Fuel Cell Stack Power Research Articles

PEMFC Electrochemical Degradation Analysis of a Fuel Cell Range-Extender (FCREx) Heavy Goods Vehicle after a Break-In Period

With the increasing focus on decarbonisation of the transport sector, it is imperative to consider routes to electrify vehicles beyond those achievable using lithium-ion battery technology. These include heavy goods vehicles and aerospace applications that require propulsion systems that can provide gravimetric energy densities, which are more likely to be delivered by fuel cell systems. While the discussion of light-duty vehicles is abundant in the literature, heavy goods vehicles are under-represented. This paper presents an overview of the electrochemical degradation of a proton exchange membrane fuel cell integrated into a simulated Class 8 heavy goods range-extender fuel cell hybrid electric vehicle operating in urban driving conditions. Electrochemical degradation data such as polarisation curves, cyclic voltammetry values, linear sweep voltammetry values, and electrochemical impedance spectroscopy values were collected and analysed to understand the expected degradation modes in this application. In this application, the proton exchange membrane fuel cell stack power was designed to remain constant to fulfil the mission requirements, with dynamic and peak power demands managed by lithium-ion batteries, which were incorporated into the hybridised powertrain. A single fuel cell or battery cell can either be operated at maximum or nominal power demand, allowing four operational scenarios: maximum fuel cell maximum battery, maximum fuel cell nominal battery, nominal fuel cell maximum battery, and nominal fuel cell nominal battery. Operating scenarios with maximum fuel cell operating power experienced more severe degradation after endurance testing than nominal operating power. A comparison of electrochemical degradation between these operating scenarios was analysed and discussed. By exploring the degradation effects in proton exchange membrane fuel cells, this paper offers insights that will be useful in improving the long-term performance and durability of proton exchange membrane fuel cells in heavy-duty vehicle applications and the design of hybridised powertrains.

Effects of Fuel Cell Size and Dynamic Limitations on the Durability and Efficiency of Fuel Cell Hybrid Electric Vehicles under Driving Conditions

In order to enhance the durability of fuel cell systems in fuel cell hybrid electric vehicles (FCHEVs), researchers have been dedicated to studying the degradation monitoring models of fuel cells under driving conditions. To predict the actual degradation factors and lifespan of fuel cell systems, a semi-empirical and semi-physical degradation model suitable for automotive was proposed and developed. This degradation model is based on reference degradation rates obtained from experiments under known conditions, which are then adjusted using coefficients based on the electrochemical model. By integrating the degradation model into the vehicle simulation model of FCHEVs, the impact of different fuel cell sizes and dynamic limitations on the efficiency and durability of FCHEVs was analyzed. The results indicate that increasing the fuel cell stack power improves durability while reducing hydrogen consumption, but this effect plateaus after a certain point. Increasing the dynamic limitations of the fuel cell leads to higher hydrogen consumption but also improves durability. When considering only the rated power of the fuel cell, a comparison between 160 kW and 100 kW resulted in a 6% reduction in hydrogen consumption and a 10% increase in durability. However, when considering dynamic limitation factors, comparing the maximum and minimum limitations of a 160 kW fuel cell, hydrogen consumption increased by 10%, while durability increased by 83%.

Bipropellant Enabled Solid Oxide Fuel Cell Stack Power Supply: Energy Agility for Space Vehicles

Spacecraft often have instances where they are required to operate for long periods of time with significant power requirements and no access to solar power. While a battery system could be designed to meet these occasional, and possibly unexpected requirements, creating a power supply to meet these infrequent demands results in having a battery system that is excessively large, massive, and inefficient. A Solid Oxide Fuel Cell (SOFC) system capable of running on the same fuel and oxidizer as the onboard thruster of a bipropellant thruster equipped spacecraft can eliminate much of the added mass and volume needed to enable batteries to meet extreme power demands and create more operational flexibility on how the chemical energy in stowed bipropellants are used. If the spacecraft needs thrust, the bipropellant can be ignited to provide thrust. If the spacecraft needs electric power, the spacecraft can consume bipropellant to generate auxiliary power. In this work, the proven bipropellant pair ammonia (NH3) and nitrous oxide (N2O) are shown to be a viable fuel and oxidant for hydrogen (H2) consuming air breathing SOFCs, as spontaneous NH3 decomposition will generate H2 and spontaneous N2O decomposition will generate O2. A scale up to a 5-cell SOFC stack fed NH3 and N2O produced power up to ~89W. Higher power can be achieved by scaling up the number of cells in a stack to achieve required power demands. The results of this study demonstrate the potential and feasibility of integrating SOFCs with a bipropellant thruster to creating a dual functioning spacecraft system that can satisfy operational power requirements and on-orbit maneuverability.This material is based on research sponsored by Air Force Research Laboratory under agreement number FA9453-21-C-0060. The views expressed are those of the authors and do not reflect the official guidance or position of the United States Government, the Department of Defense or of the United States Air Force. Approved for public release; distribution is unlimited. Public Affairs release approval #AFRL20230023. Figure 1

Bipropellant Enabled Solid Oxide Fuel Cell Stack Power Supply: Energy Agility for Space Vehicles

A Solid Oxide Fuel Cell (SOFC) system capable of running on the same fuel and oxidizer as an onboard bipropellant thruster can create enhanced operational flexibility. If a spacecraft needs thrust, the bipropellant can be ignited to provide thrust. If a spacecraft needs electric power, the spacecraft can consume bipropellant to generate auxiliary power. In this work, the proven bipropellant pair ammonia (NH3) and nitrous oxide (N2O) are shown to be a viable fuel and oxidant for SOFCs, as in situ thermal NH3 cracking will generate H2 and N2O decomposition will generate O2. A 5 cell SOFC stack produced 89 W when fueled with NH3 and N2O. The results of this study demonstrate the potential for a bifunctional spacecraft system that can satisfy both operational power and on-orbit maneuverability requirements.

Modeling of Fuel Cells Characteristics in Relation to Real Driving Conditions of FCHEV Vehicles

Fuel cells are one of the zero-emission elements of modern automotive drive systems. This article presents theoretical identification of the component parameters of indicators for the fuel cell operating conditions. Activation, ohmic, and mass transport losses were identified. Current–voltage characteristics were provided along with an analysis of typical cell losses. The actual performance characteristics of fuel cells were analyzed for Toyota Mirai I and II generation vehicles. The fuel cells operating conditions were derived and analyzed in the context of real driving conditions. Therefore, urban, rural, and motorway conditions were used. The vehicles were equipped with PEM fuel cells supplying power equal to 114 kW (1st gen.) or 128 kW (2nd gen.). The average fuel cell stack power values depend on the driving conditions: urban (about 10 kW), rural (20 kW) and motorway (about 30–40 kW) driving modes. The different power ratings of fuel cells combined with different battery generations resulted in a variation in the cells operating conditions. Analyses conducted in various traffic conditions indicated the possibility of determining losses related to the fuel cells. The analysis of fuel cell losses shows the greatest values for activation losses when the cells are under high load (for both generations)—i.e., in motorway driving conditions. The voltage of resistive losses reached its maximum in urban driving conditions when the load on the fuel cells was small.

Power evolution of fuel cell stack driven by anode gas diffusion layer degradation

Recent research has revealed that gas diffusion layer degradation has a crucial effect on fuel cell stack power density evolution. There have been several investigations focused on the influence of cathode gas diffusion layer degradation on stack performance. However, the degradation behavior and contribution of the anode gas diffusion layer on stack output power remain to be studied. Here, the 1000 h durability test of a stack was conducted under the New European Driving Cycle condition, and the effect of anode gas diffusion layer failure on the stack output power was evaluated. Carbon corrosion is the main attenuation characteristic of the anode gas diffusion layer, which significantly reduces its mechanical strength, and decreased the support capacity of the anode gas diffusion layer. Moreover, carbon corrosion also leads to exposure of new hydrophilic surfaces, reducing the hydrophobicity of the gas diffusion layer. In addition, the loss of hydrophobic agents is also one of the main characteristics of anode gas diffusion layer attenuation, which is the main reason for hydrophobicity loss. The decreased hydrophobicity will significantly improve the water retention capacity, and reduce the back diffusion of cathode water. As a result, mass transfer resistance will increase at a high current density. In conclusion, we verified the crucial impact of anode gas diffusion layer on cell output power density, and provide a new idea for the stack power attenuation investigation.

Effects of drivetrain hybridization on fuel economy, performance and costs of a fuel cell hybrid electric vehicle

Fuel cell hybrid electric vehicles (FCHEVs) are considered to be the most attractive long-term option for passenger cars. Several barriers, such as cost, durability and hydrogen refueling infrastructure, must be overcome for a wider use of FCHEVs. In this paper, a mid-sized FCHEV is modeled and simulated in ADVISOR to analyze the influence of hybridization factor on vehicle performance and costs. The results are compared with those of the Toyota Mirai in order to find the optimum size of the fuel cell stack and the number of battery modules that meet various driving requirements, minimize hydrogen consumption and vehicle cost. The best results are obtained by reducing the fuel cell stack power by 58%. A 7.7% increase in equivalent fuel economy (71.6 MPGe) and a reduction of 25% in the vehicle cost is achieved.

Study and performance test of 10\xa0kW molten carbonate fuel cell power generation system

The use of high-temperature fuel cells as a power technology can improve the efficiency of electricity generation and achieve near-zero emissions of carbon dioxide. This work explores the performance of a 10 kW high-temperature molten carbonate fuel cell. The key materials of a single cell were characterized and analyzed using X-ray diffraction and scanning electron microscopy. The results show that the pore size of the key electrode material is 6.5 µm and the matrix material is α-LiAlO2. Experimentally, the open circuit voltage of the single cell was found to be 1.23 V. The current density was greater than 100 mA/cm2 at an operating voltage of 0.7 V. The 10 kW fuel cell stack comprised 80 single fuel cells with a total area of 2000 cm2 and achieved an open circuit voltage of greater than 85 V. The fuel cell stack power and current density could reach 11.7 kW and 104.5 mA/cm2 at an operating voltage of 56 V. The influence and long-term stable operation of the stack were also analyzed and discussed. The successful operation of a 10 kW high-temperature fuel cell promotes the large-scale use of fuel cells and provides a research basis for future investigations of fuel cell capacity enhancement and distributed generation in China.

Influence of pressure losses on compressor performance in a pressurized fuel cell air supply system for airplane applications

Low ambient pressures at elevated flight altitudes lead to power losses in fuel cell powered aircrafts. As countermeasure ambient air can be pressurized with a suitable fuel cell air supply system. In this study the influence of low ambient pressures and pressure losses within the system on the performance of two turbo compressors and the resulting stack power are examined theoretically and the findings validated experimentally. Results show that decreasing ambient pressures and pressure losses in front and after the compressor reduce the maximum pressure from 2.4 to 1.6 bar(a) in the examined system. Air compression may require a significant share of the fuel cell stack power and the maximum system power is reduced from 54 to 41 kW. For air pressures higher than 1.8 bar(a) the fuel cell stack power gain due to pressurization is found to be cancelled out by the increasing power required for air compression.

Experimental Study on The Performance of FCV in Standard Test Cycle

The experiments of one FCV (Fuel Cell Vehicle) are conducted in three standard cycle conditions of NEDC (New European Driving Cycle), WLTC (Worldwide Light-duty Test Cycle) and CLTC (China Light-duty vehicle Test Cycle), and the performance of stack power, temperature and system efficiency are compared and analysed. Results show that the variation range of fuel cell system efficiency is ordered as: WLTC > NEDC > CLTC. The efficiency of fuel cell system is highest in CLTC; the fuel cell stack power and temperature are relatively low; the hydrogen consumption is lowest(0.93kg/100km). According to the analysis on experimental data of FCV in NEDC, the output power of stack is proportional to accelerator pedal when the accelerator pedal opening is greater than 25%.

Fault diagnosis of thermal management system in a polymer electrolyte membrane fuel cell

One of the barriers for commercialization of polymer electrolyte membrane fuel cell system is its reliability. One good solution for reliability improvement is to develop fault diagnosis model. This study suggests a diagnostic method for polymer electrolyte membrane fuel cell thermal management system. With the increase of fuel cell stack power these days, waste heat from the stack also increased and thereby thermal management system is also receiving attention. In this study, thermal management system fault experiments are repeatedly performed under various loads and stack degradation conditions. With the degradation of stack, waste heat from the stack increases and fault response as well as its impact on the system varies. The diagnosis model developed in this study detects faults on component-level and diagnoses severity of the faulty components. Furthermore, the diagnosis model is applicable to fuel cell system with degraded stack. In the process of model development, single-task learning technique is applied to neural network diagnosis model for higher diagnostic accuracy and compared with conventional multi-task learning technique.

Common grounded wide voltage‐gain range DC–DC converter for fuel cell vehicles

In order to meet the requirements of the fuel cell stack power interface converter applied in the fuel cell vehicles, a common ground wide voltage-gain range DC-DC converter is proposed. On the input voltage side, an interleaved structure is adopted in this converter to reduce the input current ripple. On the output voltage side, two series capacitors are combined with a diode-capacitor structure to improve the voltage gain and reduce the voltage stress of power semiconductors and capacitors. As a result, the efficiency and reliability of the proposed converter can be improved. The operating principle, steady-state characteristic, parameter design, efficiency calculation, and comparison with other converters are analysed. A 1.6 kW prototype of the proposed converter with the 400 V output voltage has been developed to validate the analytical results. Theoretical analysis and experimental results show that the proposed converter can meet the requirements of a fuel cell stack power interface converter and is suitable for use as a fuel cell stack power interface converter applied in fuel cell vehicles.

Microbial fuel cell stack power to lithium battery stack: Pilot concept for scale up

A stack to stack microbial fuel cell power to batteries storage was investigated on the pilot scale with the aim to scale up in future. A 12 unit MFC-stack, equipped with maximum power point tracking (MPPT) and lithium polymer batteries (3.7 V), was set up. The MFC-stack architecture was simplified by sharing partially electrolytes. The serial 12 unit MFC-stack was first used as a linear assembly of all MFC units and then subdivided into three MFC-sub-stacks which enhanced power extraction by 8.5 times. To balance the stack power generation, the external circuits were alternated into zigzag, braid and random figurations as well in rational directed configurations. Finally, batteries permutation along with MPPT enabled faster and balanced lithium battery stack charging. Balanced conditions resulted in time shift oscillations, the absence of unwanted power pooling and voltage reversals. All in all, the work showed how to generate and store power from an 12 L microbial fuel cell stack with partly common electrolytes.

Freeze start drive cycle simulation of a fuel cell powertrain with a two-phase stack model and exergy analysis for thermal management improvement

This paper integrates a two-phase fuel cell stack model, previously published and validated in Tang et al. (2017) for the specific purpose of investigating freeze start behavior, into a full-hybrid fuel cell powertrain model to simulate cold start. The aim of the simulation is to provide an overview of exergy loss distribution during a cold start drive cycle scenario. Another intention is to propose a methodology for suggesting the directions in thermal management development. The powertrain model simulates an Artemis-like transient drive cycle starting from −20 °C. The heater-core bypass and fuel cell stack power threshold are selected as representative thermal/energy management options. To evaluate the impact of the selected options on the warm up, the accumulated energy consumption and exergy flow rates are analyzed. The statistics from our simulation show that the inefficient energy consumption occurs mainly in the city stage shortly after the successful freeze start. The tank-to-wheel efficiency merely achieves 10.3% in the city stage, while the fuel cell stack can reach nearly 73% exergy efficiency throughout the entire drive cycle and tank-to-wheel efficiency reaches 29.3% at the end of the whole drive cycle. The improvement is suggested to be focused in the low power demand stages by cutting down to the actual power ratio needed and simultaneously minimize the relevant thermal-hydraulic inertia. Several optimization directions such as cascaded fuel cell stack alignment, split cooling and power demand threshold for active rapid warm up are drawn. The established fuel cell powertrain model combined with exergy analysis is a suitable methodology for further detailed thermal and energy management investigations.

Study on the operating pressure effect on the performance of a proton exchange membrane fuel cell power system

Proton exchange membrane fuel cell is a promising clean energy conversion device. Proton exchange membrane fuel cell power system has great potential in the automotive applications. A fuel cell stack and an air compressor are two important components in a fuel cell power system and it is meaningful to study their properties for better system performance. The aim of this study is to enhance the performance of a 20kW vehicular proton exchange membrane fuel cell power system incorporating a fuel cell stack and an air compressor, through the cathode operating pressure optimization. The fuel cell stack is investigated numerically and the air compressor characteristics are obtained experimentally. The fuel cell stack and the air compressor are matched properly, and then the operating pressure optimization for the power system is carried out. The results of this study show that the fuel cell stack power generation is increased with the system operating pressure. The compressor power consumption is also increased with the system operating pressure, but it can be reduced by using a two-speed compressor operation mode. The optimum system operating pressure is found to be 1.2atm. The optimum system operating pressure is influenced by the compressor efficiency and is increased with the compressor efficiency.

Elektryczny samochód zasilany ogniwem wodorowym. Alternatywa dla zasilania akumulatorowego?

Elektryczny samochód zasilany ogniwem wodorowym. Alternatywa dla zasilania akumulatorowego?

Performance and Limitations of 3D-Printed Bipolar Plates in Fuel Cells

3D-printing is being touted as a tool for prototyping and manufacturing metal fuel cell bipolar plate (BPP) designs as it may speed development and lower costs by avoiding costly tooling, plus the 3D parts can be made as a single piece without welding. We use the 3D-printing method of direct metal laser sintering (DMLS) to make 21 cm2 titanium-alloy BPPs with embedded flow channels. To minimize the contact resistance in an individual cell, the surface of each BPP is polished to the appropriate roughness and coated with a conductive corrosion barrier. The coated BPPs are assembled with the appropriate seals, catalyst coated membranes and gas diffusion layers into both a single-cell and a 40-cell stack and tested. The single-cell stack performs well compared to a standard, but the 40-cell fuel cell stack power is 400 W, or 20% less than expected due to inadequate flatness of several of the DMLS BPPs. This cell-to-cell mismatch leads to high contact resistance in several of the cells. DMLS clearly shows the benefit of being able to make complex flow fields and hollow parts with no welds and is useful for prototyping flow fields in single cells or short stacks. More work is needed toward reducing the weight and increasing the flatness of BPPs made by DMLS before they can be used in larger stacks.

Performance of 3D-Printed Fuel Cells and Stacks

Additive manufacturing (AM) is being touted as a possible tool for rapid prototyping fuel cell bipolar plate (BPP) designs. We use the AM method of direct metal laser sintering (DMLS) to make 21 cm2 titanium-alloy BPPs with embedded flow channels. The surface of the BPPs is then polished to the appropriate roughness and coated with a conductive corrosion barrier. The coated BPPs are assembled with the appropriate seals, catalyst coated membranes and gas diffusion layers into a 40-cell stack and tested. The resulting 400 W fuel cell stack power is 20% less than expected because of inadequate flatness of several of the DMLS BPPs as determined by white light profilometry, leading to high contact resistance. While DMLS clearly shows the benefit of being able to make complex flow fields and hollow parts with no welds, more work is needed toward reducing the weight and increasing the flatness of BPPs made by AM.

Simulation and Test of a Fuel Cell Hybrid Golf Cart

This paper establishes the simulation model of fuel cell hybrid golf cart (FCHGC), which applies the non-GUI mode of the Advanced Vehicle Simulator (ADVISOR) and the genetic algorithm (GA) to optimize it. Simulation of the objective function is composed of fuel consumption and vehicle dynamic performance; the variables are the fuel cell stack power sizes and the battery numbers. By means of simulation, the optimal parameters of vehicle power unit, fuel cell stack, and battery pack are worked out. On this basis, GUI mode of ADVISOR is used to select the rated power of vehicle motor. In line with simulation parameters, an electrical golf cart is refitted by adding a 2 kW hydrogen air proton exchange membrane fuel cell (PEMFC) stack system and test the FCHGC. The result shows that the simulation data is effective but it needs improving compared with that of the real cart test.

Decay Analysis of a 5kW PEMFC Stack in Sightseeing Bus

This paper deals with the decay of hydrogen-air proton exchange membrane fuel cell (PEMFC) stack, which has been used for three years, installing a 5kW fuel cell stack in a sightseeing bus to do the experiment, including road test and bench test. The results indicate that the hydrogen-air fuel cell stack power performance declines a lot, whose power conspicuously drops from 5kW to nearly 2.5kW, compared with that of a new one. There are many reasons of its decline, such as, proton membrane penetration and electrode destruction etc. It proves that the stack needs reasonable care and maintenance; otherwise, it tends to be easily exhaustive and thus greatly increases costs.