A Theoretical Study of the Carbon/Carbonate/Hydroxide (Electro-) Chemical System in a Direct Carbon Fuel Cell (original) (raw)
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Journal of Electroanalytical Chemistry, 2012
The Direct Carbon Fuel Cell (DCFC) is a special type of high temperature fuel cell that directly uses solid carbon particles as anode and fuel. As an electrical power generator of power plants, it has a higher achievable efficiency (80%) than the Molten Carbonate (MCFC) and the Solid Oxide (SOFC) fuel cells, and has less emission than conventional coal-combustion power plants. In this paper, we propose a comparative study based on an analytical model for polarizations calculation in DCFC producing CO 2 and a mixture of (CO/CO 2 ) and using a carbonate melt (62 Li 2 CO 3 /38 K 2 CO 3 mol%) as electrolyte. The obtained results indicate that when the CO is taken into account in the anode side, the DCFC performance increases by 15% compared to only CO 2 producing DCFC system at the same operating conditions (moves from 1350 W m À2 to 1550 W m À2 ). Simulations lead to understand the effect of the operating conditions (temperature, cathodic gas composition and inlet cathodic pressure) on the performance of the DCFC in order to solve all constraints preventing the development of this type of fuel cell. The comparison of the obtained results with data from literature illustrates a relatively good agreement with an absolute average deviation of about 4%.
Analysis of molten carbonate fuel cell performance using a three-phase homogeneous model
2003
In this study a three-phase homogeneous model was developed to simulate the performance of the molten carbonate fuel cell ͑MCFC͒ cathode. The homogeneous model is based on volume averaging of different variables in the three phases over a small volume element. This approach can be used to model porous electrodes as it represents the real system much better than the conventional agglomerate model. Using the homogeneous model the polarization characteristics of the MCFC cathode was studied under different operating conditions.
Analysis of a molten carbonate fuel cell: Numerical modeling and experimental validation
Journal of Power Sources, 2006
A detailed dynamic model incorporating geometric resolution of a molten carbonate fuel cell (MCFC) with dynamic simulation of physical and electrochemical processes in the stream-wise direction is presented. The model was developed using mass and momentum conservation, electrochemical and chemical reaction mechanisms, and heat-transfer. Results from the model are compared with data from an experimental MCFC unit. Furthermore, the model was applied to predict dynamic variations of voltage, current and temperature in an MCFC as it responds to varying load demands. The voltage was evaluated using two different approaches: one applying a model developed by Yuh and Selman [C.Y. Yuh, J.R. Selman, The polarization of molten carbonate fuel cell electrodes: I. Analysis of steady-state polarization data, J. Electrochem. Soc. 138 (1991) 3642-3648; C.Y. Yuh, J.R. Selman, The polarization of molten carbonate fuel cell electrodes: II. Characterization by AC impedance and response to current interruption, J. Electrochem. Soc. 138 (1991) 3649-3655] and another applying simplified equations using average local temperatures and pressures. The results show that both models can be used to predict voltage and dynamic response characteristics of an MCFC and the model that uses the more detailed Yuh and Selman approach can predict those accurately and consistently for a variety of operating conditions.
Thermodynamic Study of a Molten Carbonate Fuel Cell (MCFC) System
Journal of emerging technologies and innovative research, 2018
In the present work, thermodynamic analysis of a molten carbonate fuel cell (MCFC) is considered. Accordingly, a thermodynamic model is developed to understand performance of the cell at different operating conditions. The effect of operating parameters like working temperature, fuel utilization, current density, gas constituents etc. on the performance of the basic MCFC are studied to understand the behaviour of the cell. It is noticed that the cell voltage shows a strong dependence on the operating temperature. The actual cell voltage is less than the reversible cell voltage because of the losses occurs in a cell which is taken constant in the present analysis. Result shows that an operating temperature of 650 0 C offers an optimization for better performance and cell life.
2D computing model of electrochemistry coupled with mass and heat transfer in DCFC. Good agreement between numerical and experimental results (AAD of 9%). DCFC temperature distribution varied by 15 C among all the cell sub-domains. Accurate prediction of DCFC polarization curve by using peroxide mechanism. DCFC output is sensitive to electrolyte porosity and anode specific surface area. a b s t r a c t A two-dimensional modeling of a lab-scale planar Direct Carbon Fuel Cell (DCFC) of 20 mm in diameter is developed by taking into account of the electrochemical mechanisms and mass and heat transfer phenomena in all regions of the cell simultaneously. The electrodes and the electrolyte of the DCFC are both considered as distinct regions with different local properties such as permeability, conductivity and diffusivity. An improved packed bed anodic structure with a finite thickness is also adopted. General boundary conditions are implemented by taking into consideration the species concentrations at the DCFC inlet such as oxygen concentration which is a very important parameter to determine the cell efficiency. The effects of the main operating parameters such as temperature, inlet gas flow velocity and porosity of the electrolyte matrix on the DCFC efficiency are investigated. A sensitivity analysis based on numerical simulations of the effects of cathode kinetic parameters and the anode specific surface area is also performed. Good agreement is obtained between numerical results and experimental data with an absolute average deviation of about 9%.
Factors That Determine the Performance of Carbon Fuels in the Direct Carbon Fuel Cell
Industrial & Engineering Chemistry Research, 2008
The direct carbon fuel cell (DCFC) is a promising power generation device, which has a much higher efficiency (80%) and a lower emission than conventional coal-fired power plants. In this study, different commercial carbon fuels including activated carbon (AC), carbon black (CB220 and CB660), and graphitic carbon (GC) were tested in DCFC at 600-800°C. The relationship between the intrinsic properties of carbon fuels and their electrochemical performance in the DCFC was analyzed. It is found that a desirable carbon fuel for DCFC should have high mesoporous surface area and rich oxygen-containing surface groups. The anodic performance of the DCFC may also be improved by small carbon particle size, fast stirring rates, and high cell temperatures.
The effects of operating conditions on the performance of a direct carbon fuel cell
Archives of Thermodynamics, 2013
The influences of various operating conditions including cathode inlet air flow rate, electrolyte temperature and fuel particles size on the performance of the direct carbon fuel cell DCFC were presented and discussed in this paper. The experimental results indicated that the cell performance was enhanced with increases of the cathode inlet gas flow rate and cell temperature. Binary alkali hydroxide mixture (NaOH-LiOH, 90-10 mol%) was used as electrolyte and the biochar of apple tree origin carbonized at 873 K was used as fuel. Low melting temperature of the electrolyte and its good ionic conductivity enabled to operate the DCFC at medium temperatures of 723-773 K. The highest current density (601 A m−2) was obtained for temperature 773 K and air flow rate 8.3×106 m3s−1. Itwas shown that too low or too high air flow rates negatively affect the cell performance. The results also indicated that the operation of the DCFC could be improved by proper selection of the fuel particle size.
Ionics, 2020
A mathematical model is developed to study the concentration profile of gases, namely carbon dioxide and carbon monoxide, across the anode of a direct carbon solid oxide fuel cell (DC-SOFC) under anode-supported configuration. The concentration profiles are evaluated as a function of cathode and electrolyte design parameters, namely cathode porosity, cathode tortuosity, cathode composition, cathode pressure, electrolyte thickness, and length of the triple-phase boundary (TPB). The effect of operating potential on these concentration profiles is modeled. The effects of electrolyte thickness and TPB length are found to be major factors in determining the performance of the DC-SOFC. Model results are compared with experimental data and found to compare well.
Performance of direct carbon fuel cell
International Journal of Hydrogen Energy, 2011
A direct carbon fuel cell (DCFC) is a variation of the molten carbonate fuel cell (MCFC) which converts the chemical energy of carbon directly into electrical energy. Thus, the energy conversion efficiency is very high and correspondingly CO 2 emission is very low for given power output. DCFC as a high temperature fuel cell performs better at elevated temperatures (>800 C) but because of the corrosive nature of the molten carbonates at elevated temperatures the degradation of cell components becomes an issue when DCFC is operated for an extended period of time. We explored the DCFC performance at lower temperatures (at 700 C and less) using different sources of carbon, different compositions of electrolytes and some additives on the cathode surface to increase catalytic activity. Experiments showed that with petroleum coke as a fuel at low temperatures the ternary eutectic (43.4 mol % Li 2 CO 3 e 31.2 mol% Na 2 CO 3 e 25.4 mol % K 2 CO 3) spiked by 20 wt % Cs 2 CO 3 performed better than any binary or ternary eutectics described in the published work by other researchers. Maximum power output achieved at 700 C was 49 mW/cm 2 at a current density of 78 mA/cm 2 when modified cathode was fed with O 2 /CO 2 gases.