Surface modification of carbon fuels for direct carbon fuel cells (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.
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...
Modification of Coal as a Fuel for the Direct Carbon Fuel Cell †
Journal of Physical Chemistry A, 2010
As a promising high-temperature fuel cell, the direct carbon fuel cell (DCFC) has a much higher efficiency and a lower emission as compared with conventional coal-fired power plants. To develop an increased understanding of the relationship between the microstructure, surface chemistry, and electrochemical performance of coal as a fuel for the DCFC, a coal sample from Central Queensland has been subjected to various pretreatments, including acid washing, air oxidation, and pyrolysis. It has been found that an acid treatment of the coal enhanced its electrochemical reactivity due to an increase in oxygen-containing surface functional groups. By contrast, heat treatment of the coal results in a sharp decrease in the electrochemical reactivity in the DCFC due to a decrease in the oxygen-containing surface functional groups, particularly CO 2 -yielding surface groups. A higher surface area of coal may also be helpful, but much less important than surface chemistry.
−The present study proposes the application of ash-free coal (AFC) as a primary fuel in a direct carbon fuel cell (DCFC) based on a molten carbonate fuel cell (MCFC). AFC was produced by solvent extraction using microwave irradiation. The influence of AFC-to-carbonate ratio (3 : 3, 3 : 1, 3 : 0 and 1 : 3 g/g) on the DCFC performance at different temperatures (650, 750 and 850 o C) was systematically investigated with a coin-type cell. The performance of AFC was also compared with carbon and conventional hydrogen fuels. AFC without carbonate (AFC-to-carbonate ratio=3 : 0 g/g) gave a comparable performance to other compositions, indicating that the gasification of AFC readily occurred without a carbonate catalyst at 850 o C. The ease of gasification of AFC led to a much higher performance than for carbon fuel, even at 650 o C, where carbon cannot be gasified with a carbonate catalyst.
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...
Evaluation of raw coals as fuels for direct carbon fuel cells
Journal of Power Sources, 2010
As a promising high-temperature fuel cell, the direct carbon fuel cell (DCFC) has a much higher efficiency and lower emissions compared with conventional coal-fired power plants. In the present DCFC system, four Australian coals from Central Queensland are successfully tested at 600-800 • C. The electrochemical performances of these coals are highly dependent on their intrinsic properties, such as chemical composition, surface area, concentrations of oxygen-containing surface functional groups and the nature of mineral matter in their ashes. Impurities such as Al 2 O 3 and SiO 2 lead to an inhibitive effect during the anodic reaction in the DCFC, while CaO, MgO and Fe 2 O 3 exhibit a catalytic effect on the electrochemical oxidation of carbon.
Carbon Energy
In this paper, an extensive characterisation of a range of carbon blacks (CB) with similar surface area but different surface chemistry is carried out by flow calorimetry, Raman spectroscopy, dynamic water vapour sorption, instrumental gas analysis, nitrogen adsorption/desorption and high potential chronoamperometry. Using these carbon materials as supports, Pt/CB electrocatalysts are prepared by microwave-assisted polyol-mediated synthesis in gram scale. Structural, morphological and electrochemical properties of the prepared electrocatalysts are evaluated by X-ray diffraction, transmission electron microscopy, rotating disc electrode and in situ fuel cell characterisation of the corresponding membrane-electrode assemblies. The obtained results allow to establish a relationship between surface chemistry and electrochemical properties useful for the design of Pt/C catalyst layers with high performance and stability. K E Y W O R D S carbon black, electrocatalyst support, fuel cell cathodes, surface properties 1 | INTRODUCTION Cathodes of proton-exchange membrane fuel cells (PEMFC), where the oxygen reduction reaction (ORR) takes place, face many challenges to meet activity, durability and cost requirements: the reduction of noble metal loading while keeping high electroactivity, 1,2 the mitigation of catalyst and support degradation to enhance the lifetime of the devices 3,4 and the improvement in water management and mass transport to enhance their performance at high current density. 5,6 Carbon blacks (CB) are low-cost supports conventionally used in PEMFC cathodes. These materials, produced by pyrolysis or incomplete combustion of hydrocarbons, present a turbostratic structure in which the graphene layers are stacked into randomly oriented crystallites 7 and possess high electrical conductivity, porosity and surface area. 3 In start-stop conditions of a This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
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.