Composite anode for CO tolerance proton exchange membrane fuel cells

Fuel of proton exchange membrane fuel cells (PEMFC) mostly comes from reformate containing CO, which will poison the fuel cell electrocatalyst. The effect of CO on the performance of PEMFC is studied in this paper. Several electrode structures are investigated for CO containing fuel. The experimental results show that thin-film catalyst electrode has higher specific catalyst activity and traditional electrode structure can stand for CO poisoning to some extent. A composite electrode structure is proposed for improving CO tolerance of PEMFCs. With the same catalyst loading, the new composite electrode has improved cell performance than traditional electrode with PtRu/C electrocatalyst for both pure hydrogen and CO/H₂. The EDX test of composite anode is also performed in this paper, the effective catalyst distribution is found in the composite anode.     

A novel design for humidifying an open-cathode proton exchange membrane fuel cell using anode purge

The low performance of open-cathode proton-exchange-membrane fuel cells (OCPEMFCs) is attributed to the low-humidity ambient air supplied to the cathode using electric fans. To improve the OCPEMFC performance, this paper proposes a novel humidification method by collecting water purged from the anode and supplying it to the open cathode. The OCPEMFC performance is evaluated at various humidifier distances from the cathode inlet, and it is compared with that where no humidifier is used when the OCPEMFC operates under three different current levels of 1, 5, and 8 A. The results show that the novel design improves the stack power, and optimal performance is achieved at a humidifier distance of 2 cm. The energy efficiency achieves an improvement between 1.4% and 1.8% when a humidifier is used.     

A gas management strategy for anode recirculation in a proton exchange membrane fuel cell

The anode configuration and gas management strategy are two of factors that affect the energy efficiency of a proton exchange membrane fuel cell. In order to improve the hydrogen utilization, unused hydrogen can be recirculated to the inlet using a pump. However, impurities diffusing from the cathode to the anode may cause the dilution of hydrogen in the anode. As a result, a gas management strategy is required for the anode recirculation configuration. In this preliminary study, a novel configuration for anode recirculation and a gas management strategy are proposed and verified by experiments. Two valves are installed in the recirculation line. The anode is operated in four modes (dead-end, recirculation, compression, and purge), and the real-time local current density (LCD) is monitored for gas management purposes. The results show that the LCD distribution is uniform during the recirculation mode and nonuniform during the dead-end and compression modes. With this configuration and gas management strategy, the cycle duration is increased by a factor of 6.5.     

Cobalt molybdenum carbides as anode electrocatalyst for proton exchange membrane fuel cell

Cobalt molybdenum (Co-Mo) carbides were prepared by the carburization of Co-Mo oxides at temperatures of 723–973 K in a stream of CH₄/H₂ gas. The carburized catalysts were evaluated using a single-stack fuel cell and three-electrode cell. The results showed high activities for the anodic electrooxidation of hydrogen over the Co-Mo catalysts carburized at 873 and 923 K. The 873 K carburized Co-Mo catalyst had the highest activity and achieved 10.9% of the performance of a commercial Pt/C catalyst in a single-stack fuel cell. The XRD, TPC, TPR and XPS results showed that the Co-Mo oxycarbide in the bulk and on the surface are the active species for the hydrogen oxidation reaction.     

Investigation of the temperature‐related performance of proton exchange membrane fuel cell stacks in the presence of CO

H₂ is generally used as the fuel in proton exchange membrane fuel cells (PEMFCs). However, H₂ produced from reformate gas usually contains a trace of CO, which may severely affect the fuel cell performance. With the adoption of domestic short side chain, low equivalent weight perfluorosulphonic acid (PFSA) membrane, a 100 W stack is built and evaluated at elevated temperature of 95 °C for the purpose of improving its CO tolerance. The stack is operated with 5 ppm, 10 ppm and 20 ppm CO/H₂, respectively; better performance is obtained as expected. Furthermore, a 5 kW PEMFC stack is prepared with home‐made Ir–V/C and Pt/C as anode catalysts for the membrane electrode assemblies to compare their CO tolerance. Physical and electrochemical characterizations, such as transmission electron microscope and linear scan voltammogram are employed for catalyst investigation. The results demonstrate that the employment of domestic PFSA membrane enables the stack to be operated at 95 °C, which can improve the CO tolerance of all the anode catalysts. In addition, the effect of CO on cell polarization is insignificant at lower current densities. Under the same operating conditions, cells with Ir–V/C catalyst show better CO tolerance. Copyright © 2013 John Wiley & Sons, Ltd.     

Thickness effects of anode catalyst layer on reversal tolerant performance in proton exchange membrane fuel cell

Real-world driving conditions will likely cause hydrogen starvation at the anode chambers of stacks to trigger voltage reversal events, posing a tremendous challenge to the durability of proton exchange membrane fuel cells (PEMFCs). The reversal-tolerant anode (RTA), a material-based solution, that inclusion of oxygen evolution reaction (OER) catalyst into the anode is usually employed to cope with the voltage reversal issue. In this work, we investigate the impact of anode catalyst layer thickness on the voltage reversal performance of the membrane-electrode assemblies (MEAs) with conventional anodes (Pt/C catalyst) and RTAs doped with IrO₂ catalyst, a representative OER catalyst. We find that regardless of how thick the anode catalyst layer is, the conventional MEAs exhibit almost similar voltage reversal behaviors and times, only about 1 min to reach the shutdown voltage (?2.5 V). As for the RTA MEAs, a surprising thickness effect that the thinner RTA with the same IrO₂ loading shows superior voltage reversal tolerance. Notably, an ultra-thin RTA (~2 μm) exhibits the reversal tolerance time of 310 min, which is five times higher reversal tolerance time than most of the reported RTAs. We conclude that this thickness effect mainly results from the ionomer distribution on the OER catalyst. Besides, we observe that the RTA with a higher ionomer content shows the better reversal tolerance performance. Our work highlights the importance of the OER Triple-Phase-Boundary (TPB) and the need for improved electrode designs for robust RTAs.     

质子交换膜燃料电池的稳态分析

通过建立质子交换膜燃料电池稳态模型,考察了电堆温度和反应压力对电堆性能的影响。仿真结果表明,升高电堆温度使得氢气分压和氧气分压下降,但氢气分压下降的更快;在电堆工作温度范围内,电堆温度升高,热动力电势、欧姆极化电势和活化极化电势均下降,但电堆总输出电压上升;提高阴极侧压力有利于提高热动力电势,同时使得活化极化电势降低,有利于电堆整体性能的改善;提高阳极侧压力对电堆性能改善影响不大。     

Novel closed anode pressure-swing system for proton exchange membrane fuel cells

To overcome the low system efficiency and fuel efficiency in conventional recirculation systems and purging systems, a new anode closed pressure-swing system for proton exchange membrane fuel cells (PEMFCs) is proposed in this paper. Only two pressure regulators set at different pressures and a buffer tank are applied to produce pressure-swing inside the anode through the process of hydrogen feed and reaction, thereby achieving the anode-dead-end (ADE) operation (no purging). This system was successfully tested on a 20-cell open-cathode stack. The results indicate that the performance of the stack with the developed system is stable and efficient over 13,000 s, while its performance in ADE mode without purging deteriorates rapidly because of active area reduction. It can be concluded that the pressure swing system provides the following advantages: close to 100% hydrogen utilization; improved stack performance of around 12.5% for the power compare to the ADE mode with intermittent purging at 12 V load; improved humidification of the anode and membrane; and ease of implementation as there are no extra pumps.     

A novel densely connected neural network for proton exchange membrane fuel cell fault diagnosis

It is of great significance to perform proton exchange membrane fuel cell (PEMFC) fault diagnosis and take action timely to mitigate or even eliminate the faults, which can strengthen PEMFC reliability and durability. In previous studies, cell voltage is extensively used for PEMFC fault diagnosis. However, there exists similar cell voltage drop phenomenon as different PEMFC faults occur, especially for faults like flooding and air starvation having extremely similar voltage dynamic variation, which makes it difficult to capture the features sensitive to faults. Moreover, cell voltages collected from different MEAs follow different distributions even in the same operation condition, which challenges the diagnosis consistency of fault diagnosis methods. In this paper, in order to break through the hindrances, a novel densely connected neural network codenamed Inc-DenseNet is proposed for PEMFC fault diagnosis, which integrates advantages of InceptionNet and DenseNet to extract more specific and robust features from cell voltage. In the analysis, the collected PEMFC voltage signal is transformed into 2D image data, which is then used to train the Inc-DenseNet. Results demonstrate that with the trained Inc-DenseNet, the diagnostic accuracy for four PEMFC states of health (normal, flooding, dehydration, air starvation) can reach 95.3%, especially for flooding and air starvation. In addition, by using the voltage datasets collected from two different MEAs, the generalization capacity of the Inc-DenseNet is proved. With the findings, the proposed network Inc-DenseNet can not only achieve high-precision fault diagnosis, but also has a high computing efficiency, which makes it promising in real-time PEMFC fault diagnosis in the future.     

Ti4O7 supported IrOx for anode reversal tolerance in proton exchange membrane fuel cell

Fuel starvation can occur and cause damage to the cell when proton exchange membrane fuel cells operate under complex working conditions. In this case, carbon corrosion occurs. Oxygen evolution reaction (OER) catalysts can alleviate carbon corrosion by introducing water electrolysis at a lower potential at the anode in fuel shortage. The mixture of hydrogen oxidation reaction (HOR) and unsupported OER catalyst not only reduces the electrolysis efficiency, but also influences the initial performance of the fuel cell. Herein, Ti₄O₇ supported IrO_x is synthesized by utilizing the surfactant-assistant method and serves as reversal tolerant components in the anode. When the cell reverse time is less than 100 min, the cell voltage of the MEA added with IrO_x/Ti₄O₇ has almost no attenuation. Besides, the MEA has a longer reversal time (530 min) than IrO_x (75 min), showing an excellent reversal tolerance. The results of electron microscopy spectroscopy show that IrO_x particles have a good dispersity on the surface of Ti₄O₇ and IrO_x/Ti₄O₇ particles are uniformly dispersed on the anode catalytic layer. After the stability test, the Ti₄O₇ support has little decay, demonstrating a high electrochemical stability. IrO_x/Ti₄O₇ with a high dispersity has a great potential to the application on the reversal tolerance anode of the fuel cell.     

A novel intersectant flow field of metal bipolar plate for proton exchange membrane fuel cell

A novel intersectant flow field of metal bipolar plate for proton exchange membrane fuel cell (PEMFC) was proposed. The bionics, fractal theory, and Murray's law were employed to design the novel flow field to decrease the drag force for the reaction medium and product. Computational fluid dynamics method was employed to investigate the performance of the novel flow field. The performance of traditional serpentine flow field was compared with the said one to calibrate the efficiency of the novel design of flow field. A test system of PEMFC was assembled to validate the reliability of the numerical simulation. The metal bipolar plates with the intersectant flow field were fabricated by electro discharge machining for the test. The surface treatment of the bipolar plate was conducted. Results showed that the novel flow field exhibited some advantages than the serpentine flow field in terms of the uniform distribution of reaction medium and exhausting of reaction product. The polarization curve also released that the novel flow field owned the higher power and current density. The experimental results certified the accuracy of numerical simulation and validated the advantage of the novel flow field in promoting the efficiency of PEMFC. Copyright © 2017 John Wiley & Sons, Ltd.     

A novel online degradation model for proton exchange membrane fuel cell based on online transfer learning

A novel online degradation prediction model is proposed to prognosticate the future degradation trend (FDT) of proton exchange membrane fuel cell (PEMFC) stack in this paper. In order to overcome the fact that existing FDT prediction methods of PEMFC stack based on data-driven model rely on the assumption that the operating conditions of the training data and testing data need to be consistent, an end-to-end prediction algorithm based on the combination of transfer learning and transformer neural network, referred to as TLTNN, is proposed to predict the FDT of PEMFC stack. Besides, in order to demonstrate the effectiveness and superiority of the proposed method in prognostics tasks of PEMFC stack FDT, the prediction performance is validated on the PEMFC test system. The results show that the RMSE, MAE and MAPE values of the predicted degradation voltage are 0.00598 V, 0.004842 V and 0.1518%, respectively, which indicates that the proposed TLTNN strategy based on transfer online learning can be used to predict the degradation voltage of PEMFC stack and the superiority of the proposed method is better, thus solving the problem that the distribution of training and test data must be the same in traditional machine learning models.     

Effects of anode and cathode perforated flow field plates on proton exchange membrane fuel cell performance

The effects of both anode and cathode perforated flow field configurations on proton exchange membrane fuel cell performance are studied herein through electrochemical polarization techniques, electrochemical impedance spectroscopy, and cyclic voltammetry. The results demonstrate that serpentine flow field configuration in both anodes and cathodes is the best arrangement for cell performance (serpentine/serpentine, perforated/perforated, and serpentine/perforated). An electrochemical impedance spectroscopy examination shows that the serpentine/serpentine flow plate configuration results in a significant reduction in charge transfer resistance in a high current density (low voltage) regime. It further indicates that in a serpentine/serpentine flow pattern, a maximum electrochemical area is obtained with a higher Pt utilization of about 70% and is secured with full hydration at a cell temperature of 80°C. Finally, energy and exergy efficiencies analyses were also made. Data have been extracted and presented. Copyright © 2013 John Wiley & Sons, Ltd.     

Performance of carbon-supported PtPd as catalyst for hydrogen oxidation in the anodes of proton exchange membrane fuel cells

In this work, the replacement of platinum by palladium in carbon-supported catalysts as anodes for hydrogen oxidation reaction (HOR), in proton exchange membrane fuel cells (PEMFCs), has been studied. Anodes with carbon-supported Pt, Pd, and equiatomic Pt:Pd, with various Nafion^® contents, were prepared and tested in H₂|O₂ (air) PEMFCs fed with pure or CO-contaminated hydrogen. An electrochemical study of the prepared anodes has been carried out in situ, in membrane electrode assemblies, by cyclic voltammetry and CO electrooxidation voltammetry. The analyses of the corresponding voltammograms indicate that the anode composition influences the cell performance. Single cell experiments have shown that platinum could be replaced, at least partially, saving cost with still good performance, by palladium in the hydrogen diffusion anodes of PEMFCs. The performance of the PtPd catalyst fed with CO-contaminated H₂ used in this work is comparable to Pt, thus justifying further work varying the CO concentration in the H₂ fuel to assert its CO tolerance and to study the effect of the Pt:Pd atomic ratio.     

Flexible micro sensors for in-situ diagnosis of proton exchange membrane fuel cell

The temperature and flooding phenomenon during operation can strongly influence a proton exchange membrane fuel cell (PEMFC) performance. Non-uniform conditions exist in each segment of fuel cell. Previous studies have investigated these conditions on the mm scale using destructive methods or simulation, but none has been able to obtain exact data from within the fuel cell.     

A novel method for preparing proton exchange membrane fuel cell electrodes by the ultrasonic-spray technique

A novel ultrasonic-spray method for preparing gas diffusion electrodes (GDEs) for proton exchange membrane fuel cell (PEMFC) is described. Platinum (Pt) loaded on Nafion^®-bonded GDEs were prepared by the ultrasonic-spray method on various commercial woven and non-woven gas diffusion layers (GDLs) at several Pt loadings in the range of 0.40-0.05 mg cm⁻². The ultrasonic-sprayed GDEs were tested and compared to commercial and hand-painted GDEs. It was found that the GDEs prepared by the ultrasonic-spray method exhibited better performances compared to those prepared by the hand-painting technique, especially at low Pt loadings. GDEs fabricated by the ultrasonic-spray method with a platinum loading of 0.05 mg cm⁻² exhibited a peak power rating of 10.9 W mg⁻¹ compared to 9.8 W mg⁻¹ for hand-painted GDEs. For all experiments using various GDLs, Sigracet SGL 10BC exhibited the best performance with a peak power of 0.695 W cm⁻².     

A novel strategy based on salp swarm algorithm for extracting the maximum power of proton exchange membrane fuel cell

Cell temperature and water content of the membrane have a significant effect on the performance of fuel cells. The current-power curve of the fuel cell has a maximum power point (MPP) that is needed to be tracked. This study presents a novel strategy based on a salp swarm algorithm (SSA) for extracting the maximum power of proton-exchange membrane fuel cell (PEMFC). At first, a new formula is derived to estimate the optimal voltage of PEMFC corresponding to MPP. Then the error between the estimated voltage at MPP and the actual terminal voltage of the fuel cell is fed to a proportional-integral-derivative controller (PID). The output of the PID controller tunes the duty cycle of a boost converter to maximize the harvested power from the PEMFC. SSA determines the optimal gains of PID. Sensitivity analysis is performed with the operating fuel cell at different cell temperature and water content of the membrane. The obtained results through the proposed strategy are compared with other programmed approaches of incremental resistance method, Fuzzy-Logic, grey antlion optimizer, wolf optimizer, and mine-blast algorithm. The obtained results demonstrated high reliability and efficiency of the proposed strategy in extracting the maximum power of the PEMFC.     

Hydrogen utilization enhancement of proton exchange membrane fuel cell with anode recirculation system through a purge strategy

Proton exchange membrane (PEM) fuel cells are widely considered as potential alternative energy candidates for internal combustion engines because of their low-temperature start, high energy density, and ease of scale up. However, their low hydrogen utilization rate is one of the main reasons for the limited commercial development. This study focuses on improving the hydrogen utilization rate of PEM fuel cells and system efficiency using optimal active recirculation system (ARS). An anode ARS and purging strategy are introduced to enhance the hydrogen utilization rate of PEM fuel cells. An ARS simulation model with purge strategy model is developed in a MATLAB/Simulink environment. A control-oriented dynamic model is developed to study the hydrogen recirculation system characteristics. The dynamic model is used as basis to propose a proportional integration differentiation controller to maintain the anode hydrogen concentration and increase the hydrogen utilization rate. Several experiments are performed using different purging strategies in conjunction with ARS. The hydrogen utilization rate is the highest when the purge time is 0.3 s and the purge period is 10 s. Simulation results show that the PEM fuel cells with an anode recirculation configuration exhibit a better performance than other configurations in terms of hydrogen utilization. Experimental results also demonstrate the feasibility of the proposed system, the performance of which is also superior to that of other hydrogen supply system.     

Numerical study of optimized three-dimension novel Key-shaped flow field design for proton exchange membrane fuel cell

Key-shaped three-dimension (3D) flow field channel is designed to improve the performance and mass transfer of proton exchange membrane fuel cell (PEMFC). This study comprehensively analyses the impacts on the performance and mass transfer of the flow channel from multiple dimensions such as the size, shape, and placement of the blocks. In comparison with the conventional straight single flow field channel, the new channel with rectangular blocks can effectively improve performance by 30%. Semi-elliptical and quarter-elliptical blocks are designed to make forced convection and increase the diffusion area of oxygen. The results indicate that the flow velocity in the Z-axis direction can be increased to 0.08–0.2 m/s due to the narrow space formed by variable cross-sections. In conclusion, the Key-shaped design has a potential to improve the performance of mass transfer in the cathode channel, providing a new strategy for the development of flow field design in PEMFC field.     

A simple, analytic model of polymer electrolyte membrane fuel cell anode recirculation at operating power including nitrogen crossover

A simple, analytic model is presented that describes the steady state profile of anode nitrogen concentration in a polymer electrolyte membrane fuel cell operated with anode recirculation. The model is appropriate for fuel cells with straight gas channels and includes the effect of nitrogen crossover from cathode to anode through the membrane. The key analytic simplification in the model is that this crossover rate, when scaled to the gas flows in the channels, is small. This is a good approximation when the device is used at operating power levels. The model shows that the characteristic times for the anode nitrogen profiles to reach steady state are of the order of minutes and that the dilution effect of anode nitrogen is severe for pure recirculation. The model shows additionally that a small anode outlet bleed can significantly reduce the nitrogen dilution effect. Within the framework of the model, the energy efficiency of pure recirculation can be compared to hydrogen venting or partial anode bleeding. An optimal bleed rate is identified. The model and optimization analysis can be adapted to other fuel cell designs and operating conditions. Along with operating conditions, only two key parameters are needed: a nitrogen crossover coefficient and the marginal efficiency loss to compressors for increased anode stoichiometric gas flow.