Electrolyzer Performance Loss from Accelerated Stress Tests and Corresponding Changes to Catalyst Layers and Interfaces

Sustainable development of the global energy sector requires a transition from fossil fuels to renewable energies. Considering the continuously increasing energy demand, effective utilization of intermittent output from the renewable sources will depend on the efficiency of energy storage and utilization processes. Low chemical complexity and high energy density and efficiency make hydrogen produced via proton exchange membrane water electrolysis (PEMWE) a prominent solution for the mentioned challenges.Acidic conditions and high potentials at the anode side of PEM water electrolyzers, where the oxygen evolution reaction (OER) takes place, demand for materials with high catalytic activity and corrosion stability. The state-of-the-art platinum and iridium (oxide) catalysts in the cathode and anode catalyst layers (CLs), respectively, demonstrate relatively good activity and stability during steady operation at low and moderate electrical loads. Indeed, it is anticipated that a significant decrease in the noble metal amount may be achieved without sacrificing the cell performance [1]. An intermittent operation of PEMWE, however, represents a considerable risk factor as both CLs may degrade with time. The extent of such degradation, especially at low catalyst loadings and high current densities, alternated with numerous off cycles is still not well understood and hence, difficult to predict and mitigate.Recent results from our group indicate a severe discrepancy between OER catalyst dissolution in aqueous model systems (AMS) and membrane electrode assemblies (MEA), with the main reasons being a suggested discrepancy between estimated and real pH in MEA and stabilization occurring over time [2]. In this work, CLs degradation during dynamic electrolyzer operation in a specially designed PEMWE test station was studied via ex-situ inductively coupled mass spectrometry analysis (ICP-MS) and its influence on the cell’s overall performance was analyzed. The S number, a new metric for OER catalyst lifetime estimation [3], was also used to compare catalyst stability properties within the two systems.

Anion exchange membrane water electrolysis (AEMWE) is a promising technology to produce hydrogen from low-cost, renewable power sources. Recently, the efficiency and durability of AEMWE have improved significantly due to advances in the anion exchange polymers and catalysts. To achieve performances and lifetimes competitive with proton exchange membrane or liquid alkaline electrolyzers, however, improvements in the integration of materials into the membrane electrode assembly (MEA) are needed. In particular, the integration of the oxygen evolution reaction (OER) catalyst, ionomer, and transport layer in the anode catalyst layer has significant impacts on catalyst utilization and voltage losses due to the transport of gases, hydroxide ions, and electrons within the anode. This study investigates the effects of the properties of the OER catalyst and the catalyst layer morphology on performance. Using cross-sectional electron microscopy and in-plane conductivity measurements for four PGM-free catalysts, we determine the catalyst layer thickness, uniformity, and electronic conductivity and further use a transmission line model to relate these properties to the catalyst layer resistance and utilization. We find that increased loading is beneficial for catalysts with high electronic conductivity and uniform catalyst layers, resulting in up to 55% increase in current density at 2 V due to decreased kinetic and catalyst layer resistance losses, while for catalysts with lower conductivity and/or less uniform catalyst layers, there is minimal impact. This work provides important insights into the role of catalyst layer properties beyond intrinsic catalyst activity in AEMWE performance.

Their is significantly growing interests in a polymer electrolyte membrane fuel cell (PEMFC)as a promising alternative electric power generation system for stationary, backup power, and automotive applications because of high power density, low operating temperature, and reduced release of environmental pollutants relative to converntional energy conversion and storage devices [1]. In this regard, a high level of activities in materials science and engineering research for the PEMFC have been made to realize its potential applications as the advanced sustainable energy sourcecs.For realizing the widespread commercialization of the PEMFC, there are still technical hurdles including high cost, performance loss, and insufficient durability with long-term cycles [2]. Especially in automotive condition, startup/shutdown and load-cycling cause a significant degradation of Pt nanoparticles supported on high surface area carbon. Although several types of Pt-based catalysts with enhanced catalytic activity and/or durability have emerged, they are still in development [3]. Therefore,it is still of great importance to develop efficient electro-catalysts with enhancing stability as well as sustaining catalytic acitvity under the wide ranges of operating conditions.The development of a functional carbon supported Pt catalyst that has both high oxygen reduction activity and high durability would significantly contribute to the commercialization of automotive PEMFC. Herein we report a diazonium-functionalized graphitized carbon (DFGC) support prepared by grafting different types of end-functional groups on a GC support via simple diazonium chemistry that can improve the dispersion of Pt nanoparticles and reduce their sintering phenomena, resulting in higher electrochemical durability with enhanced catalytic activity as compared to the unmodified GC support. The membrane-electrode assembly (MEA) fabricated with the Pt/DFGC series as the cathode catalysts shows a power density higher than 1.0 W/cm2 under an automotivce operating condition at a low catalyst loading of 0.25 mgPt/cm2. The durability of the MEA was measured by electrocatalyst cycling and catalytst support cycling tests according to the procedures of DOE-FCTT accelerated stress test (AST) protocols. THe AST results reveal that the MEA series with the Pt/DFGC catalysts exhibit higher durability event at 30% lower catalyst loading compared to a commercial MEA. These results demonstrate that the catalyst design strategy based on simple diazonium chemistry is an effective way to fabricate highly durable catalysts with enhanced catalytic activity for the PEMFC, providing a design guide of a high performance MEA for automotive applications.We also present current development status of our developed MEA for automotive applications. Our research and development focus on the fabrication of a cost-competitive MEA with high power performance and longer durability even at lower Pt amount for automotive PEMFC systems. To achieve these goals, a high level of activities have been made to develop the MEA design for high temperature and low humidified operation including the design of highly active catalyst layer, the functionalization of polymer electrolyte membrane and interfaces in the MEA, and cost-effective manufacturing process. The development of a cost-competitive MEA with high power output, long durability, and operation flexibility is expected to contribute the widespread commercialization of automotive PEMFC systems. Further development of the MEA for automotive applications would be performed by balancing high performance against long-term durability and manufacturing cost.

Polymer electrolyte membrane water electrolyzers (PEMWE) are playing an increasingly important role in hydrogen production for clean energy deployment.1 , 2 Yet hydrogen production through water electrolysis remains a niche application due to the high capital and operating expenses driven by the cost and low durability of the catalysts. The oxygen evolution reaction (OER) on the anode is particularly challenging due to the high operating potentials required to achieve high current densities, and is also responsible for rapid degradation and performance loss.3 In this work, durability tests of the anode catalyst layer were designed and carried out to reveal the catalyst degradation pathways. Iridium dissolution from the catalyst layer at high operating potential, porosity loss and thinning of the catalyst layer were investigated with our design. Previously developed testing protocols for Accelerated Stress Test (AST) measurements were applied to the electrolyzer to mimic the dynamic operation conditions and to accelerate the degradation rate.1 The effect of catalyst layer parameters like ionomer loading in the catalyst layers, the nature of the catalysts, membrane, and the fabrication techniques on anode catalyst durability were systematically evaluated and will be reported.4 Acknowledgement This research is supported by the U.S. Department of Energy (DOE) Hydrogen and Fuel Cell Technologies Office, through the H2NEW consortium.References S. M. Alia, S. Stariha, and R. L. Borup, J. Electrochem. Soc., 166, F1164–F1172 (2019).M. Carmo, D. L. Fritz, J. Mergel, and D. Stolten, Int. J. Hydrogen Energy, 38, 4901–4934 (2013).C. Lee, J. K. Lee, B. Zhao, K. F. Fahy, and A. Bazylak, J. Electrochem. Soc., 167, 024508 (2020) http://dx.doi.org/10.1149/1945-7111/ab68c8.S. M. Alia, K. S. Reeves, J. S. Baxter, and D. A. Cullen, J. Electrochem. Soc., 167, 144512 (2020).

Perfluorosulfonic acid (PFSA) polymer electrolytes are widely used in proton exchange membrane (PEM) fuel cell fabrication for the membrane separator and the electrode binder. The PEM serves to electrically insulate the cathode catalyst layer (CCL) from anode catalyst layer (ACL), provide proton conduction between both CCL and ACL, as well as prevent gas crossover. PFSA ionomers are also used in the CCL and ACL to mechanically bind the catalyst particles into thin-films, provide proton conduction between the PEM and catalyst surface, and produce a high proton reactant concentration at the oxygen reduction reaction catalyst. Despite their versatility to be used as a membrane and catalyst binder, the typical PFSA ionomers pose challenges due to the high oxygen transport resistance that is introduced by the thin ionomer films over the catalyst. In recent years, novel high oxygen permeability ionomers (HOPIs) have been developed as the successor to the traditional Nafion™ PFSA ionomers. Despite their remarkable results as a catalyst binder due to their increased oxygen transport rates, less is known regarding their degradation and functional lifetime. Although accelerated stress tests (ASTs) for platinum (Pt)/Pt-alloy catalysts, carbon supports, and membranes are well-established and commonly applied, there is no standard and easily implemented AST for electrode ionomers. One challenge is that membrane ASTs usually quantify the fluoride emission rate (FER) to assess chemical degradation, which is difficult to apply for electrode PFSA ionomer when also using a PFSA membrane because the FER is overwhelmed by membrane signal. In addition, changes in OCV and H2 crossover are not directly indicative of electrode ionomer degradation. Furthermore, concomitant degradation of the catalyst and support can interfere with interpreting electrode ionomer degradation. Here we present an effective and easily applied electrode ionomer chemical AST protocol that can be used to evaluate degradation in the functionality of the electrode ionomer. The approach borrows the chemical AST conditions of the chemical membrane AST’s open circuit voltage (OCV) hold and avoids excessive potential cycling to minimize catalyst and support degradation that will elicit changes in electrode properties separate from ionomer degradation. During the AST, we measure the cathode’s proton conduction resistance, oxygen permeability, and electrochemically surface area (ECSA) to evaluate the degradation of the ionomer’s functionality. Thus, this protocol can be used to assess if more complex and time consuming analyses of ionomer durability are needed as new chemistries emerge. Here we present results of this AST to both conventional PFSA ionomers and HOPIs.

Device-level stress tests are developed that focus on anode catalyst layer degradation and future anticipated operating conditions, including intermittent load and reduced platinum group metal content. Square-wave cycles with an upper load limit of 2.5 A cm‒2 are utilized to screen commercial iridium (Ir) materials. Performance losses are primarily due to decreasing kinetics and are accompanied by catalyst migration into the membrane, worsening catalyst/ionomer integration, and weakening of the catalyst/membrane interface. For ruthenium-containing catalysts, the in situ performances are higher but durabilities lower than Ir baselines, and any performance advantage is lost within the test. Increased loss is likely due to the higher dissolution rate; microscopy confirmed greater degrees of ruthenium migration. For Ir metal or mixed oxides, ex situ activity improvements generally did not translate to in situ performance. The durability, however, is significantly lower and the loss rate increased from 3 (oxide) to 9 (metal) μV cycle‒1. These results are consistent with historical findings in literature, rationalize the continued use of iridium oxide as a baseline catalyst, and demonstrate that traditional catalyst development approaches may not improve device-level durability when focused on low-cost applications. A shift in focus may therefore be more effective at improving catalyst utilization and lessening load requirements.

Durability of automotive polymer electrolyte membrane fuel cells (PEMFC) strongly depends on transient operating conditions such as start-up/shut-down (SUSD). During SUSD events, the hydrogen atmosphere at the anode compartment can be replaced by air (shut-down) and vice-versa (start-up), which can lead to the formation of a hydrogen and air interface in the anode side resulting in a lack of hydrogen supply situation. In the event of a hydrogen-starved situation, the carbon-based support material can be oxidized to supply the necessary electron to complete the load circuit resulting in cell reversal mode, when the anode potential rises above 1.0 V (vs. reversible hydrogen electrode). Such events can damage the anode catalyst layer and reduce the fuel cell lifetime. One of the many ways to mitigate the cell reversal condition is to incorporate reversal tolerant anode catalysts with hydrogen oxidation reaction (HOR) catalysts to facilitate the oxygen evolution reaction (OER) over the carbon oxidation reaction (COR) 1.IrO2 is commonly used as a reversal tolerant anode catalyst because of its high activity and stability under acidic conditions. Several studies have shown the effectiveness of IrO2 as an OER catalyst to alleviate cell reversal events 2. Recent studies have shown that IrO2 can be reduced to metallic Ir under highly reducing hydrogen atmosphere in PEM fuel cell anodes 3. While IrO2 serves its purpose as an OER catalyst, the stability of IrO2 under the transient operation of a PEM fuel cell, such as SUSD, and the impact on overall catalyst durability as well as cell performance are still unresolved.In this work, we have developed an accelerated stress test (AST) which allows to simulate the transient operation during SUSD analogous to real operation of a PEM fuel cell by an active gas switch from hydrogen to air at the anode side. We discuss the consequences of this transient SUSD condition on the anode catalyst as well as cathode catalyst layer characterized by cyclic voltammetry, where hydrogen under potential deposition (Hupd) features show the change in effective catalyst surface area. The impact on reversal tolerance performance of the IrO2 OER catalyst has been determined by the extended exposure to reversal conditions. Post-characterization surface analysis by X-ray photoelectron spectroscopy (XPS) reveals the change of chemical state of the materials on both anode and cathode catalyst layers resulting from active gas switching at the anode. Finally, the overall PEM fuel cell performance and durability are discussed. References Hong, B. K., Mandal, P., Oh, J.-G. & Litster, S. On the impact of water activity on reversal tolerant fuel cell anode performance and durability. Journal of Power Sources 328, 280–288 (2016).Moore, C. E., Eastcott, J., Cimenti, M., Kremliakova, N. & Gyenge, E. L. Novel methodology for ex situ characterization of iridium oxide catalysts in voltage reversal tolerant proton exchange membrane fuel cell anodes. Journal of Power Sources 417, 53–60 (2019).Fathi Tovini, M. et al. Degradation Mechanism of an IrO2 Anode Co-Catalyst for Cell Voltage Reversal Mitigation under Transient Operation Conditions of a PEM Fuel Cell. J. Electrochem. Soc. 168, 064521 (2021).

We developed inner water circulation MEA for portable DMFC uses by introducing permeation controlled layer between anode GDL and catalyst layer. This layer features to have low permeability and reduces saturation at anode catalyst layer. Water produced at cathode catalyst layer diffuses back from cathode to anode through the membrane.

Several emerging and growing applications like biosensors, gas separation membranes, protective coatings, photonics, nanocomposites and microelectronics depend on polymers of thicknesses under 100nm[1]. Ion conducting polymers (ionomers) of thickness <100nm have induced significant advances in the performance of polymer-electrolyte fuel cells (PEFCs) by serving as binder in the catalyst layers (CLs), aiding proton conduction and extending the reaction zone of the CL porous electrode.[2] Thin and ultra-thin polymer films provide ease of processing, application specific tunable properties and reduction in material cost. However, due to deviation of nano-confined polymers from bulk behavior, they pose a challenge of predictability. This is evident in PEFCs where thin-film ionomers are large contributors to mass-transport losses at low catalyst loadings required for commercialization. In-situ investigations over the past 10 years have provided a significant amount of insight into these losses in CLs.[3] As a result, it would be misleading to employ the same principles of understanding used for bulk polymers for nano-confined polymers without modification. In our study, we aim to understand nano-confined ionomers in two ways. First, looking at impact of interfaces by using ionomers supported on different substrates and tuning substrate-ionomer interaction via reducing and oxidizing environment. Second, by examining the impact of cooperative motion and chain dynamics using thermal expansion study of nano-confined ionomers. Combining these two studies we can gain new understanding of effect of confinement on performance. Understanding ionomer-catalyst surface interface and interaction can elucidate not only how ionomers impact catalyst performance but also how catalyst surface impacts ionomer performance. In our study we use water uptake and modulus to probe the effect of platinum surface on thin-film ionomers under oxidizing(Air) and reducing(H2) conditions. Several in-situ and ex-situ methods have demonstrated that oxide formation on the active platinum catalyst surface can reduce the catalytic activity, further hampering activity in the cathode catalyst layer[4]. Despite this, our studies show continued growth of oxides on platinum surface results in higher density of water maintained in the ionomer. This indicates that nano-confined ionomers have greater water stability in the cathode than on the anode catalyst layer, enhancing proton transport in the cathode catalyst layer. Using transition temperature as a proxy for material behavior, we also looked at relaxation behavior of nano-confined ionomers under slow heating conditions. For glass-forming polymers like perfluorinated sulfonic-acid (PFSA) ionomers (such as Nafion and 3M-ionomer) cooperative motion and dynamics of chains have been used to explain changes in modulus, thermal expansion, relaxation behavior, and gas transport. Thermal transition temperatures are often used as a broad physical description for these kinetically and thermodynamically-driven changes in polymer behavior[1]. In this study, we used heated cell ellipsometry to explore the presence of transition temperatures and their dependence on thickness and substrate in thin-film ionomers. We are able to see both α and β transition temperatures using ion exchanged nano-confined ionomers supported on silicon substrates. Our results demonstrate increased rate of expansion for thin films as compared to bulk and dramatic change of transition temperatures around 50-70nm indicating impact of ionomer-surface interaction and influence of electrostatic interaction on chain relaxation and gas transport. Acknowledgement We would like to thank Douglas Kushner for providing assistance and guidance in this study. This work made use of facilities at the Joint Center for Artificial Photosynthesis at Lawrence Berkeley National Laboratory. This work was funded in part by the University of California Chancellor's Graduate Fellowship, National Science Foundation Graduate Fellowship and the Fuel Cell Technologies Office, Office of Energy Efficiency and Renewable Energy, U. S. Department of Energy under contract number DE-AC02-05CH11231.

In the recent years, the use of fuel cells for the propulsion of passenger vehicles and heavy-duty vehicles has gained renewed interest as alternative to internal combustion engine-powered vehicles. Particularly for the latter, the long-term durability of proton-exchange-membrane fuel cells (PEMFCs) is still a concern, which in part is governed by the catalyst layer durability during system operating conditions.1 During the operation of a PEM fuel cell system, certain transient conditions can occur that can lead to rapid degradation of the catalyst layers. On one hand, the widely studied start-up/shut-down (SUSD) phenomenon leads to significant degradation of the cathode catalyst layer due to the exposure of the cathode electrode to high potentials (>>1.0 V vs the reversible hydrogen electrode potential (VRHE)) that results from a H2/air-front passing through the anode flow field.2 On the other hand, an intermittent under-supply of hydrogen to one or several cells of a PEMFC stack can lead to a so-called cell-reversal (CR) event, resulting in the oxidation of the carbon support of the anode catalyst and in the subsequent collapse of the anode catalyst layer structure. The latter can be mitigated by the addition of an anode co-catalyst that facilitates the oxygen evolution reaction (OER) at much lower potentials than the carbon-supported platinum catalyst (Pt/C) that serves as anode catalyst for the hydrogen oxidation reaction (HOR).3 However, as shown by our recent study, the stability of the anode co-catalyst for the OER during SUSD events must be considered.4 In the present study, we examine different accelerated stress tests (ASTs) for single-cell PEMFCs that are designed to assess the stability of an anode co-catalyst for the OER in a PEMFC that is subjected to cell-reversal and SUSD events. Thus, we evaluated the stability of an anode co-catalyst under four conditions: i) subjecting the cell to extended SUSD cycles; ii) a cell-reversal protocol where a constant current is being drawn when feeding N2/air to the anode/cathode until a given cut-off cell potential is reached; iii) a protocol where cell-reversal cycling is induced by switching the anode feed gas between hydrogen and nitrogen while applying a constant current and supplying air to the cathode (later on referred as CR cycling); and, iv) an anode potential cycling protocol where the anode is supplied with N2, and its potential is cycled potentiostatically to different upper potential limits, with the cathode purged with air and serving as a counter electrode. With these ASTs, we examine the effect of the different anode potential cycles during SUSD and CR transients in order to elucidate the dependence of the IrO2 dissolution rate on operating potential.The stability of the IrO2 based anode co-catalyst is investigated by electrochemical measurements (cyclic voltammetry and polarization curves) and additionally via ex-situ XPS analysis. For example, Figure 1 shows the ex-situ XPS analysis of pristine and aged membrane electrode assemblies (MEAs). The upper two panels show the XPS data in the Pt 4f (BE>67 eV) and the Ir 4f (BE<67 eV) regions of the pristine Pt/C anode with an IrO2-based anode co-catalyst (Figure 1a) as well as the pristine Pt/C cathode (Figure 1b). The lower two panels show the cathode XPS data of the MEAs after 500 SUSD cycles (Figure 1c) and after 500 CR cycles (Figure 1d). In the case of the SUSD degraded MEA, a higher amount of Ir is observed on the cathode when compared to the CR degraded MEA. The mechanistic implications of these data will be discussed. References USDRIVE Fuel Cell Technical Team Roadmap (2017): https://www.energy.gov/eere/vehicles/downloads/us-drive-fuel-cell-technical-team-roadmap (accessed on 28.10.2021).T. Mittermeier, A. Weiß , F.Hasché, G. Hübner, H. A. Gasteiger. Journal of The Electrochemical Society, 164 (2), F127-F137 (2016).T. R. Ralph, S. Hudson, and D. P. Wilkinson, ECS Transactions, 1 (8), 67-84 (2006).M. Fathi Tovini, A. M. Damjanović, H. A. El-Sayed, J. Speder, C. Eickes, J.-P. Suchsland, A. Ghielmi, and H. A. Gasteiger, Journal of The Electrochemical Society, 168 (6), 064521 (2021). Figure 1

The employment of hydrogen as an energy carrier provides a promising solution toward zero carbon emission and battling climate change. To meet the DOE’s Hydrogen Shot goal of $1 per kilogram of hydrogen by 2031, proton exchange membrane (PEM) water electrolysis is a key technology of hydrogen production from renewable energy sources. Successful deployment of PEM electrolyzers requires reducing cost while simultaneously improving performance and lifetime. While cost reduction is expected from a variety of strategies including scaling up, operation optimization, and advanced manufacturing, it remains vital to reduce the use of noble-metal catalyst due to its scarcity and vulnerable supply chain subject to market disturbance. [1]Reducing the loading of iridium catalyst on the anode while maintaining electrolyzer performance and durability is of great challenge. In this talk, we discuss issues in PEM electrolyzer component development and advanced manufacturing of electrode layers related to catalyst loading reduction with an emphasize on analytical electron microscopy which provides valuable insight on materials morphology, crystalline structure, and chemical compositions. The batch-to-batch variance of catalyst morphology and elemental composition/distribution from commercial suppliers will be examined for catalyst down-selection. We then analyze the effect of reducing Ir loading on the electrode layer structure and ionomer distribution. These results are correlated with electrochemical measurements in the electrolyzer cell, which help elucidate the effect of low catalyst loading on electrolyzer performance. Morphologies of degraded low-loading anode catalyst layer and gas recombination layers will be investigated, and the dissolution and migration of iridium will be studied. We will also examine impact of different roll-to-roll manufacturing strategies for low-loading catalyst layers and on electrolyzer durability. Last but not least, we analyze MEAs subject to cation contamination and recovery procedure with electron microscopy. [2]References[1] Alia, S.M., Current Opinion in Chemical Engineering 2021, 33:100703.[2] Funding for this work was provided by U.S. Department of Energy Office of Energy Efficiency and Renewable Energy, Hydrogen and Fuel Cell Technologies Office through the H2NEW Consortium. Electron microscopy research conducted as part of a user project at the Center for Nanophase Materials Sciences (CNMS), which is a US Department of Energy, Office of Science User Facility at Oak Ridge National Laboratory.

Water electrolysis is a crucial technology for large-scale hydrogen generation, that is required for the transition to a fossil fuel-free energy system. Even though water electrolysis systems are already deployed in a limited capacity, the technology is largely constrained to liquid alkaline electrolysis. Proton exchange membrane (PEM) electrolysis could pose an alternative but it is still hindered by high investment costs, in-part due to its reliance on scarce noble-metal catalysts. Alternative structural designs of the anode catalyst layer (CL) could reduce Iridium loading of the whole system and thus accelerate its wide-spread application. In fuel cell research, it was already reported that a multi-layer design with varied ionomer content enhances performance of the CL and in-turn lowers required catalyst loading.[1,2,3]In this study, a gradient design for ionomer content is employed for anode CLs for the application in PEM water electrolysis. CLs are coated in a stacked multi-layer design via ultrasonic spray coating of Iridium/Nafion® suspensions. The target ionomer loadings (10 and 30 wt.%) are confirmed by a combination of thermo-gravimetric analysis (TGA) and X-ray photoelectron spectroscopy (XPS). The coating process yields homogenously loaded reference CLs as well as through-plane graded CLs with the desired ionomer loading. Additionally, scanning electron microscopy (SEM) in conjunction with energy dispersive spectroscopy (EDS) shows equal CL thickness across all ionomer loadings and spatially differentiated Nafion® content throughout the CLs thickness. Electrochemical characterizations are carried out in an electrolysis-adapted gas diffusion electrode (GDE) half-cell setup to allow for quick examination and prototyping of produced layers. Differences in electrochemical performance of these layers can be observed with one gradient design CL showing reduced overpotential across all current densities compared to the homogenous CLs. In-particular a high ionomer loading near the membrane improves performance, most likely due to increased proton conduction to the membrane and higher available pore volume near the porous transport layer.Further analysis is performed on electrochemical studies to deepen the understanding of the role of ionomer in anodic PEM water electrolysis CLs. Particularly, the investigation of protonic and electric conductivity through the CL is of interest, because this parameter is most influenced by ionomer loading.[4]

Heck couplings were carried out ligandless in air with very low catalyst loads under microwave or simultaneous microwave/ultrasound irradiation. Using ligand‐free palladium(II) acetate [Pd(OAc)2] in the range of 0.01–0.1 mol % or palladium‐on‐carbon (Pd/C) 10 % in the range of 1.0–2.0 mol %, most aryl iodides and bromides gave high yields under conventional heating (120 °C) in 18 h. Microwave irradiation alone or, better still, combined with high‐intensity ultrasound, strongly promotes the reaction, generally decreasing reaction times to 1 h. Electron‐poor aryl chlorides such as 4‐chloroacetophenone and 1‐chloro‐4‐nitrobenzene reacted with styrene to afford high product yields in the presence of 0.25 mol % Pd(OAc)2 or 2.0–3.0 mol % Pd/C. In several cases the addition of a co‐catalyst, either rhodium tris(triphenylphosphine) chloride, 0.005 mol %, or a copper(I) salt (iodide or bromide), 2.0–4.0 mol %, proved very advantageous. 4‐Bromo‐ and 4‐chloroacetophenone afforded up to 15 % of oxidation products, namely the corresponding 4‐halobenzoic acid and 4‐styrylbenzoic acid, a drawback that was avoided by working under a nitrogen atmosphere.

Enhancing the CO tolerance of PEMFC MEAs by combining sputter-deposited and direct-printed composite anode catalyst layers

Effect of silicon carbide particle size in the electrolyte matrix on the performance of a phosphoric acid fuel cell