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Coal is used for generating electricity and it will continue to be used in this manner until non-fossil fuel based power generation technologies are commercially proven. Since CO2, a greenhouse gas, is a main product of the conversion process, it is prudent to develop technologies that facilitate its removal from exhaust streams before it is releas...
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... processes are carried out in chemical reactors referred to as gasifiers. The reaction zones that are established in gasifiers are best described by considering a typical counter-flow fixed bed gasifier, schematically shown in Fig. 3. In this counter- flow configuration, the solid fuel enters near the top of the vertically-oriented reactor, flowing downwards, and the oxidizing agents enter near the bottom of the reactor, flowing ...
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Citations
Solid oxide carbon fuel cells (SO-CFCs), which are a part of direct carbon fuel cells (DCFCs), adopt the same chemistry of solid oxide fuel cells (SOFCs). Despite their same chemistry, a difference in electrochemical behaviors has been observed. Unlike SOFCs where gas is imposed as fuel, SO-CFCs employ solid-state carbonaceous fuel that undergoes gasification and produces gaseous fuel such as carbon monoxide (CO). The amount of CO production varies according to the physicochemical properties of carbon source. In this contribution, the authors prove that the plethora or lack of CO in SO-CFCs can cause poisoning on Ni electrocatalyst and thereby a decrease in electrochemical performance. The authors demonstrate poisoning mechanisms and they finally suggest methodologies to overcome or alleviate the poisonings.
Direct carbon fuel cell (DCFC) is a technique, converting chemical energy of carbon fuel into electric energy with high efficiency. Although it can theoretically yield high efficiency, DCFC has a considerable polarisation resistance, resulted from a solid-state interface between fuel and anode surface. Here, we have employed Sn nanoparticles (<150 nm in diameter) as an interfacial mediator to reduce a polarisation resistance at the interface, by liquid phase Sn interlayer which can improve both a mass transfer of solid carbon fuel and an electron transfer. We previously investigated that, when using Sn microparticles (>150 μm in diameter), an interfacial resistance became alleviated with the aid of liquid-state Sn; however, Sn microparticles tended to accumulate on anode surface because Sn microparticles hardly permeates into a submicron anode structure. In this sense, we chose Sn nanoparticles to demonstrate a size effect of Sn mediation on Ni/YSZ (Ni/Yttria-Stabilised Zirconia) surface in this study. Unlike microparticles, nanoparticles are observed to more deeply permeate into Ni/YSZ pores without accumulation. Nevertheless, Sn nanoparticles are more prone to oxidation, resulting in ionically and electronically insulating material. Therefore, power performance of Sn nanoparticle-mounted DCFC is, in general, lower than that of Sn microparticle-mounted DCFC. In addition, we found that there are two possible mediating mechanisms: one is physical mediation by improving both a mass transfer and an electron transfer, and the other is Sn redox looping cycle.
In a solid oxide carbon fuel cell (SO-CFC), it has been widely believed that solid-state carbonaceous materials would directly take part in electrochemical reaction to generate electrons. Of late, however, it is predicted that further-oxidizable gas-state molecules, such as CO, hydrocarbons, etc., play a crucial role in an SO-CFC operation. In this work, we controlled an anode chamber atmosphere by providing an inert purging gas to verify the role of carbon-induced gas-state molecules; that is, some experiments were carried out with a purging gas and the others were without a purging gas. Additionally, in some of the experiments, alumina wool was placed between carbon and a cell to prevent a solid-state fuel from reaching anode surface, i.e. alumina wool is a gas diffusion layer between a solid-state fuel and anode surface. As a result, maximum power density of 230 mW cm⁻² was obtained when the test was taken under no Ar without alumina wool; 80 mW cm⁻² under Ar flow without alumina wool; 212 mW cm⁻² under no Ar with alumina wool; potential value going zero under Ar with alumina wool. In other words, it is corroborated that gas-state molecules mainly govern power performance and hence SO-CFC operation.
Coal samples with 3 wt.% ash were chosen as a prospective solid fuel for direct carbon solid oxide fuel cells operating within a temperature range of 600–850 °C. Based upon X-ray and infrared spectroscopy analysis, it was found that the main inorganic impurities in this coal were dolomites. The chemical analysis of ash content in the coal, before and after 3 M HNO3 treatment, indicated that the applied purification procedure allowed a considerable decrease in the ash down to 0.4 wt.% in the coal samples. The physicochemical properties of raw and modified coal samples were investigated by analytical and physicochemical methods in order to evaluate its potential use as a solid fuel for a direct carbon fuel cell with a solid oxide electrolyte (DC–SOFC). The tests indicated that DC–SOFCs fed with this type of processed fossil coal were characterized by stable operation with reasonable current and power densities.
