Hybrid Direct Carbon Fuel Cell Research Articles

Investigation of the Abnormal I-V Curve Shape of Hybrid Direct Carbon Fuel Cell Using Lanthanum Strontium Calcium Titanate-Based Anode

Solid oxide direct carbon fuel cell are being developed for use with waste derived materials. To avoid problems of the state-of-art Ni/YSZ anode, perovskite-based anode materials are being investigated. We have fabricated solid oxide fuel cells with La0.2Sr0.25Ca0.45MxTi1-xO3- δ (M=Ni, Fe, or Co) anodes, YSZ electrolyte, and LSM cathode. Electrochemical performance of these cells have been evaluated with both hydrogen and solid carbon as the fuel and promising results have been recorded. For example, fuel cells with La0.2Sr0.25Ca0.45Ni0.05Ti0.95O3- δ anode tested in hybrid direct carbon fuel cell mode reached a maxmium power density of 82.3 mW/cm2 measured in N2 purging gas at 850 °C. During hybrid direct carbon fuel cell testing with solid carbon fuel and nitrogen purging gas, I-V curves obtained showed an abnormal shape between 0.6V to 0.7 V. To investigate the origin of this line shape, we have used methods such as electrochemical impedance spectroscopy, potentiostatic study, analyzing of off gases from fuel cell using gas choromotography, SEM imaging, EDS analysis and Raman mapping of the tested fuel cell. These results can not only help explain the observed shape of I-V curve, but also provide insight into the mechanism of hybrid direct carbon fuel cells, thus benefiting further development of fuel cells for solid waste to energy applications.

Investigation of the Abnormal I-V Curve Shape of Hybrid Direct Carbon Fuel Cell Using Lanthanum Strontium Calcium Titanate-Based Anode

Solid oxide direct carbon fuel cells are being developed for use with waste derived materials. We have fabricated solid oxide fuel cells with La0.2Sr0.25Ca0.45MxTi1-xO3-δ (M=Ni, Fe, or Co) anodes, YSZ electrolyte, and LSM cathode. Electrochemical performance of these cells has been evaluated with solid carbon as the fuel and promising results have been recorded. For example, fuel cells with La0.2Sr0.25Ca0.45Ni0.05Ti0.95O3-δ anode tested in hybrid direct carbon fuel cell mode reached a maximum power density of 82.3 mW/cm2 measured in N2 purging gas at 850 °C. During hybrid direct carbon fuel cell testing with solid carbon fuel and nitrogen purging gas, I-V curves obtained showed an abnormal shape between 0.6V and 0.7 V. To investigate the origin of this line shape, we have used methods such as electrochemical impedance spectroscopy, potentiostatic study, and analysis of off gases from fuel cell using gas chromatography.

A high-performance hybrid direct carbon fuel cell with tandem catalysis in the dendritic channeled anode

Hybrid direct carbon fuel cells (HDCFCs) are promising to achieve high power density, good fuel-electrode contact, and high carbon-fuel conversion efficiency due to increased reaction sites and hybrid routines of carbon utilization. However, the performance of HDCFC is greatly restricted by mass transfer and detrimental carbon deposition. The so-called CO–CO2 shuttle process, i. e., the coupling of the electrochemical reaction of CO to CO2 and subsequent discharge of CO2 towards the C fuel surface for gasification, is the key mass transfer process needed to be optimized. This study demonstrates a novel high-performance HDCFCs anode by integrating C-gasification tandem catalysis in dendritic channel anode support (t-HDCFCs), which greatly enhances the CO–CO2 shuttle and mitigates carbon deposition. As a result, the t-HDCFC delivers a comparable or even higher electrochemical performance than the other HDCFCs under the same operation conditions, such as a peak power density of 556 mW cm−2 at 750 °C.

Promoting effective electrochemical oxidation of CO by Cu-doping for highly active hybrid direct carbon fuel cell anode

Hybrid direct carbon fuel cells (HDCFCs) present its inherent and unparalleled advantages in converting chemical energy from organic waste, biomass, and coal directly into clean energy with high efficiency. However, the progress of HDCFC technology continues to be hampered by the sluggish anode reaction kinetics. Herein, an effective design strategy for HDCFC anode is proposed, a Cu-modified Sr2Fe1.3Cu0.2Mo0.5O6-δ (SFCM) perovskite oxide is developed to meet the requirements of intermediate-temperature HDCFC anode. The Cu-doping SFCM anode demonstrates excellent redox structural stability and catalytic activity. In addition, the electrolyte-supported single cell with Cu-doping SFCM anode has improved the peak power density from 285.5 mW cm−2 to 489.3 mW cm−2 at 800 °C with activated carbon as the fuel. The significantly enhanced anode catalytic activity is primarily due to the improved interfacial activity and chemical adsorption of CO. Therefore, the present work shows an effective strategy for designing and developing novel high-performance HDCFCs anode materials.

Ce1-xPrxO2-d (x = 0.1, 0.2, 0.3 and 0.4) as Suspended Catalysts in a Hybrid Direct Carbon Fuel Cell

Ce1-xPrxO2-d (x = 0.1, 0.2, 0.3 and 0.4) as Suspended Catalysts in a Hybrid Direct Carbon Fuel Cell

Cathode Supported Hybrid Direct Carbon Fuel Cells with Different Anodes

Cathode Supported Hybrid Direct Carbon Fuel Cells with Different Anodes

Honeycombed Porous, Size-Matching Architecture for High-Performance Hybrid Direct Carbon Fuel Cell Anode.

Direct carbon fuel cells (DCFCs) demonstrate both superior electrical efficiency and fuel utilization compared to all other types of fuel cells, and it will be the most promising carbon utilization technology if the sluggish anode reaction kinetics that derives from the use of solid fuel can be addressed. Herein, the electrode morphology and fuel particle size are comprehensively considered to fabricate an efficient DCFC anode skeleton. A honeycombed and size-matching anode architecture with dual-scale porous structure is developed by water droplet templating, which demonstrates an efficient strategy to address the challenge of poor carbon reactivity and improve the electrochemical performance of DCFCs. Single cell with this designed anode framework demonstrates excellent performance, and the maximum power density is as high as 765 mW cm-2 at 800 °C when using the matching carbon fuel. The size-matching between carbon fuel and anode framework shows a remarkable effect on the improvement of mass-transfer processes at the anodes. The significant contribution of the difficult electrochemical oxidation of carbon to the output performance is also demonstrated. These results represent a promising structural design strategy in developing high-performing fuel cells.

Enhanced Stability and Catalytic Activity on Layered Perovskite Anode for High-Performance Hybrid Direct Carbon Fuel Cells.

In this work, we investigate a novel A-site ordered layered perovskite oxide, (PrBa)0.95Fe1.8-xCuxNb0.2O5+δ (PBFCN), as an anode material for hybrid direct carbon fuel cells (HDCFCs). We study the effect of anode composition on the electrochemical performance of HDCFCs. The electrolyte-supported single cell with (PrBa)0.95Fe1.4Cu0.4Nb0.2O5+δ (PBFCu0.4N) anode achieves the highest peak power density of 431 mW cm-2 at 800 °C with activated carbon as the fuel. Moreover, a power generation unit is also made to demonstrate the practical utilization of PBFCN, which delivers a peak power of 0.51 W at 800 °C without any carrier gas, and a small fan can operate for more than 10 h by using the as-fabricated HDCFC as a power generation unit. The PBFCN anode achieves greatly enhanced catalytic activity by improving the chemical adsorption and electrochemical oxidation of CO at the anode/CO interface, which is mainly due to the high-activity Cu ions in PBFCN. The inactive element Nb doping and ordered layered structure endow the material with excellent redox structural stability. The present study provides a new idea for the design and development of high-performance anode materials for HDCFCs applications.

Investigation of Tin Liquid Anode on Hybrid Direct Carbon Fuel Cells

A novel carbon fuel cell mode was designed for improving the cell performance on hybrid direct carbon fuel cells (HDCFCs). In this paper, the effects of Sn phase as the liquid anode on HDCFCs’ performance was investigated. The comparative results indicated that the cell performance was strongly dependent on the amount of Sn loading. With selectivity of different weight ratios, 20 wt% Sn additive was optimized to be the best behavior, corresponding to considerably decreased ohmic and polarization resistance. However, other compositions showed inferior performance than that of Sn-free anode, probably due to the Li2SnO3 impurity formation impeding catalytic properties of liquid Sn and Li-K salt. Stability testing further implied the cell with 20 wt% Sn addition was the best choice because of maximum fuel efficiency and reasonable durability. Based on these results, the possible completing mechanisms of Sn participating in electrochemical reaction on HDCFCs were proposed.

Mechanism of enhanced performance on a hybrid direct carbon fuel cell using sawdust biofuels

Biomass is expected to play a significant role in power generation in the near future. With the uprising of carbon fuel cells, hybrid direct carbon fuel cells (HDCFCs) show its intrinsic and incomparable advantages in the generation of clean energy with higher efficiency. In this study, two types of biomass treated by physical sieve and pyrolysis from raw sawdust are investigated on an anode-supported HDCFC. The structure and thermal analysis indicate that raw sawdust has well-formed cellulose I phase with very low ash. Electrochemical performance behaviors for sieved and pyrolyzed sawdust combined with various weight ratios of carbonate are compared in N2 and CO2 purge gas. The results show that the power output of sieved sawdust with 789 mWcm−2 is superior to that of pyrolyzed sawdust in CO2 flowing, as well as in N2 flowing. The anode reaction mechanism for the discrepancy of two fuels is explained and the emphasis is also placed on the modified oxygen-reduction cycle mechanism of catalytic effects of Li2CO3 and K2CO3 salts in promoting cell performance.

Investigation of B-site doped perovskites Sr2Fe1.4X0.1Mo0.5O6-δ (X=Bi, Al, Mg) as high-performance anodes for hybrid direct carbon fuel cell

B-site substituted Sr2Fe1.4X0.1Mo0.5O6-δ (SFXM, X = Bi, Al and Mg) are evaluated as anode materials for hybrid direct carbon fuel cells (HDCFCs). The structure, morphology, conductivity and catalytic activity of the as-prepared SFXM anode are systematically investigated. Under a reducing atmosphere, the exsolution of metallic Fe from the SFXM perovskite lattice are demonstrated by the XRD, SEM and TEM observations. Further element valence analysis on reduced SFXM suggests the X doping significantly alters the Fe3+/Fe2+ and Mo6+/Mo5+ ratio, and thus beneficial to the intrinsic conductivity of SFXM. All these advantages are responsible for the good electrochemical performances of SFXM anodes. Meanwhile, among these SFXM anodes, the conductivity, catalytic activity and electrochemical performance all obey the order of SFBM > SFAM > SFMM. The maximum power densities of the La0.8Sr0.2Ga0.8Mg0.2O3 electrolyte supported single cell with SFBM as the anode reaches 399, 287 and 141 mW cm−2 at 800 °C, 750 °C and 700 °C, respectively. Such designed B-site substitution perovskites have great potential to be applied as HDCFC anode materials.

Ni modified Ce(Mn, Fe)O2 cermet anode for high-performance direct carbon fuel cell

Ni modified Ce0.6Mn0.3Fe0.1O2 (Ni-CMF) material is evaluated as an anode material for hybrid direct carbon fuel cell (HDCFC). The Temperature Programmed Reaction (TPR) and GC test results show that the Ni additive significantly promotes the oxidation of carbon and consequently accelerates the formation rate of CO. Moreover, the Ni-CMF material is found to show a high electrical conductivity compared to pure CMF in HDCFC operating conditions. Taking advantage of the excellent catalytic activity and high conductivity, the electrolyte-supported HDCFC with Ni-CMF anode shows a high maximum power density of 580.7mWcm−2 at 800°C, when activated carbon is used as the fuel. Furthermore, the cell displays good stability under galvanostatic operation at current density of 50mAcm−2 at 750°C. These results indicate that the designed Ni-CMF composite material has the potential to be developed as an alternative anode for HDCFCs.

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.

Cathode-supported hybrid direct carbon fuel cells

The direct conversion of coal to heat and electricity by a hybrid direct carbon fuel cell (HDCFC) is a highly efficient and cleaner technology than the conventional combustion power plants. HDCFC is defined as a combination of solid oxide fuel cell and molten carbonate fuel cell. This work investigates cathode-supported cells as an alternative configuration for HDCFC, with better catalytic activity and performance. This study aims to define the best processing route to manufacture highly efficient cathode-supported cells based on La0.75Sr0.25MnO3/yttria-stabilized zirconia infiltrated backbones. The challenges on the development of high-performance backbones are discussed. In this study, cathode-supported configuration was confirmed to be more efficient for the oxidation of carbon than anode supported configuration. The maximum power density of the cathode-supported cell increased almost by a factor of two when compared with the anode-supported cell.

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

Direct carbon fuel cells offer the opportunity of generating energy from coal at high efficiency as an alternative to the procedure of conventional power plants. In this study, raw anthracite coal and raw bituminous coal were investigated in a hybrid direct carbon fuel cell (HDCFC), which was a combination of a solid oxide fuel cell and a molten carbonate fuel cell. Mechanical mixing was confirmed to be an efficient method of mixing coal with carbonate. The coal samples had different properties, for example, carbon content, hydrogen content, volatile matter and impurities. The results showed that the maximum power density obtained by the cell with anthracite coal was similar to that obtained by the cell with bituminous coal. It was found that the total power output from coal in HDCFCs mostly depended on the carbon content, while volatile matter, hydrogen content, moisture, etc. had an effect on the short-term durability. HDCFCs were kept operating for more than 120 h with 1.6 g coal. This study demonstrates that energy can be generated efficiently by employing anthracite and bituminous coal in hybrid direct carbon fuel cells.

Studies of current collection configurations and sealing for tubular hybrid-DCFC

Direct Carbon Fuel Cells (DCFC) offer efficient conversion of coal or biomass derived carbons to electricity. A Hybrid Direct Carbon Fuel Cell (HDCFC) is a type of DCFCs that combines solid oxide cell geometry with a molten carbonate fuel cell electrode. This study focused on investigating different current collection configurations and sealant for tubular HDCFC concept. A HDCFC used a gadolinia doped ceria (GDC) or a YSZ as the electrolyte, in composites with NiO and LSM as the anode and the cathode, respectively. Three different current collection configurations of HDCFC were investigated by AC impedance in order to study the electrochemical phenomena that occur at the electrodes surface. The AC impedance results showed that both the surface area and the position of the current collector inside of the anode chamber affect drastically both the series resistance (Rs) and the polarisation resistance (Rp) values. The lowest total resistance (Rtot) was achieved on Configuration b with silver wire interwoven nickel mesh attached to the side of the anode wall by silver paste (Rtot = 2.98 Ω) and while the highest Rtot was achieved on the configuration c with silver wire interwoven nickel mesh inserted into the mixture of carbon and carbonate (Rtot = 149 Ω). The leak test carried out on several sealants demonstrated that composite sealants of Toku P-24 paste and an alumina silicate disc produced a low degree of leaks due to both the high resistance to the carbonate mixture and high density sealing after curing compared to the ceramabond.

Role of coal characteristics in the electrochemical behaviour of hybrid direct carbon fuel cells

Hybrid direct carbon fuel cells (HDCFCs) are now considered as one of the most efficient options for the generation of clean energy from mineral coals. This work sheds light on the reaction mechanism of the HDCFC operated with raw and pre-treated mineral coals which have been thoroughly characterised and tested.

Hybrid Direct Carbon Fuel Cell Performance With Anode Current Collector Material

The influence of the current collector on the performance of a hybrid direct carbon fuel cell (HDCFC), consisting of solid oxide fuel cell (SOFC) with a molten carbonate–carbon slurry in contact with the anode, has been investigated using current–voltage curves. Four different anode current collectors were studied: Au, Ni, Ag, and Pt. It was shown that the performance of the direct carbon fuel cell (DCFC) is dependent on the current collector materials, Ni and Pt giving the best performance, due to their catalytic activity. Gold is suggested to be the best material as an inert current collector, due to its low catalytic activity.

Utilisation of Coal in Direct Carbon Fuel Cells

Hybrid Direct Carbon Fuel Cells merge Solid Oxide Fuel Cell (SOFC) and MCFC technologies, using a solid oxide electrolyte to separate the cathode and anode compartments, while a molten carbonate electrolyte is utilised to extend the anode/electrolyte region. Oxygen is reduced to O2- ions at the cathode and transported across the solid electrolyte membrane to the anode compartment, where carbon is oxidised to CO2. Molten carbonate could enhance the carbon oxidation in two ways as a fuel carrier or as an electrochemical mediator. The maximum energy density can be achieved by fully oxidising carbon to CO2 offering very high efficiencies. This concept has been demonstrated using a wide range of carbons and carbon-rich fuels such as coal, plastics, carbon colloids, activated carbons and charcoals. In a short stack of 3 cells delivered a maximum power output at 650oC of 5.4 W, at over 100mWcm-2. The underlying chemical processes in DCFCs are complex involving a series of catalytic and electrochemical reactions of a complex fuel. Coal and biochars are quite far from pure carbon comprising of high hydrogen content and often significant oxygen, sulphur and nitrogen contents as well as inorganic, ash components. Here we report on the pyrolysis and oxidation reactions and processes that occur in situ and in DCFC relevant conditions. Of key importance is interplay between carbon and its oxides as direct oxidation of carbon to carbon dioxide delivers the ultimate efficiency. There is a change in process above 750oC where the reverse Boudouard reaction becomes dominant and our focus is on understanding the lower temperature electrochemical processes.

Use of Solid Carbon Anodes in the Direct Carbon Fuel Cell

Cell arrangement & advantages The direct carbon fuel cell (DCFC) offers the possibility of replacing inefficient coal fired power stations with a high efficiency and low emission option. Combustion of the carbon source, transforming chemical energy to thermal, is replaced with electrochemical transformation in a fuel cell arrangement, operating between 600-800°C. One of the major challenges of this technology is the delivery of a solid fuel to the reaction zone of the fuel cell. Fuels cells traditionally operate on gaseous fuels and this therefore presents a unique challenge. Although many different cell arrangements have been trialled, the most promising is that of the hybrid DCFC using a molten carbonate oxide transfer medium in the anodic compartment, and a solid electrolyte separating cathode and anode. A slurry of carbon and carbonate can be used along with a current collector, however this arrangement suffers from mass transport limitations as well as being susceptible to chemical corrosion of the solid fuel not in contact with the current collector via the Bouduard reaction (i.e. carbon partial oxidation by carbon dioxide gas to carbon monoxide), resulting in reduced efficiency of operation. The concept under development at the University of Newcastle involves the use of a solid fuel anode which reduces corrosion via carbon monoxide formation, as well as removing mass transport issues. The cell arrangement is visualised in the supplied figure. High conductivity of this electrode is essential as it must act as a current collector as well as a fuel. Further, mechanical stability is of high importance since the electrode will be consumed and binder materials must be stable under operating conditions as well as being less active to avoid preferential consumption and eventual degradation. Careful design of this anode arrangement is therefore required. Coal type and impact of ash Kinetics of carbon electrochemical oxidation have been observed to be sluggish and limiting in a fuel cell arrangement. Enhancing these kinetics is essential for realising an active DCFC able to operate competitively with current technologies available. It has been shown in research conducted at the University of Newcastle that kinetics at a solid carbon electrode can be enhanced through the use of common coal ash constituents. Further, kinetics are seen to be heavily affected by the coal type and pyrolysis conditions. It is believed that this is a result of the change in the distribution of ash particles and type of ash present in these coal fuels. Detailed physical characterisation, including advanced mineral liberation analysis, has been carried out on several coal chars in order to determine the reason for apparent activation of certain coal chars electrochemically when thermally treated at a specific higher heating temperature during slow pyrolysis. Formulation and design of active solid anode Solid carbon anodes are commonly used in aluminium electrowinning. However, these anodes require extensive treatment at high temperatures for operation in a commercial aluminium plant and are made from premium coking products. This process would use parasitic process heat, reducing efficiency of the DCFC, as well as using premium coke products which limits DCFC applications. At the University of Newcastle, formulation of an active and stable solid anode has been investigated using integration of thermal coal chars pre-treated in various chemical and thermal processes including acid and base demineralisation, pyrolysis and hydrothermal treatment. Coal chars produced in this way have been tested both separately using a graphite binder to assess activity, as well as in combination in order to demonstrate the possibility of using a combined solid carbon anode in the direct carbon fuel cell. The final solid anode uses minimal graphite as a binder and demonstrates high activity as well as good mechanical strength over an extended testing period.