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With the gradually accelerating pace of global decarbonization, highly efficient and clean proton exchange membrane fuel cells (PEMFCs) are considered to be an energy solution for the future. During the operation of a fuel cell, it is necessary to keep the internal proton exchange membrane in a good state of hydration, so an appropriate method of detecting the hydration state is essential. At present, fuel cell systems are rapidly developing towards high power, but methods for detecting the hydration state of high-power fuel cell systems are still relatively lacking. Therefore, this paper studies the hydration state of high-power fuel cell systems and builds a condensation tail-gas water collection device for calculating the water flow out of a fuel cell system, deriving the hydration status inside the high-power fuel cell system. To verify the proposed water balance model, a series of experiments were conducted based on controlled variables such as working temperature, air metering ratio, and load current. Experiments were conducted on a 100 KW fuel cell system to collect water flow from the fuel cell system. Finally, based on the experimental data, the change rate of the internal water content of the fuel cell system under different conditions was calculated. The results show that, under the same load current, as the working temperature and air metering ratio increase, the change rate of the internal water content of the fuel cell system gradually decreases. Therefore, at low power, it is necessary to maintain an appropriate working temperature, while at high power, maintaining an appropriate air metering ratio is more important. [ABSTRACT FROM AUTHOR]

As one of the important ways to utilize hydrogen energy, fuel cells are receiving more and more attention and research from countries and institutions. To meet the practical needs of testing the performance of high-power fuel-cell systems and simulate the actual application environment as much as possible, a fuel-cell system test bench is usually used to test the system performance, in which the cooling-temperature control of the test bench has a great impact on the results of the performance of the fuel-cell system. This paper studies the cooling-temperature control strategy of a 150-kW-class fuel-cell engine test platform, proposes a new test-bench cooling-system structure with a thermostat and heat exchanger as the main heat-dissipation components, and compares and analyzes the impact of coordinated thermostat and heat-exchanger control on the fuel-cell system test performance. The test results show that the control strategy of the coordinated operation of a thermostat and heat exchanger can maintain the steady-state error to within ±0.3℃ and maintain the temperature variation to within ±1.5℃ during the loading-condition test, so as to avoid the limitation of system output performance due to excessive cooling-temperature fluctuation and ensure that the fuel-cell engine performance-test process is carried out smoothly and efficiently. [ABSTRACT FROM AUTHOR]

Proton-exchange-membrane fuel cells (PEMFCs) have the characteristics of zero emissions, a low operating temperature and high power density, and have great potential in improving energy-utilization efficiency. However, fuel cells are still quite expensive as a result of the cost of key components, including the membranes, catalysts and bipolar plates of PEMFCs. As a result of the cost and importance of these items, most researchers have focused on improving the lifetime and performance of fuel-cell stacks in recent years. In contrast, seals, sealants and adhesives play a more mundane role in the overall performance of a fuel cell, but failure of these materials can lead to reduced system efficiency, system failure and even safety issues. Little attention has been paid to the performance and durability of these products but as other fuel-cell components improve, these seals are becoming an even more critical link in the long-term performance of fuel cells. This article highlights the importance and background of fuel-cell seals. The latest research progress on the mechanical properties and structural optimization of different sealing materials is reviewed. [ABSTRACT FROM AUTHOR]

The fuel cell reliability and durability are still the main factors limiting the large scale commercialization. To a certain degree, water content, transportation, distribution and state in the fuel cell influence the fuel cell State of Health (SOH). However, it's very difficult to measure water content inside fuel cell directly. The PEMFC system voltage fluctuate during hydrogen purging process, due to the removal of liquid water will affect the reactants transformation. Different internal water content will cause different voltage fluctuations. For this characteristic, The Energy Intensity of Reconstructed Vibrating Voltage (EIV) based on wavelet transformation is proposed and validated in this paper. The boundary value of EIV is determined to be 0.1 through experiments. The results show that the fuel cell voltage drop is reduced to 0.32 V/h from 1.39 V/h by using this method to avoid anode flooding. By several PEMFC system experiment results in test bench, this method can diagnosis the water content in PEMFC properly. • A PEMFC system voltage fluctuation model during hydrogen purge process is established. • A water content diagnosis algorithm is designed based on wavelet transformation. • The water content in PEMFC can be diagnosed properly without any other hardware. [ABSTRACT FROM AUTHOR]

Temperature and humidity are important parameters in the operation of proton exchange membrane fuel cell (PEMFC), which have an important impact on the performance of fuel cell. Fuel cell test platform is an important tool to study the performance of fuel cells, and its temperature and humidity control module is also the key in the research process of the test platform, so that it can provide the gas with precise temperature and humidity control during the test process of the fuel cell. In this paper, a humidifier combined with bubbling and spraying is adopted for the application of test platform, and the numerical simulation model of the humidifier is established. According to the model, the influence of operating conditions of humidifier on humidification performance is verified, such as inlet air velocity and the humidifying water temperature. The results indicate that the inlet air velocity and the humidifying water temperature have great influence on the humidifying performance of the humidifier. The humidifying performance decreases with the increase of the inlet air velocity and increases with the increase of the humidifying water temperature respectively. In addition, the humidification performance of the humidifier is verified. [ABSTRACT FROM AUTHOR]

Electrochemical impedance spectra is a useful tool for fuel cell water content analysis. However, the data processing efficiency is greatly reduced with the increment in the number and complexity of the experimental parameters. Thus, in this work, an impedance prediction model is developed to assess the impacts of operating conditions and cell position on fuel cell impedance. The model is based on the Randles equivalent circuit and convolutional neural networks. And after verification, this model shows satisfactory performance in impedance prediction. Based on the model, impedance parameters and impedance spectra can be obtained rapidly for any operating condition and cell position. By directly predicting the impedance parameters, a more detailed description about the impact of different operating conditions on internal state of fuel cell can be given. The model can be integrated into the fuel cell control system and determine the optimal operating parameters. • A CNNs model is used to predict the impedance parameters of the PEMFC. • The model can obtain impedance parameters rapidly under any operating condition. • The internal state of fuel cells can be analyzed based on the impedance parameters. • The optimal operating parameters can be determined more easily. [ABSTRACT FROM AUTHOR]

Abstract In the fuel cell system, hydrogen recirculation subsystem is usually used to increase efficiency of hydrogen usage. While the hydrogen recirculation subsystem is a closed circuit that the water might be accumulated, water separator is used necessarily to separate the water and gas at the anode side. As the poor swirling effect caused by the guide vane in commercial separator, a novel water separator for proton exchange membrane fuel cell system is designed and the flow field characteristics of the separator are gained by computational fluid dynamics. The structure of volute inlet and overflow pipe in the novel separator can enhance the swirling flow and increase the tangential velocity. Based on the results, the separation efficiency and steady performance throughout the flow-rate range can be improved by the novel water separator. Highlights • A novel water separator of high efficiency was designed for PEMFC system. • Volute inlet and overflow pipe enhanced the swirling flow by more than 2.5 times. • Water separation efficiency of the novel separator was improved to nearly 100%. [ABSTRACT FROM AUTHOR]

[Display omitted] • Voltage recovery after shutdown relates to water redistribution in fuel cells. • Recoverable voltage loss is limited at low current, compared to high current. • Water redistribution in the catalyst layer may take longer than that in the PEM. • Consistency of voltage recovery depends on water content within CL of single cells. • Maintaining internal water content during shutdown favors voltage recovery. The reversible degradation of proton exchange membrane fuel cells (PEMFC) restricts the high efficiency and long-term durability of fuel cells. The reversible loss, restorable only through specific procedures, significantly diminishes both the operational efficiency and the predictability of their remaining service life. Consequently, it is imperative to elucidate the recovery characteristics of reversible loss in high power PEMFC stacks for engineering applications. However, most of the studies focus on small-area single cells or short stacks, researches on the full-size stacks considering the uniformity and consistency differences are scarce. The recovery characteristics of high-power PEMFC stacks remain unclear. Therefore, in this work, an accelerated stress test with the idle and rated currents as the boundary of the cyclic condition was designed for a 100 kW PEMFC stack to investigate the recovery characteristics. The periodic voltage fluctuations along with the shutdown operations indicate that the voltage recovery may be caused by the redistribution of water content within the stack, and the reversible degradation is more pronounced and readily reversible under the high current condition. The impedance results suggest that the redistribution of water within the catalyst layer takes longer compared to that in the membrane. Furthermore, analyses of single cell voltage indicate that the consistency of voltage recovery is more closely related to variations of water content within the catalyst layer. Cells with higher water content exhibit better voltage recovery. [ABSTRACT FROM AUTHOR]

The performance of hydrogen ejectors can be affected by the working conditions of the fuel cell system especially associating with the working pressure and pressure drop of the anode. However, the pressure drop characteristics model of the anode is correlated to the fuel cell parameters. In this work, a porous jump boundary is used as a pressure drop characteristics model of the anode which is weakly relevant to the parameters of fuel cells by employing the pressure drop characteristic curve of fuel cells. Based on the model, the influence of the condition parameters on the property of the ejector can be predicted. According to our results, the entrainment performance of the ejector can be influenced by anode inlet temperature, relative humidity, and differential pressure. Also, it is helpful for the design and prediction of the ejector in different fuel cell systems depend on the pressure drop. • Porous jump boundary model can simulate the stack pressure drop characteristic. • The fuel cell parameters are not required in the pressure drop model. • Optimal ejector structure can be found by coupling the pressure drop characteristic. • The performance of the ejector is predicted accurately with pressure drop response. [ABSTRACT FROM AUTHOR]

• Vibration measurements and analysis of powertrain components and the FC in FCVs. • Quantitative analysis of the contribution of components to the vibration of the FC stack. • Analysis of the vibration effect on FC performance by in-situ FC vibration test. The proton exchange membrane fuel cell (PEMFC) in fuel cell (FC) vehicles (FCVs) is always operating in a vibration environment, which can affect the FC output performance. This effect will bring new challenges in terms of NVH (Noise, Vibration and Harshness) and should be investigated during the development of FCVs. This paper proposes an investigation method for the short-term effect of vibration on the output performance of the FC in FCVs. The method is generalized as a procedure with four stages. Firstly, the vibrations of powertrain components and FC are measured by performing measurements on overall FCV, considering different driving maneuvers and environments. The characteristics of components' vibrations are then identified and the vibration environment of the FC in the FCV is investigated by conducting vibration and contribution analysis. The analysis results are used to derive the vibration cases for the in-situ FC vibration test in the last stage to investigate the vibration effect on the FC performance. In general, vibration reduces the output power of FC by about 2% compared to the case without vibration. The fluctuation of FC power under vibration is also increased. Different FC orientations can also affect its performance, and this effect can be enlarged when vibrations are introduced. In the worst case, vibration can cause a power reduction of more than 9%. In addition, the sensitivity of the FC output power to different types of excitation varies. The knowledge obtained during the investigation provides the basis for the NVH development and optimization with the aim of improving FC output performance. [ABSTRACT FROM AUTHOR]