Novel acid–base molecule-enhanced blends/copolymers for fuel cell applications

A series of acid–base molecule-enhanced composite membranes are successfully prepared. The composite membranes are composed of a sulfonated poly(aryl ether ketone) (6FSPEEK) as an acidic component, and of aminated poly(aryl ether ketone) containing a naphthyl group (AmPEEKK-NA) as a basic component. The composite membranes exhibit obviously improved thermal, oxidative and dimensional stability. Especially, these composite membranes possess excellent tensile properties both in the dry and wet state. The proton conductivities of these membranes are higher than 2.45 × 10⁻² S cm⁻¹ at room temperature and higher than 6.0 × 10⁻² S cm⁻¹ at 80 °C. The morphology of the membranes is studied in detail by SEM and AFM. All the data prove that both composite and aminated/sulfonated copolymer membranes may be potential proton exchange membrane for fuel cell applications.     

Oxidation resistance and electrical properties of anodically electrodeposited Mn–Co oxide coatings for solid oxide fuel cell interconnect applications

Co-rich and crack-free Mn–Co oxide coatings were deposited on AISI 430 substrates by anodic electrodeposition from aqueous solutions. The as-deposited Mn–Co oxide coatings, with nano-scale fibrous morphology and a metastable rock salt-type structure, evolved into a (Cr,Mn,Co)₃O₄ spinel layer due to the outward diffusion of Cr from the AISI 430 substrates when pretreated in air. The Mn–Co oxide coatings were reduced into metallic Co and Mn₃O₄ phases when annealed in a reducing atmosphere of 5% H₂–95% N₂. In contrast to the degraded oxidation resistance and electrical properties observed for the air-pretreated Mn–Co oxide coated samples, the H₂-pretreated Mn–Co oxide coatings not only acted as a protective barrier to reduce the Cr outward diffusion, but also improved the electrical performance of the steel interconnects. The improvement in electronic conductivity can be ascribed to the higher electronic conductivity of the Co-rich spinel layer and better adhesion of the scale to the steel substrate, thereby eliminating scale spallation.     

Comparison between two optimization strategies for solid oxide fuel cell–gas turbine hybrid cycles

This paper compares the performance characteristics of a combined power system with solid oxide fuel cell (SOFC) and gas turbine (GT) working under two thermodynamic optimization strategies. Expressions of the optimized power output and efficiency for both the subsystems and the SOFC-GT hybrid cycle are derived. Optimal performance characteristics are discussed and compared in detail through a parametric analysis to evaluate the impact of multi-irreversibilities that take into account on the system behaviour. It is found that there exist certain new optimum criteria for some important design and operating parameters. Engineers should find the methodologies developed in this paper useful in the optimal design and practical operation of complex hybrid fuel cell power plants.     

Cu doped Ni–Co spinel protective coatings for solid oxide fuel cell interconnects application

Four different amount of Cu doped Ni–Co alloy coatings were fabricated on SUS430 substrate by electroplating for solid oxide fuel cells (SOFCs) interconnects application. After oxidation at 800 °C, the microstructure and oxide phase of samples were tested by scanning electron microscope (SEM) with energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). Our experimental results indicated that the Cu addition improved the electrical behavior of Ni–Co alloy coating. Cu doping reduced the activation energy (Ea) of electrons hopping and inhibited the growth of Cr₂O₃ oxide layer. Furthermore, the oxidation kinetics and electrical properties of the alloy coatings were obtained. These results showed that the 9% Cu doped Ni–Co coated steels achieved the minimum parabolic rate constant (2.05 × 10⁻¹⁴ g²cm⁻⁴s⁻¹) and area specific resistance (14.11 mΩ cm²) after the thermostatic oxidation process.     

Electrical properties of SDC–BCY composite electrolytes for intermediate temperature solid oxide fuel cell

The electrolyte material Ce_0.85Sm_0.15O_1.92 (SDC) powders are synthesized by glycine–nitrate processes and BaCe_0.83Y_0.17O_3−δ (BCY) powders are synthesized by sol–gel processes, respectively. Then SDC–BCY composite electrolytes are prepared by mixing SDC and BCY. The SDC and BCY powders are mixed in the weight ratio of 95:5, 90:10 and 85:15 and named as SB95, SB90 and SB85, respectively. The electrical properties of SDC and SDC–BCY composites are investigated. The experimental results show that SDC–BCY composites exhibit the excellent conductivity and could significantly enhance the fuel cell performances. The behavior that SDC–BCY composites display hybrid proton and oxygen ion conduction is substantiated. Among these electrolytes, the maximum power density reaches as high as 159 mW cm⁻² for the fuel cell based on SB90 composite electrolyte at 600 °C.     

Physical and sealing properties of BaO–Al2O3–SiO2–CaO–V2O5 glasses for solid oxide fuel cell applications

In this study, the properties of BaO–Al₂O₃–SiO₂ (SAB) glasses incorporated with CaO and V₂O₅ as the network modifier and additive, respectively, are evaluated. The electrical resistivities of the glasses decrease upon the addition of CaO but increase upon increasing their V₂O₅ content because the V⁵⁺ species lower the ionic mobility of the glasses. The addition of V₂O₅ improves the wettability of the glasses on the Crofer 22 APU substrate, and thus, increases the fracture strength at the glass–Crofer 22 APU couple. Among the glasses evaluated, the SAB glass with a CaO content of 20 wt% and V₂O₅ content of 2 wt% (SAB-Ca20V2) present excellent sealing properties because it adheres well to both the Zr_0·92Y_0·08O_2-δ (YSZ) and Crofer 22 APU substrates; no pores, cracks, or interfacial phases are present at the interfaces, confirming the good chemical and thermal compatibility of the glass–substrate pairs at high temperatures. After SAB-Ca20V2 is sealed on the Crofer 22 APU substrate at 850 °C, the leakage rate of the glass is low (<0.015 sccm?cm^?1 at 800 °C for 200 h), indicating negligible deterioration of its sealing efficiency and revealing its remarkable potential for use in solid oxide fuel cell applications.     

Comparison of Cu–Mn and Mn–Co spinel coatings for solid oxide fuel cell interconnects

Electrophoretic deposition (EPD) of protective coatings on solid oxide fuel cell (SOFC) interconnects is an efficient method to mitigate ‘chromium poisoning’, which is a primary reason for degradation of fuel cell performance. Cu–Mn spinels and Mn–Co spinels are the most widely used materials for such coatings. In this study, four spinel coatings were examined; CuMn₂O₄, CuNi_0.2Mn_1.8O₄, MnCo₂O₄, and MnFe_0.34Co_1.66O₄. The coatings were evaluated on multiple criteria; including phase stability, microstructural stability, conductivity, Cr gettering ability, ability to act as a diffusion barrier to outward chromium and inward oxygen diffusion, and the ability to limit the increase in the area specific resistance (ASR) during high temperature oxidation exposures. The results showed that, while different coatings have best individual characteristics, overall CuNi_0.2Mn_1.8O₄ was the best candidate for the coatings operating in the intermediate temperature range due to its best sinterability, highest conductivity, lowest ASR, phase stability over the operational temperature range, lower cost and good resistance to outward chromium and inward oxygen diffusion.     

A novel system for the production of pure hydrogen from natural gas based on solid oxide fuel cell–solid oxide electrolyzer

In this paper, a novel process for the production of pure hydrogen from natural gas based on the integration of solid oxide fuel cells (SOFCs) and solid oxide electrolyzer cells (SOECs) is presented. In this configuration, the SOFC is fed by natural gas and provides electricity and heat to the SOEC, which carries out the separation of steam into hydrogen and oxygen. Depending on the system layout considered, the oxygen available at the SOEC anode outlet can be either mixed with the SOFC cathode stream in order to improve the SOFC performance or regarded as a co-product. Two configurations of the cell stack are studied. The first consists of a stack with the same number of SOFCs and SOECs working at the same current density. In this case, since in typical operating conditions the voltage delivered by the SOFC is lower than the one required by the SOEC, the required additional power is supplied by means of an electric grid connection. In the second case, the electricity balance is compensated by providing additional SOFCs to the stack, which are fed by a supplementary natural gas feed. Simulations carried out with Aspen Plus show that pure hydrogen can be produced with a natural gas to hydrogen LHV-efficiency that is about twice the value of a typical water electrolyzer and comparable to that of medium-scale reformers.     

CuxCo3-xO4-δ (0≤x≤1) coatings for solid oxide fuel cell interconnect applications

In order to obtain the solid oxide fuel cell (SOFC) interconnect coatings with high electrical conductivity, satisfactory protectiveness, and well-fitting thermal expansion, a series of Cu_xCo_3-xO_4-δ (x = 0, 0.5, 0.8, and 1.0) coatings are prepared by supersonic spraying via subsequent sintering. The chemical composition, lattice and morphological structures, electrical properties, and thermal expansion are characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), area-specific resistance (ASR), and coefficient of thermal expansion (CTE) measurements. The experimental results show that the formation of CuCo₂O₄ is a reversible and incomplete reaction at the elevated temperature, and the coexistence of CuO, Co₃O₄, and CuCo₂O₄ is inevitable in the coatings. The concentration of the chemicals mentioned above is highly related to the coatings’ Cu:Co molar ratio. The correlation between the chemical composition and the properties is comprehensively studied in this research. The Cu_xCo_3-xO_4-δ coatings exhibit good electrical conductivity when 0 ≤ x ≤ 0.8, satisfactory protectiveness when 0.5 ≤ x ≤ 1.0, and fitting CTE with remarkable robustness through the quick heating-cooling cycles when 0.8 ≤ x ≤ 1.0. In general, Cu_0.8Co_2.2O_4-δ can be an appropriate candidate to meet the advancing interconnect coating demands with high electrical conductivity, satisfactory protectiveness, and well-fitting thermal expansion properties.     

Fabrication–microstructure–performance relationships of reversible solid oxide fuel cell electrodes–review

Abstract

A reversible solid oxide fuel cell system can act as an energy storage device by storing energy in the form of hydrogen and heat, buffering intermittent supplies of renewable electricity such as tidal and wave generation. The most widely used electrodes for the cell are lanthanum strontium manganate–yttria stabilised zirconia and Ni–yttria stabilised zirconia. Their microstructure depends on the fabrication techniques, and determines their performance. The concept and efficiency of reversible solid oxide fuel cells are explained, along with cell geometry and microstructure. Electrode fabrication techniques such as screen printing, dip coating and extrusion are compared according to their advantages and disadvantages, and fuel cell system commercialisation is discussed. Modern techniques used to evaluate microstructure such as three-dimensional computer reconstruction from dual beam focused ion beam–scanning electron microscopy or X-ray computed tomography, and computer modelling are compared. Reversible cell electrode performance is measured using alternating current impedance on symmetrical and three electrode cells, and current/voltage curves on whole cells. Fuel cells and electrolysis cells have been studied extensively, but more work needs to be done to achieve a high performance, durable reversible cell and commercialise a system.     

Comparison of oxidation behaviours among three Fe–Cr based alloys for solid oxide fuel cell interconnect

Abstract

Two metallic alloys, containing comparable amounts of Cr, underwent oxidation in hot air simulating (the solid oxide fuel cell cathode atmosphere) for various periods. The results demonstrated that the oxidation kinetics of Crofer22 APU and equivalent ZMG232 followed the parabolic rate law and oxidation rates increased with temperature. Typical oxidation rates of Crofer22 APU and ZMG232 upon annealing treatment are approximately 0·21 orders of magnitude lower than that of ZMG232. An oxide scale electron probe microanalyser, a scanning electron microscope and X-ray diffractometer were adopted to verify the applicability of Fe–Cr based alloys in the solid oxide fuel cell interconnect component. Two alloys contain comparable amount of Cr, Mn and Fe, and their surface oxides as analysed are indicated to be Cr₂O₃ and (Mn,Fe)Cr₂O₄ spinel compound. In summary, Crofer22 APU had the best oxidation resistance of any of the alloys of interest.     

ANN–supported control strategy for a solid oxide fuel cell working on demand for a public utility building

The idea of control strategy of SOFC operating to meet demand of a public utility building was presented. The strategy was formulated with the support of Artificial Neural Network. The network was used to predict the demand for electricity. The calculations were carried out on the example of a building of the Institute of Heat Engineering Warsaw University of Technology. The control strategy is influenced by various factors depending on changes in market conditions and operating characteristics of the cell. We can define different objective functions eg: working for own needs, for maximum profit and maximum service life. The article presents a simulation of SOFC operation for demand profile of the IHE building from the selected time period.     

A new nickel–ceria composite for direct-methane solid oxide fuel cells

Various Ni–La_xCe_1−xO_y composites were synthesized and their catalytic activity, catalytic stability and carbon deposition properties for steam reforming of methane were investigated. Among the catalysts, Ni–La_0.1Ce_0.9O_y showed the highest catalytic performance and also the best coking resistance. The Ni–La_xCe_1−xO_y catalysts with a higher Ni content were further sintered at 1400 °C and investigated as anodes of solid oxide fuel cells for operating on methane fuel. The Ni–La_0.1Ce_0.9O_y anode presented the best catalytic activity and coking resistance in the various Ni–La_xCe_1−xO_y catalysts with different ceria contents. In addition, the Ni–La_0.1Ce_0.9O_y also showed improved coking resistance over a Ni–SDC cermet anode due to its improved surface acidity. A fuel cell with a Ni–La_0.1Ce_0.9O_y anode and a catalyst yielded a peak power density of 850 mW cm⁻² at 650 °C while operating on a CH₄–H₂O gas mixture, which was only slightly lower than that obtained while operating on hydrogen fuel. No obvious carbon deposition or nickel aggregation was observed on the Ni–La_0.1Ce_0.9O_y anode after the operation on methane. Such remarkable performances suggest that nickel and La-doped CeO₂ composites are attractive anodes for direct hydrocarbon SOFCs and might also be used as catalysts for the steam reforming of hydrocarbons.     

The design of stationary and mobile solid oxide fuel cell–gas turbine systems

A general thermodynamic model has shown that combined fuel cell cycles may reach an electric-efficiency of more than 80%. This value is one of the targets of the Department of Energy (DOE) solid oxide fuel cell–gas turbine (SOFC–GT) program. The combination of a SOFC and GT connects the air flow of the heat engine and the cell cooling. The principle strategy in order to reach high electrical-efficiencies is to avoid a high excess air for the cell cooling and heat losses. Simple combined SOFC–GT cycles show an efficiency between 60 and 72%. The combination of the SOFC and the GT can be done by using an external cooling or by dividing the stack into multiple sub-stacks with a GT behind each sub-stack as the necessary heat sink. The heat exchangers (HEXs) of a system with an external cooling have the benefit of a pressurization on both sides and therefore, have a high heat exchange coefficient. The pressurization on both sides delivers a low stress to the HEX material. The combination of both principles leads to a reheat (RH)-SOFC–GT cycle that can be improved by a steam turbine (ST) cycle. The first results of a study of such a RH-SOFC–GT–ST cycle indicate that a cycle design with an efficiency of more than 80% is possible and confirm the predictions by the theoretical thermodynamic model mentioned above. The extremely short heat-up time of a thin tubular SOFC and the market entrance of the micro-turbines give the option of using these SOFC–GT designs for mobile applications. The possible use of hydrocarbons such as diesel oil is an important benefit of the SOFC. The micro-turbine and the SOFC stack will be matched depending on the start-up requirements of the mobile system. The minimization of the volume needed is a key issue. The efficiency of small GTs is lower than the efficiency of large GTs due to the influence of the leakage within the stages of GTs increasing with a decreasing size of the GT. Thus, the SOFC module pressure must be lower than in larger stationary SOFC–GT systems. This leads to an electrical-efficiency of 45% of a cycle used as a basis for a design study. The result of the design study is that the space available in a mid-class car allows the placement of such a system, including space reserves. A further improvement of the system might allow an electrical-efficiency of about 55%.     

Performance analysis for the part-load operation of a solid oxide fuel cell–micro gas turbine hybrid system

In this paper, the performance evaluation of a solid oxide fuel cell (SOFC)–micro gas turbine (MGT) hybrid power generation system under the part-load operation was studied numerically. The present analysis code includes distributed parameters model of the cell stack module. The conversions of chemical species for electrochemical process and fuel reformation process are considered. Besides the temperature distributions of the working fluids and each solid part of cell module by accounting heat generation and heat transfers, are taken into calculation. Including all of them, comprehensive energy balance in the cell stack module is calculated. The variable MGT rotational speed operation scheme is adopted for the part-load operation. It will be made evident that the power generation efficiency of the hybrid system decreases together with the power output. The major reason for the performance degradation is the operating temperature reduction in the SOFC module, which is caused by decreasing the fuel supply and the heat generation in the cells. This reduction is also connected to the air flow rate supplement. The variable MGT rotational speed control requires flexible air flow regulations to maintain the SOFC operating temperature. It will lead to high efficient operation of the hybrid system.     

Electroplated Ni–Fe2O3 composite coating for solid oxide fuel cell interconnect application

Ni–Fe₂O₃ composite coating was applied onto ferritic stainless steel using the cost-effective method of electroplating for intermediate temperature solid oxide fuel cell (SOFC) interconnects application. By comparison, the coated and bare steels were evaluated at 800 °C in air corresponding to the cathode environment of SOFC. The oxidation investigations indicated that the oxidation rate of the coated steel was close to that of the bare steel after initially rapid mass gain. The mass gain of the coated steel was higher than that of the bare steel owing to the formation of double-layer oxide structure with an outer layer of (Ni,Fe)₃O₄/NiO atop an inner layer of Cr₂O₃. The area specific resistance (ASR) of the double-layer oxide scale was lower than that of the Cr₂O₃ scale thermally grown on the bare steel.     

Fe doped Ni–Co alloy by electroplating as protective coating for solid oxide fuel cell interconnect application

To obtain higher electrical conductivity and lower area specific resistance (ASR), the 10% Fe doped Ni–Co (NCF) alloy was prepared on SUS 430 steel substrate by electroplating for solid oxide fuel cells (SOFCs) interconnects application. Then, the SUS 430 steels and NCF coated steels were oxidized at 800 °C. The microstructure and oxide phase of samples were tested by scanning electron microscope (SEM) with energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). These results proved that the NCF coated steel achieved the lower oxidation rate of 9.28 × 10⁻¹⁴ g²cm⁻⁴s⁻¹ and ASR of 14.72 mΩ cm².     

Synthesis and properties of a barium aluminosilicate solid oxide fuel cell glass–ceramic sealant

A series of barium aluminosilicate glasses modified with CaO and B₂O₃ were prepared and evaluated with respect to their suitability in sealing planar solid oxide fuel cells (SOFCs). At a target operating temperature of 750 °C, the long-term coefficient of thermal expansion (CTE) of one particular composition (35 mol% BaO, 15 mol% CaO, 10 mol% B₂O₃, 5 mol% Al₂O₃, and bal. SiO₂) was found to be particularly stable, due to devitrification to a mixture of glass and ceramic phases. This sealant composition exhibits minimal chemical interaction with the yttria-stabilized zirconia electrolyte, yet forms a strong bond with this material. Interactions with metal components were found to be more extensive and depended on the composition of the metal oxide scale that formed during sealing. Generally alumina-scale formers exhibited a more compact reaction zone with the glass than chromia-scale forming alloys. Mechanical measurements conducted on the bulk glass–ceramic and on seals formed using these materials indicate that the sealant is anticipated to display adequate long-term strength for most conventional stationary SOFC applications.     

Anthracite pretreatment for high-performance direct carbon solid oxide fuel cell — A green pathway for power generation

Coal-fueled direct carbon solid oxide fuel cell (DC-SOFC) is a very attractive electrochemical conversion device. However, coal contains a certain amount of ash, such as Al, Si, S, etc., which are toxicants for SOFC components. To solve the above problem, anthracite is pyrolyzed at 600 °C to obtain semi-coking coal results in better cell performance. The results show that the higher carbon gasification oxidation activity of semi-coking coal is due to the higher amount of fixed carbon and catalyst. Therefore, more fuel gas (CO) is available in the anode chamber for the Boudouard reaction. Also, the electrochemical performance of both coals as DC-SOFC fuel was compared using La_0·4Sr_0·6Co_0·2Fe_0·7Nb_0·1O_3-δ (LSCFN) as anode. The maximum power density (MPD) of the DC-SOFC with semi-coking coal is 596 mW cm⁻² at 850 °C, much higher than that of the SOFC using anthracite (396 mW cm⁻²) as the fuel. Furthermore, at the same fuel content, the cell fueled with semi-coking coal has a longer discharge time (30 h), which shows a better stability.     

Electrooxidation reactions of methanol and ethanol on Pt–MoO3 for dual fuel cell applications

Pt–MoO₃ was synthesized by microwave-assisted chemical reduction. The physicochemical characterization showed that the electrocatalyst contained nanoparticles of Pt and clusters of MoO₃. The average particle size of the catalytic material was 2.5 nm. The electrochemical results showed that the Pt–MoO₃/C was suitable to carry out the electrooxidation reactions of ethanol and methanol indistinctly, avoiding CO poisoning. It was possible to compare the results with commercial Pt/C. The synthesized material showed a better electrochemical performance. Different simulations were performed using the Nernst equation to evaluate the influence of temperature, internal resistance, and the current density losses as a function of the fuel used. The theoretical results indicated that the electrical power of the mono-cell improves by 21.5% when the energy vector is changed from methanol to ethanol at the maximum power point, obtaining an electrical potential change ΔE = 87.02 mV and a variation of the electric power of Δp = 114.14 mW cm^?2. The use of dual fuels could improve the performance of experimental fuel cells.