Lightweight current collector based on printed-circuit-board technology and its structural effects on the passive air-breathing direct methanol fuel cell

To realize lightweight design of the fuel cell system is a critical issue before it is put into practical use. The printed-circuit-board (PCB) technology can be potentially used for production of current collectors or flow distributors. This study develops prototypes of a single passive air-breathing direct methanol fuel cell (DMFC) and also an 8-cell mono-polar DMFC stack based on PCB current collectors. The effects of diverse structural and operational factors on the cell performance are explored. Results show that the methanol concentration of 6 M promotes a higher cell performance with a peak power density of 18.3 mW cm⁻². The combination of current collectors using a relatively higher anode open ratio and inversely a lower cathode open ratio helps enhance the cell performance. Dynamic tests are also conducted to reveal transient behaviors and its dependence on the operating conditions. To validate the real working status of the DMFC stack, it is coupled with an LED lightening system. The performance of this hybrid system is also reported in this study.     

Preliminary experimental study of the performances for a print circuit board based planar PEMFC stack

This paper presents a novel planar proton exchange membrane fuel cell (PEMFC) stack designed for portable electronic devices, consisting of twenty homemade membrane electrode assemblies (MEAs) arranged on a planar surface and three printed circuit boards (PCBs, including anode, interlayer and cathode PCBs) used to load these MEAs. The current collectors and electrical connectors are manufactured using printed circuit technology. The inlet holes of reaction gases are also machined on PCB substrates. The output performance tests are performed on the MEAs and the assembled planar PEMFC stack. The results show that the power densities of the MEAs and the planar PEMFC stack are 0.6 W/cm² and 0.361 W/cm² at rated voltage under ambient temperature and forced convection air conditions, respectively. The stability tests are also conducted on the planar PEMFC stack, and the results show no significant fluctuations in output current. The feasibility of the application of planar PEMFC stacks in portable electronic devices is preliminarily demonstrated, and the improvement directions for further improving the output performance are proposed accordingly.     

Development of open-cathode polymer electrolyte fuel cells using printed circuit board flow-field plates: Flow geometry characterisation

Open-cathode air-breathing fuel cells have the advantage of reduced system complexity and simplified operation, as oxygen is taken directly from ambient air without the need for blowers/compressors. In this study, printed circuit boards (PCBs) are used as flow-field plates. The use of PCBs offers the potential for significant cost reduction due to their well-established manufacturing processing and low materials cost. This study investigates the effect of varying the cathode geometry (parallel and circular) and opening ratios (43%, 53% and 63%) on fuel cell performance using polarisation curves, electrochemical impedance spectroscopy (EIS) and thermal imaging. The results obtained indicate that circular openings afford lower Ohmic resistance than parallel flow-field designs, which helps improve contact between the gas diffusion layer and flow-field plate. However, flow-field plates with circular openings suffer from greater mass transport limitation effects. Likewise, greater opening ratios offer better mass transport but increased Ohmic resistance as a result of the reduced area of lands/ribs. The thermal imaging results reveal lower temperature in the middle of the fuel cell due to “bowing” of the printed circuit board flow field plates which reduces the local current density. A trade-off between these factors results in a design with a maximum area specific power density of 250 mW cm⁻².     

Design, fabrication and performance evaluation of a miniature air breathing direct formic acid fuel cell based on printed circuit board technology

A miniature air breathing compact direct formic acid fuel cell (DFAFC), with gold covered printed circuit board (PCB) as current collectors and back boards, is designed, fabricated and evaluated. Effects of formic acid concentration and catalyst loading (anodic palladium loading and cathodic platinum loading) on the cell performance are investigated and optimized fuel concentration and catalyst loading are obtained based on experimental results. A maximum power density of 19.6 mW cm⁻² is achieved at room temperature with passive operational mode when 5.0 M formic acid is fed and 1 mg cm⁻² catalyst at both electrodes is used. The home-made DFAFC also displays good long-term stability at constant current density.     

废弃印刷线路板共热解影响因素及热解产物表征

热解是资源化利用废弃印刷线路板的重要方法之一。分别以沸石和Fe₃O₄为共热解剂,探讨了共热解剂与废弃线路板的质量比以及热解温度对液相产物产率的影响,并对热解后固、液、气三相产物进行了表征。结果表明,共热解剂的添加不会影响热解油的产率,但可有效降低液相中溴化有机物的含量。热解液相产物组分分析结果表明,直接热解废弃线路板时会有大量溴化有机物释放到液相产物中。加入共热解剂后,苯酚及其同系物成为液相产物的主要成分,溴变成主要以无机溴化物的形式存在。同时,不同共热解剂对废弃线路板的热解影响也不同。Fe₃O₄共热解时,液相产物中小分子苯类物质更多,这可能是由于铁类物质对大分子有机物的分解作用更强。共热解剂在高温下比较稳定,热解后固体主要含有共热解剂、玻璃纤维以及重金属,而热解气的主要成分则为H₂、CH₄和CO₂。     

Rapid cold start of proton exchange membrane fuel cells by the printed circuit board technology

Cold start from subzero temperature is one of the key barriers, which prevents proton exchange membrane fuel cell (PEMFC) from further commercialization. In this paper, we have applied the printed circuit board (PCB) technology to study the current density distributions of PEMFC and optimized the technology under rapid cold start. The results show that increasing the initial load, and the setup temperature can help to lower the cold start time and achieve rapid warm-up of PEMFC. The cell can be rapidly cold started for 10 s at −5 °C and 55 s at −10 °C under 0.2 V operation condition, but it failed at −15 °C and −20 °C. The inlet region and middle region produce half of the total current before the overall peak current density is reached, which is important for the successful cold start. Based on these characteristics, we optimized the rapid cold start strategy by co-operation of hot reactant gas and waste heat generation of PEMFC. It becomes possible to start up the PEMFC at temperatures down to −20 °C with about 20 min.     

Design and numerical analysis of a planar anode-supported SOFC stack

In the present study, numerical simulations are conducted to examine the flow characteristics and attributes of electrochemical reactions in the stack through three-dimensional analysis using finite volume approach prior to the fabrication of the SOFC stack. The stack flow uniformity index is employed to investigate the flow uniformity whereas in the case of electrochemical modeling, different mathematical models are adopted to predict the characteristics of activation and ohmic overpotentials that occur during electrochemical reactions in the cell. The normalized mass flow rate is found almost same in each cell with flow uniformity index of 0.999. The calculated voltage and power curves under different average current densities are compared with experimental results for the model validation. The changes in the voltage and power of the SOFC stack, current density, temperature, over potential and reactants distributions in relation to varying amounts of reactants flow are also examined. The current density distribution in each cell is observed to vary along the anode flow direction. The temperature difference in each cell is almost same along the flow direction of reactants, and the irreversible resistance showed an opposite trend with a temperature distribution in each cell.     

A preliminary study of a miniature planar 6-cell PEMFC stack combined with a small hydrogen storage canister

The fabrication and performance evaluation of a miniature 6-cell PEMFC stack based on Micro-Electronic-Mechanical-System (MEMS) technology is presented in this paper. The stack with a planar configuration consists of 6-cells in serial interconnection by spot welding one cell anode with another cell cathode. Each cell was made by sandwiching a membrane-electrode-assembly (MEA) between two flow field plates fabricated by a classical MEMS wet etching method using silicon wafer as the original material. The plates were made electrically conductive by sputtering a Ti/Pt/Au composite metal layer on their surfaces. The 6-cells lie in the same plane with a fuel buffer/distributor as their support, which was fabricated by the MEMS silicon–glass bonding technology. A small hydrogen storage canister was used as fuel source. Operating on dry H₂ at a 40 ml min⁻¹ flow rate and air-breathing conditions at room temperature and atmospheric pressure, the linear polarization experiment gave a measured peak power of 0.9 W at 250 mA cm⁻² for the stack and average power density of 104 mW cm⁻² for each cell. The results suggested that the stack has reasonable performance benefiting from an even fuel supply. But its performance tended to deteriorate with power increase, which became obvious at 600 mW. This suggests that the stack may need some power assistance, from say supercapacitors to maintain its stability when operated at higher power.     

Temperature and strain monitor of COPV by buckypaper and MXene sensor combined flexible printed circuit

Pressure vessels are always under different hazards such as leaking, fracturing, and unknown deformation. In this work, the novel micro-nano sensors were introduced based on flexible printed circuit (FPC). The temperature cycling and hydraulic pressure cycling experiments were carried out. This kind of combined sensor can be embedded and arranged between inner tank and fiber layer without any defect. The experimental results show the new sensor can detect not only thermal strain, but also elastic deformation and plastic deformation caused by pressure. Also can reflect the yield limit of COPV, which can ensure the safety of manufacture.     

Development of a 1 W passive DMFC

In this paper, development techniques for a passive DMFC prototype in the 1 W range are described in detail. The prototype includes a fuel cell stack, a fuel tank and a passive ancillary system (termed “thermal-fluids management system” in this paper). The fuel cell stack in this study incorporates a window-frame structure that provides a large open area for more efficient mass transfer and is modular. Two stack units connected in series, with a total combined active area of 72.0 cm², are used in the prototype. The thermal-fluids management system utilizes passive approaches for fuel storage and delivery, air-breathing, water management, CO₂ release, and thermal management. The air filter also serves as a waterproof layer for the cathode in order to prevent water contamination. Water immersion tests are conducted to evaluate the air filter. The performance evaluation of the prototype is performed in two fuel feeding modes: dilute methanol solution and pure methanol. A peak power output of 1.5 W is achieved with the dilute methanol solution feed.     

Multi walled carbon nanotubes based micro direct ethanol fuel cell using printed circuit board technology

Multi walled carbon nanotubes (MWNTs) have been synthesized by chemical vapour deposition technique using AB₃ alloy hydride catalyst. Platinum supported MWNTs (Pt/MWNTs) and platinum-tin supported MWNTs (Pt–Sn/MWNTs) electrocatalysts have been prepared by chemical reduction method. MWNTs and electrocatalysts have been characterized by powder X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), high resolution TEM (HRTEM) and Energy dispersive X-ray analysis (EDAX). The anode and cathode electrodes for DEFC have been fabricated using Pt–Sn/MWNTs and 1:1 Pt/MWNTs + Pt/C electrocatalyst respectively. Performances of Direct Ethanol Fuel Cell (DEFC) with these electrodes have been studied at different temperatures of the membrane electrode assembly at ambient fuel conditions and the results have been discussed. A maximum power density of 38.6 mW/cm² at a current density of 130 mA/cm² is obtained. A six cell planar Micro Direct Ethanol Fuel Cell (μ-DEFC) stack was also constructed using these electrocatalysts and etched printed circuit boards as anode and cathode current collectors. A maximum power density of 2 mW/cm² was achieved when the μ-DEFC was operated in air breathing mode at room temperature. This enhancement of the performance may be attributed to dispersion and accessibility of MWNTs support and Pt–Sn in the electrocatalyst mixture for ethanol oxidation reaction.     

Development of 1 kW class solid oxide fuel cell stack using anode-supported planar cells

We have developed a 1 kW class solid oxide fuel cell (SOFC) stack composed of 50 anode-supported planar 120-mm-diameter SOFCs. Intermediate plates, which exhibited negligible deformation under operating conditions, were placed in the stack to cancel out the cumulative error related to the position and angle of the stack parts. The stack provided an electrical conversion efficiency of 54% (based on the lower heating value (LHV) of the methane used as a fuel) and an output of 1120 W when the fuel utilization, current density, and operating temperature were 67%, 0.28 A cm⁻², and 1073 K, respectively. The stack operated stably for almost 700 h.     

Tomographic diagnostics of current distributions in a fuel cell stack

A novel tomographic scheme for analysing the state of any single membrane electrode assembly (MEA) in a stack is suggested. Plates of very high conductivity placed between every fuel cell and slitted in an appropriate manner cause surface currents at well‐defined locations of the stack. We show that knowing these surface currents, information about anomalies of the currents in a MEA can be obtained using the methods of tomography. The results are mathematically not unique. However, when assuming plausible defect structures, one can exclude improbable deficiencies by applying a special form of simulated annealing. We present numerical calculations of typical examples demonstrating that the essential defects of the MEA in any single cell of the stack can be detected and their extent can be determined. Copyright © 2009 John Wiley & Sons, Ltd.     

Effects of operations and structural parameters on the one-cell stack performance of planar solid oxide fuel cell

A three-dimensional mathematical model coupling the electrochemical kinetics with fluid dynamics is developed to simulate the heat and mass transfer in the one-cell stack of planar solid oxide fuel cells (SOFCs). Based on flow uniformity analysis, the distributions of temperature, current density, overpotential loss and other performance parameters in various operating parameters are obtained using a commercial CFD code (Fluent) coupled with the external subroutines programmed by VC++. Numerical flow data are observed in good agreement with experimental results reported in the literature. Results show that the one-cell stack in counter flow case has the advantages in better uniform current density and temperature distributions of PEN (Positive/Electrolyte/Negative) structure in the width direction, higher power output, fuel utilization factor and fuel efficiency than that in co-flow case. For counter flow case, better thermoelectric characteristics are observed in the temperature gradient, power output, fuel utilization factor and fuel efficiency with the decrease in the fuel inlet flow rate or the anode porosity. Increasing the air inlet flow rate and decreasing the fuel inlet temperature will reduce the temperature gradient; power output, fuel utilization factor and fuel efficiency are enhanced with the increase of the air inlet temperature and the decrease of the anode pore size and thickness.     

Numerical simulation and analysis of thermal stress distributions for a planar solid oxide fuel cell stack with external manifold structure

A three-dimensional numerical model based on the finite element method (FEM) is constructed to calculate the thermal stress distribution in a planar solid oxide fuel cell (SOFC) stack with external manifold structure. The stack is composed of 5 units which include cell, metallic interconnect, seal and anode/cathode current collectors. The temperature profile is described according to measured temperature points in the stack. It can be clearly seen that the maximum stress concentration area appears at the corner of the components when the stack is heated from room temperature (RT) to 780 °C. The effects of stack components on maximum stress concentration have been investigated under the operation temperature, as well as the thermal stress simulation results. It is obvious that the coefficient of thermal expansion (CTE) mismatch between the interconnect and the seal plays an important role in determining the thermal stress distribution in the stack. However, different compressive loads have almost no effect on stress distribution, and the influence of glass-based seal depends on the elastic modulus. The simulation results can be applied for optimizing the structural design of the stack and minimizing the high stress concentration in components.     

The impact of flow distributors on the performance of planar solid oxide fuel cell

This paper presents a newly established testing rig for planar solid oxide fuel cell. Two sets of nearly identical single-cell stacks except using different designs of flow distributors are measured to show how exactly the cell performance of such single-cell stacks would vary with a change in the degree of flow uniformity. It is found that by using small guide vanes around the feed header of commonly used rib-channel flow distributors to improve effectively the degree of flow uniformity, the power density of the single-cell stack can be increased by 10% as compared to that without using guide vanes under exactly the same experimental conditions. Also discussed are the start-up procedure and effects of hydrogen and air flow rates varying from 0.4 slpm to 1 slpm on cell performance of these two single-cell stacks which are measured over a range of the operating temperature varying from 650 °C to 850 °C. After 100 h of continuous cell operation, the examination of the reduction and oxidation stability of the anodic surface reveals that the improvement of flow uniformity in flow distributors is useful to achieve a more balanced use of the anodic catalyst.     

Effects of structural aspects on the performance of a passive air-breathing direct methanol fuel cell

This study systematically investigates the effects of structural aspects on the performance of a passive air-breathing direct methanol fuel cell (DMFC). Three factors are selected in this study: (1) two different open ratios of the current collector; (2) two different assembly methods of the diffusion layer; and (3) three membrane types with different thicknesses. The interrelations and interactions among these factors have been taken into account. The results demonstrate that these structural factors combine to significantly affect the cell performance of DMFCs. The higher open ratio not only provides a larger area for mass transfer passage and facilitates removal of the products, but also promotes higher methanol crossover. The hot-pressed diffusion layer (DL) can mitigate methanol permeation while the non-bonded variant is able to enhance product removal. The increase of membrane thickness helps obtain a lower methanol crossover rate and higher methanol utilisation efficiency, but also depresses cell performance under certain conditions. In this research, the maximum power density of 10.7 mW cm⁻² is obtained by selecting the current collector with a lower open ratio, the non-bonded DL, and the Nafion 117 membrane. The effect of methanol concentration on the performance of DMFCs is also explored.     

Experimental analysis of dynamic characteristics on the PEM fuel cell stack by using Taguchi approach with neural networks

This study determines the optimum operating parameters for a proton exchange membrane fuel cell (PEMFC) stack to obtain small variation and maximum electric power output using a robust parameter design (RPD). The operating parameters examined experimentally are operating temperatures, operating pressures, anode/cathode humidification temperatures, and reactant flow rates. First, the dynamic Taguchi method is used to obtain the maximum and stable power density against the different current densities, which are regarded as the systemic inputs considered a signal factor. The relationship between control factors and responses in the PEMFC stack is determined using a neural network. The discrete parameter levels in the dynamic Taguchi method can be divided into desired levels to acquire real optimum operating parameters. Based on these investigations, the PEMFC stack is operated at the current densities of 0.4–0.8 A/cm². Since the voltage shift is quite small (roughly 0.73–0.83 V for each single cell), the efficiency would be higher. In the range of operation, the operating pressure, the cathode humidification temperature and the interactions between operating temperature and operating pressure significantly impact PEMFC stack performance. As the operating pressure increasing, the increments of the electric power decrease, and power stability is enhanced because the variation in responses is reduced.     

Passive water management at the cathode of a planar air-breathing proton exchange membrane fuel cell

Water management is a significant challenge in portable polymer electrolyte membrane (PEM) fuel cells and particularly in proton exchange membrane (PEM) fuel cells with air-breathing cathodes. Liquid water condensation and accumulation at the cathode surface is unavoidable in a passive design operated over a wide range of ambient and load conditions. Excessive flooding or dry out of the open cathode can lead to a dramatic reduction of fuel cell power. We report a water management design based on a hydrophilic and electrically conductive wick. A prototype air-breathing fuel cell with the proposed water management design successfully operated under severe flooding conditions, ambient temperature 10 °C and relative humidity of 80%, for up to 6 h with no observable cathode flooding or loss of performance.     

An effective equivalent stiffness model combined with equivalent beam model to predict the contact pressure distribution for a large PEM fuel cell stack

The contact pressure distribution plays a key role to the proton exchange membrane (PEM) fuel cell performance. The purpose of this study is to propose an equivalent stiffness model combined with an equivalent beam model to predict the contact pressure distribution for a large fuel cell stack. With the established equivalent stiffness model, the equivalent values of contact pressure is revealed. Moreover, these equivalent values are extended by an iterative calculation for contact pressure distribution with an established equivalent beam model. Finally, the presented model is compared to a three-dimensional FEA model. This equivalent stiffness model has high accuracy only with a 4.1% tolerance and the correlation coefficient of FEA and equivalent beam model for the contact pressure distribution at transverse and longitudinal direction is 0.976 and 0.998. This presented equivalent model is effective and can provide a direction for future work on high-performance fuel cell stack design and optimization.