Fuel Cell Stack Research Articles

Solid oxide fuel cell stack with enhanced performance and durability utilizing a porous Ag coating layer as the current collector

This study focuses on reducing the weight of the stack applied to the unit cell during the structuring process of a solid oxide fuel cell (SOFC) stack. By using a porous Ag coating layer as a current collector, separator plates and connectors are eliminated and the manufacturing cost of the stack can thereby be reduced. Additionally, the performance and stability of the stack are significantly improved by reducing the contact resistance between cells. The Ag coating layer used in this study can be optimized by adjusting the coating thickness and the ratio of graphene and Ag paste, which affects dispersibility and porosity. The optimized Ag porous coating layer makes it possible to manufacture a stack cell with a simple structure without requiring a separator, and excellent performance is confirmed in a long-term test of 4000 h.

Numerical Study on Effect of Flow Field Configuration on Air-Breathing Proton Exchange Membrane Fuel Stacks

Air-breathing proton exchange membrane fuel cells (PEMFCs) show enormous potential in small and portable applications because of their brief construction time without the need for gas supply, humidification and cooling devices. In the current work, a 3D multiphase model of single air-breathing PEMFCs is developed by considering the contact resistance between the gas diffusion layer and bipolar plate and the anisotropic thermal conduction and electric conductive in the through-plane and in-plane directions. The 3D model presents good grid independence and agreement with the experimental polarization curve. The single PEMFC with the best open area ratio of 55% achieves the maximum peak power density of 179.3 mW cm−2. For the fuel cell stack with 10 single fuel cells, the application of the anode window flow field is beneficial to improve the stack peak power density compared to the anode serpentine flow field. The developed model is capable of providing assistance in designing high-performance air-breathing PEMFC stacks.

Improving fuel efficiency and durability in fuel cell vehicles through component sizing and power distribution management

The proposed study presents a novel approach to determining the optimal component sizes and power distribution for a vehicle, taking into account various power sources in order to prolong the lifespan of the fuel cell stack. Moreover, this technique aims to increase the vehicle's overall fuel economy. The available experimental data of Toyota Mirai has been used to model the vehicle in the MATLAB-SIMULINK software. The validated model is implemented to evaluate the vehicle power request in different standard driving cycles and routes to size the vehicle components. The arithmetic average of the steady power of different driving cycles and routes has been attributed to the fuel cell stack's maximum efficiency point. The battery size should support the requested dynamic power in any situation. Thus, the maximum power of the fuel cell stack, the high voltage battery size, and the electric motor maximum power are assigned as 96 kW, 3.05 kWh, and 59 kW, respectively. The results of fuel consumption of the vehicle is also improved at least by 10% up to 21% in different driving conditions. Economic analysis reveals that adopting this strategy can lead to a substantial reduction in the initial vehicle cost by $1,328. The operational cost has also decreased 691$ annually due to lower fuel consumption of the new strategy implementation. These advancements along with better fuel cell stack durability hold promise for prospective buyers, allowing for greater accessibility and financial flexibility.

Ex-situ Characterization of Nb-Ti Alloy/Pt Coated Stainless Steel Bipolar Plates for Proton Exchange Membrane Fuel Cells

Metallic bipolar plates are crucial for the development of compact and lightweight proton exchange membrane fuel cell stacks; however, most of them encounter durability and conductivity challenges in the fuel cell environment. In this study, Nb-Ti alloy/Pt coatings are deposited on SS316L plates to enhance corrosion resistance, surface wettability, electrical and thermal conductivity, with reduced interfacial contact resistance. Corrosion resistance is assessed by exposing test samples to a 1M H2SO4 acidic environment at 25 °C and 80 °C, respectively, via potentiostatic and potentiodynamic polarization tests. It is found that Nb-Ti alloy/Pt coatings exhibit exceptional stability, with corrosion potential increased by 2.5 (at 25 °C) and 0.5 (at 80 °C) times and corrosion current density reduced by orders of magnitude; and their anti-corrosion performance far exceeds the technical targets set by the US Department of Energy, with a protective efficiency of 99.98 % at both temperatures tested. The coated samples have reduced water affinity, indicated by significantly larger contact angle values compared to the uncoated samples in both pre-and post-corrosion tests. The incorporation of Nb-Ti alloy/Pt coatings on SS316L increases the in-plane electrical conductivity by 42.6 % and thermal conductivity by 3.5 %; surpassing the US Department of Energy's technical targets in these categories as well. At a compaction force of 140 N/cm2, the interfacial contact resistance for the coated samples is about 2.5 times lower than the Department of Energy's requirements. These results indicate the viability of Nb-Ti alloy/Pt coated SS316L bipolar plates for fuel cell applications.

Hydrogen as a deep sea shipping fuel: Modelling the volume requirements

Recent targets have increased pressure for the maritime sector to accelerate the uptake of clean fuels. A potential future fuel for shipping is hydrogen, however there is a common perception that the volume requirements for this fuel are too large for deep sea shipping. This study has developed a range of techniques to accurately simulate the fuel requirements of hydrogen for a case study vessel. Hydrogen can use fuel cells, which achieve higher efficiencies than combustion methods, but may require a battery hybrid system to meet changes in demand. A series of novel models for different fuel cell types and other technologies have been developed. The models have been used to run dynamic simulations for different energy system setups. Simulations tested against power profiles from real-world shipping data to establish the minimum viable setup capable of meeting all the power demand for the case study vessel, to a higher degree of accuracy than previously achieved. Results showed that the minimum viable setup for hydrogen was with liquid storage, a 105.6 MW PEM fuel cell stack and 6.9 MWh of batteries, resulting in a total system size of 8934 m3. Volume requirement results could then be compared to other concepts such as systems using ammonia and methanol, 8970 m3 and 6033 m3 respectively.

Direct oxidative coupling of methane into ethylene in a catalyst-enhanced planar solid oxide fuel cell stack reactor

This study presents an efficient method to convert methane into valuable olefins using a Solid Oxide Fuel Cell (SOFC) membrane reactor. Methane, abundant in natural and shale gas, serves as a sustainable feedstock due to its favorable carbon-hydrogen ratio. The SOFC membrane reactor eliminates costly air separation units and safety risks associated with explosive methane-oxygen mixtures. A planar SOFC stack achieves over 30 % methane conversion, 40 % ethylene selectivity, and power generation capabilities. Optimization with mixed-conducting ceramics enhances electrical performance without compromising catalytic activity. The stack's scalability is demonstrated, with the 5-cell configuration surpassing the 2-cell setup. This innovative approach offers a sustainable solution to methane waste, producing high-value chemicals while reducing environmental impact.

Modelling and operation characteristics of air-cooled PEMFC with metallic bipolar plate used in unmanned aerial vehicle

The air-cooled proton exchange membrane fuel cell stack composed of the metallic bipolar plate with simple system and lightweight characteristics, is regarded as an ideal power source for unmanned aerial vehicles. A zero-dimensional model is developed to analyze the operation characteristics at heights in the range of 0–3000 m. The temperature should not exceed 60 °C to ensure safe and effective operation. The peak power decreases by 20 % and the stack has good adaptability to altitudes. The performance degradation can be largely attributed to the lower oxygen pressure at high altitudes through normalization analysis. It is more significant at higher current densities owing to increased air starvation. The increase of the air stoichiometry is conducive to heat dissipation and reduces mass transfer loss. The voltage initially increases and then decreases as the air stoichiometry increases, and the optimal air stoichiometry corresponding to the maximum voltage is determined. Appropriately increasing the air stoichiometry can improve the consistency of the temperature and voltage distributions.

Study on the effects of nano-copper addition on the properties of epoxy resin/graphite composite bipolar plates

Bipolar plates (BPs) are vital components in Proton Exchange Membrane Fuel Cells (PEMFCs), and their performance and cost significantly impact fuel cell stack efficiency and affordability. BPs require excellent conductivity, strength, and corrosion resistance depending on usage conditions. Common graphite and metal-based BPs offer good conductivity, but they have their drawbacks. Graphite lacks strength and is costly to process, while metal-based BPs need additional surface treatments to prevent corrosion. In recent years, composite bipolar plates have gained widespread attention due to their excellent conductivity, mechanical properties, and outstanding corrosion resistance. In this study, we used natural graphite flakes as the main conductive filler and nano-copper as the secondary conductive filler, with epoxy resin as the binder. The composite bipolar plate was prepared using a hot-pressing method. The study found that adding 1 wt% of nmCu can increase the conductivity of the composite BP by 75.2%, but it decreases the flexural strength by 26.84%. The prepared nmCu/G/EP composite BP exhibits an ASR of only 4.00 mΩ cm2 and a corrosion current density of 2.615 × 10−7 A/cm2, meeting the DOE 2025 expectations. After conducting Cu2+ leaching experiments on the prepared composite BP, single-cell performance testing showed a maximum power density of 0.556 W/cm2. This study expands the range of conductive fillers for composite BPs, no longer limited to carbon-based conductive fillers.

A one-dimensional model of air-cooled proton exchange membrane fuel cell stack integrating fan arrangement and operational characteristics

Air-cooled proton exchange membrane fuel cell stack’s performance can be greatly affected by the arrangement and operational characteristics of the fans that generate the air flow. However, the influence mechanisms are complex and poorly understood. In this study, a one-dimensional analytical model specifically for air-cooled stacks integrating important fan features is developed to quickly (e.g. within 5 min for a 100-cell stack) and accurately predict the water and thermal states inside stacks and stack performance under various fan arrangements and operational characteristics. The model accuracy was validated against the experimental results of a 95-cell air-cooled stack, including the stack polarization curves, temperature distribution and air flow rates at different fan’s duty cycles. The model results showed that for high air flow resistance stacks, the air flow rate and maximum net power for fans arrangement in series are higher than those in parallel by about 10% and 0.5%, respectively. Moreover, integrating a single large fan can be better than two small fans as the former induces a higher air flow rate and static pressure. On the other hand, altering the air flow channel length or depth changes the air flow resistance in stacks, leading to a shift of the working point for a fixed fan at a certain duty cycle and greatly influencing stack performance. This one-dimensional air-cooled stack model can be a powerful tool to facilitate stack design and optimization.

A novel adaptive fast sliding mode control method based on fuzzy algorithm for the air management system of fuel cell stack

Proton exchange membrane fuel cells (PEMFCs) offer advantages, such as, cleanliness, high efficiency, and environmental friendliness. To achieve optimal control of the PEMFC stack's air supply and management system under complex operating conditions, a novel non-singular terminal sliding mode controller based on fuzzy algorithm is proposed. Compared with the conventional sliding mode control, the terminal sliding mode control exhibits further performance improvements. However, it still has limitations. The proposed innovative sliding mode structure would ensure finite-time convergence and avoid the issue of singularity associated with terminal sliding mode control. Moreover, fuzzy logic makes sliding mode gain adapt to the system and further enhances the performance and stability, which is benefited from a stronger sliding surface. Results indicate that, compared with the other controllers, the designed controller could reduce delay further and provide faster response to sudden changes. The overshoot of sliding surface has decreased by 70% compared to its previous level. This novel control approach significantly enhances the efficiency and reliability of the PEMFC system.

CO-tolerance behaviors of proton exchange membrane fuel cell stacks with impure hydrogen fuel

Carbon monoxide poisoning poses a significant challenge for proton exchange membrane (PEM) fuel cells operating with CO-containing hydrogen. One established solution involves air bleeding, a process that enhances the oxidation of carbon monoxide at the anode side of the fuel cell by blending a small quantity of air with the impure hydrogen before its introduction into the fuel cell. However, researchers have raised concerns regarding durability issues about catalyst sintering and membrane decomposition induced by air bleeding. The effects and underlying mechanisms of air bleeding on PEM fuel cells have yet to be comprehensively elucidated. To address this, this study conducts a detailed durability test to quantitatively evaluate the effects of air bleeding on the CO-containing hydrogen-fueled PEM fuel cells via the micro-current excitation method. The investigation substantiates that the PtRu/C catalysts significantly enhance both the performance and durability of fuel cells when air bleeding is employed, exhibiting different CO-tolerance and decay behaviors compared to the Pt/C anode catalyst. Furthermore, the evolution of MEA parameters indicates that the advantageous behaviors of PtRu/C catalysts can be attributed to their CO-tolerance capabilities, alleviated anodic catalyst sintering and loss, and decreased chemical carbon support corrosion and membrane decomposition through diminished hydrogen peroxide generation. This study contributes critical insights and empirical evidence for researchers focusing on CO-tolerant catalyst materials, the durability of PEM fuel cells, and the conversion and utilization of impure hydrogen energy derived from fossil fuels.

Velocity (μPIV) and temperature/concentration (μLIF) measurements in a dual serpentine microchannel of a micro DMFC stack

Herein, we present an experimental study of the flow, as well as the thermal and concentration characteristics of two serpentine microchannels, via micro particle image velocity/micro laser induced fluorescence optical visualization techniques, which simulate the flow channels at the anode of a typical micro direct methanol fuel cell stack (two cells: Cell A/B). The flow channel consists of two serpentine microchannels. Each channel has one channel and six paths. Channels A and B were connected by a connecting tube to create an entire flow loop with methanol as the working fluid. The velocity, temperature and concentration distribution along the channel downstream for 5.7 ≤ Re ≤ 594 were visualized and measured. At a particular operation condition of methanol flow rate of 1 ml/min and concentration of 1 M at stack temperature of 25 °C, both in series and parallel arrangements were examined with a peak power density of 61.4 mW/cm2 (current density 120 mA/cm2 and voltage 1.0 V) and of 75 mW/cm2 (current density 120 mA/cm2 and voltage 1.2 V), respectively. CO2 ellipse-like bubbles were found at the up/down stream corners with a definite major/minor axis length. Furthermore, relevant (f, Nu, and Sh) correlations regarding the relationship of the methanol solution pumping power, heat transfer and utilization with Reynolds number in form of power law were developed with 95 % accuracy of experimental data. With these related results, it might be beneficial to the configuration design of the μDMFC stack.

Forming of large scale bipolar plates for high power fuel cell stacks

Developing high-power (e.g. megawatt-scale) single fuel cell stacks is of significance to extending the application of hydrogen fuel cells in high-energy-consumption fields such as aerospace, maritime, and rail transportation. Bipolar plate is one of the core components of hydrogen fuel cell stacks. Currently, the mainstream hydrogen fuel cell stacks achieve a maximum power of about 200 kW with a bipolar plate area of approximately 600 cm2. While the megawatt-scale hydrogen fuel cell stacks requires large scale bipolar plates with an area of e.g. >2000 cm2 and higher geometric complexity of flow channel. However, the structural design and manufacturing process for such large scale bipolar plates remain unexplored. Based on the concept of “partitioned modular manufacturing”, the large scale bipolar plate is divided into multiple smaller scale bipolar plate modules in this work, and then integrated into a single component, which is then formed by applying multi-step stamping process to each module. Therefore, a so-called “partitioned multi-step stamping process” is proposed to form large scale bipolar plates with fine flow channels. Experimental validation was conducted using 0.1 mm thick titanium sheets and austenitic stainless steel sheets, demonstrating a prospective solution to manufacture large scale bipolar plates for high power hydrogen fuel cell stacks.

Experimental study of a solid oxide fuel cell afterburner for a 30 kW generator module: A comparative performance analysis

A comprehensive performance test is conducted on a diffusion burner designed for a 30 kW-class methane solid oxide fuel cell (SOFC) power generation system. To facilitate this assessment, a test system is established, capable of simulating the gas composition and temperature of the anode and cathode at the outlet of the fuel cell stack under various typical operating conditions. The test results demonstrate the afterburner's exceptional robustness, minimal pressure loss, and low emission characteristics. Notably, the afterburner can be ignited and started at low load (6LPM, 20 % of the rated methane flow rate) and can achieve low-load heating (4LPM, at approximately 13 % of the rated methane flow rate) with a significant excess air coefficient of 46.2. Remarkably, the afterburner maintains its reignition capability under all operating conditions. Operational stability is observed with a water-to-carbon ratio below 3, displaying robust resistance to fluctuations in water vapor and airflow. Under generating condition, the afterburner exhibits self-ignition capabilities without the need for an external igniter following flameout. The pressure losses within both the anode and cathode flows remain well below 200Pa, while NOx and CO emissions are recorded at 1.7mg/kWh and 66.2mg/kWh, respectively, complying with the stringent EU EN676:2020 standards.

Thermal Stress in Full-Size Solid Oxide Fuel Cell Stacks by Multi-Physics Modeling

Mechanical failures in the operating stacks of solid oxide fuel cells (SOFCs) are frequently related to thermal stresses generated by a temperature gradient and its variation. In this study, a computational fluid dynamics (CFD) model is developed and further applied in full-size SOFC stacks, which are fully coupled and implemented for analysis of heat flow electrochemical phenomena, aiming to predict thermal stress distribution. The primary object of the present investigation is to explore features and characteristics of the thermal stress influenced by electrochemical reactions and various transport processes within the stacks. It is revealed that the volume ratio of the higher thermal stress region differs nearly 30% for different stack flow configurations; the highest probability of potential failure appears in the cell cathodes; the more cells applied in the stack, the greater the difference in the predicted temperature/thermal stress between the cells; the counter-flow stack performs the best in terms of output power, but the predicted thermal stress is also higher; the cross-flow stack exhibits the lowest thermal stress and a lower output power; and although the temperature and thermal stress distributions are similar, the differences between the unit cells are bigger in the longer stacks than those predicted for shorter stacks. The findings from this study may provide a useful guide for assessing the thermal behavior and impact on SOFC performance.

Characteristic Investigation of a Novel Aircraft SOFC/GT Hybrid System under Varying Operational Parameters

In this study, the implementation of a solid oxide fuel cell–gas turbine hybrid engine for primary propulsion and electric power generation in aircraft is investigated. The following three parameters, which are crucial in attaining optimal performance at any point in the flight profile, were identified: the oxygen-to-carbon ratio of the catalytic partial oxidation reformer, the fuel utilization factor of the fuel cell, and the airflow split ratio at the outlet of the high-pressure compressor. The study assesses the impact of varying these parameters within specified ranges on the performance of the hybrid system. At the design point, the system yielded a total power output of 1.96 MW, with 102.5 kW of electric power coming from the fuel cell and 7.9 kN (1.86 MW) of thrust power coming from the gas turbine. The results indicate that varying the oxygen-to-carbon ratio affected the fuel cell’s fuel utilization and resulted in a slight decrease in gas turbine thrust. The fuel utilization factor primarily affected the power output of the fuel cell stack, with a minor impact on thrust. Notably, varying the airflow split ratio showed the most significant influence on the overall system performance. This analysis provides insights into the system’s sensitivities and contributes to the development of more sustainable aircraft energy systems.

To study the effect of geometric parameters on the performance of a typical cone-shaped tubular segmented-in-series solid oxide fuel cell stack

Long electric current transfer path has been a common problem with tubular series cells. Cone-shaped tubular segmented-in-series solid oxide fuel cells (SIS-SOFCs) have attracted much attention due to their special advantages, such as short electric current path, unsealed requirement, small thermal stress, low operating electric current, and so on. In this paper, the electrochemical and multiphysics coupling model of a typical SIS-SOFC is developed. Then, the relationship between the geometric structure and the working characteristics within the SIS-SOFC is investigated. The results show that the size of the active reaction region in the downstream cone-shaped cell depends on the length of the interconnectors. Thus, increasing the length of the interconnectors increases the active reaction area of the series cell while decreasing the current transmission path. The ratio between the interconnector length and total cell length equals 0.5 is found to be a proper geometric factor for the SIS-SOFC to achieve a good overall performance and reaction uniformity.

Analysis of Power Consumption on BOP System in a Fuel Cell Electric Bus According to the Fuel Cell Load Range

The proton exchange membrane fuel cell (PEMFC) in a fuel cell electric bus (FCEB) converts hydrogen's chemical energy into electrical energy. The fuel cell system comprises a fuel cell stack and a balance of plant (BOP) system, which efficiently controls the stack. Fuel cell and battery are sensitive to operational temperature, which directly impacts performance, lifespan, and safety. Therefore, a thermal management system (TMS) is necessary to maintain an appropriate temperature by dissipating the heat generated by the fuel cell and battery. In this study, the exponential or quadratic relationships between the power consumption of the major components of an FCEB and various factors, such as temperature and flow rate influencing the operational behavior and control of the components, were analyzed based on the results of a dynamometer vehicle test. Additionally, the vehicle's energy flow was calculated under different fuel cell load conditions. When the fuel cell operated at 56.3 kW, TMS power was 6.6 times higher than at 20 kW. At full load, under 90 kW, it increased to 17.4 times higher. The rise in fuel cell load correlated with higher heat generation, resulting in a significant increase in power consumption for both the radiator fan and coolant pump.

Leakage mechanism model of proton exchange membrane fuel cell sealing structures under vibration conditions

ABSTRACT To resolve the issue of predicting the leak rate in proton exchange membrane fuel cells (PEMFCs) under long-term random vibration conditions. Considering the mechanism of bolt vibration loosening and rubber vibration relaxation, a leakage mechanism model of the PEMFC sealing structure under vibration conditions is proposed, and the validity of the model is verified by experimental comparison. The model clearly reveals the quantitative effects of structural parameters and material parameters on the leakage rate of PEMFC under vibration conditions. The research results show that under long-term random vibration conditions, the change of PEMFC leakage rate with time is mainly divided into three stages: response stage, stable stage, and leakage stage. Compared to bolt vibration loosening, the rubber vibration relaxation has a more significant impact on PEMFC leakage, the leakage rate of the fuel cell stack is 433ppm after 10,000 hrs of vibration. In addition, increasing the bolt preload, changing the bolt distribution, reducing surface roughness, and reducing gasket thickness can effectively suppress PEMFC leakage under random vibration conditions, the minimum leakage rate of the fuel cell stack can be reduced to around 170ppm per 10,000 hours. The proposed mechanism model provides an effective method for predicting the leakage rate of PEMFC sealing structures.

Theoretical and Experimental Study of a Fuel Cell Stack Based on Perfluoro-sulfonic Acid Membranes Facing High Temperature Application Environments

Theoretical and Experimental Study of a Fuel Cell Stack Based on Perfluoro-sulfonic Acid Membranes Facing High Temperature Application Environments