Solid Oxide Fuel Cell Power Research Articles

Catalyst with CeO2 and Ni Nanoparticles on a LaCrO3-Based Perovskite Substrate for Bio-Alcohol Steam Reforming and SOFC Power Generation

A Ni/CeO2–LCeCrN catalyst was developed with a unique hierarchy of exsolved Ni and CeO2 nanoparticles dispersed on a perovskite La0.8Ce0.2–xCr0.85Ni0.15–yO3−δ (LCeCrN) substrate for steam reforming methanol, ethanol, and glycerol, producing reformate gas as fuel for solid oxide fuel cell (SOFC) power generation. Methanol, ethanol, and glycerol are almost completely steam-reformed into H2, CO, and CO2 at 450, 650, and 700 °C at a steam/carbon (S/C) ratio of 1, 2.5, and 4 with a maximum hydrogen yield of 2.2, 5.2, and 6.0 mol, respectively. The catalytic performance of Ni/CeO2–LCeCrN catalyst is durable, with no carbon deposition for methanol and slight carbon deposition for ethanol and glycerol reforming for up to 100 h, due to the presence of CeO2 nanoparticles that enhance water adsorption capability and spillover oxygen to oxidize the deposited carbon. The reformate gas is fed in sequence into the anode of an SOFC single cell for power generation. The maximum power density of the cell is comparable at 650 °C and slightly lower at 700 and 750 °C than that fueled by H2, suggesting that Ni/CeO2–LCeCrN is an excellent catalyst for steam reforming methanol, ethanol, and glycerol to produce reformate gas for SOFC power generation.

Characterizing SOFC Stack Electrochemical Performance at Elevated Pressure

Pressurized operation of high temperature fuel cell stacks is of increasing interest for a variety of applications, including high efficiency, hybrid solid-oxide fuel cell power generation systems. In this presentation, we report on our efforts to characterize the electrochemical performance of 1-kWeand 5-kWe Ceres Power SteelCell solid-oxide fuel cell stacks, with a focus on elevated pressure operation in the range of 2-5 barg. Increased pressure operation requires particular attention to pressure differentials across both the membrane electrode assembly and between the stack and surrounding atmosphere. The effort is part of a five-year U.S. DoE ARPA-E INTEGRATE program to combine the high efficiency of solid-oxide fuel cells with the high efficiency balance-of-plant equipment to demonstrate a 70%-efficient distributed power generator. In this architecture, the highly efficient solid-oxide fuel cells (SOFCs) are placed upstream of an internal combustion engine, where the anode tail gas, consisting of partially converted steam-reformed natural gas, is further utilized by the engine to produce electricity. The stacks are operated between 2-5 barg to maximize overall system efficiency and to increase SOFC power density.Few studies have been reported on SOFC stack operation at elevated pressures. The team at the Colorado School of Mines has designed and operated the pressurized stack test stand shown in the figure to characterize electrochemical performance of various kW-scale SOFC stack test modules developed by Ceres Power, Ltd. Minimizing pressure differentials across the anode and cathode during elevated-pressure operation is of primary concern. Excessive pressure on one side of the cell can cause substantial mechanical stress to the metal-supported membrane-electrode assemblies. Pressure differentials in this work are maintained below the manufacturer’s specifications of +/- 25 mbar at operating pressures of 0-5 barg. In addition to performance measurements at elevated pressures, studies have also been conducted on diluted fuel streams representative of high anode tail-gas recycle and various amounts of internal reforming. The stacks show steady, stable performance over all conditions tested.A fuel feed is produced with mass flow controllers that represents partially, steam-reformed natural gas with anode tail-gas recycle. A natural gas fuel processor will be incorporated into the stand at a later stage of the research program. Reactant gas feeds are preheated in multiple zones to properly control stack temperatures. The insulated stack test module is housed inside of a pressure vessel that has individual pressure control in order to minimize the pressure differentials between the internal flow channels of the stack and the surrounding environment. Exhaust gases exit the pressure vessel where heat exchangers are utilized to partially cool the 600°C gases before reaching back-pressure regulators.Stack operation is challenging because of the combination of a tight thermal operating window and the long system response time to changes in inlet conditions. These time constants become even larger at low air flow rates. Lower air flow (while maintaining required oxygen utilization) is desired in order to reduce the power required by the balance of plant, especially when operating at higher pressures. In order to mitigate this, a model predictive controller is being implemented. A dynamic model of the fuel cell was first tuned and validated against experimental transient response data. Then the resulting model was linearized at multiple operating points. The linearizations were then utilized within a gain-scheduled moving-horizon predictor that can take past input and output data, along with a proposed future input, and predict the future output response. The predictor performance has been validated, and then inserted into a model-predicative controller. Optimization algorithms select the input temperatures, flow rates, and electric current required to quickly reach a desired operating condition while meeting all operational constraints, including thermal constraints.In this talk, we will present our findings on the electrochemical performance of 1 and 5-kWe Ceres Power SteelCell stack test modules and the effects of pressure, fuel composition, anode recycle, and degree of internal reforming on stack performance. Results influence the design and net efficiency of the hybrid system. The trajectory of the research will be discussed. Figure 1

Design and exergy based optimization of a clean energy system with fuel Cell/MED and hydrogen storage option

The principal aim of the current research is the design and optimization of a multi-generation unit capable of generating electricity and potable water and hydrogen. The system comprises a gas turbine unit, a high-temperature solid-oxide fuel cell (SOFC), a combustion chamber, and a multi-effect desalination (MED) system. The pressurized steam and fuel enter the anode side of high-temperature SOFC and the air goes to the cathode side. Due to reactions inside the SOFC, a high amount of electricity produces, and excess H2 enters the combustion chamber. Hot flue gases can run a gas turbine and a MED unit to generate more electrical power and desalinated water. The study illustrated the impact of current density on voltage losses and output power and output voltage of SOFC. A parametric examination is also conducted to demonstrate the influence of primary design variables on the system performance. Exergo-economic multi-criteria optimization is used to determine the optimized parameters to obtain the higher efficiency and lower cost of fuel and equipment. Calculations represented that the suggested arrangement is able to generate 53.46 kg/s desalinated water, and 54.8 MW electricity and 7.43 kg/h hydrogen energy. The system exergy efficiency under this condition is about 36.45% but the results of optimization showed that this value could rise up between 50.8% and 61.17% with the lowest system cost.

(Plenary) Update on the SOFC Program at the DOE’s National Energy Technology Laboratory

The Solid Oxide Fuel Cell (SOFC) Program, managed by the U.S. Department of Energy (DOE) Office of Fossil Energy (FE) and administered by the FE’s National Energy Technology Laboratory (NETL) is currently developing low-cost SOFC power generation systems. SOFC power systems have the potential to achieve greater than 60 percent efficiency. The SOFC’s operating temperature is lower than combustion-based processes and precludes NOx formation; there are near-zero emissions of CO2, criteria pollutants, and particulates. Furthermore, SOFC power systems require approximately one-third the amount of water relative to conventional combustion-based power systems. The Program includes the testing of SOFC with natural gas in distributed applications, including data centers. In addition to SOFC, there are several projects on various aspects of high temperature solid oxide electrolysis cell (SOEC) for electrolysis of water. The development of efficient systems for hydrogen production is very interesting, especially when supplementary heat is provided from solar or other waste heat sources such as nuclear or coal power plants.

Anode-Oxidizing Critical Operating Conditions of Large Planar Solid Oxide Fuel Cell

In a solid oxide fuel cell power system, large planar cells are common central parts for electric generation. In practice, the operating conditions of a planar cell may have significant impact on the electrical efficiency and the lifespan of the cell, thus the operating and maintenance cost of the power system. Given varying electric load, the power system would dynamically adjust the operating conditions of each cell or cell module, so that the energy and heat balance in the system is maintained, the fuel consumption is minimized and the cells are protected from reactant starvation, local overheating etc. To realize this functionality, we seek a fundamental understanding of the quantitative connections among fuel cell properties, operating conditions and optimal electrical efficiency.We established a quasi-2D model for quick evaluation of fuel and oxidant concentration and current density along the flow direction. For fuel cells with very low charge transfer impedance i.e. 0.02 Ω*cm^2 operating with low fuel flow rates, the fuel concentration at the exit may reach an equilibrium where the local Nernstian potential across the cell equals the cell voltage. In such cases, the fuel utilization remains almost constant regardless of varying fuel flow rate, given a certain cell voltage. For fuel cells with local charge transfer impedance of 0.5 Ω*cm^2 operating with high fuel flow rates, such phenomenon was not observed because the fuel concentration at the exit depends strongly on the fuel flow rate. Given the fuel molar fraction at the fuel inlet, the electrical efficiency of a fuel cell has its maximum at certain cell voltage, which depends strongly on the charge transfer impedance of the fuel cell. At constant fuel flow rates, the optimal cell voltage increases with lowering charge transfer impedance. The optimal electrical efficiency appears lower with higher inlet fuel molar fraction. Given fixed and uniform fuel cell temperature, the air flow rate has little impact on the electrical efficiency for air-fuel stoichiometric ratios above 1.3.Besides the above findings, further studies are necessary on the effects of temperature distribution as well as porous electrode diffusion resistance. Figure 1

Jet Fuel Desulfurization for Portable Solid Oxide Fuel Cell Applications

Solid oxide fuel cells (SOFCs) are capable of utilizing energy-dense hydrocarbon fuels such as jet fuels for highly efficient power generation. Currently, a major challenge for using the jet fuel (e.g. JP8) in SOFC power systems is its sulfur content, which poisons the SOFC catalyst and anode. Sulfur contents in jet fuels could be as high as 3000 ppm although typical sulfur contents could be in the range from 550 and 750 ppm. The reduction of sulfur to <1 ppm is generally desired and required to ensure reliable SOFC operation. Various technologies have been developed to remove sulfur from jet fuel. However, most of these technologies are designed for large-scale desulfurization at industrial facilities or for stationary applications. Due to their complexity and substantial weight and size, these systems are not suitable for onboard integration with portable fuel cells. Therefore, our research aimed at developing a lightweight, compact desulfurization reactor for onboard applications. After several versions of improvements, including the use of selective laser sintering (SLS) 3D printing method, we have developed a miniature one-piece stainless-steel reactor which is capable of removing >99.5% sulfur in the jet fuel with the final sulfur concentrations close to a sub-ppm level. The reactor could be adapted to the desulfurization of other liquid hydrocarbon fuels such as gasoline and diesel. The reactor designs, desulfurizing materials, operation conditions and effectiveness of the technology will be discussed in this paper.

An Optimized Strategy for Fuel Cell Degradation Control in SOFC Power Systems

Solid Oxide Fuel Cell (SOFC) is an attractive energy conversion device due to its high efficiency and fuel flexibility. Key operation parameters such as current, temperature and fuel utilization are critical variables in SOFC systems that directly impact efficiency and longevity. The degradation of the SOFC performance not only limits the operating temperature range of the SOFC stack in the system, but also simultaneously generates Joule heat, which further causes the stack to deviate from its initial thermal balance.In this paper, a semi-empirical SOFC dynamic model with degradation is proposed and validated by experiment data. The degradation in the above model is developed based on current density, temperature and fuel utilization to simulate cell performance decay over time due to ohmic loss growth and the heat generation by cell resistance. The coupling between key parameters, stack performance and degradation during long-term load following and the impact of stack degradation on the entire system long-term performance is discussed and investigated. An optimized strategy uses both feedback and feed-forward control law is designed to track the desired power demand with the aim of mitigating the degradation and compensating the time differences between dynamics at different time-scale.

Optimization of Methane Reforming for High Efficiency and Stable Operation of SOFC Stacks

: Solid Oxide Fuel Cells (SOFCs) is an efficient and clean pathway to generate electricity. In addition to hydrogen, SOFCs also provide the possibility for the utilization of a variety of carbon containing fuels. However, the application of carbon-based fuels in SOFC remains to be further studied. In this study, an external reformer was used to create appropriate reforming syngas from methanol and avoid carbon deposition. The performance and the efficiency of SOFC were researched with methanol-reformed syngas as fuel. The thermodynamic calculation and experimental work of water vapor reforming reaction of methanol fuel were carried out to study the composition of reforming gas under different temperature and steam-carbon ratio conditions, where the experimental results and the computational results matched well. The mole fraction of hydrogen in reformed syngas was about 55% within the temperature of 700~800 ℃, nevertheless, this value reached 70% if the moisture was removed. Therefore, the reformed syngas should be applied to SOFCs before being condensed and dried. Based on the comparison between the experimental results and the calculated ones, the appropriate components were selected to prepare the reforming syngas, feeding into the anode of SOFC to test the performance and the efficiency. Optimal temperature and steam-carbon ratio conditions for methanol vapor reforming were obtained. Under these conditions, the power density of SOFC exceeded 0.4 W/cm2 and the efficiency reached 50% (LHV). The main conclusions confirmed the high efficiency and feasibility of the methanol-fueled SOFC power generation system.

Optimization of a Natural Gas Fuel Cell Power Plant without Carbon Capture

This work aims to optimize a solid oxide fuel cell (SOFC)-based natural gas fuel cell (NGFC) system with the potential for higher heating value (HHV) efficiencies as high as 70 percent. This work leverages the IDAES Integrated Platform (IDAES), an equation-oriented tool for the nonlinear optimization of advanced energy systems, which enables a broader exploration of the potential design space than convention case-based analyses. The NGFC system model without carbon capture consists of a natural gas reformer, SOFC power island, and steam turbine bottoming cycle. The mass and energy balances are modeled with first principles models, while the SOFC behavior is captured utilizing a machine learning-based reduced order model (ROM) developed from a validated, high fidelity CFD stack model. The objective of the study is to find the optimal NGFC configuration and operating conditions that maximize the system efficiency and reduce carbon dioxide emissions. The results of the optimization to date have led to improved system performance (higher efficiency). Further work will focus on analyzing different potential configurations to increase efficiency and reduce CO2 emissions.

Internal Conversion in the Membrane-Supported SOFC

Steam reforming is a highly endothermic process of hydrogen or synthesis gas production from methane or other hydrocarbon fuels. Metals from group VIII of the Periodic table are catalysts for steam reforming; nickel is the most commonly used among them. Platinoid catalysts: rhodium, ruthenium and palladium are more active, but less frequently used due to their high cost. Nickel catalysts have proven their effectiveness due to the simplicity of their production, stability and chemical activity [1]. It is known that the heat required for the endothermic process of steam reforming can be provided by an electrochemical reaction in a stack of high-temperature solid oxide fuel cells [2,3]. In the case of internal reforming, the process of steam reforming of methane proceeds directly at the anode of a solid oxide fuel cell (SOFC) due to the high operating temperature and the presence of nickel in the composition [4,5]. The advantage of internal reforming is not only thermal, but also chemical integration of reforming agent and generator – the water vapor produced during the SOFC anodic electrochemical reaction can be used for reforming without the need for anode recycling organization. Also, the endothermic effect of steam reforming can be used to control the temperature of the stack. As it was shown in work [6] feeding of the mixture containing 30% of methane into the electrolyte-supported SOFC stack to the input leads to 22% of methane observed at the output. Thus, based on the literature data, we cannot expect a high conversion rate in the process of internal methane reforming. Therefore, studies of the internal methane conversion process were carried out on an experimental short stack of two 100x100 mm electrolyte-supported SOFCs. A whole series of experiments were carried out on H2+CH4+H2O mixtures with different sets of conditions – an increase in the ratio and consumption of methane, and then a decrease in temperature. The ranges of methane consumption and other key parameters of the experiment were based on the results of the analysis of available literature data on the experimental study of the kinetics of methane steam conversion on cermet SOFC anodes. Prior to the experiments, discussions were mainly caused by the probable carbon deposition at the anodes and the associated rapid performance degradation, the capabilities of the anodes for internal conversion were upper estimated according to the fuel consumption of SOFCs, so it was assumed that, at worst case, the conversion provides only its internal consumption needs. The results of experiments at an operating temperature of 850°C showed that the kinetics of internal conversion was largely underestimated. The assembly of two SOFCs converts methane up to concentrations not exceeding the calculated equilibrium ones, up to the maximum available flow rate on the equipment used – 187 ml/min – even without current passing. This fuel flow rate is capable of providing a current of up to 53 A, while the rated operating current of these SOFCs is about 20 A, up to 30 A on methane-rich fuel. This means, that the conversion capabilities of SOFC even in the absence of current are at least twice higher than their own needs. The current further stimulates the conversion by generating additional steam. In order to discover the limits of conversion capabilities, the temperature was lowered to 750°C. The result of the conversion at maximum flow rate proceeding up to equilibrium values was repeated. Thus, in the course of the experiments, it was not possible to obtain methane concentrations in the exhaust gas that significantly exceed the equilibrium ones. This result turned out to be extremely unexpected and undoubtedly positive, since it demonstrates an extremely high potential of internal conversion and opens the way to a sharp decrease in the requirements for the degree of conversion of fuel supplied to SOFC, abandonment of a bulky fuel processor, reduction of costs for SOFC cooling and, thereby, an increase in efficiency and reducing the mass and dimensions of SOFC power plants. This work was carried out with financial support from the Russian Scientific Foundation, grant no. 17-79-30071.

Revised Zero-Dimensional Model for a Solid Oxide Fuel Cell with Mo-Doped Ceria Anode Using Syngas as Fuel

A zero-dimensional model was implemented to simulate the performance of a solid oxide fuel cell (SOFC) with Mo-doped ceria (CMO) anode using humidified (3%v/v water) hydrogen or syngas (50%v/v H2 – 50%v/v CO) as fuel. The model was validated preliminarily through experimental data generated at 800ºC using a SOFC with coated electrodes supported in the electrolyte (a 20 mm diameter yttria-stabilized zirconia, YSZ, disc) with a 14 mm diameter CMO|CMO-YSZ anode and a 14 mm diameter LSM-YSZ|LSM (lanthanum strontium manganite) cathode. Polarization (cell voltage vs current density, ΔEcell vs j) and power density (power density vs current density, Pelec vs j) curves were generated via linear sweep voltammetry connecting the SOFC to a Gamry Reference 3000 potentiostat/galvanostat/ZRA using platinum mesh and wires.The open circuit voltage (OCV) of the SOFC operating with humidified hydrogen was modelled directly using Nernst equations for the electrochemical hydrogen oxidation and oxygen reduction reactions. For the case of the SOFC operating with humidified syngas, the electrochemical hydrogen and carbon monoxide oxidation reactions occur simultaneously at the anode. Hence, the Nernst equation was corrected by each anodic reaction selectivity determined solving mass balances coupled to an electrochemical kinetics model.Figure 1.a shows the fitted polarization and power density curves. Maximum SOFC power densities of ca. 1295 W m-2 (at 0.53 V and 2434 A m-2) and ca. 1084 W m-2 (at 0.52 V and 2106 A m-2) are predicted for the cell operating with humidified hydrogen and humidified syngas as fuel, respectively. These values are 2 and 5% lower than the experimental values. The OCVs calculated are ca. 1.10 V and 1.01 V, respectively, which are 5 and 8% higher/lower than the experimental values. The differences observed are attributed to the non-ideality of the gases due to their interaction with the electrode surfaces, and the possible infiltration of air into the anodic chamber [1,2].The SOFC ohmic losses calculated represent ca. 72% of the total voltage losses when operating at the maximum power density, which are attributed to the low electrical conductivities of the CMO|CMO-YSZ anode (CMO electrical conductivity is ca. 0.501 S m-1 at 800ºC [3]) and the thick electrolyte (ca. 2.203 S m-1 at 800ºC [4]). Improvements are being introduced to the anode material by including nickel, which will contribute to increase the hydrogen oxidation kinetics while CMO protects the electrode from carbon deposition when syngas is used as fuel. Presently, activation losses represent ca. 28% of the total voltage losses at the maximum power density. It has been reported that for SOFCs using syngas as fuel, the anode active sites are more occupied by carbon monoxide molecules due to their slower oxidation kinetics in comparison with hydrogen. Nevertheless, carbon monoxide is also susceptible to undergo a surface reforming process via the water-gas shift reaction. Such phenomenon becomes more relevant at high carbon monoxide concentrations, which was the case in this study (50% v/v CO), thus favoring the electricity generation through hydrogen oxidation at the anode surface [2].For the SOFC using humidified syngas as fuel, the model assumes that the desorption equilibrium pressure of hydrogen (pH2 *) on the surface of molybdenum in the CMO|CMO-YSZ anode is equal to that reported for humidified hydrogen on the surface of nickel in Ni-YSZ anodes (0.09 atm) [5]. Figure 1.b shows the results obtained for the sensitivity analysis of the model as a function of pH2 *, which indicates that unless its value is increased by ca. 220% over 0.09 atm the exchange current density for carbon monoxide oxidation (j0,CO) does not go below its lower confidence limit. It is unlikely that this parameter reaches such level of discrepancy because it implies that hydrogen adsorption at the anode surface is strongly diminished, thus electrochemical oxidation kinetics decrease considerably which is not consistent with the experimental observations.Future work includes the analysis of the kinetic parameters dependence on the temperature and the fuels partial pressures.

(Plenary) Update on the SOFC Program at the DOE’s National Energy Technology Laboratory

The Solid Oxide Fuel Cell (SOFC) Program, managed by the U.S. Department of Energy (DOE) Office of Fossil Energy (FE) and administered by the FE’s National Energy Technology Laboratory (NETL), is currently developing low-cost SOFC power generation systems. SOFC power systems have the potential to achieve greater than 60 percent efficiency. The SOFC’s operating temperature is lower than combustion-based processes and precludes NOx formation; there are near-zero emissions of CO2, criteria pollutants, and particulates. Furthermore, SOFC power systems require approximately one-third the amount of water relative to conventional combustion-based power systems. The Program includes the testing of SOFC with natural gas in distributed applications, including data centers. In addition to SOFC, there are several new projects on various aspects of high temperature solid oxide electrolysis cell (SOEC) for electrolysis of water. The development of efficient systems for hydrogen production is very interesting, especially when supplementary heat is provided from solar or other waste heat sources such as nuclear or coal power plants.

An Optimized Strategy for Fuel Cell Degradation Control in SOFC Power Systems

Solid Oxide Fuel Cell (SOFC) is an attractive energy conversion device due to its high efficiency and fuel flexibility. Key operation parameters such as current, temperature, and fuel utilization are critical variables in SOFC systems that directly impact efficiency and longevity. The degradation of the SOFC performance not only limits the operating temperature range of the SOFC stack in the system, but also simultaneously generates Joule heat, which further causes the stack to deviate from its initial thermal balance.In this paper, a semi-empirical SOFC dynamic model with degradation is proposed and validated by experiment data. The degradation in the above model is developed based on current density, temperature, and fuel utilization to simulate cell performance decay over time due to ohmic loss growth and the heat generation by cell resistance. The coupling between key parameters, stack performance, and degradation during long-term load following and the impact of stack degradation on the entire system long-term performance is discussed and investigated. An optimized strategy uses both feedback and feed-forward control law is designed to track the desired power demand with the aim of mitigating the degradation and compensating the time differences between dynamics at different time-scale.

Jet Fuel Desulfurization for Portable Solid Oxide Fuel Cell Applications

Solid oxide fuel cells (SOFCs) are capable of utilizing energy-dense hydrocarbon fuels such as jet fuels for highly efficient power generation. Currently, a major challenge for using the jet fuel (e.g. JP-8) in SOFC power systems is its sulfur content, which poisons the SOFC anode and fuel reforming catalysts. The reduction of sulfur to <1 ppmw is generally desired and required to ensure reliable SOFC operation. Our research aimed at developing a lightweight, compact desulfurization reactor for onboard application in portable fuel cell systems. After several versions of improvements, including the use of a selective laser sintering (SLS) 3D printing method, we have developed a miniature one-piece stainless-steel reactor which can remove >99.5% sulfur in the jet fuel with the final sulfur concentrations close to a sub-ppm level. The reactor could be adapted to the desulfurization of other liquid hydrocarbon fuels such as gasoline and diesel.

APPLICATION OF RANGE EXTENDER BASED ON SOLID OXIDE FUEL CELLS (SOFCS) FOR ELECTRICAL BUSES: EXPERIENCE OF CERES POWER (UNITED KINGDOM) AND WEICHAI POWER (CHINA) COMPANIES

In previous articles on this topic [1-3] we examined the perspectives of application of power plants based on solid oxide fuel cells (SOFCs) as auxiliary power plants as well as range extenders for heavy freight transport [1,2] and cars [3]: we considered experience of USA [1], Europe [2] and Japan [3]. We showed, that such kind of systems give opportunity to obtain electrical power from chemical energy of hydrocarbon fuel oxidation with record-high efficiency (much higher than competitive solutions) in order to supply on-board vehicle systems during stops of main engine, as well as to significantly extend the range of electrical vehicles by means of constant charge of batteries directly during motional and their discharge due to operation of electrical engine. In current manuscript, we examine the world first experience of SOFC power plant application as range extender for electrical buses. Group of Ceres Power (UK) and Weichai Power (China) companies executed a corresponding project. As a result of project execution system prototype with power output of 30 kW was developed and manufactured, tests on bus lines are planned to be executed in nearest future. The system examined in current manuscript is the most powerful in comparison to other systems studied in this set of manuscripts: 30 kW against 1.5 and 9 kW [1], 3 kW [2] as well as 5 kW [3] for systems examined in previous works. Examined system uses compressed natural gas (CNG) as a fuel; this hydrocarbon is very convenient one due to well-developed distribution network, ecological cleanness in comparison with more complex and heavy hydrocarbon mixtures. Application of low-temperature fuel cells (with proton-exchange membrane), which are more simple in manufacture, in automobile transport leads to the demand in development of hydrogen supply networks, which is not developed nowadays at all.

Thermoeconomic analysis and multi‐objective optimization of a solid‐oxide fuel cell plant coupled with methane tri‐reforming: Effects of thermochemical recuperation

An 80-kW solid-oxide fuel cell (SOFC)-based power plant coupled with methane tri-reforming is proposed and analyzed from the viewpoint of thermoeconomics. In order to integrate the SOFC power generation section with the external reformer, part of the exhaust gases from the afterburner is recycled and utilized as a reformer agent in the reactor. The main challenge in performing the economic analysis is the determination of the costs associated with the tri-reforming process, in particular the reactor cost. To accomplish this, a mathematical procedure is suggested and applied for a fixed-bed reactor based on both the chemical equilibrium and chemical kinetics describing the tri-reforming process. The effects on system performance of important design parameters, including current density, SOFC operating temperature, and exhaust gas recirculation (EGR) percentage, are investigated. The results indicate that system performance is enhanced by using lower values of current density and higher values of SOFC operating temperature. In addition, considering the thermal and environmental performance of system as criteria, the use of EGR is not recommended. However, as the EGR percentage increases, the product unit cost decreases, making EGR advantageous from an economic perspective.

Performance assessment of a novel biomass-based solid oxide fuel cell power generation cycle; Economic analysis and optimization

In the present work, a novel combined system based on the biomass-based solid oxide fuel cell and gas turbine system combined with the organic flash cycle is regarded for power generation aim. The main objective of this work is to investigate the feasibility of the proposed system from the economic and environmental viewpoints. The optimum performance of all optimization scenarios is found by applying the multi-objective particle swarm optimization algorithm and using the technique for order of preference by similarity to ideal solution (TOPSIS) method. Regarding the obtained results, for fuel cost of 6$/GJ and electricity price of 0.10$/kWh, the total net present value at the end of plant lifetime is 9.8×105$ and the payback period is 4.25 years, which means that the plant is feasible for construction from the economic perspective. Also, the simulation results indicate that the proposed hybrid system can yield to the energy and exergy efficiencies of 49.37% and 42.50%, respectively. Also, the net output electrical power and is obtained 425.39kW. Moreover, the final optimum solution selected by the decision-making method is obtained by ηII=47.12%, LTE=23.24t/MWh, and cp,tot=5.50$/GJ.

Parametric study on electrodeposition of a nanofibrous LaCoO3 SOFC cathode

Solid oxide fuel cells (SOFCs) capable of operating at low to intermediate temperatures (600–750 °C) are vital for the development of robust SOFC power generation systems. In this regard, the oxygen reduction reaction is the rate-limiting step that requires new highly active catalysts or drastic improvements in the cathode microstructure when using the conventional cathode materials. Here, we report a parametric study on electrodeposition for synthesizing nanostructured cathodes for the SOFCs by producing a nanofibrous LaCoO3 cathode. The synthesis of the nanofibrous LaCoO3 involves preparing an electrically conductive template of carbon nanotubes onto the walls of a porous scaffold made of oxide-ion-conducting material followed by co-electrodeposition of La and Co hydroxides from an aqueous mixed-metal nitrate solution. Then, the deposited metal hydroxides are thermally converted to the LaCoO3 perovskite phase through low-temperature calcination performed at 800 °C. LaCoO3 microstructure is optimized as a function of deposition time, applied current, and solution concentration to obtain a nanofibrous morphology. Anode-supported SOFCs with the nanofibrous LaCoO3 cathode are tested for their electrochemical performance and durability. A durable performance obtained during the 200 h stability tests, performed at 750 and 800 °C and under a galvanostatic load of 1 A cm−2, shows the potential of the electrodeposition for producing robust nanostructured SOFC cathodes.

System simulation and exergetic analysis of solid oxide fuel cell power generation system with cascade configuration

A solid oxide fuel cell (SOFC) based power generation system with cascade configuration has been analyzed using the exergy-based analysis method. A cascade system has double SOFC stacks, where the unreacted fuel released from the primary SOFC stack is re-utilized in the secondary stack, generating additional power and maximizing fuel-use in the system. For comparison and evaluation, a simple SOFC system and an SOFC system with anode off-gas recirculation are also analyzed. In all the SOFC systems, efficiency increases with increasing fuel utilization. The simple and anode off-gas recirculation systems show 63.7% and 66.0% electrical efficiency at 85% and 90% fuel utilization, respectively. The cascade system shows 66.47% electrical efficiency at 90% fuel utilization, which is the highest electrical efficiency among the systems analyzed. Through the exergy analysis, the magnitude, location, and resources of the thermodynamic irreversibility within the SOFC systems are clearly identified, giving the quantified information why the cascade configuration has higher efficiency than the other configurations. The SOFC stack shows very high exergetic efficiency over 90%. In the cascade configuration, the released exergy from the primary SOFC stack can be exergetically-efficiently utilized in the secondary SOFC stack, contributing to a higher efficiency.

Analysis of a biogas-fed SOFC CHP system based on multi-scale hierarchical modeling

Biogas is an abundant renewable energy source which can be produced by anaerobic treatment of biological waste such as sewage sludge, agro-industrial waste, and industrial animal waste. The utilization of biogas instead of fossil fuels in a solid oxide fuel cell (SOFC)-based system is a promising choice to achieve a fossil-free and sustainable energy future. A biogas-fed decentralized SOFC combined heat and power (CHP) system model is proposed and analyzed. The system consists of a pre-reformer, an SOFC stack, an afterburner and a heat-recovery boiler. The system model integrates a multi-scale hierarchical three-dimensional SOFC stack model with zero-dimensional balance of power component models, which enables simultaneous investigations of both the overall system performance and the stack-internal distributed properties down to the electrode scale. The effects of steam/carbon ratio, biogas composition and operation voltage of the SOFC stack on the electrical and CHP efficiencies of the system, as well as the temperature gradient within the SOFC stack were studied. The proposed system model is demonstrated as an insightful and powerful tool for designing hybrid SOFC combined heat and power systems.