Direct Carbon Fuel Cell Research Articles

Fundamental Characteristics of High Functional Direct Carbon Fuel Cell Composed of Tubular Molten Carbonate Fuel Cell

In order to the solve global warming and the increase of food wastes, we have already proposed the High Functional Direct Carbon Fuel Cell (HF-DCFC) composed of molten salts gasification system and molten carbonate fuel cell (MCFC) since 2011. This gasification system generates CO and H2 by supplying organic wastes into molten salts. The MCFC formed to tubular (T-MCFC) is used as gas pipeline for the gasification system. This paper aimed at the evaluation of the fundamental characteristics of the T-MCFC, and the establishment of the manufacturing method of the T-MCFC stack composed of 2cells. As a result, the T-MCFC was able to obtain a good performance though it was necessary to optimize the electrolyte loading ratio. The basic manufacturing method of the T-MCFC stack was able to be also established.

Development of a Press-Type Direct Carbon Fuel Cell for Higher and More Stable Power Output

A triple phase boundary reaction site was formed in a direct carbon fuel cell (DCFC) when the char wetted by molten carbonate was in contact with the anode. It has been reported that gases such as CO2 covered the anode during discharge, leading to high anode overpotential. In this study, a press-type DCFC was developed to overcome this issue. By pressing the perforated anode on the carbon/carbonate-packed bed, it was expected that the carbon particles would remain in contact with the anode, while the gas products would be released through the perforation due to their buoyancy. As a result, the power output achieved with the press-type DCFC was higher and more stable as compared with the conventional DCFC. The anodic impedance spectra showed that the arc size of the press-type DCFC was much smaller than that of the conventional DCFC. This was particularly noticeable at the low frequencies, indicating the anode resistance caused by the mass transfer processes including the gas products and the contact between the anode and carbon particles to be significantly less in the press-type DCFC.

Fuel Cells: A High‐Performing Direct Carbon Fuel Cell with a 3D Architectured Anode Operated Below 600 °C (Adv. Mater. 4/2018)

Fuel Cells: A High‐Performing Direct Carbon Fuel Cell with a 3D Architectured Anode Operated Below 600 °C (Adv. Mater. 4/2018)

A High-Performing Direct Carbon Fuel Cell with a 3D Architectured Anode Operated Below 600 °C.

Direct carbon fuel cells (DCFCs) are highly efficient power generators fueled by abundant and cheap solid carbons. However, the limited triple-phase boundaries (TPBs) in the fuel electrode, due to the lack of direct contact among carbon, electrode, and electrolyte, inhibit the performance and result in poor fuel utilization. To address the challenges of low carbon oxidation activity and low carbon utilization, a highly efficient, 3D solid-state architected anode is developed to enhance the performance of DCFCs below 600 °C. The cell with the 3D textile anode framework, Gd:CeO2 -Li/Na2 CO3 composite electrolyte, and Sm0.5 Sr0.5 CoO3 cathode demonstrates excellent performance with maximum power densities of 143, 196, and 325 mW cm-2 at 500, 550, and 600 °C, respectively. At 500 °C, the cells can be operated steadily with a rated power density of ≈0.13 W cm-2 at a constant current density of 0.15 A cm-2 with a carbon utilization over 85.5%. These results, for the first time, demonstrate the feasibility of directly electrochemical oxidation of solid carbon at 500-600 °C, representing a promising strategy in developing high-performing fuel cells and other electrochemical systems via the integration of 3D architected electrodes.

Correlations between electrochemical resistances and surface properties of acid-treated fuel in coal fuel cells

Herein, we investigate the relationship between fuel surface properties and inner resistances of direct carbon fuel cells (DCFCs) by subjecting raw coal to a liquid-phase chemical treatment and correlating its surface property changes (e.g., degree of oxidation, surface area, and ash composition) with those of electrochemical resistances. Fuel surface characteristics are analyzed by thermogravimetry, gas adsorption, and X-ray photoelectron spectroscopy, with correlations established using the Pearson correlation analysis. The obtained results show that the surface Si content is strongly correlated with electrolyte resistance due to influencing the concentration of carbonate ions. Moreover, charge transfer resistance is strongly negatively correlated with the surface oxygen content, since oxygenated functional groups (e.g., carbonyl and quinone moieties) enhance the oxidation of solid carbon by increasing its reactivity and wettability.

Effect of grain boundary diffusion on electrolyte stability in direct carbon fuel cells with antimony anodes

Direct carbon fuel cells (DCFC) that employ solid oxide electrolytes and molten Sb anodes are promising for the efficient generation of electricity using a range of carbonaceous fuels. The present study examined the etching of yttria-stabilized zirconia (YSZ) and gadolinia-doped ceria (GDC) electrolytes by Sb2O3 produced during fuel-cell operation. Migration of Sb along grain boundaries and electrolyte corrosion were observed for both polycrystalline YSZ and GDC electrolytes; however, corrosion and electrolyte thinning were not observed for a single-crystal YSZ electrolyte, even after long-term operation. These results indicate that Sb migration along grain boundaries plays a significant role in electrolyte corrosion in DCFCs with molten Sb anodes. Several strategies for avoiding this problem are also discussed.

A High Performance Low Temperature Direct Carbon Fuel Cell

Direct carbon fuel cells (DCFCs) are one of the most efficient and cleanest energy technologies, especially when using the existing solid oxide fuel cell (SOFC) configurations. However, the conventional SOFC has issues of high cost and rapid degradation associated with high operating temperatures (> 750oC). Reduction in operating temperatures would mitigate degradation, reduce sealing problems, enable less expensive materials, and improve response to prompt start-up and repeat thermal cycling. In the present presentation, we report our research progress about DC-SOFCs operating at 400-650oC. A variety of cell configurations, material selections, fuel considerations and novel electrode optimization approaches are investigated and implemented for high-performing DC-SOFCs.

Origin of peculiar electrochemical phenomena in direct carbon fuel cells

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.

Anode modeling of a molten-carbonate based direct carbon fuel cell

Abstract The Direct Carbon Fuel Cell (DCFC) is a type of fuel cell using solid carbon as fuel and molten carbonate as electrolyte. Although the primary anodic reaction is believed to be a 4-electron carbon oxidation reaction, to explain the performance of the DCFC in practice it is necessary to consider the 2-electron CO oxidation reaction as well as the reverse Boudouard reaction. Taking these multiple reactions into account, this work develops a 1-D macrohomogeneous model, and investigates the current and concentration distribution in the DCFC anode. The result shows that the active zone is mostly located on the portion of the anode bed nearest the electrolyte matrix. The dimensionless analysis of the electrode's resistance ratios suggests that the DCFC anode performance is mainly limited by ohmic losses and the relatively slow kinetics of the anodic reactions. To improve the performance of the DCFC, increasing effective electrical conductivity of the carbon particle bed by an order of magnitude, for example by a small fraction of inert metallic additives, can increase the cell efficiency appreciably. Besides causing the anode bed to be fully used, the rise in effective electrical conductivity of the anode bed appreciably improves the power density of DCFC.

Challenges in developing direct carbon fuel cells

A direct carbon fuel cell (DCFC) can produce electricity with both superior electrical efficiency and fuel utilisation compared to all other types of fuel cells. Although the first DCFC prototype was proposed in 1896, there was, until the 1970s, little sustained effort to investigate further, because of technology development issues. Interest in DCFCs has recently been reinvigorated as a possible method of replacing conventional coal-fired power plants to meet the demands for lower CO2 emissions, and indeed for efficient utilisation of waste derived chars. In this article, recent developments in direct carbon conversion are reviewed, with the principal emphasis on the materials involved. The development of electrolytes, anodes and cathodes as well as fuel sources is examined. The activity and chemical stability of the anode materials are a critical concern addressed in the development of new materials. Redox media of molten carbonate or molten metal facilitating the transportation of ions offer promising possibilities for carbon oxidation. The suitability of different carbon fuels in various DCFC systems, in terms of crystal structure, surface properties, impurities and particle size, is also discussed. We explore the influence of a variety of parameters on the electrochemical performance of DCFCs, with regard to their open circuit voltage, power output and lifetime. The challenges faced in developing DCFCs are summarised, and potential prospects of the system are outlined.

Effect of CeO2 Addition on Hybrid Direct Carbon Fuel Cell Performance

The effect of CeO2 infiltration into the anode or CeO2 mixed with the carbon-fuel on the performance of a Hybrid Direct Carbon Fuel Cell (HDCFC) was studied through the use of polarization curves and electrochemical impedance spectroscopy. The use CeO2 in both ways helped to increase the cell performance. In particular, mixing CeO2 with carbon represents the best strategy to increase the cell power output, probably due to increased formation of CO.

Carbonate-tin composite liquid anode for solid oxide direct carbon fuel cell

The SnO2 blocking film deposited on the anode-electrolyte interface during operation degrades the performance of a liquid tin (Sn) anode direct carbon fuel cell (DCFC). In the present study, Li–K carbonate is introduced to solve the SnO2 problem. A composite anode composed of molten carbonate and Sn was fabricated. The reaction kinetics of the composite anodes were characterized by performing electrochemical tests on different anodes at various metal-carbonate ratios. The shapes of the polarization curves of the different anodes changed dramatically, indicating a significant difference in the reaction mechanism and the mass transport process inside the composite anode. Electrochemical performance of composite anode was restored during polarization tests. A composite anode with 2 mol% molten carbonate demonstrates the highest power density as well as stable performance. Carbon black was fed to the 2 mol.% molten carbonate anode as a test of carbon conversion ability. By mixing carbon black with the liquid composite anode, both the fuel cell's performance and its stability were improved.

석탄 산처리에 따른 연료의 표면 물성 변화와 직접탄소 이용 연료전지 성능 간의 상관관계 분석분석

본 논문에서는 역청탄인 Glencore 탄을 염산과 질산수용액을 이용하여 산 처리하고 원탄과 산 처리 된 석탄의 물리, 화학적 비교분석과 직접탄소 이용 연료전지(Direct Carbon Fuel Cell, DCFC)의 성능비교 분석을 수행하였다. 석탄의 물성들을 분석하기 위해 열중량 분석과 가스 흡착법, X선 광전자 분광법을 수행하였다. 열중량 분석을 통해 연료의 열적 반응성이 증가하였음을 알 수 있었고, 가스 흡착법 결과로 기공의 평균지름은 변화가 없었지만 표면적은 감소함을 알 수 있었다. X선 광전자 분광법에서는 HNO₃ 처리의 경우 가장 높은 산소/탄소 비율을 보였고, 이를 통해 다양한 표면 산소작용기가 증가한 것을 확인하였다. 연료의 표면 물성과 전기화학 성능을 비교한 결과, 표면의 산소 성분의 변화가 DCFC의 성능 향상에 가장 큰 영향을 미침을 알 수 있었다.

No.2-14 直接炭素燃料電池 (DCFC) のスケールアップのための発電特性の検討

No.2-14 直接炭素燃料電池 (DCFC) のスケールアップのための発電特性の検討

Anodic Reaction Mechanisms in Direct Carbon Fuel Cells Using Carbon Particles Dispersed in Molten Carbonate

Highly efficient technologies for the conversion of solid fuels, such as coal and biomass, to electricity are required for clean energy production and sustainable energy supply. Direct carbon fuel cells (DCFCs), which convert the chemical energy in solid carbon directly into electricity without gasification, have attracted much attention because of their theoretical ability to achieve 100 % efficiency. However, solid carbon particles have disadvantages in terms of fluidity when compared to gaseous fuels. Thus, carbon particles are dispersed into molten carbonate to form a carbon/carbonate slurry in which the carbon particles can move. Then, the anode is inserted into the carbon/carbonate slurry for discharge in the DCFC [1-5]. Carbon dispersed into the molten carbonate is easily transported to the anode, leading to an improvement of the formation of triple phase boundary (carbon, electrolyte, and anode). During discharge, carbon is supposed to be consumed through the complete electrochemical oxidation (C+2CO3 2-→3CO2+4e- (R1)) which releases four electrons per carbon. However, several studies have suggested a possible formation of CO from partial electrochemical oxidation (C+1/2CO3 2-→3/2CO+e- (R2)) which releases one electron per carbon, or even from the Boudouard reaction (C+CO2→2CO (R3)) where CO2 produced during discharge reacts with carbon particles [3,6]. Although the partial oxidation (R2) and the Boudouard reaction (R3) reduce the DCFC efficiency, little effort has been made to study the reaction mechanisms in the DCFC. The aim of this study is to investigate the anodic reaction mechanisms in the DCFC using carbon/carbonate slurry experimentally and theoretically. Figure shows setup of the DCFC using carbon/carbonate slurry stirred by gas bubbling. The working electrode (WE), counter electrode (CE), and reference electrode (RE) were made from gold sheets. Cell discharge was controlled with a potentio/galvano-stat. The reactor was heated using an electric furnace to 1073 K. Activated carbon particle with an average diameter of 44.1 μm was used as fuel. Ternary molten carbonate (Li2CO3/Na2CO3/K2CO3 (= 16.9/25/58.1 mol%)) was used as electrolyte. The carbon content in the carbonate was set to 1.0 wt% or 2.0 wt%. The carbon/carbonate slurry was contained in the porous alumina tube having an average pore diameter of 120 nm. This allowed the separation between the carbon/carbonate slurry and the molten carbonate electrolyte. In the setup, the carbon/carbonate slurry was able to be stirred by gas bubbling. CO and CO2 concentrations in off-gases were measured by FID with methanizer, and CO and CO2 production rates were determined at the open circuit mode or constant discharge mode at 20 mA/cm2. Moreover, to study the impact of Boudouard reaction (R3) on CO formation, CO2 bubbling with a flow rate of 1.0 ml/min, which was approximately 5 times of theoretical CO2 produced during discharge at 20 mA/cm2, was used in the carbon/carbonate slurry at the open circuit condition, and CO concentration in off gases was measured. As a result, an amount of CO was formed when the carbon/carbonate slurry was not stirred by Ar gas bubbling during the constant discharge at both the carbon contents. At the open circuit condition, CO was not formed by CO2 bubbling (1.0 ml/min) simulated CO2 produced during discharge. This indicated that the impact of Boudouard reaction (R3) was insignificant in the DCFC. Moreover, measured CO and CO2 production rates were well balanced on the calculation based on two electrochemical oxidations (R1 and R2). And, the partial electrochemical oxidation accounted for approximately 80 % in the carbon consumption at the carbon content of 2.0 wt%, whereas that accounted for approximately 40 % at the carbon content of 1.0 wt%. It was shown that the ratio of partial electrochemical oxidation depended on the carbon concentration near the anode. On the other hand, when the carbon/carbonate slurry was stirred by Ar bubbling with a flow rate of 50 ml/min, only CO2 was formed and the production rate of CO2 corresponded to the theoretical rate based on R1 at both the carbon contents. This indicated the carbon particles were consumed only by the complete electrochemical oxidation (R1). It was shown that stirring the carbon/carbonate slurry was effective to enhance the complete electrochemical oxidation. Reference [1] N. J. Cherepy et al., J. Electrochem. Soc., 152 (2005) A80-A87. [2] X. Li et al., Ind. Eng. Chem. Res., 47 (2008) 9670-9677. [3] H. Watanabe et al., J. Power Sources, 273 (2015) 340-350. [4] H. Watanabe et al., Energy and Fuels, 30 (2016) 1835-1840 [5] H. Watanabe et al., J. Chem. Eng. Jpn., 49 (2016) 237-242 [6] T.M. Gür, J. Electrochem. Soc., 157 (2010) B751-B759 Figure 1

Fabrication and Characterization of LSM/YSZ/GDC Tri-Composite Cathode-Supported Tubular Solid Oxide Direct Carbon Fuel Cell

The purpose of this study was to fabricate a porous and high mechanical strength cathode support for solid oxide direct carbon fuel cells. Therefore, the effect of Gd0.1Ce0.9O2-δ (GDC) addition on the phase stability, sintering behavior, thermal expansion, porosity, electrical conductivity, and mechanical strength of La0.65Sr0.3MnO3-δ/(Y2O3)0.08(ZrO2)0.92 (LSM/YSZ) composite was evaluated. The sintering temperature and the porosity of LSM/YSZ composite were observed to increase with an increase in the amount of GDC, on the contrary, the electrical conductivity and the mechanical strength was decreased. An LSM/YSZ/GDC tri-composite with optimized properties was selected to fabricate the tubular cathode-supported SOFCs (LSM/YSZ/GDC|YSZ|NiO/YSZ) through extrusion and co-firing. A special chamber was designed for the DCFC operation of the tubular cell. Electrochemical characterization was done by measuring the polarization curves and electrochemical impedance spectroscopy using dry hydrogen or the syngas produced by in situ steam gasification of carbon black.

Anodic Reaction Mechanisms in Direct Carbon Fuel Cells Using Carbon Particles Dispersed in Molten Carbonate

This study aims to investigate the anodic reaction mechanisms in direct carbon fuel cell using a carbon/carbonate slurry stirred by Ar bubbling. CO2 and CO production rates were measured during the constant discharge. Gas products were calculated based on complete (C+2CO3 2-→3CO2+4e-) and partial electrochemical oxidation (C+1/2CO3 2-→3/2CO+e-). The impact of Boudouard reaction (C+CO2→2CO) on CO production was also discussed. As a result, an amount of CO was formed without Ar bubbling, whereas CO was not formed with Ar bubbling. The impact of CO2 bubbling on CO formation was insignificant, and calculations of gas products almost agreed with experiments of those. These indicated that CO was formed through not Boudouard reaction but the partial electrochemical oxidation. Moreover, partial electrochemical oxidation helped to explain the trends of open circuit voltages. It was shown that the anodic reactions consisted of complete and partial electrochemical oxidations.

Direct Carbon Fuel Cells – Wetting behavior of graphitic carbon in molten carbonate

The wetting behavior of graphitic carbon in a eutectic melt of LiK molten carbonate was investigated at two different temperatures (650 and 750 °C) under two different CO2 partial pressures. The development of the meniscus and the formation of a super-meniscus film were followed optically over a period of 24 h after partial immersion of the graphite rods. Post-test EDX analyses of the graphite surfaces exposed to the melt, above and below the meniscus, were compared to those of surfaces not exposed to the melt. The most important feature found in the EDX analyses is the non-uniform atomic distribution of oxygen both along the length of the immersed surface and in the radial cross-section of the rods exposed to the melt. In addition, the effect of pre-test exposure to gas atmospheres at various temperatures and CO2 partial pressures was investigated. The wetting behavior is found to be influenced strongly by reactions occurring at the carbon surface before and after the start of wetting. In particular, CO produced by the reverse Boudouard reaction, which appears to be physisorbed, and chemically adsorbed oxide ion, O2−, are inferred to play a dominant role in the development of the meniscus leading to a super-meniscus film on the graphitic surface. Several reaction mechanisms are examined to explain the results observed in this work, which agree with results of earlier work from this laboratory, in terms of CO and oxide ion formation.

Efficiency of non-optimized direct carbon fuel cell with molten alkaline electrolyte fueled by carbonized biomass

The direct carbon fuel cells (DCFCs) belong to new generation of energy conversion devices that are characterized by much higher efficiencies and lower emission of pollutants than conventional coal-fired power plants. In this paper the DCFC with molten hydroxide electrolyte is considered as the most promising type of the direct carbon fuel cells. Binary alkali hydroxide mixture (NaOH-LiOH, 90–10 mol%) is used as electrolyte and the biochar of apple tree origin carbonized at 873 K is applied as fuel. The performance of a lab-scale DCFC with molten alkaline electrolyte is investigated and theoretical, practical, voltage, and fuel utilization efficiencies of the cell are calculated and discussed. The practical efficiency is assessed on the basis of fuel HHV and LHV and the values are estimated at 40% and 41%, respectively. The average voltage efficiency is calculated as roughly 59% (at 0.65 V) and it is in a relatively good agreement with the values obtained by other researchers. The calculated efficiency of fuel utilization exceeds 95% thus indicating a high degree of carbon conversion into the electric power.

Utilization of bituminous coal in a direct carbon fuel cell

Direct carbon fuel cell (DCFC), as a high efficiency and low emissions power generation device, can convert the chemical energy stored in coal directly into electricity without combustion process. In present works, the performance of DCFC with Shenfu bituminous coal as fuel has been investigated in the temperature range 650–850 °C. It has been shown that coal composition, microstructure, chemical characteristics are closely related to the performance of DCFC. The anode solid residues have been analyzed by Fourier transform infrared spectra (FT-IR) and X-ray photoelectron spectroscopy (XPS), and the exhaust gas has been investigated by gas chromatography (GS). The results show that pyrolysis gas such as H2, CO and short hydrocarbons (e.g. CH4, C2–C4) can be used as fuels to improve the performance of DCFC. The ash of coal plays a vital role in performance of DCFC. The experimental results reveal the higher ash content in coal is; the worse the performance of DCFC is. Anode atmosphere is an important factor on affecting the performance of DCFC, and the maximum power density of DCFC can reach 31.3 mW cm−2 when the carrier gas is not used.