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To meet “net zero” emission target for greenhouse gases in the year 2050, it is essential to retrieve most of the produced CO2 from emission intensive activities and store it permanently underground. This study considers integration of a 10 kW solid oxide fuel cell (SOFC) system with vacuum pressure swing adsorption (VPSA). In the integrated system, a small amount of electricity needed for the VPSA directly comes from SOFC system. The oxygen produced by VPSA is used to complete the oxidation of the unconverted fuel from the anodic side of SOFC, and then CO2 is separated automatically after the water condensation. Moreover, in this study, SOFC with VPSA has been optimized for minimizing the energy requirement and number of heat exchangers. Eight heat exchangers have been sized. Finally, the integrated system has waste heat available, to valorise the waste heat of the system, a steam cycle has been integrated for producing around additional electricity, to improve the overall efficiency. Finally, economic analysis has been performed, to understand its market competitiveness.

Solid oxide fuel cell (SOFC) systems show immense potential for efficient biogas utilization, which can significantly reduce carbon emissions by integrating with biogas cleaning units and carbon capture technologies. Despite the significant benefits, the high cost of the integrated system presents a challenge. Therefore, a techno-economic assessment is necessary to evaluate the feasibility of the integrated system and provide guidelines for cost reduction. The ideal capacity for an integrated biogas-fed SOFC power system ranges between 20 kW to 200 kW. Firstly, a comparison of different biogas types and stack technologies is conducted to evaluate the system performance. Secondly, a techno-economic investigation of the feasibility of different system designs is performed by comparing different carbon capture technologies with various biogas cleaning units. The study results can facilitate the optimization of the integrated system's design and operation and pave the way for large-scale implementation of SOFC technology in the energy industry.

This study presents the techno-economic analysis of a 100 kWe Solid Oxide Fuel Cell (SOFC) system for maritime applications fueled by methane, methanol, diesel, ammonia, and hydrogen. Two system configurations are considered for each fuel considering cathode off-gas recirculation (COGR) implementation to improve waste heat recovery both in terms of quantity and quality. The economic benefit of COGR is verified for all fuels, especially for methanol, hydrogen, and diesel, which present Levelized Cost of Exergy (LCOEx) reductions of about 10%, 9%, and 6%, respectively. Ammonia and methanol have the lowest LCOEx of about 0.260 EUR/kWh and 0.270 EUR/kWh, respectively, while hydrogen has the highest LCOEx of about 0.430 EUR/kWh. The sensitivity analyses suggest that fuel purchase cost, stack lifetime, and annual interest rate are the three parameters with the highest influence on the system cost. Overall, ammonia and methanol are the most promising fuels.

Water management of the proton exchange membrane fuel cell (PEMFC) is an important parameter to improve efficiency, especially in cold weather conditions. The generated water of the electrochemical reactions inside PEMFC may stay inside the cell and fill the pores in the gas diffusion layer (GDL), which degrades the cell and reduces the lifetime. The formation of water in PEMFC has a direct relationship with the capillary pressure that can be determined by the GDL's wettability and microstructure. Furthermore, wettability is dependent on the material, which can be changed by the contact angles of the GDL. Using the computational fluid dynamic (CFD) methods, different values of the GDL's contact angle have been examined to observe their corresponding effects on the maximum GDL liquid removal. Higher values of the GDL liquid removal result in better water management. Using the simulation data, an artificial neural network (ANN) model was trained in the current density of 0.4 (A/cm2$$ \mathrm{A}/\mathrm{c}{\mathrm{m}}2 $$) and the voltage of 0.604 (V) to predict the GDL liquid removal in 5700 points and to develop the optimization analysis. Results indicated that the highest GDL liquid removal of 0.225 (kg/m3s$$ \mathrm{kg}/{\mathrm{m}}3\mathrm{s} $$) can be obtained by the GDL's contact angle of 102.63 degrees. Highlights PEMFC three-dimensional simulation model with seven path serpentine flow field. The impacts of GDL contact angle on the maximum GDL liquid removal. Training an ANN model to calculate the maximum GDL liquid removal. At the contact angle of 102.63 degrees, maximum GDL liquid removal is 0.225 [kg/m3s$$ \mathrm{kg}/{\mathrm{m}}3\mathrm{s} $$].

This study investigates the potential application of total harmonic distortion (THD), as a fast online monitoring tool, to identify the early signs of failure modes in solid oxide fuel cells (SOFC). Indeed, the timely detection and identification of faults is crucial for applying mitigation strategies to avoid irreversible damage and increase the system lifetime. Two of the most common faulty conditions are considered in this work, namely fuel and air starvation. This experimental work aims at progressively triggering these errors in a controlled manner, by following different realistic scenarios, and recording THD values on a frequent basis. Several well-established laboratory monitoring tools, like electrochemical impedance spectroscopy (EIS), complemented by the distribution of relaxation times (DRT) are used to analyse and support the interpretation of the THD measurements. A sensitivity analysis on the THD parameters, namely the signal amplitude and the number of harmonics, is carried out to identify the optimal combination of parameters and achieve the best faults detectability. Finally, the impact of the fuel flow direction and the operating temperature are examined. The results of this work are summarised as practical guidelines to better employ the THD technique to identify the early warning signs of reactants’ starvation.

Reversible solid oxide cells (rSOC) can convert excess electricity to valuable fuels in electrolysis cell mode (SOEC) and reverse the reaction in fuel cell mode (SOFC). In this work, a five - cell rSOC short stack, integrating fuel electrode (Ni-YSZ) supported solid oxide cells (Ni-YSZ parallel to YSZ vertical bar CGO parallel to LSC-CGO) with an active area of 100 cm(2), is tested for cyclic durability. The fuel electrode gases of H-2/N-2:50/50 and H-2/H2O:20/80 in SOFC and SOEC mode, respectively, are used during the 35 reversible operations. The voltage degradation of the rSOC is 1.64% kh(-1) and 0.65% kh(-1) in SOFC and SOEC mode, respectively, with fuel and steam utilisation of 52%. The post-cycle steady-state SOEC degradation of 0.74% kh(-1) suggests improved lifetime during rSOC conditions. The distribution of relaxation times (DRT) analysis suggests charge transfer through the fuel electrode is responsible for the observed degradation. (C) 2022 The Author(s). Published by Elsevier Ltd on behalf of Hydrogen Energy Publications LLC.

Despite being a mature technology, solid oxide fuel cell (SOFC) devices are still limited by lifetime issues. In SOFC stacks, cell/interconnect interaction is the main responsible for voltage degradation at the oxygen electrode side. Corrosion and chromium evaporation might in fact increase ohmic and charge transfer losses. This study presents the evolution of the degradation phenomena inside four SOFC short-stacks tested respectively for 45, 2700, 4800 and 10000 hours. An additional stack which underwent 124 thermal cycles is also analyzed to assess the mechanical reliability of the interconnect/ceramic coupling. Metal interconnect was made of K41/AISI441 ferritic stainless steel coated with MnCo2O4 porous barrier layer. Scanning electron microscope (SEM) coupled with energy dispersive X-ray spectroscopy (EDS) characterization is applied to examine the degradation process. Observations indicate that despite a harsh initial red-ox interaction between the cathode materials and the interconnect, after 5000 h of operation the kinetic of the degradation process in the electrical contact areas slows down dramatically. An empirical model based on the scale thickness at different interconnect location gives estimation for the oxide thermal growth for a stack lifetime period. From the mechanical properties point of view, no spallation was observed and local delamination was mainly due to the sample preparation process.

In this review paper, a critical assessment of the main degradation processes in three key components of solid oxide fuel cells and electrolysers (negative and positive electrodes and the interconnect) is undertaken, attempting prioritization of respective degradation effects and recommendation of the best approaches in their experimental ascertainment and numerical modeling. Besides different approaches to quantifying the degradation rate of an operating solid oxide cell (SOC), the latest advancements in microstructural representation (3D imaging and reconstruction) of SOC electrodes are reviewed, applied to the quantification of triple-phase boundary (TPB) lengths and morphology evolution over time. The intrinsic degradation processes in the negative (fuel) electrode and the positive (oxygen) electrode are discussed, covering first the composition and governing mechanisms of the respective electrodes, followed by a comprehensive evaluation of the most important factors of degradation during operation. By this systematic identification of dominant degradation processes, measurement techniques, and modeling approaches, the foundations are laid for the definition of meaningful accelerated stress testing of SOC cells and stacks, which will help the technology achieve the constantly more demanding durability targets in market applications.

Operando characterization of SOCs generally relies on current–voltage measurements that provide the spatially averaged electrochemical response of the SOC. However, these methods do not fully capture the spatial distribution of the operating conditions (e.g., gas composition, current density). Local information on the operating conditions can be gained by using operando optical characterization methods. In this work, the spatial distribution of the electro-thermal response of an SOC with a 15 cm2 active area operated in fuel cell and electrolysis mode was investigated using lock-in thermography. Lock-in thermography consists of stimulating the solid oxide cell with a sinusoidal current perturbation and analyzing the local thermal response using Fourier transforms. A camera with a silicon-based sensor was used to record the transient temperature field on the oxygen electrode (i.e., the cathode in fuel cell operation) via a specifically designed optical access. The field of view of each pixel was approximately 0.03 mm x 0.03 mm. The Fourier transform generates a compact data set that can be conveniently represented by a phase and amplitude or a real and imaginary image. Using a real–imaginary representation provided a better thermal response contrast than an amplitude–phase representation. The local thermal response was found to be dependent on the direct current bias and the frequency of the current perturbation. The thermal response of the SOC was laterally and longitudinally inhomogeneous, thereby demonstrating the capability of active thermography to characterize the local behavior of an SOC in operando. Lock-in thermography is thus a promising method for defining regions of interest for post-mortem analysis using electron microscopy and helping to link highly localized post-test analysis with spatially averaged operando characterization methods.

The blade tip clearance loss was studied experimentally and numerically for a micro radial fan with a tip diameter of 19.2mm. Its relative blade tip clearance, i.e., the clearance divided by the blade height of 1.82 mm, was adjusted with different shims. The fan characteristics were experimentally determined for an operation at the nominal rotational speed of 168 krpm with hot air (200 °C). The total-to-total pressure rise and efficiency increased from 49 mbar to 68 mbar and from 53% to 64%, respectively, by reducing the relative tip clearance from 7.7% to the design value of 2.2%. Single and full passage computational fluid dynamics simulations correlate well with these experimental findings. The widely-used Pfleiderer loss correlation with an empirical coefficient of 2.8 fits the numerical simulation and the experiments within +2 efficiency points. The high sensitivity to the tip clearance loss is a result of the design specific speed of 0.80, the highly-backward curved blades (17°), and possibly the low Reynolds number (1 × 105). The authors suggest three main measures to mitigate the blade tip clearance losses for small-scale fans: (1) utilization of high-precision surfaced-grooved gas-bearings to lower the blade tip clearance, (2) a mid-loaded blade design, and (3) an unloaded fan leading edge to reduce the blade tip clearance vortex in the fan passage.

Many countries have set official targets to 100% phase out sales or registrations of new internal combustion engines (ICE) that use gasoline. Battery and fuel cell technologies have been suggested to be the best alternative for the current ICEs to be utilized in cars, buses, trucks, and boats. Although there have been studies to consider fuel cells and batteries for the cars, there are limited number of studies to consider these technologies for ferries. Different types of prime movers have been utilized to run the boats, however, most of the studies in the field are related to either the usage of fuel cell or battery as the prime mover of the boats, while the integrated system can improve the low range of batteries by maintaining high acceleration and fast re-fueling time. Two well-known types of industrial Li-Ion batteries in the market are Nickel Manganese Cobalt (NMC), and Lithium Titanite Oxide (LTO). Among the existing Li-Ion batteries in the market, LTO enjoys from the highest performance, lifespan, and safety by higher costs, whereas NMC provides acceptable performance with low costs and high specific energy. In comparison to the batteries, proton exchange membrane fuel cells (PEMFCs) have faster refueling time and higher ranges, hence the integration of batteries and fuel cells can provide the needs of ferries. In this study, the possibility of integrating the fuel cell technology and the battery is evaluated to provide 800kW electricity. PEMFC modules are integrated with a Li-Ion battery to have high ranges and efficiencies in fast refueling times for ferry applications. An optimization model was developed using the open source Julia programming language to determine the best combination of the batteries and fuel cells considering the size, weight, hydrogen consumption, and overall efficiency as the output parameters. The dynamic model captures the characteristics of the system by the changes in time and considers the impacts of batteries’ charging/discharging status on the overall performance. Two different novel scenarios are suggested to provide 800kW power for a ferry with a total length of 50.8m to transport 780 passengers considering the Lausanne-Evian round trip, which is 24km, in 70 mins. LTO and NMC type Li-Ion batteries are selected for these two different scenarios while PEMFC is the selected type of fuel cell for this ferry. Dynamic models have been developed in the MATLAB software for both the battery and fuel cell modules. Based on the presented flowchart in Fig. 1, a quasi-static optimization model has been utilized for the power split. Results indicate that the total size, and hydrogen consumption of around 8 , and 36.1 kg/h, respectively, are needed in the first scenario to reach the maximum power of 800kW with 49.5% overall efficiency. The operating power of the integrated battery and fuel cell system is between 80kW to 720 kW, which is 10% to 90% of the maximum power. In the second scenario, the corresponding values of the size, and hydrogen consumption are around 8.23 , and 36 kg/h to reach the same power by the overall efficiency of 49.6%. The first scenario uses 8 modules of PEMFCs and one module of NMC while the second scenario uses LTO as the battery with the same number of PEMFCs. Fig. 2 also shows the transient performance characteristics of the integrated system in the first scenario considering the output power and the hydrogen consumption of the fuel cells, in addition to the output energy and the state of charge of the batteries. Figure 1

With a growing energy demand in a carbon-constrained society, fuels cells powered by renewable fuels, and specifically solid waste, are seen as interesting contributors to the energy portfolio. The alternative energy industry needs to reduce costs, enhance efficiency, and demonstrate durability and reliability to be economically feasible and attractive. This paper addresses biomass waste gasification in distributed energy systems, using a solid oxide fuel cell (SOFC) to produce electricity and heat. The potential and optimal plant efficiency and layout (i.e., anode off-gas (AOG) recirculation point via small-scale turbomachinery and heat exchanger network) are analyzed through a multi-stage approach that includes scenario evaluation and multi-objective optimization via a hybrid optimization strategy with heuristics and mathematical programming. The results in this paper summarize the most convenient operating conditions and provide an optimized heat exchanger network (HEN). The AOG recirculation toward the gasifier combustor is the preferred option; the electrical and thermal efficiencies can separately go up to 49 and 47%, respectively. The combined total efficiency ranges between 76 and 82%, and the area of heat exchange, which corresponds to an amount of heat exchanged between 91 and 117 kW, is within 6–14 m2.

This paper describes an optimization strategy for operating solid-oxide fuel-cell systems at optimal efficiency. Specifically, we present the experimental validation of a real-time optimization (RTO) strategy applied to a commercial solid-oxide fuel-cell system. The proposed RTO scheme effectively pushes the system to higher levels of efficiency and maintains the system there despite perturbations by tracking active constraints. The optimization approach uses either steady-state measurements, or transient measurements in combination with a dynamic model, and can deal effectively with plant-model mismatch. In the reported experiments, the approach drives the system to the desired power demand at optimal efficiency. The experimental fuel-cell system reached 65% DC electrical efficiency. As such, the proposed RTO scheme is a promising candidate for enforcing optimal micro-CHP operation. In addition, the approach can deal with slow drifts such as degradation without compromising on efficiency. Finally, and important from a practical point of view, we suggest guidelines for safe and optimal operation. (C) 2019 Elsevier Ltd. All rights reserved.

While high performance of SOFC systems has already been achieved, there is still a need to increase the stack lifetime, while decreasing the system's total cost of ownership, both being linked. The increase in lifetime includes the minimization of performance degradation, but also avoidance of potentially detrimental events during operation, originating from the stack, outside the stack, or a combination of both. The present paper highlights how the detection of faulty operation as early as possible is important to implement adequate mitigation strategies, wherever applicable, according to the fault and its grade of severity. Three types of faults have been considered, fuel starvation, leakage and carbon deposition. Both hardware components and algorithms to monitor, detect, isolate, and finally correct faulty system operation have been developed and will be embedded in a real SOFC system.

A microsteam turbine with a tip diameter of 15 mm was designed and experimentally characterized. At the nominal mass flow rate and total-to-total pressure ratio of 2.3 kg h−1 and 2, respectively, the turbine yields a power of 34 W and a total-to-static isentropic efficiency of 37%. The steam turbine is conceived as a radial-inflow, low-reaction (15%), and partial admission (21%) machine. Since the steam is limited in the system (solid oxide fuel cell), a low-reaction and high-power-density design is preferred. The partial-admission design allows for reduced losses: The turbine rotor and stator blades are prismatic, have a radial chord length of 1 mm and a height of 0.59 mm. Since the relative rotor blade tip clearance (0.24) is high, the blade tip leakage losses are significant. Considering a fixed steam supply, this design allows to increase the blade height, and thus reducing the losses. The steam turbine drives a fan, which operates at low Mach numbers. The rotor is supported on dynamic steam-lubricated bearings; the nominal rotational speed is 175 krpm. A numerical simulation of the steam turbine is in good agreement with the experimental results. Furthermore, a novel test rig setup, featuring extremely thin thermocouples (ø0.15 mm) is investigated for an operation with ambient and hot air at 220 °C. Conventional zero- and one-dimensional predesign models correlate well with the experimental results, despite the small size of the turbine blades.

The Solid-oxide fuel cell is a highly efficient prime mover for biogas conversion, but a part of biogas needs to be reformulated externally to facilitate the electrochemical conversion, easy control of reforming conditions, and thermal management of the stack. Carbon deposition and external mineralcarrying water should be avoided to ensure the durability of the fuel processor and stack catalysts. This paper investigates four plant layouts with different anode off-gas recirculation schemes and biogas reforming methods: (1) pre-reforming with hot recirculation (HR), (2) pre-reforming with cold recirculation (CR), (3) no pre-reforming and hot recirculation (NR), (4) partial oxidation with hot recirculation (PO). All the schemes feature an electrolyte supported SOFC working at 860°C and 0.23 A/cm2 current density. A sensitivity analysis of the plant efficiency as a function of the Recirculation Ratio (RR) and the Reformer Temperature (RT) is performed. The results show that HR and CR schemes achieve the highest efficiency (58-63%). The HR scheme benefits from the recirculated water and does not require external water for RR > 50% and RT > 600°C; the CR scheme achieves the same result for RR > 80% and RT > 700°C. The optimal RR is within 50 – 80% for the highest system efficiency, as a trade-off between the overall fuel utilization and electrochemistry performance. The RT should be between 600 and 700°C. The HR scheme is the overall best performing if the re-circulator and stack designs do not limit the flow rates at a high RR.

Solid oxide fuel cells have a proven efficiency for the direct conversion of biogas into electricity, and their full potential from European agricultural and waste-water sites still has to be fully evaluated and harnessed. Biogases are methane-rich mixtures whose composition and trace contaminants, especially of sulfur compounds, can vary greatly. To avoid carbon deposition from the carbon-rich CH4-CO2 mixtures, some amount of steam and/or extra CO2 needs to be added to process the biogas. Ideally this can be recovered from the SOFC exhaust. In a preparatory work, biogas/SOFC integrated systems were studied and compared using Aspen Plus[1]. Best performances are reached with a catalytic methane pre-reformer when a fraction of the anode off-gas is recirculated for mixing with the biogas feed. This work provided the guidelines for the present catalytic study and predicted thermodynamic equilibria of gas mixtures. Here, the overall performance of a ruthenium exsolution catalyst[2] for the reforming of methane was evaluated for these different biogas compositions at various gas hourly space velocities. Gas chromatography and material balance calculations enabled the full measurement of inlet and outlet gas compositions which, in turn, permitted to calculate precise conversion rates, reforming ratio, and the deviation from thermodynamic equilibrium. Methane conversion reached >95 % for a dry-dominant reforming mixture, which simplifies the overall system. The longer-term stability of the catalyst as well as its tolerance towards different sulfur traces that occur in biogas was then evaluated and analyzed. [1] Shuai Ma, Gabriele Loreti, Ligang Wang, Andrea L. Facci, Stefano Ubertini, Changqing Dong, François Maréchal, and Jan Van herle, E3S Web of Conferences 2021 238:04002 DOI: 10.1051/e3sconf/202123804002 [2] Muhammad A. Naeem, Paula M. Abdala, Andac Armutlulu, Sung Min Kim, Alexey Fedorov, and Christoph R. Müller, ACS Catalysis 2020 10 (3), 1923-1937 DOI: 10.1021/acscatal.9b04555

The Laboratory for Applied Mechanical Design (LAMD) designed, manufactured, and experimentally tested a novel recirculation fan for a 10 kWe solid oxide fuel cell (SOFC). The fan uses oil-free bearings, more specifically herringbone-grooved journal and spiral-grooved thrust gas bearings. The radial inducer-less fan with a tip diameter of 19.2 mm features backward-curved prismatic blades with constant height. Prior to coupling the recirculation fan with the SOFC, the fan was experimentally characterized with air at 200 °C. At the nominal point of 168 krpm, the measured inlet mass flow rate is 4.9 kgh−1, the total-to-total pressure rise 55 mbar, the isentropic total-to-total efficiency 55 %, and the power 18.3 W. This paper compares the experimental data towards a computational fluid dynamic simulation of the full fan impeller and volute suggesting an excellent correlation at the nominal point what validates the numerical approach. However, the heat flows crossing the fan fluid domain, have an increased effect at off-design conditions, thus the experimental results need careful consideration. The fan backface leakage has negligible impact on the measurements.

Thermochemical biomass-to-fuel conversion requires an increased hydrogen concentration in the syngas derived from gasification, which is currently achieved by water–gas-shift reaction and CO2 removal. State-of-the-art biomass-to-fuels convert less than half of the biomass carbon with the remaining emitted as CO2. Full conversion of biomass carbon can be achieved by integrating solid-oxide electrolyzer with different concepts: (1) steam electrolysis with the hydrogen produced injected into syngas, and (2) co-electrolysis of CO2 and H2O to convert the CO2 captured from the syngas. This paper investigates techno-economically steam- or co-electrolysis-based biomass-to-fuel processes for producing synthetic natural gas, methanol, dimethyl ether and jet fuel, considering system-level heat integration and optimal placement of steam cycles for heat recovery. The results show that state-of-the-art biomass-to-fuels achieve similar energy efficiencies of 48–51% (based on a lower heating value) for the four different fuels. The integrated concept with steam electrolysis achieves the highest energy efficiency: 68% for synthetic natural gas, 64% for methanol, 63% for dimethyl ether, and 56% for jet fuel. The integrated concept with co-electrolysis can enhance the state-of-the-art energy efficiency to 66% for synthetic natural gas, 61% for methanol, and 54% for jet fuel. The biomass-to-dimethyl ether with co-electrolysis only reaches an efficiency of 49%, due to additional heat demand. The levelized cost of the product of the integrated concepts highly depends on the price and availability of renewable electricity. The concept with co-electrolysis allows for additional operation flexibility without renewable electricity, resulting in high annual production. Thus, with limited annual available hours of renewable electricity, biomass-to-fuel with co-electrolysis is more economically convenient than that with steam electrolysis. For a plant scale of 60 MWth biomass input with the renewable electricity available for 1800 h annually, the levelized cost of product of biomass-to-synthesis-natural-gas with co-electrolysis is 35 $/GJ, 20% lower than that with steam-electrolysis.