Yixiang Shi

Simulation of Electrochemical Impedance Spectra of Solid Oxide Fuel Cells Using Transient Physical Models

A general electrochemical impedance spectroscopy (EIS) modeling approach by directly solving a one-dimensional transient model based on physical conservation laws was applied for simulating EIS spectra of an anode-supported solid oxide fuel cell (SOFC) button cell consisting of Ni-yttria-stabilized zirconia |Ni-scandia-stabilized zirconia (ScSZ)|ScSZ|lanthanum strontium manganate (LSM)-ScSZ multiple layers. The transient SOFC model has been solved for imposed sinusoidal voltage perturbations at different frequencies. The results have then been transformed into EIS spectra. Six parameters had to be tuned (three for the cathode and three for the anode) and have been estimated using data from a symmetric cathode cell and from a button cell. The experimental and simulated EIS spectra were in good agreement for a range of temperatures (750-850°C), of feed compositions (mixture of H 2 /H 2 O/N 2 ), and of oxidants (air and oxygen). This approach can help in interpreting EIS spectra, as illustrated by identifying the contribution of transport limitation.

Recent advances in high-temperature carbon–air fuel cells

The development of environmentally clean and energy-efficient coal-based power plants is of strategic importance to meet the increasing demand for more energy and clean air in the future. Carbon–air fuel cells (CAFCs) are a promising class of clean, efficient and sustainable power generators fueled by an abundant, cheap and sometimes renewable fuel source – coal, biomass, municipal waste, and other forms of solid carbons, with low emissions of CO2, NOx, SOx and VOCs. Because of the inherent thermodynamic and environmental advantages, CAFCs have garnered much interest in recent decades. In this article, we review recent advances in material development for catalysts/anodes and novel designs of various types of CAFCs. Fundamental understanding of the mechanisms and rate-limiting steps in carbon conversion is also discussed in detail. Finally, the review is concluded with promises and challenges of CAFCs.

Numerical Simulation of Multi-Channel Planar Solid Oxide Fuel Cell Unit by Integrating Continuum Micro-Scale PEN Sub-Model

Hongjian Wang, Yixiang Shi, Ningsheng Cai Key laboratory for Thermal Science and Power Engineering of Ministry of Education Tsinghua University, Beijing 100084, China The comprehensive three-dimensional model of a 10-channel anode-supported planar solid oxide fuel cell (SOFC) unit was developed in commercial Fluent CFD modeling platform with self-designed external VC++ sub-routine for the SOFC unit by considering mass, momentum, energy and charge balance equations. The continuum micro-scale PEN sub-model coupled the processes of ionic/electronic charge transport, porous electrode diffusion as well as the effects of electrode microstructures. The PEN sub-model was well validated by the SOFC button cell experimental data. The effects of operating conditions parameters, cell unit macro structure (interconnector rib), as well as the porosity of anode and cathode on cell performance, and the distribution of temperature, flow rate and current density were studied in detail. The proposed model is a possible tool for combined optimization of micro-scale electrode structures and macro-scale channel geometries, which also can be expanded to be applied in SOFC stack level.

A bifunctional solid oxide electrolysis cell for simultaneous CO2 utilization and synthesis gas production

We hereby report on a pioneering and inspiring solid oxide cell which, assisted by natural gas, utilizes a bifunctional electrolysis cell configuration to effectively consume CO2 to produce CO at the cathode side and simultaneously synthesize highly valuable syngas (mixture of CO and H2) at the anode side via a one-step green process.

Elementary Reaction Modeling of Methane Catalytic Combustor: Effects of Hysteresis in Pd-Based Catalyst Activity

An elementary reaction model of methane oxidation over γ-Al2O3–supported palladium is developed by considering the phenomena of bulk reduction, hysteresis of catalyst activity, and negative activation during the re-oxidation. Validation of this model into a practical reactor with reverse flow operation is contained. Simulation results show residence time and full cycle time to be the predominating factors of temperature and reduction state distribution, respectively. Hysteresis of catalyst activity causes a vibrating pattern of outlet conversion, which is considered to go against industrial application.

Simulation of Two-Dimensional Electrochemical Impedance Spectra of Solid Oxide Fuel Cells Using Transient Physical Models

A two-dimensional (2D) EIS simulation approach was developed by solving a SOFC unit cell model with imposed sinusoidal voltage perturbations at different frequencies. The transient SOFC unit cell model describes the intricate interdependency among the ionic/electronic conduction, multi-component species transport, electrochemical reaction processes and electrode microstructure as well as the coupling processes of mass, energy, momentum transport within flow channels. The model calculates the local transient response and impedance spectra as a function of channel position. The effects of the reaction depletion, product accumulation as well as the temperature variation along the flow channels on the EIS spectra was numerically simulated with a counter-flow mode. The results show that the convection-diffusion process along the flow channel has significant effects on the low frequency circle of the impedance spectra. The temperature oscillations accumulate along the flow channels, and then affect the current response which probably leads to electro-heat impedance effects.

Dynamic Processes of Mode Switching in Reversible Solid Oxide Fuel Cells

AbstractWith the development of distributed energy systems (DES), energy storage has attracted much attention in the research world. Reversible solid oxide fuel cells (RSOFCs) have shown potential ...