Performance evaluation of Enhanced Cross flow Split Serpentine Flow Field design for higher active area PEM fuel cells

The present work aims to study the efficacy of the Enhanced Cross Flow Split Serpentine Flow Field (ECSSFF) design for higher active area fuel cells. It is carried out by simulating the fuel cells with active areas of 50 cm², 100 cm², 150 cm² and 200 cm² using ECSSFF design as cathode channel and parallel design as anode channel. Performance of these cells are also compared against the performance of cells with triple serpentine flow design on cathode side. The results demonstrate the superiority of ECSSFF for all active areas in terms of offering higher currents, lower pressure drop and higher power output. The percentage increase in the net power output with ECSSFF design over TSFF design increases from 4.5% to 13.5% with increase in cell area from 50 cm² to 200 cm². The percentage drop in net power density with increase in active area for ECSSFF design is almost 55% less compared to that with triple serpentine design.The study establishes that the ECSSFF is a potential flow field design to be considered for higher area fuel cells for large scale power production.     

Study of novel flow channels influence on the performance of direct methanol fuel cell

The existing flow channels like parallel and gird channels have been modified for better fuel distribution in order to boost the performance of direct methanol fuel cell. The main objective of the work is to achieve minimized pressure drop in the flow channel, uniform distribution of methanol, reduced water accumulation, and better oxygen supply. A 3D mathematical model with serpentine channel is simulated for the cell temperature of 80 °C, 0.5 M methanol concentration. The study resulted in 40 mW/cm² of power density and 190 mA/cm² of current density at the operating voltage of 0.25 V. Further, the numerical study is carried out for modified flow channels to discuss their merits and demerits on anode and cathode side. The anode serpentine channel is unmatched by the modified zigzag and pin channels by ensuring the better methanol distribution under the ribs and increased the fuel consumption. But the cathode serpentine channel is lacking in water management. The modified channels at anode offered reduced pressure drop, still uniform reactant distribution is found impossible. The modified channels at cathode outperform the serpentine channel by reducing the effect of water accumulation, and uniform oxygen supply. So the serpentine channel is retained for methanol supply, and modified channel is chosen for cathode reactant supply. In comparison to cell with only serpentine channel, the serpentine anode channel combined with cathode zigzag and pin channel enhanced power density by 17.8% and 10.2% respectively. The results revealed that the zigzag and pin channel are very effective in mitigating water accumulation and ensuring better oxygen supply at the cathode.     

Characterisation tools development for PEM electrolysers

Electrochemical impedance spectroscopy (EIS), current interrupt (CI) and current mapping (CM) were investigated as in-situ characterisation tools for PEM electrolysers. A 25 cm² cell with titanium anode and carbon cathode plates were utilised in this study. A commercial MEA consisting of 1 mg IrO₂/cm² on the anode and 0.3 mg Pt/cm² on the cathode was used. The electrocatalyst was deposited on Nafion^® membranes. The electrochemical losses in a PEM electrolyser namely: activation, ohmic and mass transfer losses were identified using EIS and CI and both the advantages and disadvantages of the methods were discussed. The current distribution over the membrane electrode assembly (MEA) at different current densities was measured using the current mapping method. It is also shown that under the given experimental conditions the current density decreases along the serpentine flow field.     

Development of a four‐cell DMFC stack with air‐breathing cathode and dendrite flow field

A four‐cell direct methanol fuel cell (DMFC) stack with an air‐breathing cathode with an active area of 0.48 cm² for each cell is designed, fabricated and tested. A pure copper sheet 300 µm thick with innovative perforated flow plates (dendrite type) is fabricated and used for the cathode. For the anode, conventional serpentine flow channels made of pure copper sheets 250 µm thick are used. An extensive parametric study is conducted to determine the optimum working conditions for the fuel flow rate (anode), methanol solution concentration, channel‐to‐land ratio and stack temperature. Comparisons are made with conventional serpentine flow channels. In addition, CO₂ (water) bubbles in the anode (cathode) channels are visualized, and the results are presented and discussed. It is found that the maximum stack power of the four‐cell μDMFC stack is up to 40 mW/cm² with a limiting current density of 335 mA/cm² at a maximum volumetric and gravimetric power density of 11.16 mW/cm³ and 3.13 W/kg, respectively. Copyright © 2014 John Wiley & Sons, Ltd.     

Performance tests of a double-passive μDMFC stack with parallel/dendrite flow field

We report an experimental study on the effect of different flow fields on the cell performance of a double-passive (both anode/cathode) μDMFC stack. Cell performance measurements were made and analyzed for seven different flow field combinations at the anode/cathode of a passive micro direct methanol fuel cell (μDMFC) stack. An optimum flow field combination, after taking a series of tests under different operating conditions, was obtained. The results show that the conventional parallel type flow field used at the anode with an innovative/new dendrite perforated type of 80° flow field can provide the best power density for both single cell and 8-cell stack which have a power density of 16.9 mA/cm² at 50 °C and 1 M methanol solution. Moreover, for an 8-cell stack, both the gravimetric and volumetric power densities can be up to 7.4 W/kg and 37.2 W/L, respectively.     

Air-breathing membraneless laminar flow-based fuel cell with flow-through anode

This paper describes a detailed characterization of laminar flow-based fuel cell (LFFC) with air-breathing cathode for performance (fuel utilization and power density). The effect of flow-over and flow-through anode architectures, as well as operating conditions such as different fuel flow rates and concentrations on the performance of LFFCs was investigated. Formic acid with concentrations of 0.5 M and 1 M in a 0.5 M sulfuric acid solution as supporting electrolyte were exploited with varying flow rates of 20, 50, 100 and 200 μl/min. Because of the improved mass transport to catalytic active sites, the flow-through anode showed improved maximum power density and fuel utilization per single pass compared to flow-over planar anode. Running on 200 μl/min of 1 M formic acid, maximum power densities of 26.5 mW/cm² and 19.4 mW/cm² were obtained for the cells with flow-through and flow-over anodes, respectively. In addition, chronoamperometry experiment at flow rate of 100 μl/min with fuel concentrations of 0.5 M and 1 M revealed average current densities of 34.2 mA/cm² and 52.3 mA/cm² with average fuel utilization of 16.3% and 21.4% respectively for flow-through design. The flow-over design had the corresponding values of 25.1 mA/cm² and 35.5 mA/cm² with fuel utilization of 11.1% and 15.7% for the same fuel concentrations and flow rate.     

Designing,modeling and performance investigation of bio-inspired flow field based DMFCs

In an attempt to improve upon conventional flow fields (e.g., serpentine flow field), Murray's Law was applied to design two different bio-inspired, leaf-shaped flow fields. This law governs the dimensions of natural networks, such as: the veins within plant leaves and human lungs. In this study, the serpentine, the lung, and the two leaf-shaped flow fields were used to form seven different anode–cathode combinations. The experiments focused on the effects of methanol concentration (0.50 M, 0.75 M, and 1.00 M) and the combined effect of methanol and oxygen flow rates (1.3 ml/min methanol and 400 ml/min oxygen, as well as 2 and 3 times both of these flow rates). An analytical model was also developed to help understand the experimental results. The results show that the highest performance could be achieved when the bio-inspired configurations were used on the cathode. The best configuration was the serpentine (anode) – second leaf design (cathode), with a peak power density of 888 W/m². For comparison, a peak power density of 824 W/m² was achieved when the serpentine flow field was used on the anode and cathode. Furthermore, of all the tested configurations, the lung-based flow field provided the lowest performance in all tests.     

Scaling factors for channel width variations in tree-like flow field patterns for polymer electrolyte membrane fuel cells - An experimental study

To have a uniform distribution of reactants is an advantage to a fuel cell. We report results for such a distributor with tree-like flow field plates (FFP). Numerical simulations have shown that the width scaling parameters of tree-like patterns in FFPs used in polymer electrolyte membrane fuel cells (PEMFC) reduces the viscous dissipation in the channels. In this study, experimental investigations were conducted on a 2-layer FF plate possessing a tree-like FF pattern which was CNC milled on high-quality graphite. Three FF designs of different width scaling parameters were employed. I–V curves, power curves and impedance spectra were generated at 70%, 60% and 50% relative humidity (25 cm² active area), and compared to those obtained from a conventional 1-channel serpentine FF. It was found that the FF design, with a width scaling factor of 0.917 in the inlet and 0.925 in the outlet pattern, exhibited the best peak power out of the three designs (only 11% - 0.08 W/cm² lower than reference serpentine FF). Results showed that a reduction of the viscous dissipation in the flow pattern was not directly linked to a PEMFC performance increase. It was found that water accumulation, together with a slight increase in single PEMFC resistance, were the main reasons for the reduced power density. As further improvements, a reduction of the number of branching generation levels and width scaling factor were recommended.     

A flexible on-fiber H2O2 microfluidic fuel cell with high power density

To promote the simplification and integration of membraneless microfluidic fuel cell (MMFC) system and combine with flexible portable devices, a flexible on-fiber MMFC exploiting H₂O₂ as sole reactant is presented, eliminating the separation requirement of fuel and oxidant. Nickel (Ni) nano-particles and Prussian blue with multiwalled carbon nanotube (PB-MWCNT) are coated on hydrophilic braided carbon fibers (BCFs) to serve as the anode and cathode, respectively. The three-dimensional (3D) flow-through anode and cathode with a wealth of exposed electroactive sites improve reactant mass transfer. The anode and cathode are respectively wound on both sides of the middle cotton thread-based flow channel for separation. Under the combination of capillary force and gravity, reactants flow continuously through the fiber-based microchannels without external pumps. Importantly, the H₂O₂ MMFC achieves the highest maximum power density (MPD) of 14.41 mW cm^?2 so far in one-chamber or single-stream H₂O₂ fuel cells. Besides, no serious deterioration in the power-generation performance is observed in complex practical operating conditions including bending with various angles, repeated folding and dropping. Three presented flexible MMFCs are connected to power a handheld calculator, indicating the tremendous potential of developing micro power supplies based on abundant flexible materials as well as green and sustainable energy.     

Optimization of process parameters using response surface methodology (RSM) for power generation via electrooxidation of glycerol in T-Shaped air breathing microfluidic fuel cell (MFC)

The present work focuses on the optimization of operating parameters using Box Behnken design (BBD) in RSM to obtain maximum power density from a glycerol based air-breathing T-shaped MFC. The major parameters influencing the experiment for enhancing the cell performance in MFC are glycerol/fuel concentration, anode electrolyte/KOH concentration, anode electrocatalyst loading and cathode electrolyte/KOH concentration. The ambient oxygen is used as the oxidant. The acetylene black carbon (C_AB) supported laboratory synthesized electrocatalyst Pd–Pt (16:4)/C_AB is used as anode electrocatalyst and commercial Pt (40 wt%)/C_HSA as the cathode electrocatalyst. The quadratic model predicts the appropriate operating conditions to achieve highest power density from the laboratory designed T-shaped MFC. The p-value of less than 0.0001 and F-value of greater than 1 i.e., 26.32 indicate that the model is significant. The optimum conditions predicted by the RSM model were glycerol concentration of 1.07 M, anode electrolyte concentration of 1.62 M anode electrocatalyst loading of 1.12 mg/cm² and cathode electrolyte concentration of 0.69 M. The negligible deviation of only 1.07% between actual/experimental power density (2.76 mW/cm²) and predicted power density (2.79 mW/cm²) was recorded. This model reasonably predicts the optimum conditions using Pd–Pt (16:4)/C_AB electrocatalyst to obtain maximum power density from glycerol based MFC.     

Three-dimensional anode engineering for the direct methanol fuel cell

Catalyzed graphite felt three-dimensional anodes were investigated in direct methanol fuel cells (DMFCs) operated with sulfuric acid supporting electrolyte. With a conventional serpentine channel flow field the preferred anode thickness was 100 μm, while a novel flow-by anode showed the best performance with a thickness of 200-300 μm. The effects of altering the methanol concentration, anolyte flow rate and operating temperature on the fuel cell superficial power density were studied by full (2³ + 1) factorial experiments on a cell with anode area of 5 cm² and excess oxidant O₂ at 200 kPa(abs). For operation in the flow-by mode with 2 M methanol at 2 cm³ min⁻¹ and 353 K the peak power density was 2380 W m⁻² with a PtRuMo anode catalyst, while a PtRu catalyst yielded 2240 W m⁻² under the same conditions.     

Analyze the effects of flow mode and humidity on PEMFC performance by equivalent membrane conductivity

A three‐dimensional and two‐phase numerical model is developed for a 25‐cm² proton exchange membrane fuel cell (PEMFC) to investigate the effects of flow mode (coflow and counterflow) and relative humidity (anode 0%/100%; cathode 60%/100%) on the cell performance. Experimental studies are performed to validate this developed model. An equivalent membrane conductivity is proposed to describe the match level between current flux and membrane conductivity. It is found that the cell performance is enhanced under low relative humidity conditions because of the optimized equivalent membrane conductivity. More specifically, the voltage is improved from 0.611 to 0.637 V, and the equivalent membrane conductivity is enhanced from 10.35 to 11.11 S m^?1 by replacing the coflow mode with counterflow mode at 1000 mA cm^?2 when anode gas is dry and cathode gas is 100% hydrated. Both the anode and cathode relative humidities show an obvious influence on the PEMFC performance, and a suitable inlet humidity could ensure adequate hydration of membrane and avoid water flooding in gas diffusion layers simultaneously.     

Investigation of the effect of cathode stoichiometry of proton exchange membrane fuel cell using localized electrochemical impedance spectroscopy based on print circuit board

Proton Exchange Membrane Fuel Cell can have a large active area, and the working condition in different areas can be entirely different. Localized electrochemical impedance spectroscopy can directly observe the proton exchange membrane fuel cell internal reaction conditions. In this work, localized electrochemical impedance spectroscopy test system based on print circuit board is implemented in a 50 cm² multi-channel serpentine flow fields. The localized electrochemical impedance spectroscopy performances of different segments with different cathode stoichiometry (1.8, 2.3 and 2.8) at different current density (100  mA cm⁻², 500  mA cm⁻² and 900 mA cm⁻²) are studied. The result demonstrates that the fuel cell may suffer from local drying and flooding at the same time. To make full use of the potential of a fuel cell, a suitable cathode stoichiometry should be identified to control the drying of the inlet and the flooding of the outlet at the same time. It is shown that a cathode stoichiometry of 2.3 is close to the optimum cathode stoichiometry to keep the fuel cell in good consistency without gas waste. Besides, a current density distribution measurement is performed to verify the conclusions of this work.     

Direct methanol fuel cell operation with pre-stretched recast Nafion

Direct methanol fuel cell operation with uniaxially pre-stretched recast Nafion^® membranes (draw ratio of 4) was investigated and compared to that with commercial (un-stretched) Nafion^®. The effects of membrane thickness (60–250 μm) and methanol feed concentration (0.5–10.0 M) on fuel cell power output were quantified for a cell temperature of 60 °C, ambient pressure air, and anode/cathode catalyst loadings of 4.0 mg cm⁻². Pre-stretched recast Nafion^® in the 130–180 μm thickness range produced the highest power at 0.4 V (84 mW cm⁻²), as compared to 58 mW cm⁻² for Nafion^® 117. MEAs with pre-stretched recast Nafion^® consistently out-performed Nafion^® 117 at all methanol feed concentrations, with 33–48% higher power densities at 0.4 V, due to a combination of low area-specific resistance (the use of a thinner pre-stretched membrane, where the conductivity was the same as that for commercial Nafion^®) and low methanol crossover (due to low methanol solubility in the membrane). Very high power was generated with a 180-μm thick pre-stretched recast Nafion^® membrane by increasing the cell temperature to 80 °C, increasing the anode/cathode catalyst loading to 8.0 mg cm⁻², and increasing the cathode air pressure to 25 psig. Under these conditions the power density at 0.4 V for a 1.0-M methanol feed solution was 240 mW cm⁻² and the maximum power density was 252 mW cm⁻².     

In situ investigation of water transport in an operating PEM fuel cell using neutron radiography: Part 1 – Experimental method and serpentine flow field results

Effective management of liquid water produced in the cathodic reaction of a polymer electrolyte membrane (PEM) fuel cell is essential to achieve high cell efficiency. Few experimental methods are available for in situ measurements of water transport within an operating cell. Neutron radiography is a useful tool to visualize water within a cell constructed of many common materials, including metals. The application of neutron radiography to measurements of water content within the flow field channels of an operating 50 cm² PEM fuel cell is described. Details of the experimental apparatus, image processing procedure and quantitative analysis are provided. It is demonstrated that water tends to accumulate in the 180° bends of the serpentine anode and cathode flow fields used in this study. Moreover, the effects of both the current density and cathode stoichiometric ratio on the quantity of accumulated water are discussed.     

Investigation of anode flow field for direct dimethyl ether fuel cell

In this work, we presented the novel anode flow field for direct dimethyl ether fuel cell (DDFC). The anode flow field of the DDFC consisted of hydrophilic, hydrophobic, and diffusion region (with a ratio of region areas of 3:6:1). The maximum power density of the DDFC with novel anode flow field was 67 mW cm⁻², which was higher than that of the cell fed with conventional flow field (60 mW cm⁻²). The electrochemical impedance spectra analyses revealed that the mass transfer resistance of novel anode flow field was lower than that of conventional flow field. The constant current operation curves showed that the performance decay ratio of the novel anode flow field was lower than that of conventional one. It indicated that the novel flow field benefited the long-term operation of DDFC.     

Development of micro direct methanol fuel cells for high power applications

A micro direct methanol fuel cell (μDMFC) with active area of 1.625 cm² has been developed for high power portable applications and its electrochemical characterization carried out in this study. The fragility of the silicon wafer makes it difficult to compress the cell for good sealing and hence to reduce contact resistance in the Si-based μDMFC. We have instead used very thin stainless steel plates as bipolar plates with the flow field machined by photochemical etching technology. For both anode and cathode flow fields, widths of both the channel and rib were 750 μm, with a channel depth of 500 μm. A gold layer was deposited on the stainless steel plate to prevent corrosion. This study used an advanced MEA developed in-house featuring a modified anode backing structure with a compact microporous layer. Maximum power density of the micro DMFC reached 62.5 mW cm⁻² at 40 °C, and 100 mW cm⁻² at 60 °C at atmospheric pressure, which almost doubled the performance of our previous Si-based μDMFC.     

Effect of non-uniform parallel channel on performance of passive direct methanol fuel cell

In this paper, the effects of current collector on passive direct methanol fuel cell's (passive DMFC) performance and removing CO₂ gas is studied. For this purpose, a single cell with two arrangements of current collector in anode and cathode side is considered. In first arrangement, non-uniform parallel channels with 53.76% open ratio is used in the anode side and a perforated flow field with 34.5% open ratio is applied in the cathode side. In second arrangement, uniform parallel channels with 42.28% open ratio has been used in both anode and cathode sides. At the first arrangement, a maximum power of 20 mW cm⁻² in 4 M methanol concentrations and in the second arrangement a maximum power of 17.7 mW cm⁻² in 5 M methanol concentrations has been obtained. Furthermore, it is shown that using the current collector with non-uniform parallel channels is more effective in removing CO₂ gas than other parallel channels.     

High performance alkaline-acid direct glycerol fuel cells for portable power supplies via electrode structure design

Alkaline-acid direct glycerol fuel cells (AA-DGFC) were fabricated and primarily proven to be used as portable power generating devices. Pt/C catalyst was used as electrocatalyst for both anode and cathode. The optimal operating condition for cathode was firstly tested. Then the effects of types of backing and microporous layer on the cell performance and stability were investigated to obtain the optimal electrode structure. The cell performance was determined by using both chronoamperometry technique at a constant voltage of 0.4 V, and cell polarization with impedance measurement. The maximum peak power density obtained from the cell was 375 mW cm⁻² and the highest average current density discharged from the cell was 451 mA cm⁻². Non-wetproof carbon cloth is suitable as the backing layer for both the anode and cathode. Although MPL did not directly affect the cell performance, it greatly improved stability of the current discharged during chronoamperometric test. The cathode favors hydrophilic MPL, while hydrophobic MPL was preferred on the anode.     

Investigating the effects of operational factors on PEMFC performance based on CFD simulations using a three-level full-factorial design

This study uses the 3³ full-factorial design, a factorial arrangement with three factors at three-levels, to investigate the main and interaction effects of design parameters on the performance of a single 25 cm² PEMFC cell. The factors considered in this study include the flow channel design, the operational temperature, and the relative humidity of the cathode gas mixture. The gas flow channel patterns for both the anode side and the cathode side are the same as a straight parallel channel design and two modified parallel channel designs. The operational temperatures are selected as 333 K, 343 K, and 353 K. The relative humidity of the cathode gas mixture varies from 50% to 100% at 25% intervals, while the relative humidity of the anode gas mixture remains fixed at 100%. All runs are conducted with a three-dimensional, non-isothermal steady-state fuel cell computational fluid dynamic model (FCFD) with specified boundary conditions. The FCFD model can not only output the polarization curve, but also predict complex multi-physics flow, thermal, mass and ion transport phenomena inside the tiny fuel cell multi-layer structures. This full-factorial design of experimental method reveals that it is possible to not only explore the main effects of this complex multi-physics problem, but also investigate the effects of two-factor interactions for generating maximum power density. Results show that the flow channel design has the most significant effect on the polarization curve; the next is the cell temperature, while the relative humidity of the cathode gas mixture plays only a minor role.