Experimental evaluation of CO poisoning on the performance of a high temperature proton exchange membrane fuel cell

We experimentally studied a high temperature proton exchange membrane (PEM) fuel cell to investigate the effects of CO poisoning at different temperatures. The effects of temperature, for various percentages of CO mixed with anode hydrogen stream, on the current-voltage characteristics of the fuel cell are investigated. The results show that at low temperature, the fuel cell performance degraded significantly with higher CO percentage (i.e., 5% CO) in the anode hydrogen stream compared to the high temperature. A detailed electrochemical analysis regarding CO coverage on electrode surface is presented which indicates that electrochemical oxidation is favorable at high temperature. A cell diagnostic test shows that both 2% CO and 5% CO can be tolerated equally at low current density (<0.3 A cm⁻²) with high cell voltage (>0.5 V) at 180 °C without any cell performance loss. At high temperature, both 2% CO and 5% CO can be tolerated at higher current density (>0.5 A cm⁻²) with moderate cell voltage (0.2-0.5 V) when the cell voltage loss within 0.03-0.05 V would be acceptable. The surface coverage of platinum catalyst by CO at low temperature is very high compared to high temperature. Results suggest that the PEM fuel cell operating at 180 °C or above, the reformate gas with higher CO percentage (i.e., 2-5%) can be fed to the cell directly from the fuel processor.     

Performance of alkaline electrolyte-membrane-based direct ethanol fuel cells

A single alkaline direct ethanol fuel cell (alkaline DEFC) with an anion-exchange membrane and non-platinum (non-Pt) catalysts is designed, fabricated, and tested. Particular attention is paid to investigating the effects of different operating parameters, including the cell operating temperature, concentrations of both ethanol and the added electrolyte (KOH) solution, as well as the mass flow rates of the reactants. The alkaline DEFC yields a maximum power density of 60 mW cm⁻², a limiting current density of about 550 mA cm⁻², and an open-circuit voltage of about 900 mV at 40 °C. The experimental results show that the cell performance is improved on increasing the operating temperature, but there exists an optimum ethanol concentration under which the fuel cell has the best performance. In addition, cell performance increases monotonically with increasing KOH concentration in the region of low current density, while in the region of high current density, there exists an optimum KOH concentration in terms of cell performance. The effect of flow rate of the fuel solution is negligible when the ethanol concentration is higher than 1.0 M, although the cell performance improves on increasing the oxygen flow rate.     

Effect of cathode design on the performance of an air-breathing PEM fuel cell

Effect of cathode design on the performance of an air-breathing fuel cell is studied using a three dimensional, non-isothermal, steady state and single phase model developed using commercial CFD software FLUENT (version 6.3). Performances of ducted (channel) and ribbed (planar) cathode designs are compared and the cell characteristics such as current density, species, temperature distributions, velocity and net water transport coefficient are presented. Peak power density obtained for the cell with ducted cathode is 205 m W/cm², whereas with ribbed cathode it is 232 m W/cm². The limiting current density of the cell with ribbed cathode (690 m A/cm²) is much higher than that of the cell with ducted cathode (430 m A/cm²). The performance curves as well as the cell characteristics show that the ribbed cathode design is a better configuration compared to ducted design. Cell orientation has a significant effect on the cell performance. Best performance is obtained when the cell is oriented vertically for both ribbed and ducted cathode designs.     

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.     

Fabrication and evolution of catalyst-coated membranes by direct spray deposition of catalyst ink onto Nafion membrane at high temperature

An improved fabrication technique for catalyst-coated membrane (CCM), characterized by high-temperature spray deposition and immobilization of the membrane with a pyrex glass via Van der Walt force, was developed. The high heating temperature minimized the adsorption of liquid ethanol by the Nafion membrane and also resulted in the firm adhesion of the membrane to the pyrex glass, both processes suppressed the dimensional change of the membrane during the fabrication. The as-fabricated CCMs were analyzed by I–V polarization, cyclic voltammetry and electrochemical impedance spectroscopy. A comparative study was also made with the conventional hot-pressed membrane-electrode assembly with identical Pt catalyst loading of 0.4 mg cm⁻². Higher catalyst utilization and better cell performance were observed for the cell based on the CCM configuration. A peak power density of ∼715 mW cm⁻² was achieved when oxygen was the cathode atmosphere and hydrogen was the fuel at ambient pressure.     

Experimental analysis of spatio-temporal behavior of anodic dead-end mode operated polymer electrolyte fuel cell

During the anodic dead-end mode operation of fuel cells, the inert gases (nitrogen and water) present in the cathode side gas channel permeate to the anode side and accumulate in the anode gas channel. The inert gas accumulation in the anode decreases the fuel cell performance by impeding the access of hydrogen to the catalyst. The performance of fuel cell under potentiostatic dead-end mode operation is shown to have three distinct regions viz. time lag region, transient current region and a steady state current region. A current distribution measurement setup is used to capture the evolution of the current distribution as a function of time and space. Co- and counter-flow operations of dead-end mode confirm the propagation of inert gas from the dead-end of anode channel to the inlet of anode. Experiments with different oxidants, oxygen and air, under dead-end mode confirm that nitrogen which permeates from cathode to anode causes the performance drop of the fuel cell. For different starting current densities of 0.15 A cm⁻², 0.3 A cm⁻² and 0.6 A cm⁻² the inert gas occupies 35%, 45% and 57%, respectively of anode channel volume at the end of 60 min of dead-end mode operation.     

Low and high temperature storage characteristics of membrane electrode assemblies for direct methanol fuel cells

This paper investigates changes in the performance of membrane electrode assemblies (MEAs) of Direct Methanol Fuel Cells (DMFC) that are caused by undergoing storage at −10 °C and 60 °C under different experimental conditions. Storage at 60 °C exhibited negative effects on an MEA’s performance only when storing the MEA at a 4 M CH₃OH solution. Here, application of a reverse current for 10 s was found to reinstall the original performance. The effect of storage at −10 °C on an MEA’s performance strongly depends upon the MEA’s properties. MEAs are grouped into three different categories with regard to their suitability for low temperature storage: not affected, temporarily affected, irreversibly affected. The temporarily affected MEAs could be instantly and completely reactivated by a reverse current. Changes in the MEA properties that had been caused by being stored at −10 °C were investigated for two MEAs using electrochemical methods, scanning electron microscopy and porosity measurements. The following MEA materials and manufacturing methods had been found to be principally suitable to build MEAs tolerant to storage at −10 °C: the manufacturing methods CCM (catalyst coated on the membrane) and CCS (catalyst coated on the substrate), several hydrocarbon membranes, high Pt and Pt-Ru catalyst loadings. By carefully selecting the proper MEA material, MEAs with tolerance towards low and high storage temperatures can be designed.     

Polymer electrolyte fuel cells based on phosphoric acid doped polybenzimidazole (PBI) membranes

In order to make fuel cells with high power density the structure and morphology for the three-dimensional gas diffusion electrodes (GDEs) are very important. A preparation technique for GDEs for phosphoric acid doped polybenzimidazole (PBI) is presented. Teflon treatment of the backing material was found to be beneficial for the performance of the electrodes, and explained by higher total porosity. In general the open circuit voltage (OCV) with PBI-based cells is 0.9 V. The observed low OCV was explained by slow kinetic for the oxygen reduction and cross over of the reactants. The performance of the fuel cells is found to increase with increasing temperature; this was explained by faster reaction kinetic and higher membrane conductivity. A typical power output was 0.3–0.4 W cm⁻² at 0.6 V and 175 °C.     

Effect of various coal contaminants on the performance of solid oxide fuel cells: Part I. Accelerated testing

The contaminants that are potentially present in the coal-derived gas stream and their thermochemical nature are discussed. Accelerated testing was carried out on Ni-YSZ/YSZ/LSM solid oxide fuel cells (YSZ: yttria stabilized zirconia and LSM: lanthanum strontium manganese oxide) for eight main kind of contaminants: CH₃Cl, HCl, As, P, Zn, Hg, Cd and Sb at the temperature range of 750-850 °C. The As and P species, at 10 and 35 ppm, respectively, resulted in severe power density degradation at temperatures 800 °C and below. SEM and EDX analysis indicated that As attacked the Ni region of the anode surface and the Ni current collector, caused the break of the current collector and the eventual cell failure at 800 °C. The phosphorous containing species were found in the bulk of the anode, they were segregated and formed “grain boundary” like phases separating large Ni patches. These species are presumably nickel phosphide/phosphate and zirconia phosphate, which could break the Ni network for electron transport and inhibit the YSZ network for oxygen ion transport. The presence of 40 ppm CH₃Cl and 5 ppm Cd only affected the cell power density at above 800 °C and Cd caused significant performance loss. Whereas the presence of 9 ppm Zn, 7 ppm Hg and 8 ppm Sb only degraded the cell power density by less than 1% during the 100 h test in the temperature range of 750-850 °C.     

Performance of an integrated composite membrane electrode assembly in DMFC

We report here the performance of a metal-based integrated composite membrane electrode assembly (IC-MEA) in direct methanol fuel cell (DMFC). The IC-MEA integrates the multi-functions of a conventional MEA, gas diffusion layer (GDL) and current collector. It was fabricated by impregnating Nafion electrolyte into a sandwiched structure containing expanding-Polytetrafluoroethylene (e-PTFE) and porous titanium sheets and subsequently coating with catalyst layer and microporous layer (MPL). While operating with air and 2 M methanol under ambient pressure, the IC-MEA in DMFC can yield a maximum power density of 19 mW cm⁻² at 26 °C, higher than a in-house made Nafion 115 MEA under the same working conditions. The IC-MEAs has been successfully applied to planar multi-cell stacks.     

Nafion/SiO2 hybrid membrane for vanadium redox flow battery

Sol–gel derived Nafion/SiO₂ hybrid membrane is prepared and employed as the separator for vanadium redox flow battery (VRB) to evaluate the vanadium ions permeability and cell performance. Nafion/SiO₂ hybrid membrane shows nearly the same ion exchange capacity (IEC) and proton conductivity as pristine Nafion 117 membrane. ICP-AES analysis reveals that Nafion/SiO₂ hybrid membrane exhibits dramatically lower vanadium ions permeability compared with Nafion membrane. The VRB with Nafion/SiO₂ hybrid membrane presents a higher coulombic and energy efficiencies over the entire range of current densities (10–80 mA cm⁻²), especially at relative lower current densities (<30 mA cm⁻²), and a lower self-discharge rate compared with the Nafion system. The performance of VRB with Nafion/SiO₂ hybrid membrane can be maintained after more than 100 cycles at a charge–discharge current density of 60 mA cm⁻². The experimental results suggest that the Nafion/SiO₂ hybrid membrane approach is a promising strategy to overcome the vanadium ions crossover in VRB.     

Performance of a high temperature polymer electrolyte membrane water electrolyser

A high temperature polymer electrolyte membrane water electrolyser (PEMWE) was investigated at temperatures between 80 and 130 °C and pressures between 0.5 and 4 bar. Nanometer size Ru_0.7Ir_0.3O₂ and Pt/C were employed as anode and cathode catalysts respectively. The catalyst coated on membrane (CCM) method was used to fabricate the membrane electrode assemblies. The membrane, oxygen evolution catalysts and MEAs were characterized with SEM, XRD and TEM. The influence of high temperature and pressure was investigated using in situ electrochemical measurements. Increasing temperature and pressure produced higher current densities for oxygen evolution, and smaller terminal voltages. The high temperature PEMWE achieved a voltage of 1.51 V at a current density of 1 A cm⁻², at 130 °C and 4 bar pressure.     

Membrane electrode assembly degradation by dry/wet gas on a PEM fuel cell

The vehicle that use a Polymer Electrolyte Membrane Fuel Cell (PEMFC) as a power source frequently experiences start up and shut down. Membrane Electrode Assembly (MEA) degradation by wet/dry gas repetition was studied for vehicle start up and shut down. The time of the wet/dry equilibrium state on the PEMFC was measured with High Frequency Resistance (HFR). The gas injection time was 20 min and 5 min for dry gas and wet gas, respectively. An experiment was carried out using electrochemical methods and a cross-section of the MEA was visualized with a Field Emission Scanning Electron Microscope (FE-SEM). After 1200 wet/dry cycles, the performance of the cell decreased by 45.7% to its current density of 800 mA/cm². Ohmic and charge transfer resistances of the cell increased in the Electrochemical Impedance Spectroscopy (EIS). The crossover current of hydrogen also increased in the linear sweep voltammetry (LSV). The reduction of the electrochemical active surface area (ECSA) was confirmed through cyclic voltammetry (CV). The interface among the membrane, catalyst layer, and gas diffusion layer was separated and significantly deteriorated compared with fresh MEA.     

Performance of micro-PEM fuel cells with different flow fields

Four designs of flow fields were applied to micro-proton exchange membrane fuel cells (μ-PEMFCs) using microelectromechanical system (MEMS) technology. The flow fields and membrane electrolyte assembly (MEA) of 2.25 cm² active area were assembled to μ-PEMFCs. Electrochemical behaviors of these μ-PEMFCs were investigated by polarization method at reactants flow rates of 15 ml min⁻¹, 30 ml min⁻¹ and 50 ml min⁻¹, respectively. This study emphasized the effects of different topologies of flow fields on performance of μ-PEMFCs. Results demonstrated that μ-PEMFCs with different flow fields have similar behavior at reactants flow rates of 50 ml min⁻¹. However, at reactants flow rates of 15 ml min⁻¹ and 30 ml min⁻¹, performance of the μ-PEMFC with long and narrow micro-channels rapidly deteriorated due to the flooding in micro-channels. The mixed serpentine design had a good ability to resist the flooding, but it displayed a low maximum power density because of its short effective length of micro-channels. The results in this study suggested that the μ-PEMFC with a mixed multichannel design flow field and long micro-channels yielded the best performance.     

Effect of platinum amount in carbon supported platinum catalyst on performance of polymer electrolyte membrane fuel cell

The performance of polymer electrolyte membrane fuel cells fabricated with different catalyst loadings (20, 40 and 60 wt.% on a carbon support) was examined. The membrane electrode assembly (MEA) of the catalyst coated membrane (CCM) type was fabricated without a hot-pressing process using a spray coating method with a Pt loading of 0.2 mg cm⁻². The surface was examined using scanning electron microscopy. The catalysts with different loadings were characterized by X-ray diffraction and cyclic voltammetry. The single cell performance with the fabricated MEAs was evaluated and electrochemical impedance spectroscopy was used to characterize the fuel cell. The best performance of 742 mA cm⁻² at a cell voltage of 0.6 V was obtained using 40 wt.% Pt/C in both the anode and cathode.     

Improved performance of air-cathode single-chamber microbial fuel cell for wastewater treatment using microfiltration membranes and multiple sludge inoculation

Substantial optimization and cost reduction are required before microbial fuel cells (MFCs) can be practically applied. We show here the performance improvement of an air-cathode single-chamber MFC by using a microfiltration membrane (MFM) on the water-facing side of the cathode and using multiple aerobic sludge (AES), anaerobic sludge (ANS), and wetland sediment (WLS) as anodic inoculums. Batch test results show that the MFC with an MFM resulted in an approximately two-fold increase in maximum power density compared to the MFC with a proton exchange membrane (PEM). The Coulombic efficiency increased from 4.17% to 5.16% in comparison with the membrane-less MFC, without a significant negative effect on power generation and internal resistance. Overall performance of the MFC was also improved by using multiple sludge inoculums in the anode. The MFC inoculated with ANS + WLS produced the greatest maximal power density of 373 mW m⁻² with a substantially low internal resistance of 38 Ω. Higher power density with a decreased internal resistance was also achieved in MFC inoculated with ANS + AES and ANS + AES + WLS in comparison with those inoculated with only one sludge. The MFCs inoculated with AES + ANS achieved the highest Coulombic efficiency. Over 92% COD was removed from confectionery wastewater in all tested MFCs, regardless of the membrane or inoculum used.     

Investigations on high performance proton exchange membrane water electrolyzer

In order to improve proton exchange membrane water electrolyzer (PEMWE) performance, some factors related to the processes of preparing the Membrane Electrode Assemblies (MEAs), such as iridium (Ir) electrocatalyst loading and Nafion^® content at the anode, thicknesses of proton exchange membrane and gas diffusion layers (GDLs), were examined. In addition, a home-made supported Ir/titanium carbide (Ir/TiC, 20% Ir by weight) was developed for the anode. With best commercial Ir catalyst loading of 1.5 mg cm⁻² Ir at the anode, the cell's current densities of 1346 mA cm⁻², 1820 mA cm⁻² and 2250 mA cm⁻² were achieved at the cell potentials of 1.80 V, 1.90 V and 2.00 V, respectively. A PEMWE with 0.3 mg cm⁻² Ir loading of Ir/TiC anode catalyst was comparatively stable and gave current densities of 840 mA cm⁻², 1130 mA cm⁻² and 1463 mA cm⁻² at the cell potentials of 1.80 V, 1.90 V and 2.00 V, respectively. Based on catalysis efficiency of Amperes per milligram of Ir, the Ir/TiC catalyst is found to be more active than unsupported Ir catalyst.     

Effect of carbon fiber paper made from carbon felt with different yard weights on the performance of low temperature proton exchange membrane fuel cells

This study employed fuel cell gas diffusion layers (GDLs) consisting of carbon fiber paper made from carbon fiber felt with different yard weights in proton exchange membrane fuel cells (PEMFCs), and investigated the relationship between the yard weight of the carbon fiber paper and the fuel cell performance and thickness of the gasket. In this paper we discuss the relationship between carbon fiber felt with different yard weights and fuel cell performance and also explore the effect of carbon fiber paper thickness, air permeability, surface resistivity, and structural study. We focused on the material used for the gas diffusion layer in this study. Carbon fiber paper made in-house in this study contained 10 wt% (all percentages are by weight unless otherwise noted) phenolic resin. When the tested area was 25 cm², the test temperature was 40 °C, the gasket thickness was 0.06 mm, and the yard weight 70 g m⁻², fuel cell current density was 1968 mA cm⁻² at a load 0.3 V. When the gasket thickness was 0.36 mm and yard weight was 190 g m⁻², fuel current density was 1710 mA cm⁻² at a load of 0.3 V.     

The influence of gas diffusion layer wettability on direct methanol fuel cell performance: A combined local current distribution and high resolution neutron radiography study

The influence of the anode and cathode GDL wettability on the current and media distribution was studied using combined in situ high resolution neutron radiography and locally resolved current distribution measurements. MEAs were prepared by vertically splitting either the anode or cathode carbon cloth into a less hydrophobic part (untreated carbon cloth ‘as received’) and a more hydrophobic part (carbon cloth impregnated by PTFE dispersion). Both parts were placed side by side to obtain a complete electrode and hot-pressed with a Nafion membrane. MEAs with partitioned anode carbon cloth revealed no difference between the untreated and the hydrophobised part of the cell concerning the fluid and current distribution. The power generation of both parts was almost equal and the cell performance was similar to that of an undivided MEA (110 mW cm⁻², 300 mA cm⁻², 70 °C). In contrast, MEAs with partitioned cathode carbon cloth showed a better performance for the hydrophobised part, which contributed to about 60% of the overall power generation. This is explained by facilitated oxygen transport especially in the hydrophobised part of the cathode gas diffusion layer. At an average current density of 300 mA cm⁻², a pronounced flooding of the cathode flow field channels adjacent to the untreated part of GDL led to a further loss of performance in this part of the cell. The low power density of the untreated part caused a significant loss of cell performance, which amounted to less than 40 mW cm⁻² (at 300 mA cm⁻²).     

Performance decay of proton-exchange membrane fuel cells under open circuit conditions induced by membrane decomposition

The degradation in performance of proton-exchange membrane fuel cells (PEMFCs) under open circuit conditions was investigated. The oxygen reduction reaction (ORR) kinetic current density at 0.9 V was found to decrease from 36 to 4 mA cm⁻² (geometric) without significant crossover increase or loss in the electrochemically active surface area. Cyclic voltammograms for the electrodes show characteristic changes, e.g. appearance of peaks at ∼0.2 V and shift of the onset of platinum oxide formation to higher potentials. It was identified that the large ORR kinetic decay has its origins in the reduction of available Pt sites due to adsorption of anions, which are postulated to be membrane decomposition products such as sulfate ions. Procedures carried out to condense water in the fuel cell led to the expulsion of anions out of the membrane electrode assembly (MEA) resulting in the partial recovery of ORR kinetic current density to 15 mA cm⁻². In order to attain complete performance recovery of the catalyst, a more effective and practical method to flush out the anions is desirable.