Effect of temperature on the electrochemical oxidation of ash free coal and carbon in a direct carbon fuel cell

Duc-Luong Vu,이충곤 한국화학공학회 2016 Korean Journal of Chemical Engineering Vol.33 No.5

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 oC) 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 oC. The ease of gasification of AFC led to a much higher performance than for carbon fuel, even at 650 oC, where carbon cannot be gasified with a carbonate catalyst.

On-demand supply of slurry fuels to a porous anode of a direct carbon fuel cell: Attempts to increase fuel-anode contact and realize long-term operation

Li, Chengguo,Yi, Hakgyu,Lee, Donggeun Elsevier 2016 Journal of Power Sources Vol.309 No.-

<P><B>Abstract</B></P> <P>In this paper, we propose a novel idea that might allow resolution of the two biggest challenges that hinder practical use of direct carbon fuel cells (DCFC). This work involved 1) the use of three types of porous Ni anode with different pore sizes, 2) size matching between the anode pores and solid fuel particles in a molten-carbonate (MC) slurry, and 3) provision of a continuous supply of fuel-MC slurry through the porous Ni anode. As a result, larger numbers of smaller pores in the anode were preferred for extending the triple phase boundary (TPB), as long as the fuel particles were sufficiently small to have full access to the inner pore spaces of the anode. For example, the maximal power density achieved in the case of optimal size matching, reached 645 mW cm<SUP>−2</SUP>, which is 14-times greater than that for the case of poorest size-matching and 64-times larger than that for a non-porous anode, and lasted for more than 20 h. After 20 h of steady operation at a fixed current density (700 mA cm<SUP>−2</SUP>), the electric potential slightly decreased due to partial consumption of the fuel. The cell performance readily recovered after restarting the supply of MC-fuel slurry.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A potentially continuous fuel supply with increasing fuel-anode contacts in a DCFC. </LI> <LI> Of importance was the size match between the anode pores and fuel particles. </LI> <LI> Maximal power density under the optimal size-matching reached 645 mW cm<SUP>−2</SUP>. </LI> <LI> More than 20-h steady operation was achieved at a current density of 700 mA cm<SUP>−2</SUP>. </LI> </UL> </P>

Gas Analysis of Carbon Oxidation in a Coin‐Type Direct Carbon Fuel Cell

Lee, C. G.,Pak, J. WILEY-VCH 2014 Fuel Cells Vol. No.

<P><B>Abstract</B></P><P>Carbon oxidation behaviors were illuminated in terms of gas composition in a coin‐type direct carbon fuel cell. The main gas species in the anode chamber at 850 °C was mostly carbon monoxide, which was generated from the chemical reaction of carbon and molten carbonates. The concentration of CO was reduced as time passed because the reactivity of carbonates was weakened. The open circuit voltage was directly dependent on the CO concentration. The gases in the anode chamber had a vertical concentration distribution; the highest CO and the lowest CO<SUB>2</SUB> concentrations were observed near the electrode. However, the voltage in the polarization state was less dependent on the gas composition. A polarization state of 150 mA cm<SUP>–2</SUP> allowed the oxidation of CO, resulting in an increased CO<SUB>2</SUB> concentration near the electrode. The enlarged CO<SUB>2</SUB> partial pressure facilitated CO generation through the recombination of carbonate ions (CO<SUB>3</SUB><SUP>2–</SUP>). Decreasing the temperature from 850 to 750 °C reduced the level of carbon monoxide at the anode. The presence of CO as a main component in the anode concludes that the oxidation of solid carbon takes place through the gasification of carbon to CO, then electrochemically to CO<SUB>2</SUB>.</P>

Consideration of reversed Boudouard reaction in solid oxide direct carbon fuel cell (SO-DCFC)

Zuh Youn Vahc,이성철 한양대학교 세라믹연구소 2018 Journal of Ceramic Processing Research Vol.19 No.6

The direct carbon fuel cell (DCFC) has attracted researcher’s attention recently, due to its high conversion efficiency and itsabundant fuel, carbon. A DCFC mathematical model has developed in two-dimensional, lab-scale, and considers Boudouardreaction and carbon monoxide (CO) oxidation. The model simulates the CO production by Boudouard reaction and additionalelectron production by CO oxidation. The Boudouard equilibrium strongly depends on operating temperature and affects theamount of produced CO and consequentially affects the overall fuel cell performance. Two different operating temperatures(973 K, 1023 K) has been calculated to discover the CO production by Boudouard reaction and overall fuel cell performance. Moreover, anode thickness of the cell has been considered to find out the influence of the Boudouard reaction zone in fuel cellperformance. It was found that in high temperature operating DCFC modeling, the Boudouard reaction cannot be neglectedand has a vital role in the overall fuel cell performance.

초청정 석탄의 석탄연료전지 응용기술

최호경(Hokyung Choi),김상도(Sangdo Kim),유지호(Jiho Yoo),임정환(Jeonghwan Lim),임영준(Youngjoon Rhim),이시훈(Sihyun Lee) 한국연소학회 2010 KOSCOSYMPOSIUM논문집 Vol.- No.40

This paper describes the potential application of ash-free coal to direct carbon fuel cell (DCFC). DCFC can be made of typical fuel cell components and generates the electric energy by direct electrochemical oxidation of carbon, replacing hydrogen with solid carbon fuel. Carbon is mostly originated from coal, which is readily available, easily transportable, and economical. However, employing coal as a carbon source has been excluded, mainly due to its high ash content. The ash-free coal, produced by solvent extraction of combustibles from raw coal, can be applicable as carbon fuel to DCFC. The successful adaption may cut the fuel cost to one third of usual hydrogen fuel cells. In addition, 80% of power generation efficiency can be achieved and CO₂ emission from the conventional coal-fired power plant can be reduced by 90%.

직접탄소 연료전지에서 RDF 및 RPF의 전기화학반응 특성에 관한 실험적 연구

안성율,이영훈,엄성용,성연모,문철언,강기중,최경민,김덕줄 한국수소및신에너지학회 2012 한국수소 및 신에너지학회논문집 Vol.23 No.5

The electrochemical reaction of refuse derived fuel (RDF) and refuse plastic/paper fuel (RPF) was investigated in the direct carbon fuel cell (DCFC) system. The open circuit voltage (OCV) of RPF was higher than RDF and other coals because of its thermal reactive characteristic under carbon dioxide. The thermal reactivity of fuels was investigated by thermogravimetric analysis method. and the reaction rate of RPF was higher than other fuels. The behavior of all sample’s potential was analogous in the beginning region of electrochemical reactions due to similar functional groups on the surface of fuels analyzed by X-ray Photoelectron Spectroscopy experiments. The potential level of RDF and RPF decreased rapidly comparing to coals in the next of the electrochemical reaction because the surface area and pore volume investigated by nitrogen gas adsorption tests were smaller than coals. This characteristic signifies the contact surface between electrolyte and fuel is restricted. The potential of fuels was maintained to the high current density region over 40 mA/cm2 by total carbon component. The maximum power density of RDF and RPF reached up to 45~70% comparing to coal. The obvious improvement of maximum power density by increasing operating temperature was observed in both refuse fuels.

A study of the gasification of carbon black with molten salt of Li₂CO₃ and K₂CO₃ for application in the external anode media of a direct carbon fuel cell

Hwang, J.Y.,Yu, J.H.,Kang, K. Elsevier 2015 CURRENT APPLIED PHYSICS Vol.15 No.12

The characteristics of gasification reactions for carbon-carbonate mixtures were experimentally investigated at high temperatures up to 900 <SUP>o</SUP>C, considering the application of the mixtures to the external anode media of a direct carbon fuel cell. A thermo-gravimetric analysis (TGA) was conducted in either a nitrogen or carbon dioxide ambient environment for Li<SUB>2</SUB>CO<SUB>3</SUB>, K<SUB>2</SUB>CO<SUB>3</SUB> and a mixture of these two substances with carbon black. Changes in the exit gas composition were also monitored during the heating process. It was shown that gasification in the mixture media occurs much more rapidly than carbonate decomposition at elevated temperatures, even for low concentrations of CO<SUB>2</SUB>. It was also shown that the loading of carbonates to carbon significantly affects the global gasification reaction; it increased the reaction rate by an order of magnitude and decreased its activation energy. Based on the experimental observations, a simplified reaction model of gasification was suggested for the anode media of a DCFC, regarding carbonate-catalysed and metal-catalysed pathways of Boudouard reactions.

A study of the gasification of carbon black with molten salt of Li2CO3 and K2CO3 for application in the external anode media of a direct carbon fuel cell

황준영,유준호,강경태 한국물리학회 2015 Current Applied Physics Vol.15 No.12

The characteristics of gasification reactions for carbonecarbonate mixtures were experimentally investigated at high temperatures up to 900 C, considering the application of the mixtures to the external anode media of a direct carbon fuel cell. A thermo-gravimetric analysis (TGA) was conducted in either a nitrogen or carbon dioxide ambient environment for Li2CO3, K2CO3 and a mixture of these two substances with carbon black. Changes in the exit gas composition were also monitored during the heating process. It was shown that gasification in the mixture media occurs much more rapidly than carbonate decomposition at elevated temperatures, even for low concentrations of CO2. It was also shown that the loading of carbonates to carbon significantly affects the global gasification reaction; it increased the reaction rate by an order of magnitude and decreased its activation energy. Based on the experimental observations, a simplified reaction model of gasification was suggested for the anode media of a DCFC, regarding carbonate-catalysed and metal-catalysed pathways of Boudouard reactions.

직접탄소 연료전지에서 고체 탄소 연료에 따른 전기화학 임피던스 비교 연구

조재민,엄성용,이광섭,안성율,김덕줄,최경민 한국수소및신에너지학회 2014 한국수소 및 신에너지학회논문집 Vol.25 No.6

Direct Carbon Fuel Cell(DCFC) is one of new power generation that the chemical energy of solidcarbon can be converted into electrical energy directly. At the high temperature, the electrochemical reaction ofthe carbon takes place and the carbon reacts with oxygen to produce carbon dioxide as followed overall reaction(C + O2 → CO2). However, in case of using the raw coals as a fuel of DCFC, the volatile matter containing carbon,hydrogen, and oxygen produces at operating temperature. In this study, the electrochemical reaction of Adaro coalwas compared with Graphite. This work focused on the electrochemical reaction of two kinds of solid carbonby Electrochemical Impedance Spectroscopy(EIS). The EIS results were estimated by equivalent circuit analysis. The constant phase element(CPE) was applied in Randle circuit to explain an electrode and fuel interface. Thecorrelation between the fuel characteristic and electrochemical results was discussed by elements of equivalentcircuit of each fuel.

A study on the electrochemical performance of 100-cm² class direct carbon-molten carbonate fuel cell (DC-MCFC)

Choi, S.H.,Park, D.n.,Yoon, C.W.,Yoon, S.P.,Nam, S.W.,Hong, S.A.,Shul, Y.G.,Ham, H.C.,Han, J. Pergamon Press ; Elsevier Science Ltd 2015 International journal of hydrogen energy Vol.40 No.15

We study the effect of various operating parameters such as temperature, molten carbonate/carbon ratio, and the type of Ni thin layer inserted between the matrix (electrolyte support) and carbon green sheet on the electrochemical performance of a 100-cm<SUP>2</SUP> class direct carbon-molten carbonate fuel cell (DC-MCFC). In addition, we attempt to understand the oxidation behavior of carbon in the wet carbon anode (the composite of carbon and molten carbonates) of the DC-MCFC. We find that in the DC-MCFC, CO is produced via a two-electron transfer reaction [C(s) + CO<SUB>3</SUB><SUP>-2</SUP> → CO<SUB>2</SUB>(g) + CO(g) + 2e<SUP>-</SUP>] and is further oxidized with CO<SUB>3</SUB><SUP>-2</SUP> [CO(g) + CO<SUB>3</SUB><SUP>-2</SUP> → 2CO<SUB>2</SUB>(g) + 2e<SUP>-</SUP>] under closed circuit voltage conditions, indicating that CO is responsible for determining the DC-MCFC performance.