Open Cathode Research Articles

Gas Diffusion Media for Open-Cathode Fuel Cells in Atmospheric Flight

Operating a proton exchange membrane fuel cell (PEMFC) in a planar, open cathode configuration can enable significant reductions in overall device weight and system complexity compared to a conventional fuel cell stack. This decrease in device weight makes an array of open-cathode, planar fuel cells a compelling candidate power source for unmanned aerial vehicles. The flow of ambient air over vehicle-mounted cells can improve oxygen, waste heat, and water transport between the catalyst layer and bulk air. We previously studied the effect of environmental conditions on cell polarization and found that ambient temperature, relative humidity, altitude and air speed all influence cell temperature, which affects water balance and oxygen transport to the catalyst layer. In this work, we relate gas diffusion media (GDM) properties to cell polarization behavior in a broad range of anticipated flight conditions. We study the effect of gas diffusion layer thickness and porosity on cell polarization and discuss its influence on cell temperature, oxygen transport and water management. Similarly, we investigate the polytetrafluoroethylene (PTFE) content in the GDM and the influence of hydrophobicity on cell water management and performance in a broad range of anticipated flight conditions. We use cyclic voltammetry and AC impedance spectroscopy to characterize performance losses associated with GDM properties to guide GDM selection.

Gas Diffusion Media for Open-Cathode Fuel Cells in Atmospheric Flight

Operating a proton exchange membrane fuel cell (PEMFC) in a planar, open cathode configuration can enable significant reductions in overall device weight and system complexity compared to a conventional fuel cell stack. This decrease in device weight makes an array of open-cathode, planar fuel cells a compelling candidate power source for unmanned aerial vehicles (UAVs) that can utilize the flow of ambient air over the vehicle-mounted cells to improve oxygen transport, waste heat rejection, and ultimately, water transport in the open-cathode. The effectiveness of each of these processes is largely influenced by the thickness and porosity of the cathode gas diffusion layer (GDL). We relate these cathode GDL properties to open-cathode fuel cell polarization behavior in a broad range of atmospheric conditions in active air flow and in passive, air-breathing mode to study the effect of gas diffusion layer thickness and porosity on cell performance through polarization and AC impedance measurements. Reducing cathode GDL porosity leads to a decrease in cell temperature and ohmic resistance, which improves water retention. Reducing cathode GDL thickness facilitates O2 and H2O transport, increasing oxygen availability to the electrocatalyst at the expense of improved water retention. After observing open-cathode fuel cell performance in a broad range of environmental conditions including ambient temperature, relative humidity, altitude, and in active and stagnant air flows, we find that application of a thicker cathode GDL (315 μm) with lower porosity (75%) yields the highest open-cathode fuel cell voltages and power generation; the open-cathode fuel cell achieves a maximum power-to-weight ratio of 1.44 kW kg-1.

Hydrogen preheating through waste heat recovery of an open-cathode PEM fuel cell leading to power output improvement

The electrochemical reaction kinetics in a Polymer Electrolyte Membrane (PEM) fuel cell is highly influenced by the reactants supply pressures and electrode temperatures. For an open cathode PEM fuel cell stack, the power output is constrained due to the use of air simultaneously as reactant and coolant. Optimal stack operation temperatures are not achieved especially at low to medium power outputs. Based on the ideal gas law, higher reactant temperatures would lead to higher pressures and subsequently improve the reaction kinetics. The hydrogen supply temperature and its pressure can be increased by preheating; thus, slightly offsetting the limitation of low operating stack temperatures. The exit air stream offers an internal source of waste heat for the hydrogen preheating purpose. In this study, a PEM open-cathode fuel cell was used to experimentally evaluate the performance of hydrogen preheating based on two waste heat recovery approaches: (1) open-loop and (2) closed loop hydrogen flow. The stack waste heat was channelled into a heat exchanger to preheat the hydrogen line before it is being supplied (open loop) or resupplied (closed loop) into the stack. At a constant 0.3bar hydrogen supply pressure, the preheating increases the hydrogen temperature in the range of 2–13°C which was dependant on the stack power output and cathode air flow rates. The achievable maximum stack power was increased by 8% for the closed loop and 10% for the open loop. Due to the small hydrogen flow rates, the waste heat utilization was only 3–6% from the generated stack heat. The analysis indicates a better potential for open loop hydrogen preheating using fuel cell waste heat for open-cathode stacks.

The effect of algae species on the bioelectricity and biodiesel generation through open-air cathode microbial fuel cell with kitchen waste anaerobically digested effluent as substrate

Five strains algae (Golenkinia sp. SDEC-16, Chlorella vulgaris, Selenastrum capricornutum, Scenedesmus SDEC-8 and Scenedesmus SDEC-13) were screened as an effective way to promote recover electricity from MFC for kitchen waste anaerobically digested effluent (KWADE) treatment. The highest OCV, power density, biomass concentration and total lipid content were obtained with Golenkinia sp. SDEC-16 as the co-inoculum, which were 170mV, 6255mWm−3, 325mgL−1 and 38%, respectively. Characteristics of the organics in KWADE were analyzed, and the result showed that the hydrophilic and acidic fractions were more readily degraded, compared to the neutral fractions during the operation. Maximum COD and TN removal efficiency were 43.59% and 37.39% when inoculated with Golenkinia sp. SDEC-16, which were roughly 3.22 and 3.04 times higher than that of S. capricornutum. This study demonstrated that Golenkinia sp. SDEC-16 was a promising species for bioelectricity generation, lipid production and KWADE treatment.

Development of the anode bipolar plate/membrane assembly unit for air breathing PEMFC stack using silicone adhesive bonding

Polymer electrolyte membrane fuel cells (PEMFC) exhibit a wide power range, low operating temperature, high energy density and long life time. These advantages favor PEMFC for applications such as vehicle power sources, portable power, and backup power applications. With the push towards the commercialization of PEMFC, especially for portable power applications, the overall balance of plants (BOPs) of the systems should be minimized. To reduce the mass and complexity of the systems, air-breathing PEMFC stack design with open cathode channel configuration is being developed. However, the open cathode channel configuration incurs hydrogen leakage problem.In this study, the bonding strength of a silicon adhesive between the Nafion membrane and the carbon fiber/epoxy composite bipolar plate was measured. Then, an anode bipolar plate/membrane assembly unit which was bonded with the silicone adhesive was developed to solve the hydrogen leakage problem. The reliability of the anode bipolar plate/membrane assembly unit was estimated under the internal pressure of hydrogen by the FE analysis. Additionally, the gas sealability of the developed air breathing PEMFC unit cell was experimentally measured. Finally, unit cell performance of the developed anode bipolar plate/membrane assembly unit was tested and verified under operating conditions without humidity and temperature control.

Performance analysis of polymer electrolyte membrane (PEM) fuel cell stack operated under marine environmental conditions

The marine environmental condition, especially NaCl, has been identified as one of the major sources of contamination on the performance of open cathode Proton Exchange Membrane Fuel Cells (PEMFC) system, when the power source is based on fuel cells for marine applications like submarines, navy ships etc., In the present paper, we have studied the performance of PEMFCs under the marine environment for a longer duration and also the recovery mechanism of the PEMFC power pack after contamination. It has been observed that the NaCl is a major contaminant for PEMFC, compared to NO x and SO x , which are major contaminants for fuel cells operating in the land regions. We have observed a performance loss of 60 % in PEMFC, when operated for 48 h, due to poisoning of PEMFC by NaCl vapours. The recovery of the stack is attempted by repeated water washing on the cathode side of the fuel cell, presuming that the salts get deposited only on the surface of the electrodes and the performance is easily recoverable. The recovery mechanisms are analysed by constant-current discharging operation and by modified experimental methods and are reported here. The performance vagaries in fuel cells due to sea water contamination is also analysed by linear fit and it is found that the rate of power increment after water wash is higher than the rate of power increment, around 11.5 W/10 h compared to normal environmental conditions, which is 4.1 W/10 h.

Optimum design of the carbon composite bipolar plate (BP) for the open cathode of an air breathing PEMFC

The proton exchange membrane fuel cells (PEMFCs) are a promising source of portable power due to its high energy density, low emissions and wide power range. However, PEMFCs have some limitations for portable applications because of the supplementary power consumption and the mass increase by balance of plants, such as the fuel pump, air compressor and humidifier.In this study, a light mass PEMFC system was developed using carbon composite bipolar plates (BPs) and an air breathing stack design with open cathode channel configurations to reduce the mass of the stack. However, under the high compaction pressure, the failure occurred in the carbon composite BPs for the open cathode.To enhance the durability of the BP against the compaction pressure, the finite element analysis, the compressive test and the fracture toughness test were performed. The maximum compaction pressure on the BP was calculated by applying the maximum strain failure criterion to the composite BP. Then, the optimum thickness and stacking sequence of the open cathode bipolar plate were determined by considering the mass and the maximum compaction pressure.

Compact open cathode feed system for PEMFCs

The open cathode design is commonly adopted for small sized proton exchange membrane fuel cells (PEMFCs) as it allows for smaller footprint and thus, higher power density. Axial fans are typically used to supply oxygen in these PEMFC systems. Apart from controlling stoichiometry, they also play a critical role in regulating internal temperature. This suggests that its location could have significant impact on fuel cell performance. In this work, the location of the fan is varied from the front to the rear in order to blow air or draw air into the stack respectively. The latter configuration reduces the non-uniformity in temperature and velocity by around 2 and 4 times respectively, resulting in a 16% increase in overall stack performance.

Exergy Efficiency Profile of A 1kW Open Cathode Fuel Cell with Pressure and Temperature Variations

A proposed electric vehicle using proton exchange membrane (PEM) as clean energy have been attracting due to their high efficiency, high energy density and zero emissions. Standard exergy analysis of a mini urban vehicle powered by a 1kW Proton Exchange Membrane (PEM) fuel cell engine system has been presented in this manuscript. A sensitivity analysis has been studied in order to evaluate the effect of variable operating temperatures and pressures on the physical exergy and efficiency of a 1kW PEM fuel cell engine. The calculation of the physical and chemical exergies, mass flow rate and exergy efficiency are performed at temperature ratio (T/T0) and pressure ratio (P/P0) ranging from 1 to 1.15 and 1 to 4, respectively. The findings of the exergy analysis reveal that the overall efficiency of the fuel cell system was observed to be 61.3%. The result of the parametric study show that an increase in operating temperature and pressure results in an increase in exergy efficiency of the system.

An Open Cathode Fuel Cell for Atmospheric Flight

Our previous work has shown that fuel cells are ideal power sources for long endurance unmanned air vehicles (UAVs) (1). An open-cathode fuel cell system has the cathode exposed to the open air to harness the motion of a UAV through the atmosphere to provide O2 to the cathode. By removing the balance of plant (BOP) associated with pumping and preconditioning the incoming air, an open cathode fuel cell may be an ideal power source for atmospheric flight because of its simplicity and reduced weight. A custom open cathode fuel cell based on flexible circuits is fabricated and characterized in a custom wind tunnel/environmental chamber setup to ascertain whether open cathode fuel cells can operate in atmospheric flight conditions. A numerical model is also developed to quantify the associated loss mechanisms in the cell. Wind tunnel experiments show that open cathode operation is possible without catastrophic failure over a wide range of ambient temperatures (5-55 °C), ambient relative humidities (22-90% RH), air speeds (2.6-15.4 m s-1) and altitudes (< 10-914 m); with the largest losses associated with mass transport and catalyst activation.

Enhancing wettability of high density polyethylenes (HDPE) through microplasma jets

This paper aims at the characterization of plasma microjets generated by open microhollow cathodes to ionize gases such as air, N2, He and O2. The electrical and optical parameters were raised. Through the optical emission spectroscopy, gas temperature (Tg) and the excitation temperature were estimated. Tg ranging from 2100K to 600K for a gas flow rate ranging from 0 to 400ml/min. From 150 to 400ml/min Tg remained close to 700K. As an application, the treatment of smooth surfaces of high density polyethylenes (HDPE) was performed with a view to improve the hydrophilic property of the surface.

An Open Cathode Fuel Cell for Atmospheric Flight

An open cathode proton exchange membrane fuel cell (PEMFC) could be an ideal power source for unmanned air vehicles because the motion of the aircraft through the atmosphere can be leveraged to provide oxygen to the PEMFC and extract waste heat, eliminating many traditional balance of plant components such as air and coolant pumps, bipolar plates, gaskets, humidifier, and radiator. One challenge presented by this fuel cell arrangement is that the ambient air cannot be conditioned before entering the PEMFC, potentially limiting its operating envelope. This research examines the performance of an open cathode fuel cell in an environmentally controlled wind tunnel that reproduces the atmospheric flight environment. The cell was constructed by laminating a flexible circuit current collector with a membrane electrode assembly (MEA). The effects of ambient temperature, ambient relative humidity, air speed and altitude on polarization behavior are discussed in detail. A simple 1-D fuel cell model shows that the dominant factor influencing the polarization behavior is the temperature of the cell, which is determined by the ability of the cell to reject heat.

Performance assessment of partially sulfonated PVdF-co-HFP as polymer electrolyte membranes in single chambered microbial fuel cells

In the present study, PVdF-co-HFP copolymer and its sulfonated derivatives have been analyzed as polymer electrolyte membrane in single chamber MFCs. The sulfonation of PVdF-co-HFP copolymer was performed by treating with chlorosulfonic acid for 5, 7 and 9h, resulting in 23%, 30%, and 18% of degree of sulfonation (DS) in the respective SP-5, SP-7, and SP-9 membranes. On observing the membranes under field emission scanning electron microscope fitted with EDAX, porosity was found to be increasing with increase in the duration of sulfonation except for 9h duration. The elemental analysis of the membranes indicated the presence of higher sulfur and oxygen content with the increasing sulfonation duration except for 9h duration, for which crosslinks were formed via sulfone linkages. The membranes were characterized for their ion exchange capacity (IEC) and proton conductivity; IEC value of 0.21meqg−1, 0.42meqg−1, and 0.12meqg−1 and proton conductivity of 0.0012Scm−1, 0.00363Scm−1, and 0.0006Scm−1 were observed for SP-5, SP-7, and SP-9 membranes. Open air cathode MFCs with membrane electrode assemblies (MEA) containing sulfonated and non-sulfonated PVdF-co-HFP membranes have been analyzed for their overall MFC performance. It was observed that amongst these membranes, MFC with SP-7 membrane showed the maximum power and current density of 290.176±15mWm−2 and 1390.866±70mAm−2 with an overall ∼89% COD removal in 28days operation, using electrogenic mixed firmicute consortium. In overall, the study illustrates the impression of sulfonated PVdF-co-HFP membranes as PEM and its application in MFC for harvesting bio-energy.

600 W급 연료전지(PEMFC)의 설계 및 제작

The design of a fuel cell stack is important to achieve optimal output power. This study focuses on the evaluation of a fuel cell system for unmanned aerial vehicles (UAVs). Low temperature proton exchange membrane (LTPEM) fuel cells are the most promising energy source for robot applications because of their unique advantages such as high energy density, cold startup, and quick response during operation. In this paper, a 600 W open cathode LTPEM fuel cell was tested to evaluate the performance and to determine optimal operating conditions. The open cathode design reduces the overall size of the system to meet the requirements for robotic applications. The cruise power requirement of 600 W was supported entirely by the fuel cell while the additional power requirements during takeoff was extended using a battery. A peak of power of 900 W is possible for 10 minutes with a lithium polymer (LiPo) battery. The system was evaluated under various load cycles as well as start-stop cycles. The system response from no load to full load meets the robot platform requirements. The total weight of the stack was 2 kg, while the overall system, including the fuel processing system and battery, was 4 kg.

Cell level modeling of the hygrothermal characteristics of open cathode polymer electrolyte membrane fuel cells

Open cathode designs that utilize ambient air for both cooling and oxygen supply are a useful feature for low- to medium-power polymer electrolyte membrane fuel cell (PEMFC) stacks. Elimination of balance-of-plant subsystems greatly reduces the complexity, parasitic power, and cost of the overall system, and therefore increases the appeal of open cathodes. The present research addresses the key challenges of open-cathode PEMFCs related to thermal management and membrane hydration, two highly coupled phenomena. Accurate knowledge of the temperature and relative humidity (RH) distributions in the cell is essential in order to optimize heat removal by suitable strategies. In the present work, a three-dimensional numerical model is developed that can predict the hygrothermal characteristics in a complete open-cathode cell. The model is validated using experimental data obtained with Ballard Power Systems' FCgen®-1020ACS stack under a range of operating conditions. The model is then used to analyze the key flow conditions and properties that control the hygrothermal behavior of open-cathode stacks. Based on the obtained results, flow conditions can affect temperature and RH distributions significantly; in-plane plate thermal conductivity can provide a uniform temperature distribution while adversely reducing the RH; and edge cooling can increase temperature and RH gradients in the cell. Recommendations for hygrothermal design and operation of open cathode stacks are provided.

Performance Analysis of an Open-Cathode PEM Fuel Cell Stack

Hydrogen is known to be an ideal fuel that provides zero-emission energy. Fuel cells have emerged as one of the most promising candidates for fuel-efficient and emission-free vehicle power generation. PEMFC stacks require liquid cooling which can be operated in an open-cathode mode with air supplied by one or several fans, thus reducing the overall complexity of the PEMFC system. In this study, an open cathode PEMFC is used as the dependable power source and experiments are carried out to investigate the temperature characteristic of open cathode PEMFC. Combined with the using of oxidant and cell stack cooling, the optimal air fan supply voltage is 9.0V, and the maximal power can be obtained is 355W.

Advanced Diagnostic Applied to a Self Breathing Fuel Cell Using Printed Circuit Board Technology

Fuel cells are currently been considered as promising alternatives for portable power applications (1-100 W) due to their good energy conversion efficiency, flat geometry, high power and the energy density of their fuel sources, making them advantageous over batteries [1]. The increasing importance of compact design for portable devices necessitates miniaturization of fuel cell stack components in order to maximize power density and for easy system integration [1]. In this study, an air breathing fuel cell has been developed using printed circuit board (PCB) technology. The use of PCBs affords cost-effective prototypes and design flexibility, which can help to reduce the cost of developing fuel cell stacks.In an open cathode or self-breathing fuel cell, supply of oxygen to the cathode is achieved through free or natural convection of air-flow. The output power densities of these type of fuel cells are typically low when compared with forced convection fuel cells [2]. However, they are still considered attractive options for portable application due to other key advantages over forced convection designs, such as simplicity of natural convection air delivery, lower cost, less noise and no pumps required. The cathode performance is usually the major source of voltage loss as a result of natural convection of air which can lead to mass transport limitations (Fig 1) and inadequate water removal. This work explores the use of advanced diagnostic techniques to understand the internal working of a novel self-breathing polymer electrolyte fuel cell. This includes the use of a thermal imaging camera to observe the production and distribution of heat (Fig 2 ) and direct visualization of open channels to observe water formation. The PEMFC fabricated consisted of two printed circuit board (PCB) current collectors (anode and cathode), an MEA, gaskets and two end plates. The PCB current collectors were were coated with conductive carbon ink for corrosion protection. The flow fields were machined onto the PCBs using a CNC milling machine. The gaskets used for gas manifolds were made of silicone. The cathode end plates were made from aluminium sheets and contained a 13cm2 window for direct visualization of the flow field. A double serpentine flow field was used for the anode. The cathode geometries employed were parallel and circular openings. The two cathode geometries employed will be compared using polarization curve and impedance spectrscopy.Polarization perfomance of the open cathode fuel cells have indicated mass transport limitation as the dominant source of voltage loss. The circular opening geometry also performs better than the parallel opening geomerty at the ohmic region of the curve but performance drops in the mass transport region. The impedance spectra obtained also points at severe mass transport issues especially with the circular openings. This is as a result of water bubbles blocking the path of air flow. Thermal imaging results indicates the existence of hotspots which is very important as the membrane could fail if the hotspot exceeds its maximum design limitation. The work presented will be of interest to both academic and industrial personell as it gives an indication of the stable operating points of air breathing fuel cell and also provides potential water management strategies.

J0610103 オープンカソードファン式小型携帯PEFCにおける熱管理と最適流路構造([J061-01]燃料電池・二次電池とマイクロ・ナノ現象(1))

J0610103 オープンカソードファン式小型携帯PEFCにおける熱管理と最適流路構造([J061-01]燃料電池・二次電池とマイクロ・ナノ現象(1))

Testing of Lightweight Fuel Cell Vehicles System at Low Speeds with Energy Efficiency Analysis

A fuel cell vehicle power train mini test bench was developed which consists of a 1 kW open cathode hydrogen fuel cell, electric motor, wheel, gearing system, DC/DC converter and vehicle control system (VCS). Energy efficiency identification and energy flow evaluation is a useful tool in identifying a detail performance of each component and sub-systems in a fuel cell vehicle system configuration. Three artificial traction loads was simulated at 30 kg, 40 kg and 50 kg force on a single wheel drive configuration. The wheel speed range reported here covers from idle to 16 km/h (low speed range) as a preliminary input in the research work frame. The test result shows that the system efficiency is 84.5 percent when the energy flow is considered from the fuel cell to the wheel and 279 watts of electrical power was produced by the fuel cell during that time. Dynamic system responses was also identified as the load increases beyond the motor traction capabilities where the losses at the converter and motor controller increased significantly as it tries to meet the motor traction power demands. This work is currently being further expanded within the work frame of developing a road-worthy fuel cell vehicle.

Steady - State Potential Energy Recovery Modeling of an Open Cathode PEM Fuel Cell Vehicle

Waste heat recovery in automotive engineering is part of the sustainable energy effort to optimize energy utilization. For vehicles running on hydrogen fuel cells, the potential of heat recovery is perceived to be limited due to the low quality energy generated from the fuel cell stack. It has been established in fuel cell operation that increasing the inlet hydrogen temperature improves the conversion efficiency through higher kinetic reaction rates. A fuel cell power plant for a mini vehicle that will be competing in Shell Eco Marathon Asia 2014 was studied to identify the potential energy recovery limits for an improved power plant design with regenerative hydrogen pre-heater. Using modeling approach for fuel cell power generation and efficiency relationships, the first-order waste energy potential was identified based on test bench studies on the electrical and thermal power relationship of the fuel cell stack performance. The corresponding result is then mapped to a driving cycle to investigate the thermal power generated during the race in both aggressive and passive driving cycle. The energy recovery potential for 4 laps course under aggressive and passive driving cycle are 529 kJ and 501.8 kJ consecutively. The mean thermal powers are 485 W and 410 W respectively which is the reference energy for extended heat exchanger design purposes.