The effects of operating conditions on the performance of a direct carbon fuel cell (original) (raw)
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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.
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.
Performance of Direct Carbon Fuel Cells Operated on Coal and Effect of Operation Mode
Journal of the Electrochemical Society, 2014
Previous experimental results have shown that a system with molten carbonate and solid oxide electrolyte is feasible for Direct Carbon Fuel Cell (DCFC). A study is presented to investigate cell performance with a range of solid carbon (i.e. coals, biochars, graphite) and operation mode in this hybrid electrolyte system. The results show that less crystalline coal with high fixed carbon, low sulfur, medium volatile material and moisture is best suited to this system. Using high rank of fuel such as anthracite coal, good cell performance can be obtained only by elevating temperature and with adequate pretreatment to remove impurities. Discussion of cell operation indicates that cell degradation and operation failure were due to coal agglomeration, ash buildup, and limited fuel supply in potentiostatic mode. Instead, galvanostatic operation gave stable cell performance over 60 hours. This result allows better understanding of anode reaction mechanism on the hybrid electrolyte system. Thus, long-term operation is promised when suitable solid fuel and optimized operation parameters are applied.
Effect of carbon type on the performance of a direct or hybrid carbon solid oxide fuel cell
RSC Advances, 2014
The impact of carbon type on the performance of the direct carbon fuel cell (DCFC) or hybrid carbon fuel cell (HCFC) is investigated by utilizing bare carbon or carbon/carbonate mixtures as feedstock, respectively. In this regard, four different types of carbons, i.e. bituminous coal (BC), demineralised bituminous coal (DBC), anthracite coal (AC) and pine charcoal (PCC), are employed as fuels in a SOFC of the type: carbon (carbonate)|Cu-CeO 2 /YSZ/Ag|Air. The results reveal that in the absence of carbonates (DCFC configuration) the optimum performance, in terms of maximum power density (P max ), is obtained for the charcoal sample, which demonstrated a power output of $12 mW cm À2 at 800 C, compared to 3.4 and 4.6 mW cm À2 with the anthracite and bituminous samples, respectively. Demineralization treatment of bituminous coal is found to improve the DCFC performance resulting in a maximum power density of 5.5 mW cm À2 . A similar trend in terms of maximum power density, i.e., PCC > DBC > BC > AC, is obtained in the hybrid carbon fuel cell (HCFC) employing a eutectic mixture of lithium and potassium carbonates (62 mol% Li 2 CO 3 + 38 mol% K 2 CO 3 ) in the anode compartment at a carbon/carbonate weight ratio of 4 : 1. An enhancement of up to 185% in the maximum power density is achieved by admixing molten carbonates with carbon feedstock, with its extent being dependent on carbon type and temperature. The obtained results are interpreted on the basis of carbon physicochemical characteristics and their impact on DCFC performance. It is found that the observed trend in volatile matter, porosity and structure disorder is perfectly correlated with the achieved power output. In contrast, high ash and sulfur contents notably inhibit the electrochemical performance.
2015
The electrochemical performances of a single cell molten carbonate electrolyte direct carbon fuel cell (MCDCFC) using miscanthus and switchgrass biomass carbon fuels subjected to hand and ball milling treatments are presented in this paper. Conventional direct carbon fuel cell (DCFC) uses carbon derived from coal, a fossil fuel with adverse consequences on the environment. This paper explores a more benign carbon fuel source which is the biomass to power the DCFC. The performances of the hand milled (HM) carbon fuels were slightly higher than those of the ball milled (BM) carbon fuels. At 800oC for the open circuit voltage, miscanthus fuel (1.03 V) has higher values for the HM and switchgrass fuel (0.77 V) for the BM. Higher peak power densities were observed for switchgrass fuel (21.60 and 12.32 mW/cm2) for both the HM and BM. Switchgrass fuel (74 mA/cm2) gave the maximum current density for both the HM and BM. Miscanthus fuel (0.72 V) show higher voltage at peak power generation f...
Actual State of Technology in Direct Carbon Fuel Cells
Zeitschrift für Physikalische Chemie, 2013
At medium term, electricity could be partially provided by the utilization of carbon in high temperature fuel cells. The thermodynamic efficiency of a direct carbon fuel cell (DCFC) slightly exceeds 100% in a wide temperature range due to the positive value of the reaction entropy change. Thus, the thermodynamic efficiency is higher than those of conventional fuel cell types for gaseous fuels. In DCFC technology, three different main electrolyte concepts are used up to now: two types of liquid salt electrolytes (molten carbonate or molten hydroxide) and a solid oxide electrolyte (solid ceramic layer). For instance, it has been reported that power densities up to 210 mW cm-2 can been achieved at 750 ºC in a molten carbonate based cell, resulting to a real practical efficiency of about 60%. Recently, also combined technologies have been developed in which a maximum power density of 500 mW cm-2 is possible. In this paper, the actual state of technology will be discussed for the differe...
NiO-Samaria-Doped-Ceria (NiO-SDC) composite powders was synthesized by a traditional mechanical mixing process and tested as anode material for Direct Carbon Fuel Cell (DCFC), which uses almond shell biochar as fuel and molten carbonate-doped ceria composite as electrolyte. A three-layer pellet cell, viz. cathode (Lithiated NiO-SDC), composite electrolyte and anode (NiO-SDC) is fabricated by a die-pressing, screen printing and sin-tering method. In Part I, a bi-layer DCFC pellet powered by almond shell biochar was tested and demonstrated a good potential. In this paper, we report an improvement in the cell stability and performance by adding the (NiO-SDC) anode layer to the bi-layer pellet containing only cathode and electrolyte. The peak power density of the three-layer pellet cell at 700 C increases to reach 150 mW cm À2 instead of 127 mW cm À2 while, the stability period is ameliorated to be around 130 min. The results indicated that this porous anode material is promising as anode for DCFCs. The DCFC single cells experiments demonstrated that the anode polarization is dominating the total cell polarization. Therefore, improved power output could be achieved with an improved anode.
Journal of Power of Technologies, 2018
The direct carbon fuel cell (DCFC) is a power generation device that converts the chemical energy of carbonaceous fuels (e.g. fossil coals, charred biomass, activated carbons, graphite, coke, carbon black, etc.) directly into electricity. However, the use of coal in the DCFC is sometimes problematic particularly if volatile matter evolves from the fuel during fuel cell operation. The recommended course of action to minimize that problem is to pre treat thermally or even pyrolyze the coal and remove the volatiles before the fuel is used in the fuel cell. In this paper, three raw and thermally-treated coals of various origins have been compared for electrochemical activity in a direct carbon fuel cell with molten hydroxide electrolyte (MH-DCFC). The thermal pre-treatment of selected coals was carried out in an inert gas atmosphere at 1023 K. It was found that—compared to raw coals—the pyrolyzed coals presented lower maximum current and power densities at 723 K but simultaneously provi...
2015
Direct carbon fuel cell offers an efficient alternative to conventional combustion system for electricity generation. The most attractive feature is its remarkably high overall system efficiency. However, the implementation of this technique is restricted by the limited solid-solid contact between the carbon fuel and electrode. This reviews discusses a sets of chemical and physical properties of the carbon fuel that contribute to the electrochemical performance of the fuel cell. These properties include chemical composition, surface functional groups, graphitic structure and textural properties. Meanwhile, biomass can be employed as a sustainable carbon fuel source after undergoing pyrolysis, a thermal pretreatment process. It is essential to control the pyrolysis operating conditions such as the temperature, heating rate and residence time as these conditions would affect the chemical and physical properties of the carbon fuel, ultimately contributing to the electrochemical perform...