefficients ( α b , a , α f , a , α b , c , α f , c ) and the exchange current densities ( i o , a , i o , c ) in the Butler–Volmer equation ( i.e. electrochemical model). The fitting of the electrochemical parameters in the SOFC, SOEC and SORFC modelling literature is reviewed in this work. It is found that this process is only vaguely discussed, if mentioned at all. In the authors׳ opinion, this practice contributes with uncertainty rather than guidance, since this fitting process is of utmost significance for making reliable quantitative predictions. In this work, we further introduce a comprehensive model for the simulation of solid oxide regenerative fuel cells, i.e. a model that simulates, without any ad hoc adjustments or tuning, both the SOFC and SOEC modes. We also describe in detail how the electrochemical parameters are fitted, and discuss the applicability of the values commonly used in the literature for these fitted parameters and their proper validation. Finally, the validity of the proposed model and fitted parameters is shown by comparison of the numerical results with experimental data.

Gas transport in hydrogen electrode of solid oxide regenerative fuel cells for power generation and hydrogen production

To further develop solid oxide regenerative fuel cell (SORFC) technology, the effect of gas diffusion in the hydrogen electrode on the performance of solid oxide fuel cells (SOFCs) and solid oxide electrolysis cells (SOECs) is investigated. The hydrogen electrode-supported cells are fabricated and tested under various operating conditions in both the power generation and hydrogen production modes. A transport model based on the dusty-gas model is developed to analyze the multi-component diffusion process in the porous media, and the transport parameters are obtained by applying the experimentally measured limiting current data to the model. The structural parameters of the porous electrode, such as porosity and tortuosity, are derived using the Chapman–Enskogg model and microstructural image analysis. The performance of an SOEC is strongly influenced by the gas diffusion limitation at the hydrogen electrode, and the limiting current density of an SOEC is substantially lower than that of an SOFC for the standard cell structure under normal operating conditions. The pore structure of the hydrogen electrode is optimized by using poly(methyl methacrylate) (PMMA), a pore-forming agent, and consequently, the hydrogen production rate of the SOEC is improved by a factor of greater than two under moderate humidity conditions.

High performance air electrode for solid oxide regenerative fuel cells fabricated by infiltration of nano-catalysts

A high performance air electrode fabricated by infiltration of highly active nano-catalysts into a porous scaffold is demonstrated for high-temperature solid oxide regenerative fuel cells (SORFCs). The nitrate precursor solution for Sm0.5Sr0.5CoO3 (SSC) catalyst is impregnated into a porous La0.6Sr0.4Co0.2Fe0.8O3 (LSCF)–gadolinia-doped ceria (GDC) composite backbone, and extremely fine SSC nano-particles are uniformly synthesized by in-situ crystallization at the initial stage of SORFC operation via homogeneous nucleation induced by urea decomposition. The SSC nano-catalysts are in the size range of 40–80 nm and stable against coarsening upon the SORFC operation at 750 °C. The electrochemical performance is significantly improved by incorporation of SSC nano-catalysts in both power generation and hydrogen production modes. Systematic analysis on the impedance spectra reveals that the surface modification of the air electrode with nano-catalysts remarkably accelerates the chemical surface exchange reactions for both O2 reduction and O2− oxidation, which are the major limiting processes for SORFC performance.

Performance and Aging of Microtubular YSZ‐based Solid Oxide Regenerative Fuel Cells

AbstractFuel electrode supported microtubular solid oxide fuel cells (SOFC) fabricated at ICMA have been characterised in both solid oxide steam electrolyser (SOEC) and fuel cell modes. The cells consists of a fuel electrode supporting tube of Ni/YSZ with 40% porosity, ∼400 μm thickness, 2.4 mm diameter and 100–150 mm length, a 15 μm thick YSZ electrolyte and a 50 vol% LSM/YSZ composite air electrode of 20 μm thickness and LSM/YSZ (80/20 vol%) up to 2 cm2 area as current collector in the air side. Platinum paste and wires were used as interconnectors in the air chamber and Ni felt in the fuel side. SOFC and SOEC experiments were performed at temperatures between 750 and 950 °C using synthetic air in the oxygen electrode and different partial pressures of steam in the fuel side. Analysis of the polarisation contributions to the j–V curve in FC operation mode was performed using theoretical models, as discussed in the text. The effect of the steam concentration and temperature on the electrolysis and fuel cell experiments is presented and discussed. The cells are reversible in both modes of operation at low fuel conversion rates. According with previous observations, when cells are operated at high steam conversion rates the cell voltage tends to saturate. Irreversible damage was observed by SEM at the YSZ–oxygen electrode interface after operation, probably due to the electrolyte reduction produced at high voltages.

Applications and Markets for Solid Oxide Regenerative Fuel Cells

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Optimization and Demonstration of a Solid Oxide Regenerative Fuel Cell System

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Applications and Markets for Solid Oxide Regenerative Fuel Cells

To avoid the approaching oil infrastructure crisis, alternate energy supply scenarios and energy use patterns will have to be embraced. Fuel cells will undoubtedly play a major role in such a change. Regenerative Fuel Cells (RFCs) coupled to renewables could be one of the technologies having an impact in easing the approaching energy supply difficulties. RFCs have been researched for ∼50 years but are not yet found in the marketplace. There are multiple reasons for lack of market penetration, including: economic, efficiency, and durability. Solid Oxide Regenerative Fuel Cell (SORFC) test results to date, combined with volume cost projections for solid oxide fuel cells (SOFCs), indicate that several applications can be competitively met with SORFC systems. These applications include on-grid and off-grid distributed energy storage with or without co-produced hydrogen fuel; high altitude long endurance military and commercial aircraft and airships; and nuclear submarine life support and regenerative energy storage.