Experimental study on the dynamic performance of an air-cooled proton exchange membrane fuel cell stack with ultra-thin metal bipolar plate

In this paper, a compact 3 kW air-cooled fuel cell stack consists of 95 single cells with metallic bipolar plate is designed. Compared with graphite bipolar plates, metal stamping bipolar plates are lighter in weight, smaller in size and faster in heat conduction, therefore the transient behaviors of the voltage and temperature of each cell are analyzed. The results show that the heat distribution of the air-cooled fuel cell is very uniform, and the temperature difference between the inlet and outlet of cathode air of the fuel cell is lower than 15 °C. The individual cell voltage uniformity percentage variation value reaches 7% when the drop in the loading current is over 25 A. Moreover, the voltage uniformity variation value is higher than 4% when the loading current output exceeds 35A. Thus, a large drop in loading and a high loading current easily increase the voltage uniformity variation value. Long-term continuous operation has a negative influence on the performance of the stack, especially the last fuel cell near the anode outlet. Anode purging can effectively alleviate the uniformity percentage variation in the voltages. The designed air-cooled fuel cell exhibits good performance and strong environmental adaptability.     

Experimental study and mitigation of abnormal behavior of cell voltage in a proton exchange membrane fuel cell stack

The aim of this study is to investigate the abnormal behavior of cell voltage in a proton exchange membrane fuel cell stack and a mitigation strategy. The proposed strategy is simple and requires only a three‐way solenoid valve to replace the direct way solenoid valve of the original system. It is applied to a proton exchange membrane fuel cell stack with a dead‐ended anode to verify its validity. The behavior of the cell voltages in the stack is discussed in detail, especially the cell reversal process. The results show that the proposed strategy can significantly reduce the severity of hydrogen starvation. And the maximum power of the stack is increased by 10.67%. It is a sudden increase related to cell reversal mitigation. Uneven hydrogen distribution is the cause of low cell voltage and cell reversal. This strategy increases the cell voltage by increasing the hydrogen content in the anode flow channel downstream. It also significantly reduces the fluctuations in cell voltage and improves the uniformity of the cell voltage. This experimental study contributes to mitigate hydrogen starvation in cells of proton exchange membrane fuel cell stacks in application.     

Corrosion behavior of TiN-coated stainless steel as bipolar plate for proton exchange membrane fuel cell

Stainless steel is a potential material to be used as the bipolar plate for proton exchange membrane fuel cell (PEFC) because of its suitable physical and mechanical properties. Several coating techniques have been applied to improve its corrosion resistance. But seldom study is focused on the microstructure evolution with corrosion. In the present study, the use of TiN-coated stainless steel as the bipolar plate is evaluated. Two surface coating techniques, pulsed bias arc ion plating (PBAIP) and magnetron sputtering (MS), are adoped to prepare the TiN-coated stainless steel. Their corrosion resistances and electrical conductivities of the coated substrates are evaluated. The performance shows strong dependance on microstructural characteristics. The corrosion of SS304/Ti₂N/TiN prepared by MS mainly occurs on the grain boundary. The corrosion of SS304/TiN prepared by PBAIP mainly takes place from the large particles on the coating. The Ti₂N/TiN multilayer coating provides superb corrosion protective layer for stainless steel. Both the TiN and Ti₂N/TiN coatings provide low contact resistance.     

质子交换膜燃料电池双极板的设计与模拟分析

质子交换膜燃料电池是直接将化学能转换为电能的装置,双极板上的流道结构对燃料电池的工作性能具有较大的影响。根据应用要求设计了具有平行流道、蛇形流道及希尔伯特分形流道的双极板结构,模拟计算了氢气在不同类型的流道和气体扩散层中的分布状态,分析了燃料电池的输出电流密度和功率密度随电极间电压的变化特点,比较了不同的流道结构对燃料电池输出电流密度的影响,以及不同的工作温度及气体压强的情况下,燃料电池输出电流密度随温度及压强的变化规律。     

Development of preform moulding technique using expanded graphite for proton exchange membrane fuel cell bipolar plates

A preform moulding technique using expanded graphite is developed to manufacture composite bipolar plates for proton exchange membrane fuel cells (PEMFCs). The preform is composed of expanded graphite, graphite flake and phenol resin. Preforms utilizing the tangled structure of expanded graphite are easily fabricated at a low pressure of 0.07–0.28 MPa. A pre-curing temperature (100 °C) slightly above the melting point of phenol powders (90 °C) induces moderate curing, but also prevents excessive curing. After the preform is placed in a steel mould, compression moulding is carried out at high pressure (10 MPa) and temperature (150 °C). The fabrication conditions are optimized by checking the electrical conductivity, flexural strength and microstructure of the composite. The optimized electrical conductivity and flexural strength, 250 S cm⁻¹ and 50 MPa, respectively, met the requirements for PEMFC bipolar plates.     

Effect of humidified water vapor on heat balance management in a proton exchange membrane fuel cell stack

Thermal management has been considered as one of the most important issues for the operation of proton exchange membrane fuel cells (PEMFCs). Phase change affects the performance and even the heat balance of the stack during operation. A 46 single cell PEM stack with anode and cathode humidification is developed to investigate, both theoretically and experimentally, the effect of phase change on the heat generation and removal characteristics of the stack. The results show that the heat removed by the coolant water is greater than that generated by the electrochemistry reaction, and heat released due to the phase change of water vapor cannot be neglected. Heat generated in the stack can be removed completely by the coolant water, which need to be forced cooling for recycling use when the current density reaches 1000 mA·cm^?2. The arithmetic product of the specific heat capacity and mass of the stack can be used as a novel criterion to evaluate the validity of the heat balance in the system. The exothermic reaction is very fast in the stack, which consequently requires bipolar plates with high heat conductivity coefficient to improve the temperature uniformity at the elevated operational current density. Copyright © 2014 John Wiley & Sons, Ltd.     

Review on current research of materials,fabrication and application for bipolar plate in proton exchange membrane fuel cell

Bipolar plate (BP) in proton exchange membrane (PEM) fuel cells provides conducting paths for electrons between cells, distributes and blocks the reactant gases, removes waste heat, and provides stack structural integrity. It is a key component to ensure the aforementioned functions while maintaining a low cost of fuel cell stack. This paper presents a comprehensive review about the BP materials (metallic, non-porous graphite and composite materials) and the corresponding fabrication methods, flow field layouts, and PEM fuel cells applications. Among the materials, the metallic BP has attracted high attention in automotive application due to its superior mechanical and physical properties, competitive cost compared with non-porous graphite and composite materials, but the fabrication technology and corrosion resistance are the major concerns for metallic bipolar plates. In recent studies, the protective coatings reported such as the conductive polymer, metal nitride/carbide and noble coatings have become the hot topics. They have been widely applied in different kinds of metallic bipolar plates, and the metal nitride coatings exhibit relatively low corrosion current and moderate interfacial contact resistance in comparison to other coatings. In future, developing excellent corrosion resistance and electrical conductivity coatings or novel metallic materials for bipolar plates will greatly enhance PEM fuel cells application in transportation field.     

Thermal and electrochemical durability of carbonaceous composites used as a bipolar plate of proton exchange membrane fuel cell

Thermal and electrochemical durability of carbonaceous composite plates, which are made from graphite powders and a resin for use as bipolar plates of PEMFC (proton exchange membrane fuel cell), were investigated. The thermal durability was investigated by TG (thermal gravimetry) coupled with DTA (differential thermal analysis) technique under air up to 600 °C. A weight loss was significant over 300 °C, but the hydrophobicity was decreased after heated at 80 °C for 192 h.The electrochemical durability was investigated in 10 μmol dm⁻³ of hydrochloric acid solution under nitrogen or oxygen atmosphere by means of potential holding test from 0.8 to 1.5 V against RHE (reversible hydrogen electrode) at 80 °C. During the potential holding tests, CO₂ production due to the corrosion was quantified by a GC (gas-chromatography) and the production was detectable above 1.3 V irrespective with atmosphere; on the other hand, it was clarified from the contact angle measurements that the hydrophobicity was changed below 1.3 V. The results of this study showed that the carbonaceous composite plates were electrochemically degraded under PEMFC condition and were seriously degraded in URFC (unitized regenerative fuel cell) condition.     

Performance of a proton exchange membrane fuel cell stack using conductive amorphous carbon-coated 304 stainless steel bipolar plates

In this study, 304 stainless steel (SS) bipolar plates are fabricated by flexible forming process and an amorphous carbon (a-C) film is coated by closed field unbalanced magnetron sputter ion plating (CFUBMSIP). The interfacial contact resistance (ICR), in-plane conductivity and surface energy of the a-C coated 304SS samples are investigated. The initial performance of the single cell with a-C coated bipolar plates is 923.9 mW cm⁻² at a cell voltage of 0.6 V, and the peak power density is 1150.6 mW cm⁻² at a current density of 2573.2 mA cm⁻². Performance comparison experiments between a-C coated and bare 304SS bipolar plates show that the single cell performance is greatly improved by the a-C coating. Lifetime test of the single cell over 200 h and contamination analysis of the tested membrane electrode assemble (MEA) indicate that the a-C coating has excellent chemical stability. A 100 W-class proton exchange membrane fuel cell (PEMFC) short stack with a-C coated bipolar plates is assembled and shows exciting initial performance. The stack also exhibits uniform voltage distribution, good short-term lifetime performance, and high volumetric power density and specific power. Therefore, a-C coated 304SS bipolar plates may be practically applied for commercialization of PEMFC technology.     

Dynamic performance for a kW-grade air-cooled proton exchange membrane fuel cell stack

In this study, a kW-grade air-cooled proton exchange membrane fuel cell (PEMFC) stack with a dead-end anode (DEA) operation is designed and manufactured. The gravity-assisted drainage principle is applied for the stack to design the wettability of gas diffusion layers (GDLs) and the anode channel geometry, which can help the liquid water that diffuses to the anode to drain out of the anode porous electrode and move down the anode channel outlets. As a result, the stack can stably operate in a long purge interval of 268 s and in a short purge time of 2 s. In addition, using this design, only four small-power fans are employed to pump air to the cathode to provide oxygen for the electrochemical reaction and cool the stack. With a constant load current of 30, 45, or 60 A, the stack output voltage is experimentally tested at various cathode air flow rates (CAFRs). The local temperatures (60 measurement points) inside the stack and the pressure differences across anode channels are also monitored to understand heat dissipation and the back diffusion of liquid water. In a wide range of operating conditions, the designed stack possesses superior and stable voltage output characteristics with relatively uniform temperature distributions. The measured maximum output power is 3.83 kW, and the parasitic powers of fans are only 80～112 W.     

Stack shut-down strategy optimisation of proton exchange membrane fuel cell with the segment stack technology

In the previous researches, researchers mainly focus on the single cell which is far away from the practical application. In this paper, shut-down process is studied in a 5-cell stack with segment technology. In the unprotected group, the hydrogen/air boundary is observed, and the output voltage performance degrades greatly after 300 start-stop cycles. A 2-phase auxiliary load strategy is proposed to avoid the hydrogen/air boundary. The lifetime is extended. But a serious local starvation is observed during the shut-down process. And corrosion happened in the inlet region. To avoid the starvation, the second strategy is designed, which combines 2-phase auxiliary and air purge (2-phase load& air purge strategy). With the new strategy, the degradation of the stack after 1500 cycles is acceptable, and the carbon corrosion in the inlet is effectively reduced. It could conclude that the hydrogen/air boundary is the main cause of the degradation of fuel cell during an unprotected shut-down process. And a strategy only with auxiliary load may suffer from the local starvation. The purge process can avoid the vacuum effect in the fuel cell caused by the auxiliary load. Therefore, adding an air purge during the shut-down process is promising in vehicle fuel cell.     

Carbon monoxide poisoning of proton exchange membrane fuel cells

Proton exchange membrane fuel cell (PEMFC) performance degrades when carbon monoxide (CO) is present in the fuel gas; this is referred to as CO poisoning. This paper investigates CO poisoning of PEMFCs by reviewing work on the electrochemistry of CO and hydrogen, the experimental performance of PEMFCs exhibiting CO poisoning, methods to mitigate CO poisoning and theoretical models of CO poisoning. It is found that CO poisons the anode reaction through preferentially adsorbing to the platinum surface and blocking active sites, and that the CO poisoning effect is slow and reversible. There exist three methods to mitigate the effect of CO poisoning: (i) the use of a platinum alloy catalyst, (ii) higher cell operating temperature and (iii) introduction of oxygen into the fuel gas flow. Of these three methods, the third is the most practical. There are several models available in the literature for the effect of CO poisoning on a PEMFC and from the modeling efforts, it is clear that small CO oxidation rates can result in much increased performance of the anode. However, none of the existing models have considered the effect of transport phenomena in a cell, nor the effect of oxygen crossover from the cathode, which may be a significant contributor to CO tolerance in a PEMFC. In addition, there is a lack of data for CO oxidation and adsorption at low temperatures, which is needed for detailed modeling of CO poisoning in PEMFCs. Copyright © 2001 John Wiley & Sons, Ltd.     

质子交换膜燃料电池故障检测研究

针对质子交换膜燃料电池(PEMFC)发电系统的故障检测和系统稳定性问题,结合其多传感器特性,采用基于实时PCA的质子交换膜燃料电池故障检测方法,根据燃料电池反应信号数据建立PCA模型,通过窗口过滤方式和遗忘因子算法实时更新模型,并将降维后获得的数据用统计方法进行处理,从而检测出故障。有效地简化了燃料电池系统故障检测的过程,改善了故障检测的实时性,提高了燃料电池系统工作的稳定性和可靠性。     

Pre-oxidized and nitrided stainless steel alloy foil for proton exchange membrane fuel cell bipolar plates. Part 2: Single-cell fuel cell evaluation of stamped plates

Thermal (gas) nitridation of stainless steel alloys can yield low interfacial contact resistance (ICR), electrically conductive and corrosion-resistant nitride containing surface layers (Cr₂N, CrN, TiN, V₂N, VN, etc.) of interest for fuel cells, batteries, and sensors. This paper presents results of proton exchange membrane (PEM) single-cell fuel cell studies of stamped and pre-oxidized/nitrided developmental Fe-20Cr-4V weight percent (wt.%) and commercial type 2205 stainless steel alloy foils. The single-cell fuel cell behavior of the stamped and pre-oxidized/nitrided material was compared to as-stamped (no surface treatment) 904L, 2205, and Fe-20Cr-4V stainless steel alloy foils and machined graphite of similar flow field design. The best fuel cell behavior among the alloys was exhibited by the pre-oxidized/nitrided Fe-20Cr-4V, which exhibited ∼5-20% better peak power output than untreated Fe-20Cr-4V, 2205, and 904L metal stampings. Durability was assessed for pre-oxidized/nitrided Fe-20Cr-4V, 904L metal, and graphite plates by 1000+ h of cyclic single-cell fuel cell testing. All three materials showed good durability with no significant degradation in cell power output. Post-test analysis indicated no metal ion contamination of the membrane electrode assemblies (MEAs) occurred with the pre-oxidized and nitrided Fe-20Cr-4V or graphite plates, and only a minor amount of contamination with the 904L plates.     

Development and performance evaluation of a high temperature proton exchange membrane fuel cell with stamped 304 stainless steel bipolar plates

In this work, a high temperature proton exchange membrane fuel cell (HT-PEMFC) with stamped SS304 bipolar plates is successfully developed. Its performance was evaluated under two types of gaskets at different assembly torques and air stoichiometric ratios. The rates of pressure loss at a torque of 7 N-m with 50 Shore A hardness gaskets was 2.0 × 10^?3 MPa min^?1, which is acceptable. The best performance of the developed HT-PEMFC with stamped SS304 bipolar plates was 228.33 mW cm^?2, which approaches the performance of HT-PEMFCs with graphite bipolar plates. The optimal air stoichiometric ratio for the HT-PEMFC with stamped SS304 bipolar plates was 4.0, which is higher than that for proton exchange membrane fuel cells with CNC milled graphite bipolar plates. This is probably because of the deformation of the flow channels under the assembly compression force, which causes an elevated gas-diffusion drag in the flow channels. After the test, it was observed that some products of corrosion reaction formed on the surface of the SS304 bipolar plate. This phenomenon may lead to a decrease in the operating life of the HT-PEMFC.     

Novel dynamic semiempirical proton exchange membrane fuel cell model incorporating component voltages

This paper introduces a novel dynamic semiempirical model for the proton exchange membrane fuel cell (PEMFC). The proposed model not only considers the stack output voltage but also provides valid waveforms of component voltages, such as the no‐load, activation, ohmic, and concentration voltages of the PEMFC stack system. Experiments under no‐load, ramping load, and dynamic load conditions are performed to obtain various voltage components. According to experimental results, model parameters are optimised using the lightning search algorithm by providing valid theoretical ranges of parameters to the lightning search algorithm code. In addition, the correlation between the vapour and water pressures of the PEMFC is obtained to model the component voltages. Finally, all component voltages and the stack output voltage are validated by using the experimental/theoretical waveforms mentioned in previous research. The proposed model is also compared with a recently developed semiempirical model of PEMFC through particle swarm optimisation. The proposed dynamic model may be used in future in‐depth studies on PEMFC behaviour and in dynamic applications for health monitoring and fault diagnosis.     

Effect of surface roughness of composite bipolar plates on the contact resistance of a proton exchange membrane fuel cell

Polymer electrolyte membrane fuel cell performance strongly depends on properties of the fuel cell stack bipolar plates. Composite bipolar plates, though low cost and convenient in manufacturing, raise a major concern due to their high interfacial contact resistance caused by the mechanical treatment used to remove the polymer-rich layer on the surface. It is observed that most of this contact resistance is governed by electrical properties of the interface layer between the contacting surfaces. Measurements of contact resistance of mechanically polished composite bipolar plate/gas diffusion layer interface reveal a substantial influence of surface topography on the contact resistance, which varies significantly depending on the substrate surface treatment and roughness of composite bipolar plates.     

Durable ultra-low-platinum ionomer-free anode catalyst for hydrogen proton exchange membrane fuel cell

An ultra-low-platinum catalyst based on finely dispersed platinum (Pt) deposited on a highly porous complex microporous layer was investigated as a candidate of durable anode catalyst for hydrogen oxidation reaction (HOR) in proton exchange membrane fuel cells. Etching of teflonated and nitridized base carbon substrate in oxygen plasma and simultaneous deposition of cerium oxide were applied to increase active surface area and electrochemical activity of the platinum nanocatalyst. Ultra-low loadings of Pt (between 0.85 and 8.5 μg cm⁻²) deposited by magnetron sputtering on this substrate were assembled with Nafion 212 membrane and commercially available Pt/C cathodes (300-400 μg cm⁻² Pt). Such membrane electrode assembly (MEA) with extremely low Pt content at anode can deliver high output power densities, reaching 0.95 W cm⁻² or 0.65 W cm⁻² with only 1.7 μg cm⁻² of Pt, using H₂ as fuel and pure O₂ or air as an oxidant, respectively. Although electrocatalysts with highly dispersed active metals are known to often suffer from irreversible degradation, the above MEAs proved to be very stable when the cell was subjected to a durability test under heavy duty conditions of on/off cycling. The system with lower Pt content is more prone to water flooding which can, however, be eliminated by maintaining better control over the fuel humidity. Average decay of the cell voltage less than 50 μV h⁻¹ was obtained in the cycling regime, while excellent stability <10 μV h⁻¹ is achievable under the static load of 0.4 A cm⁻².     

基于Python的质子交换膜燃料电池引射器自动仿真设计

质子交换膜燃料电池（PEMFC）引射器设计通常需经过结构参数计算、计算域建模、网格划分和数值模拟等步骤,并经过多轮迭代得到一个性能较优的设计方案,所需时间成本较高。针对PEMFC引射器,通过Python编程语言将以上功能进行集成,自动计算引射器结构参数,并调用OpenFOAM软件中的blockMesh工具进行计算域建模、网格划分,以及rhoSimpleFoam求解器进行数值仿真验证,形成一套参数化的自动仿真设计工具。研究表明,该工具可显著提高PEMFC引射器设计开发的速度,从而促进汽车工业的发展。     

Development of a proton exchange membrane fuel cell cogeneration system

A proton exchange membrane fuel cell (PEMFC) cogeneration system that provides high-quality electricity and hot water has been developed. A specially designed thermal management system together with a microcontroller embedded with appropriate control algorithm is integrated into a PEM fuel cell system. The thermal management system does not only control the fuel cell operation temperature but also recover the heat dissipated by FC stack. The dynamic behaviors of thermal and electrical characteristics are presented to verify the stability of the fuel cell cogeneration system. In addition, the reliability of the fuel cell cogeneration system is proved by one-day demonstration that deals with the daily power demand in a typical family. Finally, the effects of external loads on the efficiencies of the fuel cell cogeneration system are examined. Results reveal that the maximum system efficiency was as high as 81% when combining heat and power.