• Energy Research

Abstract An electrochemical model is developed to investigate capacity recovery methods for cycled lithium ion batteries. Different capacity recovery methods are evaluated and compared. The center recovery method for commercial batteries is found to be impractical because it causes severe solid surface concentration gradients which may harm the batteries. On the contrary, the center recovery method for novel batteries with porous current collector sheets is better than the bottom recovery method because smaller solid surface concentration gradients are detected and less relaxation time is required during capacity recovery. Capacity recovery methods which discharge negative electrodes is superior to those which discharge positive electrodes of cycled batteries as smaller solid surface concentration gradients is generated and less relaxation time is required at the same discharging current.

Abstract A two-dimensional (2D) model is developed to analyze the performance and efficiency of H 2 O/CO 2 co-electrolysis in tubular SOEC (solid oxide electrolysis cell). The model fully considers the fluid flow, heat/mass transfer and electrochemical/chemical reactions in the SOEC. The results show that RWGSR (reversed water-gas shift reaction) significantly promotes CO 2 conversion ratio. The effect of important operating parameters was comprehensively studied and optimal operating condition was determined. When the inlet gas flows in parallel flow mode with the velocity of 1 m s −1 , TSOEC with the H 2 O/CO 2 molar ratio of 1 at 700 °C at 1.4 V achieves the highest efficiency of 59.4% and the syngas conversion ratio of 43.8%. Lowering gas flow velocity decreases the syngas yield but promotes H 2 O/CO 2 convert ratio and efficiency. Finally, calculation found that counter flow is superior to parallel flow.

In this study, the fuel-rich combustion of methane in a two-layer porous media burner consisting of dense alumina pellets of different diameters was investigated experimentally and numerically. For a fixed inlet gas velocity of 0.15 m/s, methane-rich flames were stabilized near the interface of two layers for equivalence ratios from 1.4 to 1.6. It was found that 40% of the methane was converted to syngas at the equivalence ratio of 1.6 using a reforming efficiency based on low heating values. To further increase the hydrogen yield and make the burner more suitable for applications in fuel cells, a portion of the downstream layer was coated with 0.08 wt % Ni catalyst. The reforming efficiency of methane to hydrogen increased from 18.2% to 23.9% after the catalytic enhancement. A combined homogeneous and heterogeneous elementary reaction mechanism was developed for methane partial oxidation in the porous media burner with catalytic enhancement. A one-dimensional model was explored by coupling the combined m...

Abstract A Solid oxide fuel cell (SOFC) with a liquid antimony anode (LAA) is a potential energy conversion technology for impurity-containing fuels. Atmospheric plasma spraying (APS) technology has become a promising LAA-SOFC preparation method because of its economy and convenience. In this paper, button SOFCs with different cathode materials and ratios of pore former were prepared by the APS method and measured at 750°C. The effect of the cathode structure on the electrochemical performance of the LAA-SOFCs was analyzed, and an optimized spraying method for LAA-SOFCs was developed. A tubular LAA-SOFC was prepared by the APS method based on the optimized spraying method and a peak power of 2.5 W was reached. The tubular cell was also measured at a constant current of 2 A for 20 hours and fed with a sulfur-containing fuel to demonstrate its impurity resistance and electrode stability.

Abstract A comprehensive model considering all forms of polarization was developed. The model considers the intricate interdependency among the electrode microstructure, the transport phenomena, and the electrochemical processes. The active three-phase boundary surface was expressed as a function of electrode microstructure parameters (porosity, coordination number, contact angle, etc.). The exchange current densities used in the simulation were obtained by fitting a general formulation to the polarization curves proposed as a function of cell temperature and oxygen partial pressure. A validation study shows good agreement with published experimental data. Distributions of overpotentials, gas component partial pressures, and electronic/ionic current densities have been calculated. The effects of a porous electrode structure and of various operation conditions on cell performance were also predicted. The mechanistic model proposed can be used to interpret experimental observations and optimize cell performance by incorporating reliable experimental data.

AbstractThe elevated temperature pressure swing adsorption (PSA) is a promising technology for pre-combustion CO2 capture in Integrated Gasification Combined Cycle (IGCC) power plant by taking the advantages of high partial pressure (1.0-2.0MPa) of CO2 in the syngas after water-gas shift reaction. An elementary reaction kinetic model was developed to predict the CO2 adsorption capacity and adsorption kinetic behavior for potassium promoted hydrotalcite-like compound (K-promoted HTlcs). Thermo gravimetric analysis (TGA) and a high pressure adsorption apparatus were respectively used below atmospheric pressure and above atmospheric pressure. The results indicate that the modeling results agreed well the experimental results. The elevated temperature PSA system modeling framework is developed by considering comprehensive coupling effects from mass, heat, and momentum transport mechanisms. The modeling framework is implemented in the gPROMS commercial simulation platform by integrating adsorption bed with dynamic boundary condition and realistic operating procedures. The presented modeling framework can be further applied for the system optimization and controller design for multi-column elevated temperature PSA processes.

Abstract This paper is the first part of a two-part paper and presents the development, calibration and validation of a two-dimensional isothermal mechanistic model of a composite yttria/scandia-stabilized zirconia anode-supported multiple layers solid oxide fuel cell (Ni–YSZ|Ni–ScSZ|ScSZ|LSM–ScSZ). This model was developed to describe the intricate interdependency among the ionic conduction, electronic conduction, multi-component species transport, electrochemical reaction processes and electrode microstructure for intermediate temperatures operation between 750 and 850 °C. This model takes into account the fact that the electrochemical reactions take place throughout the electrodes and not only at the electrolyte/electrode boundaries. The model was calibrated using experimental polarization curves and then validated by comparing each cell component polarizations (anodic, cathodic and electrolyte) determined from the simulation and from specific experiments using a symmetric cell and EIS measurements.

The feasibility of inkjet printing of electrodes for DC-SOFC was tested. A variety of materials was deposited by direct ceramic inkjet printing (DCIJP). The technology allows for easy modification of the coatings, including thickness control, porosity graduation and precise infiltration with catalytically active materials. The comparative tests showed a similar performance for screen printed and inkjet printed cells (peak power density of ca. 80 mW cm-2 at 780°C). In addition DCIJP offers minimization of the usage of expensive precursor materials. It was also found that infiltration of the anode by inkjet printing of sol inks (CuNiO3) can lead to an improvement in DC-SOFC performance.