Types Of Fuel Cells Research Articles

An Evaluation of Turbocharging and Supercharging Options for High-Efficiency Fuel Cell Electric Vehicles

Mass-produced, off-the-shelf automotive air compressors cannot be directly used for boosting a fuel cell vehicle (FCV) application in the same way that they are used in internal combustion engines, since the requirements are different. These include a high pressure ratio, a low mass flow rate, a high efficiency requirement, and a compact size. From the established fuel cell types, the most promising for application in passenger cars or light commercial vehicle applications is the proton exchange membrane fuel cell (PEMFC), operating at around 80 °C. In this case, an electric-assisted turbocharger (E-turbocharger) and electric supercharger (single or two-stage) are more suitable than screw and scroll compressors. In order to determine which type of these boosting options is the most suitable for FCV application and assess their individual merits, a co-simulation of FCV powertrains between GT-SUITE and MATLAB/SIMULINK is realised to compare vehicle performance on the Worldwide Harmonised Light Vehicle Test Procedure (WLTP) driving cycle. The results showed that the vehicle equipped with an E-turbocharger had higher performance than the vehicle equipped with a two-stage compressor in the aspects of electric system efficiency (+1.6%) and driving range (+3.7%); however, for the same maximal output power, the vehicle’s stack was 12.5% heavier and larger. Then, due to the existence of the turbine, the E-turbocharger led to higher performance than the single-stage compressor for the same stack size. The solid oxide fuel cell is also promising for transportation application, especially for a use as range extender. The results show that a 24-kWh electric vehicle can increase its driving range by 252% due to a 5 kW solid oxide fuel cell (SOFC) stack and a gas turbine recovery system. The WLTP driving range depends on the charge cycle, but with a pure hydrogen tank of 6.2 kg, the vehicle can reach more than 600 km.

Fuel Cell Stack Emulation for Cell and Hardware-in-the-Loop Testing

The high costs of fuel cell stacks are often prohibitive for research applications. Instead, researchers tend to either perform tests on individual cells under emulated load conditions, or they use model-based emulated fuel cell stacks to test realistic loads. This paper presents an alternative technique that allows the simultaneous investigation of both cell and hardware. In this technique, an amplifier takes as input the voltage of a reference fuel cell and reproduces the “scaled-up” voltage that would be provided by a stack of similar cells. The output terminals of this simulated stack can be connected to realistic loads, which are series connected with the reference cell to maintain a one-to-one correspondence of cell and load currents. This technique allows the simultaneous investigation of stack/load interactions, stack electrochemical performance characteristics, and stack durability under load. The amplifier electronics are independent of the fuel cell allowing its use with all fuel cell types, e.g., solid oxide fuel cells (SOFCs) or proton exchange membrane fuel cells. We demonstrate the emulator using a single planar SOFC and under several real loads. The data collected reveal good steady-state and dynamic accuracy, and the observed electrical interactions highlight the utility of the emulator in cell and hardware-in-the-loop testing. Ultimately, this technique provides fuel cell system researchers and developers a low-cost, easily implemented tool for rapid assessment of novel fuel cell technologies under real-world loading conditions.

Durability and Degradation of Direct Dimethyl Ether High Temperature Polymer Electrolyte Membrane Fuel Cells

Dimethyl ether (DME) combines high energy density with low toxicity and good electro-oxidation kinetics due to the absence of carbon-carbon bonds. It has therefore been identified as an attractive fuel for various fuel cell types, including the high temperature polymer electrolyte membranes (HT-PEM) fuel cells utilizing phosphoric acid doped polybenzimidazole (PBI) membranes [1, 2]. The HT-PEMFC technology has been intensively developed during the last two decades, and recently lifetimes exceeding 9000 h with degradation rates as low as 0.5 μV h-1 have been achieved at 160 °C and 200 mA cm-2 with hydrogen and air [3]. This type of cell was originally developed for a direct methanol fueled system [4], but lifetimes exceeding a few hundred hours have yet not been reported in this mode. We recently demonstrated that this is, at least partly, due to severe chemical incompatibility between methanol and the phosphoric acid within the polymer membrane. It results in formation of organic phosphoric acid ester derivatives, which not only reduces the conductivity of the membrane but also promotes the acid loss [5]. This work presents durability studies of direct DME HT-PEM fuel cells, and extends to a discussion about the predominating degradation mechanisms responsible for the limited lifetimes. The cells were operated at a constant current load at 160 or 200 °C and periodically characterized by polarization curves and electrochemical impedance spectroscopy. Supported by studies on a model system of phosphoric acid and DME, a main degradation pathway is suggested, where methyl phosphates are formed within the membrane. In analogy with the direct methanol cells, this reduces the proton conductivity of the membrane and promotes the acid loss, which leads to gradually increasing internal resistance. [1] J.O. Jensen, A. Vassiliev, M.I. Olsen, Q.F. Li, C. Pan, L.N. Cleemann, T. Steenberg, H.A. Hjuler, N.J. Bjerrum, J. Power Sources, 211 (2012) 173-176. [2] J. Neutzler, G. Qian, K. Huang, B. Benicewicz, J. Power Sources, 216 (2012) 471-474. [3] T. Søndergaard, L.N. Cleemann, H. Becker, D. Aili, T. Steenberg, H.A. Hjuler, L. Seerup, Q. Li, J.O. Jensen, J. Power Sources, 342 (2017) 570-578. [4] J.S. Wainright, J.T. Wang, D. Weng, R.F. Savinell, M. Litt, J. Electrochem. Soc., 142 (1995) L121-L123. [5] D. Aili, A. Vassiliev, J.O. Jensen, T.J. Schmidt, Q. Li, J. Power Sources, 279 (2015) 517-521

Determination of Long-Term Stability and Quality of HT-PEM MEAs

Durability and stability are the quality features for any type of product, including High Temperature (HT) Polymer Electrolyte Membrane (PEM) Fuel Cells. Compared with the low temperature (LT) representatives of this fuel cell type, the degradation rates of HT-PEM fuel cells are slightly higher [1-2]. Nevertheless, HT-PEM fuel cells are steadily improving [3-5], as shown by Søndergaard et al. with ultralow degradation rates of 1.4 µV/h [6], and are on the rise, as their higher CO tolerance represents a significant advantage over the LT-PEM fuel cells [7]. However, while stability and quality of HT-PEM MEAs is constantly improving, durability is still a challenge. For this reason, within the framework of the German project QUALIFIX funded by BMWi, the longevity of MEAs was investigated by means of long term tests (duration: 1 year) under constant load of 0.3 A/cm². In addition, qualities of MEAs are reviewed by carrying out small series evaluations under load cycling conditions at high current densities, start/stop and potential cycling conditions [8-9]. In the results from the annual tests, for which MEAs of FUMATECH BWT GmbH were used, were noticeable quality differences observed. The first test (AT 01) had to be stopped already after one third of the planned runtime, as End of Life (EoL=starting voltage value - 10%) was reached. By contrast, the second annual test (AT 02) ran longer than the estimated 8,760 hours (currently still in operation). The voltage curves of the two tests are shown in Figure 1 a) and the two graphs exhibit significant differences. In addition to the shortened life, the starting voltage value of the AT 01 is significantly lower (0.559 V), while the starting value of the second annual test is 13% higher (0.631 V). In addition to extensive electrochemical characterizations during operation time (BoL (Begin of Life)/EoT (End of Test)), the MEAs were comprehensively analyzed ante- and post-mortem. These include, among others, the phosphoric acid concentration determinations with the help of titration as well as optical imaging. With the help of micro-computed tomography, structural changes of the MEAs, which occur during the experimental procedure, can be visualized. As shown in Figure 1 b), one possible reason for the rapid performance drop of the AT 01-MEA could be found with this method: the destruction of the membrane. The different lifetimes can be due to the varied membranes (AT 01 = fumapem AM and AT 02 = fumapem AP). After completion of the second annual test, this comprehensive post-mortem will be performed, analyzed and compared with AT 01. In summary, it can already be observed that these MEAs of the same manufacturer perform very differently and the MEAs achieved a significantly higher quality standard in the course of the project. Still, the different performances make stack construction difficult because a single poorly performing MEA can adversely affect the performance of the entire stack. Therefore, a uniform quality management in the production of single cells is necessary to fix the quality – as already summarized in the acronym of the QUALIFIX project. Figure 1 a) Voltage as function of time for both long term tests and b) reconstructed 3D-µ-CT-images of MEA AT 01.

Direct methanol fuel cell (DMFC) and H2 proton exchange membrane fuel (PEMFC/H2) cell performance under atmospheric flight conditions of Unmanned Aerial Vehicles

Abstract Recently, there has been growing interest in fuel cell implementation on aircraft, particularly for Unmanned Aerial Vehicle (UAV) propulsion. The performance of both fuel cell types, cathode air-breathing H2 Proton Exchange Membrane Fuel Cells (PEMFC/H2) and passive Direct Methanol Fuel Cells (DMFCs), is dependent on atmospheric conditions such as pressure, relative humidity and temperature. In this study, models at the single-cell level have been used to simulate the corresponding polarization curves on flight conditions, which constitutes a contribution to the use of fuel cells in UAV. After validating these models, several cases of interest relating to UAV operation have been considered, such as cruise flight at different altitudes and horizontal flight when crossing clouds, to compare the performance of both types of fuel cells. Fuel cell temperature has been controlled to avoid high performance degradation. The results show that the effects of atmospheric flight conditions are more important for PEMFC/H2 than for DMFCs. Low pressure affects PEMFC/H2 performance to a greater extent than DMFC performance. Atmospheric relative humidity affects PEMFC/H2 performance, especially at high cell temperatures, whereas DMFC performance is barely affected. Although performance is lost, it is possible to operate fuel cells in UAV propulsion systems at low-medium altitudes.

Effects of Surface Modification on the Electrochemical Oxidation Reactivity of Activated Carbon in Direct Carbon Fuel Cells

A direct carbon fuel cell (DCFC) is the only fuel cell type that converts the chemical energy stored in solid carbon, which could be obtained from coal and biomass, into electricity directly via an electrochemical route with a higher energy efficiency and less pollution than conventional coal-fired power plants [1, 2]. In this work, the effect of the surface properties of carbon fuel on its electrochemical oxidation reactivity is investigated. Activated carbon (AC) is pre-treated with HNO3 and NaOH, respectively, both of which decrease the graphitization degree and increase the oxygen content of AC. The amount of hydroxyl groups on the surface of AC increases after the treatments with HNO3 and NaOH, and then decreases during the subsequent heating process in an inert atmosphere. On the contrary, the carbonyl groups on the surface of AC-HNO3 remain stable during the heating process. AC-HNO3 shows the highest reactivity towards oxidation and reverse Boudouard reactions due to its lowest graphitization degree and highest oxygen content. The performance of the cell supported by a 380-μm-thick yttria stabilized zirconia electrolyte layer with 60 mol% La0.6Sr0.4Co0.2Fe0.8O3-40 mol% Gd2O3 doped CeO2 as the electrodes is investigated with various fuels. The cell with AC-HNO3 as the fuel exhibits the highest maximum power density of 81 mW cm-2 at 800 oC. Fig. 1. I-V and I-P curves of single cells with various carbon fuels at 800 oC References [1] Jiang C, Ma J, Corre G, et al. Chemical Society Reviews, 2017, 46(10): 2889-2912 [2] Jang H, Park Y, Lee J. Chemical Engineering Journal, 2017, 308: 974–979. Figure 1

Electrooxidation of Propylene to Acrolein

Short chain alkanes and alkenes (C1-4) typically have little economic value and are difficult to transport since they are gases. Because of this, these hydrocarbons are of so low value that they are often flared during extraction of oil.1 This talk investigates electrochemically partially oxidizing these materials to high-value liquid products, thus increasing both the value and ease in transportation. If the oxidation is cathodic enough (< ~ +0.9 V vs. RHE) this can be combined with a standard oxygen reduction reaction cathode in a PEM fuel cell type approach to produce a device that does not consume electrical power, but actually has the potential to produce a small amount of power.2 Specifically this talk focuses on partial electrochemical oxidation of propylene to a variety of high value products such as acrolein, propylene oxide, propylene glycol, and acrylic acid and low value products such as CO2, and acetic acid. Using a Pd catalyst, we analyse the effects of pre-treatment, potential, pH and other factors in optimizing high value products while minimizing low value products. As shown below, one of the most promising findings is a high degree of acrolein selectivity at 0.9 V vs RHE in acidic solutions. The figure below shows that we can achieve stable electrochemical oxidation of propylene for 1 hour and produce acrolein with a selectivity of near 80%. Elvidge, C. D.; Ziskin, D.; Baugh, K. E.; Tuttle, B. T.; Ghosh, T.; Pack, D. W.; Erwin, E. H.; Zhizhin, M., A Fifteen Year Record of Global Natural Gas Flaring Derived from Satellite Data. Energies 2009, 2 (3), 595-622.Yamanaka, I., Active control of catalysis and product selectivity by a fuel cell system. Research on Chemical Intermediates 2006, 32 (3-4), 373-38 Figure 1

Cell and Electrode Development for the Hydrogen Peroxide Production Via Partial Oxygen Reduction Reaction

Hydrogen peroxide is an important industrial commodity. For large scale industrial use, the production via the established anthraquinone process is still economical most favourable. However, smaller applications would require substantial logistic efforts for the distribution. For these applications the local production could be more suitable. Electrochemical methods using renewable energy would further support the environmental friendliness. A simple electrochemical way to produce hydrogen peroxide is the partial reduction of oxygen from air according to equation [1]. A limiting factor is the undesired further reduction of hydrogen peroxide to water at the same electrode according to equation [2]. As the reversible potential for this reaction is much higher than that for the oxygen reduction, the reaction is kinetically favoured. Some efforts were made to find catalyst with a low activity for this undesired reaction. One candidate material for an acidic environment are gold catalyst with a small amount of added palladium (1, 2). In own test this was confirmed in RRDE tests (3). In this contribution the transfer into a full cell will be described. As cell a Micro Flow Cell with 10 cm2 electrode area and n Electro MP Cell with 100 cm2 electrode area were used, both ElectroCell A/S, Denmark. Both cells were modified to accommodate house made gas diffusion electrodes. On the cathode side commercial oxygen evolution electrodes by ElectroCell A/S were employed. The gas diffusion electrodes were made from fuel cell type GDLs H23C8 by Freudenberg, Germany. Catalyst layer was either applied by sputter coating or by airbrushing a catalyst ink of carbon supported catalyst. 2 M sulphuric acid was used as electrolyte on both sides. The electrolyte was flown through gaps between the electrode and the separation membrane made from FumaSep F-101020 PK by Fumatech, Germany (cf. Fig. 1). The gap width in 10 cm2 cell was 4 mm on both sides. In the 100 cm2 cell the anodic gap width was increased to 8 mm on the anode side in order to decrease the gap on the cathode side to 1.5 mm. Hydrogen peroxide concentrations were measured using a commercial electrochemical sensor by AMT, Germany downstream of the cell. Tests were either performed by passing a small electrolyte flow through the cathode side once a sampling the product (single pass) or by cycling the electrolyte at a high flow rate till a stable concentration was reached (cycled batch). For the 10 cm2 cell tests with electrodes sputtered with a 50 nm platinum layer were compared to testes with electrodes coated with 20 wt% PdAu/C catalyst with 0.15 mg cm-2 metal loading. In single pass tests with the platinum electrode the highest observed hydrogen peroxide concentration of 0.3 wt% was obtained at an electrolyte flow rate of 0.1 ml min-1 at a current of 250 mA corresponding to a current efficiency of ca. 11% (c.f. Fig. 2). Increasing the flow rate to 0.5 ml min-1 decreased the H2O2 concentration to 0.2% wt% which, however, corresponds to a current efficiency of 37.8%. This can be seen as indication for hydrogen peroxide reduction at longer residence time. Accordingly, no built up in concentration of H2O2 was observed in cycled batch operation. Surprisingly, for the electrode coated with PdAu/C catalyst a much lower hydrogen peroxide concentration of 0.1 wt% was obtained at 0.1 ml min-1 flow rate in spite of a higher current of 550 mA (c.f. Fig. 3), so that the current efficiency was less than 2%. This can only be explained by a long hold back time of hydrogen peroxide in the porous structure of the supported electrode. The strong influence of the local concentration is further supported by the finding that during first tests in the larger cell with smaller gap and thus stronger flow it was possible to obtain hydrogen peroxide concentrations of 0.5 wt% with the sputtered platinum electrode. Here, also an accumulation of hydrogen peroxide during cycled batch operation was possible so that hydrogen peroxide concentrations up to 0.6 wt% were accomplished. In the contribution more details on the tests will be discussed supporting the importance of the cell design for the reaction selectivity. J. S. Jirkovsky, I. Panas, E. Ahlberg, M. Halasa, S. Romani and D. J. Schiffrin, Journal of the American Chemical Society, 133, 19432 (2011).J. S. Jirkovsky, I. Panas, S. Romani, E. Ahlberg and D. J. Schiffrin, Journal of Physical Chemistry Letters, 3, 315 (2012).C. Cremers, B. Kintzel, K. P. Duraisamy, K. Pinkwart and J. Tübke, Meeting s, MA2016-02, 1652 (2016). Figure 1

Achievements and trends of solid oxide fuel cells in clean energy field: a perspective review

The main concerns in the world today, especially in the energy field, are subjected to clean, efficient, and durable sources of energy. These three aspects are the main goals that scientist are paying attention to. However, the various types of energy resources include fossil and sustainable ones, but still some challenges are chasing these kinds from energy conversion, storage, and efficiency. Hence, the most reliable and considered energy resource nowadays is the utilized one which is as highly efficient, clean, and everlasting as possible. So, in this review, an attempt is made to highlight one of the promising types as a clean and efficient energy resource. Solid oxide fuel cell (SOFC) is the most efficient type of the fuel cell types involved with hydrogen and hydrocarbon-based fuels, especially when it works with combined heat and power (CHP). The importance of this type is due to its nature of work as conversion tool from chemical to electrical for generation of power without noise, pollution, and can be safely handled.

Comprehensive Analysis of Trends and Emerging Technologies in All Types of Fuel Cells Based on a Computational Method

Fuel cells have been attracting significant attention recently as highly efficient and eco-friendly energy generators. Here, we have comprehensively reviewed all types of fuel cells using computational analysis based on a citation network that detects emerging technologies objectively and provides interdisciplinary data to compare trends. This comparison shows that the technologies of solid oxide fuel cells (SOFCs) and electrolytes in polymer electrolyte fuel cells (PEFCs) are at the mature stage, whereas those of biofuel cells (BFCs) and catalysts in PEFCs are currently garnering attention. It does not mean, however, that the challenges of SOFCs and PEFC electrolytes have been overcome. SOFCs need to be operated at lower temperatures, approximately 500 °C. Electrolytes in PEFCs still suffer from a severe decrease in proton conductivity at low relative humidity and from their high cost. Catalysts in PEFCs are becoming attractive as means to reduce the platinum catalyst cost. The emerging technologies in PEFC catalysts are mainly heteroatom-doped graphene/carbon nanotubes for metal-free catalysts and supports for iron- or cobalt-based catalysts. BFCs have also received attention for wastewater treatment and as miniaturized energy sources. Of particular interest in BFCs are membrane reactors in microbial fuel cells and membrane-less enzymatic biofuel cells.

Preparation of Ni/NiO-C catalyst with NiO crystal: catalytic performance and mechanism for ethanol oxidation in alkaline solution

Highly active and durable catalysts are imperative for the development of alcohol oxidation research. Herein, a Ni/NiO-C catalyst with hollow NiO crystal can be used in ethanol oxidation. The hollow NiO nanoparticles are absolutely coated in the amorphous carbon and the generated NiO crystal remarkably raises the electrocatalytic performances of catalysts. Among all samples, the Ni/NiO-C3 catalyst shows the highest current density in 0.5 M ethanol solution. This is mainly derived from the synergistic effect of the crystallographic form, carbon coating, and hollow structure. Besides, the reaction mechanism of Ni/NiO-C3 electrode is controlled by charge transfer in high-concentration ethanol. With the concentration of ethanol decreased, a diffusion control mechanism is observed on Ni/NiO-C3 electrode. The attenuation rate of current density is only 0.1% after 3600 s by chronoamperometry in 0.1 M ethanol aqueous solution, indicating that the Ni/NiO-C3 electrode has a superior stability. Moreover, Ni/NiO-C3 electrode exhibits an rapid current response in 0.1 mM ethanol solution and a linear relationship between 0.69 and 40.17 mM, which provides a new idea for the research of fuel cell type ethanol sensor.

Role of electrical resistance and geometry of porous electrodes in the performance of microfluidic fuel cells

Significant electrical resistance is observed in porous electrodes of microfluidic fuel cell due to the size limitation of this energy system. In this work, role of electrical resistance and geometry of porous electrodes in the performance of microfluidic fuel cells is studied with a three-dimensional numerical model. Parametric simulations are performed to find proper ways to reduce the electrical resistance, including increasing the electrical conductivity of the electrode, changing the electrode geometry, and optimizing the current collector design. The results indicate that the cell cannot fully get rid of the negative influences of the electrical resistance by increasing the electrical conductivity due to the material restriction. Decreasing the electrode length or increasing the electrode width is also not feasible due to the trade-off between current and current density. Optimization of the aspect ratio of the electrode active region is proved effective in realizing the enhancement of both current and current density. Extending the current collector area from the exposed end to the active region of the porous electrode is also promising as it can decrease the electrical resistance and boost the cell performance simultaneously. The present findings are generally applicable to various miniaturized fuel cell types using porous electrodes.

Energy from Salinity Gradients

Osmotic power or salinity gradient power (SGP) is the energy available from the difference in the salt concentration between seawater and river water. Two practical methods for this are reverse electrodialysis (RED) and pressure retarded osmosis (PRO). SGP can be generated from reversible mixing of two kinds of water with different salt contents. A process for generating potential from salinity concentration gradient produced in single cell (25 cm2) and multi-cell assembly is presented. The salinity gradient is created using a fuel cell type cell with a micro-porous ion exchange membrane, both anionic (AEM) and cationic (CEM). The study was performed for various gradients. Salt : Fresh, from 100 : 0 to 16000 : 0 was established using NaCl solution, in the electrode chambers. A potential of 25 mV/cm was realized at ambient temperatures and pressures for a bipolar AEM/CEM cell. The achievable potential is still below theoretical value. The performance was optimized for various static and dynamic flow rates of the saline and fresh water. For this purpose the cell flow field was simulated using ANSYS and the flow field design was optimized for maximum coverage of the cell area. The cell performance can further be optimized for various Membrane Electrode System (MES) structure. Cyclic Voltammetry (CV) studies were made to understand the redox process. The electrochemical and electrical efficiency was discussed for various gradients and flow rates. The higher the salinity gradient the larger is the potential generated. This is limited by the membrane characteristics. The membrane characteristics have been studied for optimal ion crossover for various gradients and flow.

Development of Cell-Protecting Methods for Carbon-Removal from Porous Ni-YSZ Anodes and Regeneration of the Cell Performance

Solid oxide fuel cells are highly efficient units, which directly convert the chemical energy of gaseous fuels into electrical energy without additional conversion steps. The overall efficiency can be increased by using heat losses occurring during the operation at high temperatures between 600–1000°C. SOFCs further offer a great fuel flexibility and compared to other fuel cell types they can internally reform hydrocarbons. Internal conversion of carbon-containing fuels over nickel as the most widely used catalyst tends to promote carbonaceous deposits on the anode surface as well as inside the anode, causing deactivation of the fuel cells. Nevertheless, undisturbed operation with conventional fuels and early detection of the cell degradation are highly important for the commercial usage of solid oxide fuel cells in industry, such as in auxiliary power units or especially for mobile application. Formation and deposition of carbonaceous species on the anode surface of solid oxide fuel cells may be prevented under specific operating conditions such as high steam/carbon ratio or high current density. The increasing amount of steam in fuel can chemically remove carbon adsorbed on the anode surface thus reducing the total amount of carbon deposits. However, this would significantly dilute the fuel thus reducing the overall power and the cell efficiency. Further possibility to avoid carbon formation is to operate the cells under load higher than the critical current density. However, increase of the steam amount or variation of the cell load is neither realistic nor advantageous for the commercial purpose. Without the need for the variation of the operating conditions, such as higher amount of steam or higher load, early detection of degradation phenomenon and applying of appropriate cell-protecting regeneration strategies can improve the operating reliability of the SOFC systems. In order to prolong the cell’s lifetime and to accelerate the market access of SOFCs, diverse approaches for carbon removal in a cell-protecting manner and regeneration of the cell performance were developed and detailed examined. They are outlined within this study. The practicability of the developed methods for industrial application was also considered. The regeneration strategies are based on application of: (1) gaseous components, for the gasification of carbon deposits, and (2) electrochemical methods, which remove carbon during the cell loading. Operation under gaseous components as hydrogen, water vapour or oxygen-enriched gas mixtures allowed complete carbon removal. Nevertheless, under operation in a fuel cell mode, only the approach that combined hydrogen and water vapour removed carbon from the anode while also protecting it from further undesired degradation. It is important to note that very high amount of water can deteriorate the cell performance and even provoke unwanted nickel oxidation, which thus must be considered. However, the allowed water vapor amount must thus me determined. Furthermore, feeding the anode with a very low amount of oxygen in a wide temperature range showed high carbon removal rates but resulted in further deterioration of the cell performance, and eventually led to mechanical degradation. Both methods for carbon removal in a cell-protecting manner and approaches that induced further microstructure degradation are presented within this study.

In-Operando Detection of Carbon Depositions and Carbon Formation Predictions for Industrial-Sized SOFCs Fueled with Synthetic Diesel Reformate

Solid oxide fuel cells (SOFCs) present an attractive and innovative technology for environmentally-friendly electricity and heat generation. Their high operating temperatures and the excellent catalytic performance make SOFCs the most efficient fuel cell type, with a high level of fuel flexibility. Feeding the SOFCs with conventional or alternative carbon-containing fuels carries the risk of carbon formation and its deposition on the anode, which can reduce cell’s activity, cause irreversible cell degradation, and decrease the cell’s lifetime. In order to prolong the cell’s lifetime and to ensure the undisturbed operation of SOFCs, an in-depth understanding of this degradation phenomenon is required. The problematic of carbon deposition phenomenon is detailed explained and supported with numerical and experimental results for planar, industrial-sized, anode-supported solid oxide fuel cells within this study. Possible reactions to carbon build-up are presented and the methods and calculation principles used to predict the carbon formation are demonstrated. The key parameters that enable carbon predictions are: the components involved in a used gas mixture, temperature, the steam/carbon-ratio, equilibrium state, and C-H-O ternary diagram. All of the mentioned carbon prediction methods and analysis of the basic calculation principles are explicitely explained. For the detailed analysis and prediction of coking propensity, various diesel reformate mixtures, containing H2, CO, CO2, CH4, H2O and N2, are used. In order to examine the impact of water vapor on carbon deposition, the amount of H2O in the fuel mixture is varied between 0 vol%, 11.3 vol% and 20 vol%. The operating conditions, under which carbon can be formed and deposited on the anode side can thus be generated. In the course of the experimental analysis of the carbon deposition phenomenon, the polarized single cells were fed with synthetic diesel reformate mixtures, thus representing realistic operating conditions. In order to obtain information about the degradation of cell performance, such as the critical operating time or degradation voltage, the methane volume fraction in the fuel mixture was varied between 2.3 vol% (as expected in APUs), 9 vol%, 14 vol% and 20.3 vol%. The carbon build-up process on the Ni-catalyst, and, in fact, anywhere in the cell’s fuel supply manifold, was detected at an early stage by means of electrochemical impedance spectroscopy, current/voltage measurement, temperature measuremens and gas analysis. In addition to the in-situ characterization techniques used, an ex-situ post-mortem analysis was introduced to support the knowledge gained in the experimental analysis and to confirm the occurrence of the carbon identified via employed in-situ characterization techniques. Methane, including the decreasing steam/carbon ratio, was identified as having a major impact on the degradation rate at the typical operating temperature of 800°C for anode-supported solid oxide fuel cells. The critical operating time for carbon to form and be deposited on the anode was found to be strongly dependent on the amount of methane in the fuel mixture. For lower amounts of methane in the fuel mixture, such as 2.3 vol%, degradation of the cell performance was observed after 44 h. After accelerated carbon deposition process, due to an increase in the methane concentration of the gas mixture in use, the total critical operating time was significantly reduced. The approaches that allow early identification of carbon build-up in order to avoid irreversible deterioration of cell performance and its microstructure were originated and they are provided. A detailed microscopic investigation showed that carbon was uniformly formed over the Ni- and YSZ-sites. Massive carbon deposits not only caused the degradation of the cell performance, but also changed the Ni-YSZ structure. The crushing of YSZ-particles and their deposition on the Ni-catalyst were determined to be degradation phenomenona that occur if the carbon formation process in not interrupted at an early stage.

Highly effective oxygen reduction reaction electrocatalysis: Nitrogen-doped hierarchically mesoporous carbon derived from interpenetrated nonporous metal-organic frameworks

Nitrogen-doped carbon materials with hierarchically mesoporous structure are synthesized in the present work via the pyrolysis of an interpenetrated non-porous metal-organic framework (MOF), viz. [Zn2(TPT)(BDC)2]·H2O (SCUT-11, TPT=tris(4-pyridyl)triazine, BDC=1,4-benzenedicarboxylate), as the precursor. X-ray diffraction reveals that the synthesized metal-organic framework (MOF) is of high purity of the crystalline phase, and its structure follows our previously reported SCUT-11. This triply-interpenetrated MOF features high density of Zn cations in their interwoven packing structure, which act as effective pore-forming agent to generate mesopores in final carbon. Physicochemical characterizations reveal that the resultant carbon has high specific surface area and bimodal mesopore size distribution, which originate from the removal of metal oxide and/or metal zinc. These textual features favour both oxygen mass transfer and accessibility of catalytically active sites. Electrochemical results confirm that the resultant carbon, synthesized by pyrolysis at 900°C, shows a superior oxygen reduction reaction (ORR) activity, which is associated with high onset and half-wave potential up to 1.0 and 0.88V, respectively. Further investigation suggests that the as-synthesized carbon catalyst exhibits a remarkable insensitivity towards anions, like sulphate and phosphate, compared with the Pt counterpart. The above features make this carbon catalyst promising to be widely used in different fuel cell types.

Water Management in Low Temperature Fuel Cells through in-Operando X-Ray Computed Tomography

For polymer-electrolyte fuel cells (PEFCs) and anion exchange membrane fuel cells (AEMFCs) optimal water management is essential. During start-up and at low operating temperatures, where water is present in a liquid form, it can block reactant delivery to electrocatalyst sites, resulting in significant mass-transport losses, flooding and low fuel cell power densities. Using synchrotron X-ray computed tomography (CT) we have previously shown how water transport properties depend on porous materials morphology and chemical composition, as well as cell compression.1-3 These ex- and in-situ studies isolate specific porous membrane / electrode assembly (MEA) component’s effect on water management (such as micro-porous (MPL) or gas-diffusion layer (GDL)). To understand water transport under operating conditions we use in-operandoX-ray CT studies, where water distribution is observed under various steady-state conditions. In-operando single serpentine channel (1x1 mm) fuel cell testing hardware for synchrotron X-ray CT is used with active area of 1 cm2. Steady-state water generation and removal is observed in PEFCs and AEMFCs for temperature of 30oC with chronoamperometric holds at current densities ranges of 20 – 100 mA/cm2. Furthermore, comparison of water distribution in PGM and PGM-free catalysts for both type of fuel-cells will be presented. In all of these systems water pooling is observed at the component interfaces, indicating the importance of interfaces design. Acknowledgment: The Advanced Light Source is supported by the Director, Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231. This research used resources of the Advanced Photon Source, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357.

Potential Generation Using Salinity Gradients

Salinity Gradient Power (SGP) is one such power, which is environmentally sound as well as sustainable, that can be generated from reversible mixing of two kinds of water with different salt concentrations. This Reverse Electrodialysis (RED) technology uses a concentration gradient to derive a potential. The salinity gradient is created using a fuel cell type cell with a micro-porous ion exchange membrane, both anionic (AEM) and cationic (CEM). The study was performed for various gradients. Salt : Fresh, from 100 : 0 to 16000 : 0 was established using NaCl solution, in the electrode chambers. A potential of 25mV/cm was realized at ambient temperatures and pressures for a bipolar AEM/CEM cell. The achievable potential is still below theoretical values. The higher the salinity gradient the larger is the potential generated. This is limited by the membrane characteristics. This process is a unique technology for potential generation.

연료전지와 마이크로 열병합 발전기술

연료전지는 전기를 발전하면서 동시에 열도 생산하며, 본 고는 이 두 가지를 함께 이용하는 가정용의 마이크로 연료전지-열병합발전(<TEX>${\mu}FC$</TEX>-CHP) 시스템에 관한 조사보고서이다. 열병합발전 시스템을 구성하는 몇 가지 방안 중에서 연료전지는 전기와 열 효율을 합쳐 90%가 넘는 가장 높은 에너지 효율을 갖는 시스템을 구현할 수 있어 유용성이 높다. 연료전지에는 크게 다섯 가지 종류가 있으며, 이 중 가정용 <TEX>${\mu}FC$</TEX>-CHP로 적합한 것은 프로톤교환 막연료전지(PEMFC)와 고체산화물연료전지(SOFC)이다. <TEX>${\mu}FC$</TEX>-CHP시스템은 독립전원으로서 송배전 손실을 줄일 수 있고 전기생산단가를 낮출 수 있으며, 오염물질을 배출하지 않는 친환경 기술이란 점 등의 장점이 많다. 단점은 초기 투자비용이 높다는 점인데, 기술의 발달로 제작 단가를 줄여 이를 해결해나가고 있다. 현재는 일본이 시장을 선점하고 있으나 우리나라도 100만대 보급 계획을 가지고 있고, 정부가 반 정도의 설치보조금을 제공하여 시장을 견인하고 있다. 본 고에서는 이와 함께 연료전지와 열병합발전을 연결하는 기술적 내용 및 각국의 동향을 기술한다. This article reports current status of micro fuel cell-combined heat and power (<TEX>${\mu}FC$</TEX>-CHP) systems which utilize both power and heat generated by fuel cells. There are several options for constructing CHP systems and among them, fuel cells are the most useful and their total energy efficiency combining heat and power can reach up to about 90%. Fuel cells are classified as five types based on the electrolyte, but the most suitable fuel cell types for the <TEX>${\mu}FC$</TEX>-CHP system are proton exchange membrane fuel cells (PEMFCs) and solid oxide fuel cells (SOFCs). <TEX>${\mu}FC$</TEX>-CHP systems have several advantages such as decrease of the transmission-distribution loss, reduced costs of electricity due to distributed power generation, and environmental-friendliness owing to zero emission. The main drawback of the <TEX>${\mu}FC$</TEX>-CHP systems is the high initial investment, however, it keeps decreasing as the technology development reduces production costs. Currently, Japan is the most leading country of the <TEX>${\mu}FC$</TEX>-CHP market, however, Korea tries to expand the market by planning the deployment of 1 million units of <TEX>${\mu}FC$</TEX>-CHP systems and governmental subsidiary supporting of half of the install price. In this report, integration technologies for connecting FC and CHP, and technology trends of leading countries are presented as well.

Fabrication of Symmetrical La0.7Ca0.3Cr0.8Mn0.2O3- d Electrode Scaffold-Type Micro Tubular Solid Oxide Fuel Cells By Electrophoretic Deposition

Solid oxide fuel cells (SOFCs) have the highest energy conversion efficiency among various fuel cell types. SOFCs can be divided into two categories according to their cell design: planner and tubular type. Tubular SOFCs have many advantages in terms of good mechanical strength, easy sealing, and simple stacking process. Meanwhile, electrophoretic deposition (EPD) is very useful technique to deposit thin or thick layers due to easy layer thickness control by voltage and time. When a dc electric field is applied to the carbon rod in the slurry, the charging agent carries the particles to a substrate. One of major advantages of EPD is to fabricate multi-layer structure at the same time. In this study, symmetrical La0.7Ca0.3Cr0.8Mn0.2O3- δ(LCCM) electrode scaffold-type micro tubular SOFCs with the configuration of LCCM-YSZ anode // YSZ electrolyte // LCCM-YSZ cathode have been fabricated by EPD process. LCCM is considered as promising symmetrical electrode because it is very stable in both oxidizing and reducing atmosphere. The microstructure of the symmetrical electrode was controlled by the amount of pore former (PMMA). LCCM-YSZ electrode slurry for highly porous microstructure with uniform pore distribution was obtained with 40 vol.% PMMA, 2.5 wt.% polyvinyl butyral (PVB), 100 ml anhydrous ethanol, and 3 wt.% charging agent (polyethyleneimine). YSZ electrolyte slurry with highly dense microstructure was prepared with polyvinyl butyral (PVB), 100 ml anhydrous ethanol, and 5 wt.% charging agent (phosphate ester). After weighing of each slurry, ball-milling process was performed for 24 hour to obtain well-dispersed and uniform slurry. Carbon rod was deposited by LCCM-YSZ anode slurry, YSZ electrolyte slurry, and LCCM-YSZ cathode slurry in order. Deposition condition affected the microstructure and on thickness of each layers. LCCM-YSZ anode had thick layer for supporting the single cell with the deposition condition of the applied voltage of 20 V for 100 second. YSZ electrolyte was deposited on anode with the deposition condition of the applied voltage of 20 V for 20 second. At last, LCCM-YSZ electrode was deposited on electrolyte with the deposition condition of the applied voltage of 20 V for 20 second. After deposition of all layers by EPD, the single cell was co-filed at 1400 °C for 5 hour. Various processing conditions such as amount of charging agent, applied voltage, deposition time and sintering temperature were investigated. Stoichiometry amount of co-catalysts such as Pd or Co-Ni-Mo for better performance were impregnated into both sides of the LCCM scaffold by a glycine mediated solution impregnation method. Finally, the single cell performances of the fabricated LCCM symmetrical scaffold-type micro tubular SOFCs were evaluated in the temperature range of 600-800°C. Additionally thermal shock and redox cycling tests have been carried out.