Balance Of Plant Components Research Articles

RELAP5-based thermal-hydraulic assessment of the STEAM facility for DEMO WCLL balance of plant analysis

DEMO power station aims to demonstrate the generation of hundred MWs of electrical power from fusion reactions, then transmitted from the Tokamak reactor to the grid through the Balance of Plant (BoP). The design approach for the Water Cooled Lithium Lead (WCLL) Breeding Blanket (BB) Primary Heat Transfer Systems (PHTSs) leverages nuclear industry expertise but faces challenges due to DEMO pulsed operation and low-load periods. To assess the feasibility of these components, ENEA Experimental Engineering Division at Brasimone R.C. is designing STEAM, a facility investigating water technologies applied to the DEMO BB and BoP systems and components. STEAM is mainly composed of a primary system reproducing the DEMO WCLL BB PHTS thermodynamic conditions (15.5 MPa, 328–295 °C) and a secondary two-phase (liquid/steam) loop reproducing the DEMO power conversion system conditions (6.4 MPa, 238–300 °C). Experimental validation will reproduce steady-state and transient operation under DEMO-relevant conditions, including dedicated tests on the DEMO once through steam generator mock-up.STEAM objectives and description are presented in this paper, together with the RELAP5/Mod3.3 nodalization of the facility. The latter is used to, thermal-hydraulically characterize the facility behaviour. The outcomes of the steady-state qualification supported the optimization of the system layout appraising the performances of key components under the specified operating conditions.

Direct ammonia SOFC – A potential technology for green shipping

International shipping carries about 90% of the global trade, thereby emitting significant amounts of greenhouse gasses by using fossil based fuels. Zero-emission technologies using green fuels are crucial to reduce the environmental impact of this important transport sector. Among the considered concepts is green ammonia in a solid oxide fuel cell (SOFC).The present study investigated SOFCs fueled with ammonia regarding cracking, electrochemical performance and durability. Ammonia cracking was for the first time directly measured over a planar, anode supported SOFC at open circuit voltage and during operation, as well as in presence of several balance of plant components. At temperatures around 700 °C, ammonia is significantly cracked when passing over hot metallic low surface area components (like Ni current collectors) even in the absence of the SOFC. The Ni/YSZ SOFC anode is active for the cracking as well. The area specific resistance of the SOFC is larger when using ammonia as compared to a H2/N2 mixture, due to two origins, (i) a decrease of the cell temperature due to the endothermal cracking, which leads to larger ohmic resistance and (ii) presence of unconverted ammonia, which increases the polarisation resistance in the low frequency region. Durability tests reveal increased cell voltage degradation when using ammonia fuel at 700 °C, mainly due to increase of the ohmic contributions. Micro structural analysis suggests nitridation as cause of this degradation. A stable SOFC operation is possible at 750 °C.

Mobile Proton-Exchange Membrane Fuel Cell Powered by Diesel Fuel: System Simulation and Life Cycle Analysis

Diesel engine generators used at construction sites generate noise, vibration, and large amounts of pollutant emissions. With the strengthening of emission standards for construction equipment, technologies must be developed to meet new requirements. We proposed and analyzed a mobile proton-exchange membrane fuel cell diesel-powered system to address these issues. The proposed system consisted of an autothermal reformer, a proton-exchange membrane fuel cell, and a balance of plant components. Previous studies on the system have not explored the optimal design and operating condition of the system and have not shown whether the proposed system is superior to the system using the hydrogen-fueled proton-exchange membrane fuel cell system in the life-cycle greenhouse gas emissions point of view. In this study, we clarified system operation characteristics, determined the operational design point, and evaluated system performance and life-cycle greenhouse gas emissions. The system was analyzed by constructing a zero-dimensional simulation model. Several control parameters were varied in parametric studies to determine the operational design point (steam-to-carbon ratio of 2, oxygen-to-carbon ratio of 0.5, fuel utilization factor of 0.85, and heat exchanger effectiveness of 0.85). Considering system performance, the determined design point achieved a 32.3% efficiency. Additionally, we assessed the life-cycle greenhouse gas emissions of the system and compared them with those of an alternative system, which is a hydrogen-fueled proton exchange membrane fuel cell system. It was confirmed that in the United States of America, the proposed system emits 1010.2 g-CO2-eq/kWh of greenhouse gas at a 300 km fuel transportation distance, which is similar to a hydrogen-fueled proton-exchange membrane fuel cell system (1001.1 g-CO2-eq/kWh). The proposed system emits less greenhouse gas emissions than the hydrogen-fueled proton-exchange membrane fuel cell system if the distance from the hydrogen production site to the construction site is more than 318 km. Therefore, for a construction site far from a hydrogen production plant, the proposed diesel-fueled proton-exchange membrane fuel cell system is preferable from both the greenhouse gas emissions and convenience perspectives.

Reversible Metal Supported Solid Oxide Cells

Solid oxide fuel cells (SOFCs) excel by high efficiencies in fuel cell as well as electrolysis modes, and by being able to operate in both modes as a reversible cell (solid oxide cell – SOC). This allows for production of electricity and heat from a green fuel, and for storage of electricity as gas or use as fuel. Lifetime and costs are major factors enabling such reversible SOCs to enter green energy systems. Metal supported SOCs (MSCs) provide cost-competitive materials within the cell. Furthermore, targeting the lower operating temperatures around 650 oC, MSCs will allow for cheaper stack and balance of plant components as well. Lowering operating temperatures leads to a reduction of thermally activated degradation processes, thereby prolonging the lifetime. The present study investigates the option to operate MSCs, fabricated at DTU Energy by tape casting, lamination, and screen-printing, in reversible mode between fuel cell (FC) and electrolysis (EC). Emphasis is on the effect of reversible operation on performance and durability of the MSC, compared to steady state operation in either mode, and to the behavior of state-of-the-art (SoA) fuel electrode supported SOC with Ni/YSZ fuel electrode. The MSCs are composed of a FeCr support, a Ni/GDC (gadolinium-doped ceria) infiltrated LSFNT (lanthanum-doped strontium iron nickel titanate) fuel electrode, a YSZ (yttria-stabilized zirconia) electrolyte, a GDC barrier layer, and an in situ sintered LSC (lanthanum-doped strontium cobaltite) air electrode. The reversible operation was carried out by switching between FC and EC modes at current densities of 0.25 and -0.25 A/cm2, respectively, at 650 oC using a gas mixture of 50/50 H2O/H2 to the fuel electrode and air to the oxygen electrode.Figure 1 shows the evolution of the cell voltages for the SoA cell and the MSC. The degradation rate of the SoA cell was larger during operation in EC as compared to FC mode. Similar observations were made previously, even though these tests were typically carried out at temperatures higher than 650 oC as in this work [1]. Furthermore, the degradation rate decreases over time, more particularly in EC mode, which is also a known phenomenon at this type of cells [2, 3]. In the final ca. 200 h, both degradation rates are in the range of 3%/1000 h, which is an interesting observation, i.e., the longer-term degradation rates are similar in both modes (EC and FC). The analysis of electrochemical impedance spectroscopy (EIS) recorded under current allowed to conclude that the main contribution to the degradation is the increase of polarization resistance, i.e., related to electrodes degradation.In the initial ca. 400 h hundred hours, the cell voltage degradation on the MSC is larger in fuel cell mode, while there is nearly no degradation in electrolysis mode. The good stability in EC mode over a few hundred hours confirms the findings of steady-state electrolysis tests with the same type of cells [4]. In the final period from ca. 600 h, both degradation rates increase but stay fairly constant with ca. 4%/1000 h in EC and ca. 16%/1000 h in FC mode, when calculated as linear increase. EIS reveals that both, the serial and the polarization resistances increase in parallel, which indicates a combination of degradation of electrode and probably corrosion and/or interface attachment. Details will be presented, including comprehensive EIS evaluation combined with micro-structural characterization.Figure 1. Cell voltage vs. operating time under current in reversible mode at 650 oC, 0.25 A/cm2 in fuel cell and -0.25 A/cm2 in electrolysis mode, 50/50 H2O/H2 fuel and air to the oxygen electrode, (a) SoA cell, (b) MSC, gaps in the cell voltage are interruptions of operation due to technical issues in the labReferences[1] X. Sun, B.R. Sudireddy, X. Tong, M. Chen, K. Brodersen, A. Hauch, Optimization and Durability of Reversible Solid Oxide Cells, ECS Trans. 91 (2019) 2631.[2] A. Hagen, R. Barfod, P.V. Hendriksen, Y.-L. Liu, S. Ramousse, Degradation of anode supported SOFCs as a function of temperature and current load, J. Electrochem. Soc. 153(6) (2006) A1165.[3] A. Hauch, K. Brodersen, M. Chen, C. R. Graves, S. H. Jensen, P. S. Jørgensen, P. V. Hendriksen, M. B. Mogensen, S. Ovtar, X. Sun, A Decade of Solid Oxide Electrolysis Improvements at DTU Energy, ECS Transactions, 75(42) (2017) 3.[4] A. Hagen, R. Caldogno, F. Capotondo, X. Sun, Metal Supported Electrolysis Cells, Energies 15 (2022) 2045. Figure 1

Layout and Experimental Results of an 10/40 Kw rSOC Demonstration System

Scientific Approach Within the last years, the development work on reversible solid oxide cell (rSOC) systems has been intensified. This is mainly because this technology can deliver a valuable contribution to carbon-neutral energy supply by storing surplus electrical power into hydrogen and converting it again if necessary. Motivated by this application, in 2018 research by Frank et al. [1] suggests that a round trip efficiency of 50% is possible for a pressurized storage at 70 bars. Based on these results, Forschungszentrum Jülich developed an rSOC demonstration system whose design point is 10 kWAC in fuel cell mode and 40 kWAC in electrolysis mode. The system layout and the evaluation of balance of plant components (BoP) are described by Peters et al. [2].Figure below shows on the left side the core components of the demonstrator system including the Integrated Module (IM). This IM consists of four 20-layer sub-stacks in the mark H20-design by Forschungszentrum Jülich. The fuel and air heaters are located at the top and bottom of the module. The system can be heated up by in total five heating plates which are arranged on top and below each sub-stack. These plates are also used to maintain the temperature management of the stacks during the endothermic electrolysis operation. In order to ensure the most compact system design, the BoP components are suitably arranged in the vicinity of the IM. The right side of Figure shows the core system installed in the laboratory test environment including the full thermal insulation. This environment provides the necessary media supply and disposal as well as the supporting safety equipment and control units.The system was set into operation on the first of June in 2021. The operation started with stationary operating points in fuel cell and electrolysis mode, after passing the commissioning phase. The performance and efficiency data achieved during this operating phase are shown below.An overall power range from 1.7 kWAC to 13 kWAC was achieved in fuel cell mode. At an output power of 10.4 kWAC and a fuel utilization of 98 %, a system efficiency of 63.3 % could be achieved. During the electrolysis mode, an efficiency of 71.1 % could be achieved with an input power of -49.6 kWel and a steam utilization of 80 %. An analysis of the loss mechanisms showed that in the fuel cell mode about 75 % of the losses are caused by the heat production of the stack itself. In the electrolysis mode, the largest share of about 65 % is caused by the power consumption of the steam generator. The system efficiency can be further increased by a skillful heat recovery from the fuel side off-gas into the steam generation process. Outlook In future work new methods of stack temperature control based on artificial neural networks will be investigated on basis of the presented system. Afterwards it is planned to apply realistic load profiles to the system while investigating the performance, temperature and degradation behavior. Furthermore, electricity and gas storage as well as heat decoupling for district heating application will be studied. Acknowledgement The authors would like to thank their colleagues at Forschungszentrum Jülich GmbH for their great support and the Helmholtz Society, the German Federal Ministry of Education and Research as well as the Ministry of Culture and Science of the Federal State of North Rhine-Westphalia for financing these activities as part of the Living Lab Energy Campus.

Cost assessment of selected nuclear driven hybrid thermochemical cycles for hydrogen production

This article presents compared cost assessment of selected nuclear-driven hybrid thermochemical cycles using International Atomic Energy's (IAEA) Hydrogen Economy Evaluation Program (HEEP). Cost estimations are made and evaluated for capital, fuel, decommissioning, O&B, and consumables, in addition to thermal energy and electricity cost details. Thanks to the data obtained with these cost estimates, 4 different nuclear hydrogen production systems were evaluated comparatively. Hybrid thermochemical cycles are expected to decrease operational expenses for hydrogen production. However, the capital expenses might be higher than pure electrolysis since they require more components for balance of plant components (BoP). The results obtained indicated that the levelized cost of hydrogen is 10%–30% less in the case of selected hybrid thermochemical cycles than that of pure electrochemical cycle.

Design of High Specific Power Solid Oxide Fuel Cells

Fuel-Cell Electric-Vehicle demonstrated by PCI was fueled with military-spec F-24/JP-8 and does not require on-board hydrogen storage. An onboard fuel reformer with integrated sulfur trap was used for processing these fuels. The 10-kW electric generator included a SOFC and balance of plant components. It was hybridized with a rechargeable battery for startup, peak loads, and load following. The power produced was sufficient for vehicle propulsion and export power. Both 28-32 VDC and 110 VAC for charging batteries and supporting external load demands were available onboard. Initial off-road demonstrations were successfully conducted at PCI and customer sites. This prototype unit showed the feasibility of utilizing hydrocarbon fuels with on-board reforming and SOFC stack to generate power suitable for mobile applications while the system weight and start-up time still need to be improved. To reduce the system weight and start-up time, we are separately investigating advanced SOFC’s that show potential to address the known limitations of the state-of-the-art technology. These advanced SOFC’s demonstrated potential for fast start-up and high-power density on the cell level at 750-800°C of operating temperatures. By optimizing the configuration and design, the system performance is expected to be further improved.

Life cycle greenhouse gas emissions of residential battery storage systems: A German case study

AbstractBattery storage systems (BSSs) are popular as a means to increase the self‐consumption rates of residential photovoltaics. However, their environmental impact is under discussion, given the greenhouse gas emissions caused by the production and the efficiency losses during operation. Against this background, we carry out a holistic environmental assessment of residential BSSs by combining a partial life cycle assessment for the production phase with a detailed simulation of 162 individual German households for the operational phase. As regards the production phase, we only find small differences between the carbon footprints of different cell chemistries. Moreover, we can show that the balance of plant components have a comparable impact on the global warming potential as the cell modules. In terms of the operational phase, our simulations show that BSSs can compensate at least parts of their efficiency losses by shifting electricity demand from high‐emission to low‐emission periods. Under certain conditions, the operational phase of the BSSs can even overcompensate the emissions from the production phase and lead to a positive environmental impact over the lifetime of the systems. As the most relevant drivers, we find the exact emissions at the production stage, the individual household load patterns, the system efficiency, and the applied operational strategy.

Development of a 10/40 Kw Rsoc Demonstration System

Scientific ApproachIn the last decade, work on the development of a reversible Solid Oxide Cell (rSOC) technology has been greatly intensified because it can contribute to the storage and the reconversion of electricity from regenerative energy sources.In this context, Forschungszentrum Jülich GmbH first examined the feasibility in a thermodynamic analysis. Here, Frank et al. [1] show that electrical efficiencies of 67% in fuel cell mode and 76% in electrolysis mode can be achieved when such a system is operated with a 70 bar hydrogen storage. This corresponds to a round-trip efficiency of more than 50%.Based on these results, an rSOC system demonstrator with a nominal power of 10 kWel in fuel cell mode and 40 kWel in electrolysis mode was developed. The attached figure shows the simplified system flow diagram.The Integrated Module (IM) is the main component of the rSOC system and consists of four Jülich 20-layer sub stacks in combination with an air and a fuel heat exchanger. Also, five electrically operated heating plates are located within the module to heat up the system from ambient temperature to operating temperature and to support endothermal electrolysis operation. The supporting balance of plant components (BoP) are arranged in the direct vicinity of the IM in order to achieve the most compact layout possible.To be able to classify the efficiency results listed below, the calculation method for the fuel cell efficiency is shown in equation (1), for the electrolysis efficiency in equation (2) and for the power consumption of the BoP in equation (3).\U0001d73c_(\U0001d439\U0001d436, \U0001d446\U0001d466\U0001d460, \U0001d434\U0001d436) = (\U0001d448_\U0001d446\U0001d461\U0001d44e\U0001d450\U0001d458 ∙ \U0001d43c_\U0001d446\U0001d461\U0001d44e\U0001d450\U0001d458 ∙ \U0001d702_\U0001d43c\U0001d45b\U0001d463\U0001d452\U0001d45f\U0001d461\U0001d452\U0001d45f − ∑\U0001d443_(\U0001d435\U0001d45c\U0001d443, \U0001d434\U0001d436))/(\U0001d45b_(\U0001d43b2, \U0001d460\U0001d466\U0001d460\U0001d461\U0001d452\U0001d45a \U0001d456\U0001d45b) ∙ [\U0001d43f\U0001d43b\U0001d449]_\U0001d43b2 ) (1)\U0001d7b0_(\U0001d438\U0001d43f, \U0001d446\U0001d466\U0001d460, \U0001d434\U0001d436) = (\U0001d45b_(\U0001d43b2, \U0001d45d\U0001d45f\U0001d45c\U0001d451\U0001d462\U0001d450\U0001d452\U0001d451) ∙ [\U0001d43f\U0001d43b\U0001d449]_\U0001d43b2)/((\U0001d448_\U0001d446\U0001d461\U0001d44e\U0001d450\U0001d458 ∙ \U0001d43c_\U0001d446\U0001d461\U0001d44e\U0001d450\U0001d458)/\U0001d7b0_\U0001d445\U0001d452\U0001d450\U0001d461\U0001d456\U0001d453\U0001d456\U0001d452\U0001d45f + ∑\U0001d443_(\U0001d435\U0001d45c\U0001d443, \U0001d434\U0001d436)) (2)∑\U0001d443_(\U0001d435\U0001d45c\U0001d443, \U0001d434\U0001d436) = \U0001d443_(\U0001d44e\U0001d456\U0001d45f \U0001d450\U0001d45c\U0001d45a\U0001d45d.) + \U0001d443_(\U0001d451\U0001d456\U0001d44e\U0001d45dℎ\U0001d45f. \U0001d450\U0001d45c\U0001d45a\U0001d45d.) + \U0001d443_(ℎ\U0001d452\U0001d44e\U0001d461\U0001d456\U0001d45b\U0001d454 \U0001d45d\U0001d459\U0001d44e\U0001d461\U0001d452\U0001d460) + \U0001d443_(\U0001d450\U0001d45c\U0001d45b\U0001d461\U0001d45f\U0001d45c\U0001d459 \U0001d460\U0001d466\U0001d460.) + \U0001d443_(\U0001d460\U0001d461\U0001d452\U0001d44e\U0001d45a \U0001d454\U0001d452\U0001d45b\U0001d452\U0001d45f\U0001d44e\U0001d461\U0001d45c\U0001d45f) (3)System operation was started on 06/01/2021. After a short commissioning phase, stationary power points were approached for both operating modes, fuel cell and electrolysis. In fuel cell mode, a power range from 1.7 kWel to 13 kWel could be shown. At the operating point of 500 mA cm-2 with a system fuel gas utilization of 98%, a system output of 10.3 kWel with a maximum efficiency of 63.3% could be achieved. In the case of electrolysis, a system output of - 49.6 kWel with a system efficiency of 71.1% was measured with a steam utilization of 80%.OutlookIn the future it is planned to implement new methods of the stack temperature control based on artificial neural networks. After a successful implementation, realistic load profiles are developed and examined during the system operation.As further development work in the area of SOC system technology, it is planned to investigate combinations with storage on the electrical and gas side, heat recuperation for district heating application as well as further demonstration projects in the area of co-electrolysis with corresponding upstream integration of different CO2 sources and downstream integration of synthesis technologies for the generation of chemicals and e-fuels.AcknowledgementThe authors would like to thank their colleagues at Forschungszentrum Jülich GmbH for their great support and the Helmholtz Society, the German Federal Ministry of Education and Research as well as the Ministry of Culture and Science of the Federal State of North Rhine-Westphalia for financing these activities as part of the Living Lab Energy Campus.References Frank M, Deja R, Peters R, Blum L, Stolten D. Bypassing renewable variability with a reversible solid oxide cell plant. Applied Energy. 2018; 217:101-12. Figure 1

(2021-2022 ECS Toyota Young Investigator Fellowship) Understanding and Suppression of Cation Transport into Polymer Electrolyte Membrane Fuel Cell

Polymer electrolyte membrane fuel cells (PEMFCs) are a viable zero-emissions option for the electrification of the heavy duty transportation sector. However, PEMFCs still suffer from degradation of materials over the fuel cell lifetime. Cation contaminants can be generated from corrosion of bipolar plates and balance of plant components, water contaminants, and environmental sources (e.g., Fe3+, Ca2+, Na+), making them present in the fuel or oxidant stream during operation(1). Cations have been shown to be detrimental to the performance of the PEMFC by reducing water uptake, ionic conductivity, and O2 transport, resulting in performance loss and degradation. Metal cations such as Fe3+ can also lead to chemical degradation of the membrane ionomer (2-4). It is critical to understand the mechanism and rate of cation transport from the bipolar plate channel to the membrane to develop mitigation strategy to suppress the cation transport.In this work, we present the study of the cation (Fe3+) transport mechanism through the gas diffusion layer (GDL) by introducing a cation solution in the cathode channel. Transport rates across the GDL are studied using an ex-situ GDL holder where Fe solution is introduced in the GDL substrate side with water transported through to the microporous layer side (MPL) and is collected and analyzed for Fe concentration, as shown in Figure 1a. Effect of the Fe concentration on transport rates is also studied using computational modeling. Understanding of the transport mechanism is then leveraged to identify mitigation solutions and suppress cation transport from the flow field to the electrode using a GDL with dual MPL architecture as shown in Figure 1b. Optimization of the dual MPL architecture for both durability and performance is also presented. Acknowledgements This research is supported by the 2021-2022 ECS Toyota Young Investigator fellowship and U.S. Department of Energy (DOE) Hydrogen and Fuel Cell Technologies Office, through the Million Mile Fuel Cell Truck Consortium (M2FCT). Authors acknowledge the Laboratory Directed Research and Development (LDRD) program at Los Alamos National Laboratory (LANL). References D. D. Papadias, R. K. Ahluwalia, J. K. Thomson, H. M. Meyer, M. P. Brady, H. L. Wang, J. A. Turner, R. Mukundan and R. Borup, Journal of Power Sources, 273, 1237 (2015).R. K. Ahluwalia, D. D. Papadias, N. N. Kariuki, J. K. Peng, X. P. Wang, Y. F. Tsai, D. G. Graczyk and D. J. Myers, Journal of the Electrochemical Society, 165, F3024 (2018).J. P. Braaten, X. M. Xu, Y. Cai, A. Kongkanand and S. Litster, Journal of the Electrochemical Society, 166, F1337 (2019).A. Kneer, J. Jankovic, D. Susac, A. Putz, N. Wagner, M. Sabharwal and M. Secanell, Journal of The Electrochemical Society, 165, F3241 (2018). Figure 1

Online Fault Diagnosis for Open-Cathode PEMFC Systems Based on Output Voltage Measurements and Data-Driven Method

Fault diagnosis is essential for the stable and efficient operation of the proton exchange membrane fuel cell (PEMFC) system. However, the manifold balance of plant (BOP) components and the coupling phenomenon involving multiple physical fields will significantly increase the probability of system fault, which makes it difficult to realize a timely and effective diagnosis. In this study, a novel online diagnosis method for an open-cathode PEMFC system is proposed, which is only based on output voltage measurements, and both the normal state and fault states caused by abnormal BOP components operation are taken into consideration. Specifically, the fault identification is realized based on the fusion of t-Distributed Stochastic Neighbor Embedding (t-SNE) and eXtreme Gradient Boosting (XGBoost), where the t-SNE is adopted to extract the diagnostic features from the individual cell output voltages and the XGBoost is adopted to identify the fault type based on the extracted diagnostic features. A facile method based on the gray relational analysis (GRA) is also proposed to quantify the fault degree, which can contribute to the condition-based maintenance of the system. The results validated by the fuel cell system diagnostic experiments reveal that the novel method can effectively identify the five health states and the fault degree. The overall accuracy is 99.31%, and the diagnosis period is shortened from 0.3375 to 0.1416 s after processing by t-SNE, which indicates that the proposed method can have a better performance compared with the traditional methods.

PEFC System Reactant Gas Supply Management and Anode Purging Strategy: An Experimental Approach

In this report, a 5 kW PEFC system running on dry hydrogen with an appropriately sized Balance of Plant (BoP) was used to conduct experimental studies and analyses of gas supply subsystems. The improper rating and use of BoP components has been found to increase parasitic loads, which consequently has a direct effect on the polymer electrolyte fuel cell (PEFC) system efficiency. Therefore, the minimisation of parasitic loads while maintaining desired performance is crucial. Nevertheless, little has been found in the literature regarding experimental work on large stacks and BoP, with the majority of papers concentrating on modelling. A particular interest of our study was the anode side of the fuel cell. Additionally the rationale behind the use of hydrogen anode recirculation was scrutinised, and a novel anode purging strategy was developed and implemented. Through experimental modelling, the use of cathode air blower was minimised since it was found to be the biggest contributor to the parasitic loads.

Fuel cell behavior and energy balance on board a Hyundai Nexo

Hydrogen fuel consumption measuring methodologies of a fuel cell vehicle without modifying the fuel path has been tested and benchmarked. In this work, they are applied to a Hyundai Nexo fuel cell electric vehicle driving different mission profiles on a chassis dynamometer. Three methods respectively based on hydrogen tank pressure, tailpipe oxygen concentration, and IR-shared (infrared) tank data are compared to the reference method relying on fuel cell current measurements. In addition to the hydrogen fuel consumption results, the installed electrical measuring equipment made possible to yield the fuel cell efficiency map at both stack and system levels as well as the energy consumption of its balance-of-plant (BoP) components during steady-state operation. A maximum steady-state efficiency of 66.8% is reported along with a rated system power of 82 kWe involving a 9.1-kWe power consumption for the electric compressor. It is shown that the compressor and the 12-V accessories are the most energy consuming devices among the BoP components accounting for 2%–3% of the total electric energy generated by the fuel cell. Furthermore, the behavior of the powertrain system is monitored and discussed during warm-up phases and during a long idling period. Finally, based on non-intrusive temperature measurements, a short analysis is conducted about the temperature impact on the fuel cell efficiency.

A Compact, Self-Sustaining Fuel Cell Auxiliary Power Unit Operated on Diesel Fuel

A complete fuel cell-based auxiliary power unit in the 7.5 kWe power class utilizing diesel fuel was developed in accordance with the power density and start-up targets defined by the U.S. Department of Energy. The system includes a highly-integrated fuel processor with multifunctional reactors to facilitate autothermal reforming, the water-gas shift reaction, and catalytic combustion. It was designed with the help of process analyses, on the basis of which two commercial, high-temperature PEFC stacks and balance of plant components were selected. The complete system was packaged, which resulted in a volume of 187.5 l. After achieving a stable and reproducible stack performance based on a modified break-in procedure, a maximum power of 3.3 kWe was demonstrated in a single stack. Despite the strong deviation from design points resulting from a malfunctioning stack, all system functions could be validated. By scaling-up the performance of the functioning stack to the level of two stacks, a power density of 35 We l−1 could be estimated, which is close to the 40 We l−1 target. Furthermore, the start-up time could be reduced to less than 22 min, which exceeds the 30 min target. These results may bring diesel-based fuel cell auxiliary power units a step closer to use in real applications, which is supported by the demonstrated indicators.

Solid Oxide Electrolysis System Optimization for Lunar Production of H2 and O2

Remote sensing spacecraft have located extensive surface ice in lunar permanently shadowed regions (PSRs) associated with craters near the poles. Producing H2 and O2 propellants from icy regolith in these regions requires development of integrated, robust electrolysis systems capable of operating in cryogenic environments. This team is demonstrating the feasibility of propellant production from lunar ice using high-temperature solid-oxide electrolysis (SOXE) and an optimized integrated balance-of-plant (BOP). High-temperature steam electrolysis has an efficiency advantage over PEM and alkaline electrolyzers, requiring less than 45 kWhelec kgH2 -1 [1], much less than liquid-phase electrolysis. SOXE systems require efficient steam generation and compression, heat recuperation, and subsequent drying of the H2 product stream. In this study, optimization of a demonstration system using less than 4.0 kWelec is based on OxEon’s SOXE stack that can deliver exceptionally high steam-utilization, (U H2O > 95%) and direct electrochemical O2 compression to facilitate O2 liquification with passive cooling at lunar PSR temperatures. This optimization forms the basis for the implementation of a lab-scale system for testing in a cryo-vac chamber, in order to demonstrate the viability of the optimized system for potential further, flight-scale development.The SOXE stack utilizes rare-earth stabilized zirconia electrolyte similar to technology in the MOXIE (Mars Oxygen In-Situ Resource Utilization Experiment) system [2]. The stack operates at 800ºC to balance trade-offs between area-specific resistance (ASR) and degradation. The 800ºC operating temperature requires efficient thermal integration of BOP to minimize specific energy and mass for reliable operation in the PSRs’ ‘cryo-vac’ conditions, where temperatures can reach as low as 40 K. This study shows how high U H2O enables optimization of the BOP components for system designs that can operate in the cryo-vacuum conditions with specific power w sp < 45 kWhelec kgH2 -1.Figure 1a illustrates principal BOP components including a steam generator, a compressor, cathode and anode heat recuperators, and a H2cooler/dryer. Passive radiative coolers for lunar operation prepare exhaust O2 and H2 product streams for liquification. The team developed a MATLAB-based process model to optimize the system configuration and operation. Performance of the stack, heat exchangers, and compressor are parameterized with both design parameters and system operating conditions that served as optimization variables. The system model is called by the MATLAB function ‘fmincon’ to minimize w sp under constraints that maintain reasonable system mass.The optimization study fixes H2 production rate at 0.075 kg H2 h-1 for the demonstration system in the lab-scale cryo-vac chamber. Optimization variables n this study for this lab-scale prototype system include 1) SOXE stack steam utilization U H2O ; 2) SOXE stack anode electrochemical compression DP a, for the O2 exhaust pressure; 3) steam generator vapor outlet temperature T vap; 4) compressor (scroll) pressure ratio P rat; and 5) inlet steam mass-flow split between recuperators. The SOXE electrolysis stack has a fixed cell area (110.8 cm2) and an experimentally measured area specific resistance (ASR). An electric preheater for the flow out of the cathode recuperator set the inlet steam flow to the 800 ℃ operating temperature, and this preheater added to the power (and thus specific work) required for the system. The SOXE cell operates at the thermoneutral voltage (V tn ≈ 1.28 V/cell @ 800℃) and stack current I tot is proportional to (V tn – V OCV)/ASR, where V OCV, open-circuit voltage, increases with U H2O. Primary BOP power demands include the compressor motor, SOXE stack steam preheater, thermal enclosure heater, and supplemental electric heating for the steam generator, but overall, the stack represented more than 80% of total power demand.Optimization of the system operating at 0.075 kg H2 h-1 shows that w sp had the highest sensitivity to U H2O with values above 0.85 required to achieve w sp < 45 kWhelec kgH2 -1 as shown in the contour plots of Figures 1b and 1c. Minimizing w sp encourages lower compressor pressure ratiosP rat which is limited to a minimum of 2.0. Increasing the steam generator temperature reduces compressor power demand but increases supplemental electrical heating for the steam generation, Thus, steam generator outlet temperature has minimal impact on w sp as shown in Figure 1c. Electrochemical compression of the O2 anode product does not benefit w sp, but it will greatly reduce the O2 passive cooler size which reduces mass/costs for a lunar deployed system. Additional studies are ongoing to look at trade-offs between system mass and system power with an eye toward optimizing both cost and reliability in a full-scale lunar deployed system. References Poszdeich, K. Schwarze, and J. Brabandt, Intl. J. Hydrogen Energy, 44(35), 19089-19101, 2019.Hartvigsen, S. Elangovan, J. Elwell, and D. Larsen, ECS Trans., 78(1), 2953-2963, 2017. Figure 1

Evaluating candidate materials for balance of plant components in SOFC: Oxidation and Cr evaporation properties

Balance of plant (BOP) components made of metallic materials in solid oxide fuel cells are subject to high-temperature corrosion and are a significant source of volatile chromium species. Prospective Fe and Ni-base alloys, AISI 441, AISI 444, a FeCrAl alloy A197/Kanthal® EF101, alloy 600, and alloy 800H are investigated for their suitability to BOP components. Oxidation kinetics and chromium evaporation were employed to study the selected alloys at 650 °C and 850 °C for 500 h. A197 performed the best while AISI 441 and AISI 444, performed the worst. Pre-oxidation significantly improved the performance of the alloys at 650 ⁰C.

Development of Alumina-Forming Austenitic Alloys for Solid Oxide Fuel Cell Balance of Plant Components

Solid oxide fuel cells (SOFC) are of great interest for cleaner energy production. As the technology moves to more widespread commercial adoption, balance of plant (BOP) components such as heat exchangers and other structural components are becoming increasingly important [1]. These components operate at ~600-950°C in the presence of aggressive species such as water vapor. Currently used chromia-forming Fe-based stainless steels and Ni-based alloys suffer from accelerated oxidation under these operation conditions due to enhanced internal oxidation and Cr oxy-hydroxide volatility [1,2]. Further, the volatilization of Cr species from BOP alloys results in Cr poisoning of the SOFC stack and a concomitant reduction in performance [1]. The use of alumina-forming alloys in SOFC BOP applications is a promising approach to reducing Cr contamination of the SOFC stack [3]. Alumina scales offer 1 to 2 orders of magnitude lower oxide growth rate than chromia and are far more stable in water vapor. Most alumina-forming alloys also make use of Cr alloying additions to promote the formation of the protective alumina; however, studies suggest > 10x reduction in Cr release can be achieved despite the presence of Cr in these alumina-forming alloys [3].Alumina-forming austenitic (AFA) alloys are a new class of stainless steels that offer the potential for improved oxidation resistance via an alumina scale combined with good creep resistance due to their austenitic structure, in a lower cost Fe-based alloy formulation [4]. The alloy design compromises to achieve both creep resistance and alumina formation result in a loss of protective oxidation and a transition to internal oxidation of Al with increasing temperature, typically in the range of ~750-900°C for wrought 20-25Ni mass % based AFA alloys depending on composition [5]. (A 35Ni-based cast grade of AFA alloy capable protective alumina formation to 1100-1200°C is available but is not suitable for SOFC BOP components) [6].The goal of the present work was to develop a lower cost, 25 Ni mass % grade AFA alloy capable of long-term SOFC BOP use at ~800-950°C in water vapor containing environments. The composition range of interest was based on Fe-25Ni-(13-18)Cr-4Al-(1-2.5)Nb-(0.5-2)Mn-(0.15-0.5)Si-(0-2)W-(0-2)Mo-(0-1)Cu-(0-0.1)Ti-(0.1)V-(0.05-0.2)Zr-(0.05-0.2)Hf-(0-0.1)Y-(0.02-0.2)C-(0.005-0.015)B mass %. The effort focused on systematic variation of C, Cr, and Nb levels ± Hf, Y, and Zr, which impact oxidation resistance, manufacturability, and cost. Key findings to achieve oxidation resistance at ≥850-900°C in air with 10% H2O without loss of creep resistance included: Protective alumina formation was enhanced by use of Zr additions, rather than previously demonstrated, more costly additions of Hf and Y.Levels of Nb as low as 1.5 mass % were sufficient to achieve protective alumina formation, as compared to previously used 2.5 mass % Nb levels, which reduces cost and aids manufacturability.The Cr addition levels were critical to pushing protective alumina formation past 900°C, with the critical transition occurring between ~14.5 and 16 mass % Cr.Protective alumina formation was achieved with lower than expected C addition levels, as low as 0.02 to 0.03 mass % C, which aids manufacturability to thin product forms by reducing primary coarse NbC formation. Details of the alloy design strategy and oxidation behavior out to 10,000 h of exposure at 900-1000°C in air with 10% H2O will be presented. Insights for the oxidation mechanism relative to Cr evaporation behavior will also be discussed.References L. Zhou, J. H. Mason, W. Li, and X. Liu, Renewable and Sustainable Energy Reviews Volume 134, December 2020, 110320 S.R.J. Saunders, M. Monteiro, F. Rizzo, Progress in Materials Science, 53 (2008) 775-837.M. Stanislowski, E. Wessel, T. Markus, L. Singheiser, W.J. Quadakkers, Solid State Ionics 179 (2008) 2406–2415.Y. Yamamoto, M.P. Brady, M.L. Santella, H. Bei, P.J. Maziasz, B.A. Pint, Metallurgical and Materials Transactions A, 42 (2011) 922-931.M.P. Brady, K.A. Unocic, M.J. Lance, M.L. Santella, Y. Yamamoto, L.R. Walker, Oxidation of Metals, 75 (2011) 337-357M. P. Brady, G. Muralidharan, Y. Yamamoto, B.A. Pint, , Oxidation of Metals, 87 (1), pp. 1-10 (2017) Notice: This manuscript has been authored by UT-Battelle, LLC, under contract DE-AC05-00OR22725 with the US Department of Energy (DOE). The US government retains and the publisher, by accepting the article for publication, acknowledges that the US government retains a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this manuscript, or allow others to do so, for US government purposes. DOE will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan (http://energy.gov/downloads/doe-public-access-plan).

Exergetic evaluation of operation results of 5-kW-class SOFC-HCCI engine hybrid power generation system

A solid oxide fuel cell (SOFC)-based hybrid power generation system using homogeneous charge compression ignition (HCCI) was previously proposed, based on which a proof-of-concept test has already been conducted by the Korea Institute of Machinery and Materials. In this study, energy and exergy analyses were performed to evaluate the experimental data obtained from the proof-of-concept test of the SOFC-HCCI engine hybrid system. In the analyses, particular attention is paid to the SOFC stack, HCCI engine, balance of plant (BOP) hot-box subsections and, accordingly, the energy and exergy flows within and between the above subsections. For the BOP hot-box, the energy and exergy analyses reveal different results. The energy analysis demonstrated that 75.1% of the transferred heat was recovered by the BOP components and pipes; only 25% of the heat, i.e., 638 W, was lost. However, the exergy analysis identified that only 35.1% of the transferred exergy was recovered; thus, 64.9% of the exergy was destroyed. Based on the energy and exergy analysis results, it is observed that the amount of exergy destruction exceeds the heat loss as the latter contributes to the former; this is in addition to the exergy destruction due to the irreversibility of the heat transfer between the components located in the BOP hot box. Based on the analyses of the entire system, the various heat losses and exergy destruction are quantitatively identified. In particular, significant heat loss and exergy destruction occur in the engine, additional burner, and BOP components. To improve the efficiency of the system, the insulation of the system can be reinforced, thereby reducing heat loss and exergy destruction and burner usage can be minimized. This suggests that the heat losses from the system components, mostly in the HCCI engine, should be reduced or reused to improve the overall efficiency of the system.

(Invited) Mitigating PEMFC Durability Limitations

A key requirement for PEM fuel cells for transport applications is longevity with a targeted lifetime of 5,000-6,000 h for light duty electric vehicles (LDV) and 25,000-30,000 h for heavy duty vehicles (HDV) [1]. In parallel, other KPIs such as high power density at certain voltage level (2024 target: 1.8 A cm-2 at 660 mV for LDV) and low Pt-loading (2024 target: 0.14 mg cm-2 total Pt loading for LDV) need to be achieved. This makes the durability targets even more challenging. Thereby, the lifetime of a PEMFC stack is determined by i) material properties and ii) by operation strategy. Hence, to increase PEMFC durability, investigations are pursued to propose improved components [2,3] as well as to define appropriate operation conditions for different applications [4,5].The performance limitations of PEMFC become substantial particularly at low Pt loadings [6] Moreover, performance and material degradation is particularly critical at low Pt loadings as well; in this context the cathode catalyst layer contributes the most to performance decay. The dissolution of Pt nanoparticles and the degradation of the carbon support as well as ionomer are dominating processes. One approach to mitigate performance degradation is the development of stabilized catalysts [7]. Low Pt loaded electrodes with the nano-cage stabilized Pt/C catalyst mitigate Pt dissolution, as will be shown in this presentation. The positive effect is clearly demonstrated by comparing the accelerated stress tests (ASTs) of a MEA with conventional Pt/C catalyst against a MEA with a stabilized Pt/C catalyst. In our tests, the conventional MEA exhibits dramatic ECSA loss, while it remains stable in case of the stabilized MEA as shown in panel (A) of the image.To assess durability of new MEA components, ASTs are necessarily required to avoid testing times of thousands of hours. Moreover, to provide realistic results, these ASTs need to simulate stressors occurring in the course of real operation conditions. To quantify the impact of specific operando stressors (such as high current density or high operation temperature) on individual MEA components (i.e. CCM and GDL), specific degradation tests have been carried out as part of the European ID-Fast project [8]. Progress on these investigations will be shown in this presentation. In addition, special focus is dedicated to the analysis of reversible degradation losses and the corresponding recovery procedures. Within this framework, different recovery protocols proposed in the literature as well as by projects funded by the European Commission and the DOE are compared.The second approach focuses on increasing the lifetime by optimizing operation conditions of the PEMFC stack [4]. This includes considering the power demand and dynamics of the subsystems and their balance of plant components in a hybrid system using a PEMFC and an energy storage system (i.e. battery or capacitor). Thereby the system power demand is derived from the velocity profiles of the target applications and has to be distributed between the subsystems. This approach allows mitigation of detrimental system operation, such as i) uncovered power demand, ii) discharged energy storage (no buffering of power peaks) and fully charged energy storage (no recuperation) and iii) excess of energy storage maximum charge current (partial buffering) as shown in panel (B) of the image. Moreover, faulty stack operation is mitigated thanks to using operando state-of-health monitoring.AcknowledgementsThis project has received funding from the Fuel Cells and Hydrogen 2 Joint Undertaking under grant agreement No 779565 (ID-Fast). This Joint Undertaking receives support from the European Union’s Horizon 2020 research and innovation programme. Moreover, financial support by German Federal Ministry of Education and Research through the COALA project (grant no. 01LX1601A of the Polish-German Sustainability Research Call STAIR II) is acknowledged.

A Portable Direct Methanol Fuel Cell Power Station for Long-Term Internet of Things Applications

With regard to the best electro-chemical efficiency of an active direct methanol fuel cell (DMFC), the stacks and their balance of plant (BOP) are complex to build and operate. The yield of making the large-scale stacks is difficult to improve. Therefore, a portable power station made of multiple simpler planar type stack modules with only appropriate semi-active BOPs was developed. A planar stack and its miniature BOP components are integrated into a semi-active DMFC stack module for easy production, assembly, and operation. An improved energy management system is designed to control multiple DMFC stack modules in parallel to enhance its power-generation capacity and stability so that the portability, environmental tolerance, and long-term durability become comparable to that of the active systems. A prototype of the power station was tested for 3600 h in an actual outdoor environment through winter and summer. Its performance and maintenance events are analyzed to validate its stability and durability. Throughout the test, it maintained the daily average of 3.3 W power generation with peak output driving capability of 12 W suitable for Internet of Things (IoT) applications.