Catalyst-coated Membrane Research Articles

Enhanced Degradation of Sulfamethoxazole (SMX) in Toilet Wastewater by Photo-Fenton Reactive Membrane Filtration.

Pharmaceutical residuals are increasingly detected in natural waters, which made great threat to the health of the public. This study evaluated the utility of the photo-Fenton ceramic membrane filtration toward the removal and degradation of sulfamethoxazole (SMX) as a model recalcitrant micropollutant. The photo-Fenton catalyst Goethite (α-FeOOH) was coated on planar ceramic membranes as we reported previously. The removal of SMX in both simulated and real toilet wastewater were assessed by filtering the feed solutions with/without H2O2 and UV irradiation. The SMX degradation rate reached 87% and 92% respectively in the presence of UV/H2O2 for the original toilet wastewater (0.8 ± 0.05 ppb) and toilet wastewater with a spiked SMX concentration of 100 ppb. The mineralization and degradation by-products were both assessed under different degradation conditions to achieve deeper insight into the degradation mechanisms during this photo-Fenton reactive membrane filtration. Results showed that a negligible removal rate (e.g., 3%) of SMX was obtained when only filtering the feed solution through uncoated or catalyst-coated membranes. However, the removal rates of SMX were significantly increased to 67% (no H2O2) and 90% (with H2O2) under UV irradiation, respectively, confirming that photo-Fenton reactions played the key role in the degradation/mineralization process. The highest apparent quantum yield (AQY) reached up to approximately 27% when the H2O2 was 10 mmol·L−1 and UV254 intensity was 100 μW·cm−2. This study lays the groundwork for reactive membrane filtration to tackle the issues from micropollution.

Towards a Harmonized Accelerated Stress Test Protocol for Fuel Starvation Induced Cell Reversal Events in PEM Fuel Cells: The Effect of Pulse Duration

Global fuel starvation is an undesired event during fuel cell operation that results in serious degradations at the anode catalyst layer caused by the concomitant reversal of the cell potentials. Several groups have therefore intensified their research efforts towards the implementation of suitable diagnostic tools and accelerated stress test (AST) protocols that mimic cell reversal events. However, the current number of different test protocols requires consolidation and harmonization to define durability targets towards cell reversal tolerance and to benchmark newly developed materials. To create a basis for harmonization, this study examines the difference between pulsed and quasi-continuous AST protocols at the catalyst-coated membrane level. Utilizing a single-cell setup combined with an on-line mass spectrometer, a 2.5-fold increase in the carbon corrosion rates were found for short-pulsed compared to long-lasting cell reversal events. The enhanced corrosion was associated with a 2.2-fold higher loss of electrochemically active surface area and a 15% higher reduction in anode catalyst layer thickness. By contrast, the overall cell performance decreased additionally by 40–50 mV for samples under long-lasting cell reversal events. The decay is mainly driven by an increased ohmic resistance, presumably originating from a more pronounced surface oxide formation on the carbon support.

Green and Low-Cost Membrane Electrode Assembly for Proton Exchange Membrane Fuel Cells: Effect of Double-Layer Electrodes and Gas Diffusion Layer

The success of fuel cells depends on the design structure meanwhile catalysts electrodes and membrane allowing easy access of oxygen and protons. Using non-precious catalyst electrodes based on recyclable carbon nanostructures is most important to produce clean energy and increase the ability to commercialize the fuel cells. Herein, reduced graphene oxide (rGO) and graphene/magnetic iron oxide nanocomposite (rGO/MIO) are successfully synthesized as anode and cathode respectively from polyethylene terephthalate (PET) waste bottles using easy steps in order to simplify the method and reducing the production cost. While, the membrane is prepared from low cost and eco-friendly ternary polymers blend which are polyvinyl alcohol (PVA), polyethylene oxide (PEO) and polyvinyl pyrrolidone (PVP) then doped with sulfonated graphene oxide. The prepared electrodes have characteristic high porosity and their electrocatalytic performances are evaluated using three-electrode cell electrochemical studies as cyclic voltammetry and linear scan voltammetry combined with rotating disk electrode. A new assembly of the membrane between two non-precious catalyst electrodes as a single polymer electrolyte membrane fuel cell (PEMFC) was developed using a catalyst-coated membrane technique. The membrane electrode assembly (MEA) design parameters which affect its performance in hydrogen fuel cells as number of used catalyst layers (CL) or using gas diffusion layer (GDL) were evaluated in a single cell set-up with H2/O2 operation and the results revealed that the performance MEA was enhanced with using GDL more than that of MEA without GDL by 66% at a current density of 0.8 A cm−2 while the performance with double CL was better than that of the conventional single CL by 30 % at a current density of 0.98 mA cm−2.

Enhanced degradation of antibiotics by photo-fenton reactive membrane filtration

Micropollution such as pharmaceutical residuals potentially compromises water quality and jeopardizes human health. This study evaluated the photo-Fenton ceramic membrane filtration toward the removal of sulfadiazine (SDZ) as a common antibiotic chemical. The batch experiments verified that the photo-Fenton reactions with as Goethite (α-FeOOH) as the photo-Fenton catalyst achieved the degradation rates of 100% within 60 min with an initial SDZ concentration of 12 mg·L−1. Meanwhile, a mineralization rate of over 80% was obtained. In continuous filtration, a negligible removal rate (e.g., 4%) of SDZ was obtained when only filtering the feed solution with uncoated or catalyst-coated membranes. However, under Ultraviolet (UV) irradiation, both the removal rates of SDZ were significantly increased to 70% (no H2O2) and 99% (with H2O2), respectively, confirming the active degradation by the photo-Fenton reactions. The highest apparent quantum yield (AQY) reached up to approximately 25% when the UV254 intensity was 100 μW·cm-2 and H2O2 was 10 mmol·L−1. Moreover, the photo-Fenton reaction was shown to effectively mitigate fouling and prevent flux decline. This study demonstrated synchronization of photo-Fenton reactions and membrane filtration to enhance micropollutant degradation. The findings are also important for rationale design and operation of photo-Fenton or photocatalytic membrane filtration systems.

Directly coated membrane electrode assemblies for proton exchange membrane water electrolysis

We present a novel membrane electrode assembly (MEA) fabrication method for proton exchange membrane water electrolysis (PEMWE). Inspired by previous work on PEM fuel cells (PEMFCs), we fabricated PEMWE-MEAs via direct membrane deposition (DMD). DMD-MEAs were fabricated by spray coating the membrane directly onto the cathode electrode – in this case, a carbon cloth substrate with microporous layer coated with Pt/C. The complete DMD-MEAs consisted of the membrane-cathode compound assembled with an anode electrode, which is a porous titanium fiber substrate coated with IrO2. Polarization experiments of DMD-MEAs show promising results: In comparison to a reference catalyst coated membrane (CCM) and a porous transport electrode (PTE) type MEA using a freestanding Nafion 117 membrane, we found very good electrochemical performances for DMD-MEAs. DMD-MEAs show slightly higher activation losses than the reference CCM. However, DMD-MEAs seem to exhibit reduced ohmic and mass transport losses compared to those manufactured using the CCM approach. Compared to the PTE-type reference DMD shows improvements for all three loss mechanisms. Similar as for PEMFCs, DMD may allow for a simplified fabrication route and higher degree of design freedom in PEMWE-MEA manufacturing due to the simple layer by layer fabrication approach.

Reusability of decal substrates for the fabrication of catalyst coated membranes

The use of decal substrates to produce catalyst coated membranes (CCMs) for polymer electrolyte membrane water electrolyzers or fuel cells is a common procedure. For economic and ecological reasons, the reuse of decal substrates would be desirable. Thus far, it has not been investigated whether reuse is possible. Therefore, this study focuses on the repeated coating and transfer in decal processes and investigates changes in substrate properties. After coating Kapton and PTFE with a Carbon-Nafion dispersion, the dry layer was transferred onto a Nafion membrane. This procedure was repeated 50 times. The change in substrate thickness and surface free energy (SFE), as well as the transfer rate (TR), were monitored. The residues on the substrate and scattering of the TR were higher for Kapton compared to PTFE. None of the decal substrates changed its SFE and thickness within the measurement uncertainties. Because of the smaller scattering in the TR, PTFE is more suitable for reuse.

Performance of Catalyst Coated Membrane (CCM) at different operating conditions in Proton Exchange Membrane (PEM) fuel cell

In this paper, performance of Catalyst Coated Membrane (CCM) has been studied. Effect of various parameters on current density and power density has been analysed. Observations has been depicted using polarisation as well as power curves. CCM always gives better performance as catalyst it has direct ionic contact with membrane. CCM manufactured by Paxitech fuel cells, France has been used to perform the experiment along with stack fabricated. It is prepared with catalyst coating of 0.5mgPt/cm2 by ultrasonic spray coating method. The SEM analysis has been carried out to study morphological characteristics of CCM. Out of other parameters, hydrogen humidification and air stoichiometry have good effect on CCM performance. Maximum current density obtained was 1.28A/cm2 with hydrogen humidification temperature as 550C. The performance has been analysed by polarization curve, Description of various parameters has been given in detail.

Unexpected Performance of Inkjet‐Printed Membrane Electrode Assemblies for Proton Exchange Membrane Fuel Cells

The effect of the deposition substrate on the performance of inkjet‐printed membrane electrode assemblies (MEAs) is investigated. MEAs are fabricated from inkjet‐printed catalyst‐coated membranes (CCMs), gas diffusion electrodes (GDEs), and a bilateral sandwich of a CCM and a GDE. All MEAs are tested in proton exchange membrane fuel cells (PEMFCs). When a hot‐pressing step is included in the MEA construction, the power density achieved with the GDE‐based MEA is 1.067 W cm−2, exceeding that achieved with the CCM‐based MEA (0.579 W cm−2), and the bilateral sandwich MEA (0.792 W cm−2). The origin of the superior performance of the inkjet‐printed GDE‐based MEAs is investigated through electrochemical impedance spectroscopy and analysis of the microstructure of the printed membranes and electrodes. Atomic force microscopy and energy dispersive X‐ray spectroscopy suggest that the greater surface and interfacial areas of the GDE‐printed catalyst layer may drive the unexpectedly high performance of the GDE‐based MEA as compared with its CCM and bilateral sandwich counterparts. These results provide new insights into the connections between the substrate, inkjet‐printed catalyst layer microstructure, and catalyst utilization.

Detecting cathode corrosion in polymer electrolyte membrane fuel cells in dead-ended anode mode via alternating current impedance

In this work, an in-operando alternating current (AC) impedance-based method is developed to detect cathode corrosion in a polymer electrolyte membrane (PEM) fuel cell operating in dead-ended anode (DEA) mode. Polarization resistances are measured over a 2.0 s sampling time with this method, exhibiting a 10 times higher temporal resolution than conventional electrochemical impedance spectroscopy methods. The performance characteristics of a PEM fuel cell in DEA mode are investigated with both a pristine membrane electrode assembly (MEA) and a corroded MEA, and the sudden rise in the cathode polarization resistance accompanied by a uniform anode polarization resistance is identified as a new indicator for a corroded cathode. The accumulation of nitrogen in the corroded cathode leads to a rise in cathode polarization resistance. This elevated cathode polarization resistance leads to a dehydrated catalyst-coated membrane (CCM) evident through a reduction of the liquid water saturation at the CCM—microporous layer interface (observed using synchrotron X-ray radiography).

Development of Mass-Production-Scale High Performance and Reliable Catalyst Coated Membrane (CCM) for PEMFC Via Optimized Electrode Slurry for Direct Coating Process

The mass production of polymer electrolyte membrane fuel cells (PEMFCs) requires a reduction in the materials cost. The most costly component of a PEMFC is the membrane electrode assembly (MEA), which contains the precious metal catalyst, platinum. Most related research is focused on cost-reduction of the catalysts, or cost-reduction of the proton exchange membranes (PEMs), and little fundamental research has focused on alternative MEA manufacturing routes as a means of cost-reduction. The MEAs are generally manufactured by decal transfer method. The decal transfer method necessitates coating wider catalyst layers to address alignment tolerance stack up and membrane shrinkage issues at lamination. The costs of existing processes are too high and not scalable and the film quality can be too low for long life. In order to support large scale manufacturing, alternative methods for MEA fabrication are imperative. Available fabrication techniques, such as direct coating by brushing, screen printing, spraying and reactive spray deposition. The direct coating method is more simple and efficient than indirect coating process, decal transfer method and has no risk of uneven and incomplete transfer of catalyst in the catalyst layer (CL). Furthermore, it also produces a higher MEA performance than the conventional decal transfer method due to an easier controllability of the CL thickness as well as a better ionic connection between the CLs and the membrane resulted from a strong attachment of the solvent on the membrane. However, the direct coating of electrode slurry onto the membrane has a critical problem that the membrane has a high tendency to swell or wrinkle with a contact of many solvents in the electrode slurries, which could give rise to the deformation of the CL by fast volume changes of the membrane. Therefore, the optimization of electrode slurry and control of dry process is very important in the direct coating method for the high quality MEA fabrication. Additionally, the effects of direct roll-to-roll coating conditions on the electrode structure and PEMFC performance are poorly understood in many systems. This provides a detailed protocol and materials for the fabrication of reproducible, high-performance, mass-production-scale catalyst coated membranes (CCMs) through implementation of an advance slot-die coating approach of the CLs directly onto PEMs. And this work is to investigate the influence of direct coating parameters on CCM structure and performance, with a particular focus on the slot-die system because of its ability to produce very high performance CCMs at low initial capital cost, particularly at mass-production-scale. The CCMs were analyzed by scanning electron microscopy (SEM) to assess surface morphology, as well as cross-section thickness and porosity. The performance of these CCMs was tested in PEMFCs with standard protocols and their resistance during PEMFC testing was studied by electrochemical impedance spectroscopy. Figure 1. (a) Procedure of direct roll-to-roll coating process, and (b) catalysts coated membrane. Figure 1

Measurement of Protonic Conductivity of PEM Water Electrolyzer Electrodes

Polymer electrolyte membrane water electrolyzer (PEMWE) performance mostly depends on the catalyst layer (CL) composition and microstructure. The CL microstructure is influenced by catalyst ink composition and fabrication process [1]. Due to the use of an unsupported catalyst (IrOx) in PEMWE, the porosity of the CL is low, resulting in a low CL surface area and high activation loss. By increasing the porosity of the CL, it is hypothesized that more catalyst surface area will be exposed to the reactant and electrolyte. One method to increase the CL porosity is to use pore formers: sacrificial particles that are added to the ink and then removed after CL fabrication, leaving additional pores. Limited work has been done on the use of pore formers in fuel cell applications [2–6] which resulted in an increase of the porosity [3,5] and the surface area [2–4]. No work has been done using pore formers in PEMWE application. In this study, a pore former is used to study the effect of pore former addition on PEMWE microstructure and performance. In order to fabricate the catalyst coated membranes (CCMs), an anode catalyst ink was prepared by dispersing iridium oxide powder (Tanaka Kikinzoku Kogyo, ELC-0110) and pore former in a dispersion media as described in ref. [7]. The pore former to IrOx volume ratio was varied between 0 to 0.25 (Table 1). The ionomer content was kept constant at 35 wt.%. The cathode ink was prepared using the method and material described in ref. [8]. The CCMs were prepared by inkjet printing method as described in ref. [7] with catalyst loading as shown in Table 1. Two CCMs for each pore former to IrOx volume ratio were tested and the results are reported. The effect of the pore former on the electrochemical surface area (ECSA) was studied using cyclic voltammetry (CV). ECSA was estimated, after conditioning and obtaining a polarization curve, using the method developed by Tan et al. [9]. The average ECSA of CCM-0.1 is increased by 38 % compared to the CCM-0 as shown in Figure 1b and Table 1. While CCM-0.1 shows the highest ECSA, a similar improvement is not seen from CCM-0.25, indicating that the removal of pore former is having an impact beyond increasing the ECSA. To study the electrode performance without the effect of varying loading between electrodes, the normalized electrochemical performance with respect to IrOx loading are compared in Figure 1a. CCM-0.1 exhibits the highest performance and shows an average improvement of 30 mV at 2 A/mg, compared to the CCM-0. CCM-0.25 shows an improved performance in the kinetic region, however, the performance in the ohmic region is significantly worse than the other two CCMs. This is despite having a similar high frequency resistance (HFR) to the other CCMs. The pore former has a complex impact on the CL microstructure. These preliminary results indicate that the PEMWE performance can be improved by using pore formers, and that there might be an optimal pore former content. References K.-H. Kim, K.-Y. Lee, H.-J. Kim, E. Cho, S.-Y. Lee, T.-H. Lim, S. P. Yoon, I. C. Hwang and J. H. Jang, Int. J. Hydrog. Energy, 35, 2119 (2010). Y. Song, Y. Wei, H. Xu, M. Williams, Y. Liu, L. J. Bonville, H. R. Kunz and J. M. Fenton, J. Power Sources, 141, 250 (2005). T. V. Reshetenko, H.-T. Kim and H.-J. Kweon, J. Power Sources, 171, 433 (2007). Q. Huang, J. Jiang, J. Chai, T. Yuan, H. Zhang, Z. Zou, X. Zhang and H. Yang, J. Power Sources, 262, 213 (2014). A. Fischer, J. Jindra and H. Wendt, J. Appl. Electrochem., 28, 277 (1998). Y.-H. Cho, N. Jung, Y. S. Kang, D. Y. Chung, J. W. Lim, H. Choe, Y.-H. Cho and Y.-E. Sung, Int. J. Hydrog. Energy, 37, 11969 (2012). M. Mandal, A. Valls, N. Gangnus and M. Secanell, J. Electrochem. Soc., 165, F543 (2018). S. Shukla, K. Domican, K. Karan, S. Bhattacharjee and M. Secanell, Electrochimica Acta, 156, 289 (2015). X. Tan, J. Shen, N. Semagina and M. Secanell, J. Catal., 371, 57 (2019). Figure 1

Understanding Interfaces of PEM Electrolyzers with Operando Synchrotron X-Ray Computed Tomography and Radiography

Polymer electrolyte membrane (PEM) electrolyzers are electrochemical energy-conversion devices that convert electricity into hydrogen fuel at high efficiencies. The state-of-the-art systems use high IrOx loading (~2-3 mg/cm2), largely due to a lack of stable electrocatalyst supports that can effectively disperse the catalyst particles. Currently, the catalyst layers are made of IrOx and ionomer without an additional support. Without micro-porous layers (MPLs), the rough contact between the porous transport layer (PTL) and catalyst layer presents a challenge. In this study we use operando x-ray computed tomography (CT) and x-ray radiography to visualize operation of PEM electrolyzer under two current densities: 500 and 800 mA/cm2. First, we compare performance of electrolyzer with catalyst-coated membrane (CCM) and that with porous transport electrode (PTE) and correlate polarization curves to morphology of the interfaces observed with x-ray CT. At 1 A/cm2, the micro-CT CCM electrolyzer showed 200 mV improvement in potential primarily due to better contact between the electrocatalyst, membrane, and PTL. From the nano-CT imaging we discovered non-homogeneous distribution of IrOx electrocatalsyt and from the images it is also not clear whether the larger IrOx agglomerates are electrically connected via a percolating conductive network of nanoparticles. The modeling study shows that the primary reason for performance loss in PTE configuration is low connectivity of catalyst particles with membrane. This causes bottlenecks in proton transport and results in high potential losses in anode. We also compared the polarization behavior and morphology of cells with CCMs but two types of PTLs. One was made with sintered Ti and the other with Ti fiber. The Ti fiber PTL showed higher porosity and lower tortuosities, both in-plane and thru-plane. However these better morphological properties did not necessarily translate into lower potentials, as 1 A/cm2 was not a high enough current density to resolve differences attributable to improved two phase flow. This was also confirmed by radiography study, where oxygen residence fraction in the channels showed similar fractions for both types of the PTLs.

Contamination of Pt Catalyst with Carbon Monoxide during Hydrogen Evolution

Absorption of carbon monoxide (CO) on the platinum catalyst hampers the hydrogen oxidation and evolution reactions by affecting the reaction kinetics and reducing the electrochemical active surface area [1, 2]. In this paper, we use electrochemical impedance spectroscopy (EIS) to investigate the electrode poisoning on the hydrogen evolution reaction (HER) with the presence of CO. Single cell proton exchange membrane fuel cell (PEMFC) hardware with a low loading catalyst coated membrane (CCM) is operated in electrochemical hydrogen pump (EHP) mode. EIS data is collected every 5 minutes during poisoning with pure H2 or CO-H2 mixture on the anode and cathode. The Nyquist plot shows only one semicircle due to reaction kinetics, and this semicircle diameter increases significantly with time. EIS measurements are performed in galvanostatic and potentiostatic modes. Both methods show that cathode poisoning has significant influence on hydrogen evolution, however, electrochemical surface area is significantly reduced at constant potential compared to constant current. At constant current operation, cell potential tends to increase accelerating the removal of CO. The highest impact on reaction kinetics is observed while both anode and cathode electrodes are poisoned at the same time. Anode electrode poisoning is more effective than cathode electrode poisoning on the rate of oxidation and evolution reactions at constant current. However, both electrodes have similar impacts at constant potential. Moreover, over potential of the anode electrode increases significantly during the CO poisoning at constant current operation compared to over potential of cathode electrode. References G.A. Camara, E.A. Ticianelli, S. Mukerjee, S.J. Lee and J. McBreen, 149(6), A748 (2002).N.R. Elezovic, Lj. Gajic-Krstajic, V. Radmilovic, Lj. Vracar and N.V. Krstajic, Electrochim. Acta, 54, 1375 (2009). Figure 1

Overpotential Analysis of Low Loading Pt/C Electrodes at Low Humidity Conditions

In 2014, the transportation sector accounted for 35.3% of all greenhouse gas emissions in the State of Connecticut [1]. A significant amount of greenhouse gases emitted can be primarily attributed to the use of fossil fuels in passenger vehicles and other light-duty trucks. In an effort to reduce the amount of transportation-related emissions, there is a need to produce low- and zero-emission vehicles, such as fuel cell vehicles. Compared to vehicles with traditional internal combustion engines which emit greenhouse gases, fuel cell vehicles only emit water vapor. Through research and development of fuel cell and electrolyzer technologies, fuel cell vehicles have the potential to significantly reduce the greenhouse gas emissions related to the transportation sector. In order to improve the viability of fuel cell vehicles, fuel cell performance must be optimized at low relative humidity conditions while keeping production costs low. One such method for improving the fuel cell performance at low relative humidity is examined by changing the ionomer used in the fuel cell electrodes. Research has been shown that reducing the ionomer side chain length as well as reducing the ionomer equivalent weight may be beneficial to low humidity operation [2]. While low humidity operation is important, fuel cell production costs must also be kept to a minimum in order to offer these zero-emission vehicles to a broader market. The primary method that will be used in this work to reduce the cost of fuel cell production is Reactive Spray Deposition Technology (RSDT). RSDT is a one-step flame-based process which can directly spray a Pt/C electrode onto a membrane using without additional drying steps. Previous work by Yu et al examined the use of RSDT to create low Pt loading electrodes for fuel cell applications [3]. With the cost-effective RSDT method chosen for the development of the fuel cells, the RSDT-produced catalyst coated membranes (CCMs) will be tested in 100% relative humidity conditions as a baseline as well as reduced humidity conditions used in fuel cell vehicle applications. While it is important to improve low humidity fuel cell performance, it is important to have a better understanding of how low humidity directly impacts the electrochemical mechanism. This work will analyze collected polarization and impedance data using a six-step overpotential analysis technique used by Yu et al [3, 4]. This overpotential analysis looks to separate the contributions of different polarization sources to have a better understanding of what is impacting the cell performance. This technique used at low humidity should allow us to have a better understanding about low humidity operation and how to improve fuel cell production by minimizing losses. The work presented will incorporate the RSDT process to make the change in ionomer with the target of improving and better understanding the performance of the fuel cells at low humidity conditions. Along with utilizing the six levels of overpotential analysis technique, we can determine how the changes to the ionomer and membrane as well as the carbon support all affect the polarization sources which will allow to better optimize the fuel cells moving and improve the future viability of fuel cell vehicles.

Electrochemical and Rheological Investigations of Catalyst-Solvent-Polymer Ink Formulations for Electrospun Fuel Cell Electrode Structures

The rational design of electrode structures and interfaces has emerged as a potential route for increasing the efficiency of electrochemical devices. As a fabrication technique, electrospinning allows for the creation of electrode structures possessing purported improvements in proton conductivity, gas transport and durability[1], while economic assessments [2] have shown electrospinning to be cost competitive with other Roll-to-Roll manufacturing techniques.[3] However, at present, very little is known about the particle-solvent-polymer interactions which occur at the ink level. Understanding how the electrospun electrode morphology relies not only on precursor material properties, but also on the interactions between the catalyst, ionomer and solvents being utilized can help improve the ability to dictate and tune relevant interactions within the electrode structure. Unfavorable interactions between ionomer, carrier polymer and Pt active sites can lead to reductions in activity and fuel cell performance. Hence, its imperative to understand the properties that dictate the fundamental chemistry and materials properties of various electrospun ink formulations in order to rationally design electrode structures. In support of this process-focused study, detailed exploration of particle-polymer-solvent interactions in the subject inks and slurries will be undertaken utilizing both electrochemical in-situ diagnostics as well as ex-situ advanced characterization techniques to achieve a fundamental understanding of various ink fabrication processes and colloidal structure of inks and dispersions as a function of solids content, solvent type, and particle size. In particular, we will investigate different electrospun ink formulations for fuel cell electrodes including small-scale studies of various material sets, carrier polymers, slurry compositions and excitation conditions. The resulting ink level interactions will be discussed in conjunction with varying synthetic and fabrication parameters. The resulting electrode structure, ionomer-Pt interactions, and coverage of ionomer on both Pt and carbon, will be related to performance related phenomena at high current density (i.e. oxygen transport resistance and proton conductivity). [4] The electrospinning inks will be characterized via ink/dispersion surface charge stabilization (zeta potential measurements) and rheological studies as function of ink composition and processing variables.[5] Morphological properties of electrospun nanofiber electrodes will also be characterized using various spectroscopic and microscopic techniques (USAXS, TEM, SEM, EDS). Following ink/fiber optimization, electrodes will be conditioned [6] and examined with in-situ electrochemical diagnostics such as electrochemical surface area (ECA), CO-displacement measurements, oxygen transport resistances (Rnf) and electrochemical impedance spectroscopy (EIS) in the catalyst layers will be measured to elucidate the effects of different ink compositions, excitation parameters and electrode structures on PEMFC performance. Preliminary results have demonstrated significant improvements in mass activity, up to a factor of 2, for electrospun electrodes compared to traditional ultrasonically sprayed catalyst coated membrane (CCM) electrodes. Moreover, rheological measurements of Pt/Vu-ionomer (Nafion), Pt/Vu-polymer(PAA) and ionomer-polymer ink slurries have shown that the concentration of carrier polymer (PAA) in the ink slurries plays a significant role in determining rheological properties, which may ultimately play a role in the final electrode structure, ionomer coverage and interaction with the Pt-surface.

Catalyst-coated membrane with a laminate structure: Johnson Matthey Fuel Cells Ltd.

Catalyst-coated membrane with a laminate structure: Johnson Matthey Fuel Cells Ltd.

Cyclic Hygral Swelling and Shrinkage Behavior of Fuel Cell Membranes

Mechanical membrane durability is a key factor for the overall lifetime of PEM fuel cells. It is therefore important to understand the impact of the dynamic membrane hygral swelling and shrinkage characteristics on the in-situ mechanical stresses and the associated mechanical durability. In this work, an in-depth experimental investigation was carried out to determine the cyclic hygral swelling and shrinkage properties of four commonly used types of fuel cell membranes: Nafion® NRE211, two different expanded polytetrafluoroethylene (ePTFE) reinforced perfluorosulfonic acid ionomer membranes, and one hydrocarbon membrane. In addition to the bare membranes, the effect of coating the membranes with catalyst layers on the hygral swelling/shrinkage behavior was also investigated. Tensile specimens were subjected to ex-situ hydration and dehydration cycles using a dynamic mechanical analyzer (TA Instruments Q800 DMA) equipped with an environmental chamber, wherein the dynamic swelling and shrinkage characteristics as well as the residual stresses were measured for each membrane by displacement sensor and load cell, respectively. Hydrocarbon and reinforced PFSA ionomer membranes revealed higher shrinkage than swelling at each RH cycle, resulting in an overall shrinkage. Inside a fuel cell stack where membrane swelling and shrinkage is constrained, the observed shrinkage would result in internal tensile stress in the membrane and adjacent components, and hence reduce the overall membrane mechanical durability. The accumulation of residual stress during successive RH cycles was therefore measured explicitly using a custom-designed constrained shrinkage test and compared to the tensile properties of each individual membrane. For example, the hydrocarbon membranes analyzed in this work showed large residual stresses (severe contraction) during confined shrinkage at 80oC that exceeded their yield stress, and are therefore deemed prone to failure after repeated RH cycles. In addition, the hygral swelling and shrinkage behavior of each membrane was compared to the corresponding catalyst-coated membranes and the reinforcement offered by the catalyst layers was determined. The identified swelling and shrinkage properties, generalized into three different categories of overall cyclic behavior, have vital implications for the development of durable fuel cell membranes and membrane electrode assemblies. In addition to providing good mechanical strength, the membranes are also expected to accommodate or preferably eliminate progressive shrinkage stresses during dynamic fuel cell operation.

Direct thermal visualization of micro-scale hydrogen evolution reactions in proton exchange membrane electrolyzer cells

The heat generated from electrochemical reactions has been considered one of the most significant issues in terms of the reliability of energy conversion devices. So far, no systematic study on the relation between heat generation and electrochemical reaction exists, especially in the form of experiments. In this study, changes of the temperature distribution and hydrogen evolution reaction (HER) on the catalyst coated membrane (CCM) in proton exchange membrane electrolyzer cells (PEMECs) are in-situ visualized with the help of a novel PEMEC design, thermal spectroscopy and high-speed visualization system. At the channel-scale, the temperature increases rapidly for most of the active areas, and finally reaches the equilibrium state at 27 °C. The temperature distribution is non-uniform throughout the process. In addition, a series of pore-scale analyses are provided to clarify the relation between the temperature distribution and electrochemical reaction area. More interestingly, the rapid heat generation areas are found to be in a good agreement with the electrochemical reaction areas, which confirms that the heat is released during the reaction processes. Finally, the temperature evolution phenomena on the LGDL surface have also been recorded. These findings could help better understand the correlation between the cathode side electrochemical reaction and heat generation.

Impact of clamping pressure and stress relaxation on the performance of different polymer electrolyte membrane water electrolysis cell designs

One promising option for storing surplus electricity from renewable energy sources is the conversion of electricity to hydrogen by polymer electrolyte membrane (PEM) electrolysis and the subsequent storage of the hydrogen produced. In order to obtain good contact, the components of an electrolysis cell are compressed at a certain clamping pressure. However, too high of a pressure can have a negative effect on cell performance. This work discusses how clamping pressure affects the cell performance of different PEM electrolysis cell designs. A special test cell is designed that makes it possible to apply pressure directly onto the active area of the cell. Polarization curves are measured at different clamping pressures, while electrochemical impedance spectroscopy (EIS) is used to show the effect of pressure on performance losses. Above a critical clamping pressure of 2.5 MPa ohmic losses are found to rise. In addition, it is tested as to whether the clamping pressure remains constant over time. The results show that stress relaxation of the catalyst coated membrane (CCM) leads to a pressure loss and thus to a decline in performance. Therefore, not only is it shown that pressure is crucial for cell performance but also, for the first time, a mechanical effect is described as an element of the cell's degradation.

Roll-to-roll stack and lamination of gas diffusion layer in multilayer structured membrane electrode assembly

A membrane electrode assembly is the core component of a proton-exchange membrane fuel cell stack. It consists of multilayer structured membranes which are flexible, heterogeneous and have variable cross section. To improve the efficiency of membrane electrode assembly processing and manufacturing, a roll-to-roll system with gas diffusion layer is designed. By peeling the protective membrane and the upper and lower gas diffusion layers’ hot-pressing, proton-exchange membrane is manufactured into a five-layer catalyst-coated membrane. Then, the catalyst-coated membrane is manufactured into membrane electrode assembly by multilayer membrane breakpoint die-cutting and laying-off. The system integrates multiple key technologies, including roll-to-roll precise feeding, gas diffusion layer multi-degree accurate operation and multichannel temperature control, to realize the precise positioning of flexible multilayer membrane and brittle gas diffusion layer. The tension inhomogeneity and critical wrinkling tension are modeled for web traveling in the continuous roll-to-roll manufacturing equipment. The proposed roll-to-roll stack and lamination system effectively combines discontinuous hot-pressing, die-cutting, laying-off technics to realize the high-efficiency manufacturing of membrane electrode assembly.