Performance of Direct Carbon Fuel Cells Operated on Coal and Effect of Operation Mode

Abstract

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. Direct Carbon Fuel Cell (DCFC) is a promising technology to use solid carbon for energy production. This technology allows direct conversion of chemical energy to electricity, thus giving a high thermodynamic efficiency, i.e. 100%, when carbon is oxidized to carbon dioxide. The concept of DCFC is simple. Solid carbon is fed to a fuel cell and electrochemically oxidized at the anode to produce electricity.1-3 Pure product, carbon dioxide (CO 2 ), is obtained in complete oxidation and is easy for carbon sequestration. Furthermore, application of DCFC benefits from sufficient fuel supply with abundant coal and biomass in the world. These advantages as well as established infrastructure of transportation, storage, and processing for solid carbon make a DCFC feasible and very attractive.One of design challenges to develop a DCFC is choice of fuel. 4Despite large reserves of solid carbon available, different sources of carbon have varying activity and indeed affect DCFC performance. In the past, many attempts have been made to evaluate effect of solid carbon on DCFC for electric power generation. Cooper et al. 5 reported cell polarization on nine particulate carbon derived from fuel oil, coal, biochar, petroleum coke, etc. The highest discharge rate, 100-125 mA cm −2 at 0.8 V and 800• C, was obtained with biochar-derived carbon. They found that properties of carbon fuel which control discharging rates are (i) crystallographic disorder, (ii) electrical conductivity, (iii) active surface sites, and (iv) sulfur and ash impurities. Less graphitized and high disordered carbon such as chars is more reactive to oxidation; however, this property counterbalances electrical conductivity since chars are poor conductors. By contrast, neither particle size, surface area, nor morphology was found to have much impact on the electrochemical discharge rate. Moreover, Zhu et al 6 investigated factors that determine performance of carbon fuel in the D...

Application of infiltrated LSCM–GDC oxide anode in direct carbon/coal fuel cells

“…These two peaks are very broad in the XRD pattern of xerogel sample, indicating a very disordered structure that is beneficial for carbon oxidation in DCFC. It has been agreed by several researchers that less crystalline carbon tends to have more edges sites and defects which are considered reactive sites for carbon oxidation in DCFC [3][4]13 . One may argue that xerogel has quite low fixed carbon (53.6%) and a very high amount of volatile matter (46.4%), both of which were believed to impact DCFC performance negatively 13 The enhanced performance from the DCFC with a GDC-LSCM SOFC anode is probably attributed to the high ionic conductivity and electro-catalytic activity the oxide anode offers.…”

“…It has been agreed by several researchers that less crystalline carbon tends to have more edges sites and defects which are considered reactive sites for carbon oxidation in DCFC [3][4]13 . One may argue that xerogel has quite low fixed carbon (53.6%) and a very high amount of volatile matter (46.4%), both of which were believed to impact DCFC performance negatively 13 The enhanced performance from the DCFC with a GDC-LSCM SOFC anode is probably attributed to the high ionic conductivity and electro-catalytic activity the oxide anode offers. GDC is a wellknown oxide ion conductor, especially at temperature below 800 o C. Besides, it offers mixed electronic and ionic conductivity in reducing atmosphere, which is beneficial for facile charge transfers and surface mass diffusions compared to the electrode has dual phases with separate electronic and ionic conductivity, for instance, Ni-YSZ cermet.…”

Comparative study of durability of hybrid direct carbon fuel cells with anthracite coal and bituminous coal

“…Recent work on coal fuel cells was renewed by the energy demands for the reduction of CO 2 emissions. Researchers have focused on the application of different types of coal samples in DCFCs 3,4 . So far, lignite, bituminous and anthracite coal have been tested in DCFCs [5][6][7] .…”

“…The fast degradation rate with raw coal was attributed to its ash accumulation on the anode surface, and also to the continuous carbon consumption 14 . In our previous research, different types of coal were selected for a primary test in hybrid DCFCs 3,15,16 . Lignite coal, bituminous coal and anthracite coal were evaluated in a button cell with a NiO-YSZ anode, a YSZ electrolyte and a LSM-YSZ cathode.…”

“…As one of the main types of coal, anthracite coal is suggested as a good candidate for DCFCs due to its high carbon content, usually is above 90%, but there are not many publications about anthracite fuel for DCFCs. 3,4 In our previous research, we initially discussed the effect of chemical compositions (e. g. carbon content, P D F C r e a t e 8 T r i a l w w w . n u a n c e .…”