Membrane electrode assembly with Pt/SiO2/C anode catalyst for proton exchange membrane fuel cell operation under low humidity conditions

In this work, a novel self-humidifying membrane electrode assembly (MEA) with Pt/SiO₂/C as anode catalyst was developed to improve the performance of proton exchange membrane fuel cell (PEMFC) operating at low humidity conditions. The characteristics of the composite catalysts were investigated by XRD, TEM and water uptake measurement. The optimal performance of the MEA was obtained with the 10 wt.% of silica in the composite catalyst by single cell tests under both high and low humidity conditions. The low humidity performance of the novel self-humidifying MEA was evaluated in a H₂/air PEMFC at ambient pressure under different relative humidity (RH) and cell temperature conditions. The results show that the MEA performance was hardly changed even if the RHs of both the anode and cathode decreased from 100% to 28%. However, the low humidity performance of the MEA was quite susceptible to the cell temperature, which decreased steeply as the cell temperature increased. At a cell temperature of 50 °C, the MEA shows good stability for low humidity operating: the current density remained at 0.65 A cm⁻² at a usual work voltage of 0.6 V without any degradation after 120 h operation under 28% RH for both the anode and cathode.     

A parametric study of a platinum ruthenium anode in a direct borohydride fuel cell

Data on the performance of a direct borohydride fuel cell (DBFC) equipped with an anion exchange membrane, a Pt–Ru/C anode and a Pt/C cathode are reported. The effect of oxidant (air or oxygen), borohydride and electrolyte concentrations, temperature and anode solution flow rate is described. The DBFC gives power densities of 200 and 145 mW cm⁻² using ambient oxygen and air cathodes respectively at medium temperatures (60 °C). The performance of the DBFC is very good at low temperatures (ca. 30 °C) using modest catalyst loadings of 1 mg cm⁻² for anode and cathode. Preliminary data indicate that the cell will be stable over significant operating times.     

Experimental Investigation of Air Relative Humidity (RH) Cycling Tests on MEA/Cell Aging in PEMFC Part I: Study of High RH Cycling Test With air RH at 62%/100%

The effect of high air relative humidity (RH) cycling (RH_C 62%/100%) on the degradation mechanisms of a single (5 × 5 cm²) proton exchange membrane fuel cells was investigated. The cell performance was compared to a cell operated at constant humidification (RH_C = 62%). Runs were conducted over approximately 1,500 h at 0.3 A cm^–2. The overall loss in cell performance for the high RH cycling test was 12 μV h^–1 whereas it was at 3 μV h^–1 under constant humidification. Impedance spectroscopy reveals that the ohmic and charge transfer resistances were little modified in both runs. H₂ crossover measurement indicated that both high RH cycling and constant RH test did not promote serious effect on gas permeability. The electroactive surface loss for anode and cathode during high air RH cycling was more significant than at constant RH operation. The water uptake determined by ¹H nuclear magnetic resonance within the membrane electrode assembly (MEA) after high RH cycling was reduced by 12% in comparison with a fresh MEA. Transmission electron microscopy showed bubbles and pinholes formation in the membrane, catalyst particles agglomeration (also observed by X‐ray diffraction), catalyst particles migration in the membrane and thickness reduction of the catalytic layers. Scanning electron microscopy was conducted to observe the changes in morphology of gas diffusion layers after the runs.     

A Study on Process Parameters of Direct Ethanol Fuel Cell

Ethanol is one of the promising future fuels of Direct Alcohol Fuel Cells (DAFC). The electro‐oxidation of ethanol fuel on anode made of carbon‐supported Pt‐Ru electrode catalysts was carried out in a lab scale direct ethanol fuel cell (DEFC). Cathode used was Pt‐black high surface area. The membrane electrode assembly (MEA) was prepared by sandwiching the solid polymer electrolyte membrane, prepared from Nafion^® (SE‐5112, DuPont USA) dispersion, between the anode and cathode. The DEFC was fabricated using the MEA and tested at different catalyst loadings at the electrodes, temperatures and ethanol concentrations. The maximum power density of DEFC for optimized value of ethanol concentration, catalyst loading and temperature were determined. The maximum open circuit voltage (OCV) of 0.815 V, short circuit current density (SCCD) of 27.90 mA/cm² and power density of 10.30 mW/cm² were obtained for anode (Pt‐Ru/C) and cathode (Pt‐black) loading of 1 mg/cm² at a temperature of 90°C anode and 60°C cathode for 2M ethanol.     

Degradation of proton exchange membrane by Pt dissolved/deposited in fuel cells

An accelerated single cell test and single electrode cell test were carried out to investigate membrane degradation by Pt dissolved/deposited on the membrane. For a cell operating under accelerated conditions (OCV, 90°C, anode RH 0%, cathode O₂ supply), MEA analyses revealed that Pt particles were deposited in the membrane at the anode side, with a decrease in F, O, and C content near the anode side of the membrane. Dissolved Pt from the cathode showed that Pt existed mainly in the form of Pt²⁺ ionic species. Oxygen and hydrogen helped Pt dissolution from the cathode and Pt deposition in the membrane, respectively. Radical formation on deposited Pt in the membrane was detected by electron spin resonance (ESR). Fluoride emission rate (FER, an indicator of membrane degradation rate) increased with an increase in the amount of Pt in the membrane.     

Performance Study of Direct Borohydride Fuel Cells Employing Polyvinyl Alcohol Hydrogel Membrane and Nickel‐Based Anode

A direct borohydride fuel cell (DBFC) employing a polyvinyl alcohol (PVA) hydrogel membrane and a nickel‐based composite anode is reported. Carbon‐supported platinum and sputtered gold have been employed as cathode catalysts. Oxygen, air and acidified hydrogen peroxide have been used as oxidants in the DBFC. Performance of the PVA hydrogel membrane‐based DBFC was tested at different temperatures and compared with similar DBFCs employing Nafion® membrane electrolytes under identical conditions. The borohydride–oxygen fuel cell employing PVA hydrogel membrane yielded a maximum peak power density of 242 mW cm^–2 at 60 °C. The peak power densities of the PVA hydrogel membrane‐based DBFCs were comparable or a little higher than those using Nafion® 212 membranes at 60 °C. The fuel efficiency of borohydride–oxygen fuel cell based on PVA hydrogel membrane and Ni‐based composite anode was found to be between 32 and 41%. The cell was operated for more than 100 h and its performance stability was recorded.     

Characterization of an electrochemical reactor for the ozone production in electrolyte-free water

The filter-press electrochemical ozonizer is characterized as a function of the applied electric current, temperature, and linear velocity of the electrolyte-free water. Lead dioxide electroformed on surface of a non-platinized fine mesh stainless steel support was used as anode. Electrolysis of the electrolyte-free water was carried out using the membrane electrode assembly (MEA) adequately compressed by means of a specially designed clamping system. Electrochemical characterization studies were carried out galvanostatically as a function of temperature and linear velocity of the circulating water. It was verified that the electrochemical ozone production (EOP) taking place at the reacting zones formed at the solid polymer electrolyte (SPE)/mesh electrode interface is not considerably affected by circulating water when the linear velocity inside the distribution channels is higher than 1.20 cm s⁻¹. A current efficiency for the EOP of 13% and a specific electric energy consumption of 70 Wh g⁻¹ were obtained when an electric current of 130 A was applied at 30 °C. The reactor service life test revealed that the MEA using the lead dioxide fine mesh electrode as anode and a fine mesh stainless steel electrode as cathode, pressed against the SPE, is stable for the ozone production.     

Fluorination of Vulcan XC-72R for cathodic microporous layer of passive micro direct methanol fuel cell

The effect of adding fluorinated Vulcan XC-72R into the microporous layer (MPL) of the cathode in a passive micro direct methanol fuel cell (μDMFC) has been investigated. Upon fluorination with fluoro-alkyl silane (FAS), the surface of XC-72R becomes more hydrophobic, as indicated by contact angle measurements. The performance of the membrane electrode assembly (MEA) is improved significantly when fluorinated Vulcan XC-72R is used in MPL of the cathode. The maximum power density of a passive μDMFC reached ca. 36.2 mW cm⁻² at room temperature, and the constant-current discharging test exhibits enhanced stability. Also observed is a decreased water transport coefficient (α), calculated from discharging test, attributable to the greater hydrophobicity resulting in higher liquid pressure on the cathode, which forces more water to flow back to the anode. Additionally, A.C. impedance analysis indicates that the improvement in performance results from the decrease of charge transfer resistance of the cathodic reaction.     

Studies of some operating parameters and cyclic voltammetry for a direct ethanol fuel cell

A direct ethanol fuel cell (DEFC) of 5 cm² membrane-electrode area was studied systematically by varying the catalyst loading, ethanol concentration, temperature and different Pt based electro-catalysts (Pt–Ru/C, Pt-black High Surface Area (HSA) and Pt/C). A combination of 2 M ethanol at the anode, pure oxygen at the cathode, 1 mg cm⁻² of Pt–Ru/C (40%:20%) as the anode and 1 mg cm⁻² of Pt-black as the cathode gave a maximum open circuit voltage (OCV) of 0.815 V, a short circuit current density of 27.90 mA cm⁻² and a power density of 10.3 mW cm⁻². The optimum temperatures of the anode and cathode were determined as 90 °C and 60 °C, respectively. The power density increased with increase in ethanol concentration and catalyst loading at the anode and cathode. However, the power density decreased slightly beyond 2 M ethanol concentration and 1 mg cm⁻² catalyst loading at the anode and cathode. These results were validated using cyclic voltammetry at single electrodes under similar conditions to those of the DEFC.     

Carbon supported Ru–Se as methanol tolerant catalysts for DMFC cathodes. Part II: preparation and characterization of MEAs

Cathode catalyst layers were prepared and characterized as part of membrane electrode assemblies (MEA) and catalyst coated membranes (CCM) on the basis of carbon supported methanol tolerant RuSe _x catalysts. Preparation parameters varied were: catalyst loading (0.5–2 mg RuSe _x cm⁻²), PTFE content (0, 6, 18 wt.%), carbon support (Vulcan XC 72 or BP2000), and fraction of RuSe _x in the carbon supported catalysts (20, 44, 47 wt.%). The MEAs and cathode catalyst layers were electrochemically characterized under Direct Methanol Fuel Cell (DMFC) operating conditions by recording polarization curves, galvanostatic measurements, and impedance spectra. The morphology of the catalyst layers was investigated by means of confocal laser scan microscopy (CLSM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD) measurements. MEAs with Ru(44.0 wt.%)Se(2.8 wt.%)/VulcanXC72 cathode catalyst achieved the highest performance of all RuSe _x catalysts investigated, i.e. ∼40 mW cm⁻² at 80 °C under ambient pressure and λ_MeOH = λ_air = 4. This is 40% of the value obtained with commercial platinum cathode catalyst under the same operating conditions. The RuSe _x catalysts investigated are stable over a period of more than 1,000 h. This was confirmed by TEM and XRD measurements, where no increase in mean RuSe _x particle size (∼5 nm) after fuel cell operation was found. Enhancement of specific catalyst activity, mass transport, and active surface offer potential for a further improvement of RuSe _x catalyst layers.     

Fabrication and performance of PEN SOFCs with proton-conducting electrolyte

A positive-electrolyte-negative (PEN) assembly solid oxide fuel cell (SOFC) with a thin electrolyte film for intermediate temperature operation was fabricated. Instead of the traditional screen-printing method, both anode and cathode catalysts were pressed simultaneously and formed with the fabrication of nano-composite electrolyte by press method. This design offered some advantageous configurations that diminished ohmic resistance between electrolyte and electrodes. It also increased the proton-conducting rate and improved the performance of SOFCs due to the reduction of membrane thickness and good contact between electrolyte and electrodes. The fabricated PEN cell generated electricity between 600°C and 680°C using H₂S as fuel feed and air as oxidant. Maximum power densities 40 mW·cm⁻² and 130 mW·cm⁻² for the PEN configuration with a Mo-Ni-S-based composite anode, nano-composite electrolyte (Li₂SO₄+Al₂O₃) film and a NiO-based composite cathode were achieved at 600°C and 680°C, respectively.     

Preparation of a PVA/HAP composite polymer membrane for a direct ethanol fuel cell (DEFC)

A novel PVA/Hydroxyapatite (HAP) composite polymer membrane was prepared by the direct blend process and solution casting method. The characteristic properties of the PVA/HAP composite polymer membranes were investigated using thermal gravimetric analysis (TGA), X-ray diffraction (XRD), scanning electron microscopy (SEM), micro-Raman spectroscopy and the AC impedance method. An alkaline direct ethanol fuel cell, consisting of an air cathode with MnO₂ carbon inks based on Ni-foam, an anode with PtRu black on Ni-foam, and the PVA/HAP composite polymer membrane, was assembled and investigated. It was found that the alkaline direct ethanol fuel cell comprising of a novel cheap PVA/HAP composite polymer membrane showed an improved electrochemical performance in ambient temperature and air. As a result, the maximum power density of the alkaline DEFC, using a PtRu anode based on Ni-foam (10.74 mW cm⁻²), is higher than that of DEFC using an E-TEK PtRu anode based on carbon (7.56 mW cm⁻²) in an 8M KOH + 2M C₂H₅OH solution at ambient temperature and air. These PVA/HAP composite polymer membranes are a potential candidate for alkaline DEFC applications.     

Pore‐forming technology and performance of MEA for direct methanol fuel cells

BACKGROUND: The commercialization of DMFCs is seriously restricted by its relatively low power density. Lots of work has been concentrated on catalysts with high activity, the optimization of flow path design, development of new kinds of proton exchange membrane and modification of Nafion membrane. Meanwhile, very few reports have involved the structure optimization of the membrane electrode assembly (MEA). To improve the performance of direct methanol fuel cells (DMFCs), the catalyst layer (CL) structures of anode and cathode were optimized by utilizing ammonium carbonate as pore forming agent. RESULTS: The polarization curves showed that in catalyst slurry the optimal content of ammonium carbonate was 50 wt%, and the DMFC performance was enhanced from 75.65 mW cm^?2 to 167.42 mW cm^?2 at 55 °C and 0.2 MPa O₂. Electrochemical impedance spectroscopy and electrochemical active surface area (EASA) testing revealed that the improved performance of optimized MEAs could be mainly attributed to the increasing EASA and the enhanced mass transfer rate of CLs. But poor methanol crossover limited the performance enhancement of MEAs with porous anodes. CONCLUSION: With regard to improving cell performance, this pore‐forming technology is better applied to the cathode catalyst layer to improve its structure rather than the anode catalyst layer. © 2012 Society of Chemical Industry     

带增湿区的质子交换膜燃料电池

Water management is of great importance to maintain performance and durability of proton exchange membrane fuel cells. This paper presents a novel proton exchange membrane (PEM) fuel cell with a humidification zone in the membrane electrode assembly (MEA) of each cell, in which the moisture of the cathode exhaust gas could transfer through the membrane to humidify anode or cathode dry gas. With a simple model, the relative humidity (RH) of the dry air exhaust from a membrane humidifier with 100% RH stream as a counter flow is calculated to be 60.0%, which is very close to the experimental result (62.2%). Fuel cell performances with hydrogen humidifying, air humidifying and no humidifying are compared at 50, 60 and 70˚C and the results indicate that humidifying is necessary and the novel design with humidifying zone in MEA is effective to humidify dry reactants. The hydrogen humidifying shows better performance in short term, while water recovered is limited and the stability is not as good as air hu-midifying. It is recommended that both air and hydrogen should be humidified with proper design of the humidifying zones in MEA and plates.     

Preparation and testing of Nafion/titanium dioxide nanocomposite membrane electrode assembly by ultrasonic coating technique

Membrane electrode assemblies with Nafion/nanosize titanium dioxide (TiO₂) composite membranes were manufactured with a novel ultrasonic‐spray technique (UST) and tested in proton exchange membrane fuel cell (PEMFC). The structures of the membranes were investigated by scanning electron microscopy (SEM), X‐ray diffraction (XRD), and thermogravimetric analysis. The composite membranes gained good thermal resistance with insertion of TiO₂. The SEM and XRD techniques have proved the uniform and homogeneous distribution of TiO₂ and the consequent enhancement of crystalline character of these membranes. The existence of nanometer size TiO₂ has improved the thermal resistance, water uptake, and proton conductivity of composite membranes. Gas diffusion electrodes were fabricated by UST. Catalyst loading was 0.4 (mg Pt) cm^?2 for both anode and cathode sides. The membranes were tested in a single cell with a 5 cm² active area operating at the temperature range of 70°C to 110°C and in humidified under 50% relative humidity (RH) conditions. Single PEMFC tests performed at different operating temperatures indicated that Nafion/TiO₂ composite membrane is more stable and also performed better than Nafion membranes. The results show that Nafion/TiO₂ is a promising membrane material for possible use in PEMFC at higher temperature. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40541.     

Development and characterization of a silicon-based micro direct methanol fuel cell

A silicon-based micro direct methanol fuel cell (μDMFC) for portable applications has been developed and its electrochemical characterization carried out in this study. Anode and cathode flowfields with channel and rib width of 750 μm and channel depth of 400 μm were fabricated on Si wafers using the microelectromechanical system (MEMS) technology. A membrane-electrode assembly (MEA) was specially fabricated to mitigate methanol crossover. This MEA features a modified anode backing structure in which a compact microporous layer is added to create an additional barrier to methanol transport thereby reducing the rate of methanol crossing over the polymer membrane. The cell with the active area of 1.625 cm² was assembled by sandwiching the MEA between two micro-fabricated Si wafers. Extensive cell polarization testing demonstrated a maximum power density of 50 mW/cm² using 2 M methanol feed at 60 °C. When the cell was operated at room temperature, the maximum power density was shown to be about 16 mW/cm² with both 2 and 4 M methanol feed. It was further found that the present μDMFC still produced reasonable performance under 8 M methanol solution at room temperature.     

Mathematical model for a direct propane phosphoric acid fuel cell

A mathematical model was developed and used to predict the performance of direct propane phosphoric acid (PPAFC) fuel cells, utilizing both Pt/C state-of the-art electrodes and older Pt black electrodes. It was found that the overpotential caused by surface processes on the platinum catalyst in the anode is much greater than the potential losses caused by either ohmic resistance or propane diffusion in gas-filled and liquid-filled pores. In one comparison, the anode overpotential (0.5 V) was larger than the cathode overpotential (0.3 V) at a current density of 0.4 A cm⁻² for Pt loadings 4 mg Pt cm⁻². The need for sufficient water concentration at the anode, where water is a reactant, was indicated by the large effect of H₃PO₄ concentration. In another comparison, the model predicted that at 0.2 A cm⁻², modern carbon supported Pt catalysts would produce 0.35 V compared to 0.1 V for unsupported Pt black catalysts that were used several decades ago, when the majority of the research on direct hydrocarbon fuel cells was performed. The propane anode and oxygen cathode catalyst layers were modeled as agglomerates of spherical catalyst particles having their interior spaces filled with liquid electrolyte and being surrounded by gas-filled pores. The Tafel equation was used to describe the electrochemical reactions. The model incorporated gas and liquid-phase diffusion equations for the reactants in the anode and cathode and ionic transport in the electrolyte. Experimental data were used for propane and oxygen diffusivities, and for their solubilities in the electrolyte. The accuracy of the predicted electrical potentials and polarization curves were normally within ±0.02 V of values reported in experimental investigations of temperature and electrolyte concentration. Polarization curves were predicted as a function of temperature, pressure, electrolyte concentration, and Pt loading. A performance of 0.45 V at 0.5 A cm⁻² was predicted at some conditions.     

Preparation of a high-performance Pt–Pd/C-electrocatalyst-coated membrane for ORR in PEM fuel cells via a combined process of impregnation and seeding: Effect of electrocatalyst loading on carbon support

The influence of the electrocatalyst loading (2.0–40.7 wt.%) on a carbon support on its suitability as a cathode for proton-exchange membrane (PEM) fuel cells was evaluated at a constant membrane electrocatalyst loading of 0.15 mg/cm². The results clearly demonstrate that different electrocatalyst loadings on a carbon support in the investigated range significantly affect not only the electrocatalyst activity but also the performance in H₂/O₂ fuel cells. Increasing the electrocatalyst loading on a carbon support led to an increase in the particle size of electrocatalyst and the pore size of the membrane electrode assembly (MEA) but a decrease in the particle size distribution and MEA thickness. The maximum oxygen-reduction reaction (ORR) activity and cell performance (745 mA/cm² and 520 mW/cm² at 0.6 V) were obtained at an electrocatalyst loading of 24.1 wt.% on a carbon support.     

A Solid-polymer Electrolyte Direct Methanol Fuel Cell with a Methanol-tolerant Cathode and its Mathematical Modelling

Solid-polymer electrolyte direct methanol fuel cells (SPE-DMFCs) employing carbon-supported Pt–Fe as oxygen-reduction catalyst to mitigate the effect of methanol on cathode performance while operating with oxygen or air have been assembled. These SPE-DMFCs provided maximum power densities of 250 and 120 mW cm^–2 at 85 °C on operating with oxygen and air, respectively. The polarization data for the SPE-DMFCs and their constituent electrodes have also been derived numerically employing a model based on phenomenological transport equations for the catalyst layer, diffusion layer and the membrane electrolyte.     

Preparation and evaluation of RuO2–IrO2, IrO2–Pt and IrO2–Ta2O5 catalysts for the oxygen evolution reaction in an SPE electrolyzer

IrO₂–RuO₂, IrO₂–Pt and IrO₂–Ta₂O₅ electrocatalysts were synthesized and characterized for the oxygen evolution in a Solid Polymer Electrolyte (SPE) electrolyzer. These mixtures were characterized by XRD and SEM. The anode catalyst powders were sprayed onto Nafion 117 membrane (catalyst coated membrane, CCM), using Pt catalyst at the cathode. The CCM procedure was extended to different in-house prepared catalyst formulations to evaluate if such a method could be applied to electrolyzers containing durable titanium backings. The catalyst loading at the anode was about 6 mg cm⁻², whereas 1 mg cm⁻² Pt was used at the cathode. The electrochemical activity for water electrolysis was investigated in a single cell SPE electrolyzer at 80 °C. It was found that the terminal voltage obtained with Ir–Ta oxide was slightly lower than that obtained with IrO₂–Pt and IrO₂–RuO₂ at low current density (lower than 0.15 A cm⁻²). At higher current density, the IrO₂–Pt and IrO₂–RuO₂ catalysts performed better than Ir–Ta oxide.