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Proton exchange membrane water electrolysis is technically the most suitable technology for the production of green hydrogen on a large scale. Although it is still more expensive than hydrogen produced from fossil sources, it has already been commercialized. Novel components with cost-effective materials and efficient manufacturing processes are being rapidly developed. However, these components must endure durability tests that can guarantee a lifetime of at least 50,000 operation hours. Consequently, there is an urgent need to develop accelerated stress test protocols based on a deep understanding of degradation mechanisms of stack components. Recent reports show that the main degradation mechanisms are associated to anode catalyst dissolution, membrane chemical decomposition, and formation of semiconducting oxides on the metal components. These mechanisms can be accelerated by stressors such as high current density, dynamic operation, and shutdown modes. On the basis of these reports and knowledge of the operational requirements for large-scale proton exchange membrane water electrolysis, we propose an accelerated stress test protocol for the fast evaluation of newly developed cost efficient and durable components.

The production of green hydrogen by a cost-effective electrolysis technology is of paramount importance for future energy supply systems. In this regard, proton exchange membrane (PEM) electrolysis...

Hydrogen is expected to play an important role as a crosslinking technology between power generation on one hand and transport and industry on the other hand. It can directly replace fossil fuels in transport and industry when produced by water electrolysis renewable energies such as solar or wind, which are converted with low efficiencies. The relevant technologies are either the mature alkaline electrolysis or the newer proton exchange membrane (PEM) water electrolysis. The main advantage of PEM electrolysis technology is that it provides high efficiency, high power density with low footprint, and flexibility without the need of corrosive chemicals such as KOH (alkaline electrolysis). On the other hand, questions about degradation mechanisms, long-term stability and the high capital costs compared to the alkaline technology hinder the large-scale industrial penetration of this technology in the market. Moreover, these challenges are mutually dependent. Cost reductions of materials and stack components, for example, can have a negative impact on long-term stability. Thus, more information about the degradation mechanisms is necessary to determine an optimum between cost reduction and long-term stability. Furthermore, degradation measurements are expensive and evidently require a lot of time. Consequently, the development of accelerated stress tests (AST) protocols is in the focus of the current research by the academy and industry in particular. This presentation will discuss degradation processes of MEAs under high current density which has been found to accelerate degradation in our laboratory. Degradation was investigated in a HYLYZER™ Hydrogen Generator (HHG) from Hydrogenics under operation at 4 A cm-2 for almost 3000 h. The degradation of the bipolar plates and gas diffusion layers are neglected since these components are well protected against corrosion. The cells were analyzed by electrochemical impedance spectroscopy. Furthermore samples of ion exchange resin, which keeps the water resistivity above 10 MΩ, were collected and analyzed by XPS to quantify the accumulated ions. In addition, post-test investigations of the aged MEAs by conductive and material sensitive AFM, SEM with EDX and XPS were performed to identify degradation mechanisms. An important observation is a decrease of the ohmic resistance during operation at high current densities which is associated to fluoride release into the water. To analyze the time dependence of the cells in the hydrogen generator system a zero-dimensional system model with effective parameters was developed. This model enables quantifying the degradation measurements and the discussion in the context of system behavior. Preventing metal oxidation by corrosion protective layers leads to increased efficiency mainly due to decreasing ohmic resistances. This decrease is assumed to be depending on current density and time. The observed F release rate supports this conclusion. The degradation mechanism is assumed to be an increased permeability for water, oxygen and hydrogen with corresponds to a membrane thinning and ionomer loss in the electrodes. Such an interpretation was backed by the ex-situ post-test analysis. At the anodes a general increase of conductive area fraction evaluated by AFM indicates a loss of ionomer. At the cathodes, a general decrease of conductive area fraction indicates a loss of catalysts. EDX confirmed the loss of Pt and Ir from cathode and anode respectively, and in addition a loss of Ti from the anode was found. Membrane thinning occurred in all cells. It is explained by ionomer decomposition catalyzed by the well distributed Pt content in the membranes detected by XPS. Acknowledgements The research leading to these results has received funding from the European Union’s Seventh Framework Program (FP7/ 2007-2013) for the Fuel Cells and Hydrogen Joint Technology Initiative under grant n° 621237, “ INSIDE- In -situ Diagnostics in Water Electrolyzers“ and from national projects “LastElSys” and “WESpe” by Federal Ministry for Economic Affairs and Energy. Figure 1

Hydrogen is expected to play an important role as a crosslinking technology between power generation on one hand and transport and industry on the other hand. It can directly replace fossil fuels in transport and industry when produced by water electrolysis with renewable energies such as solar or wind. The relevant technologies are either the mature alkaline electrolysis or the newer proton exchange membrane (PEM) water electrolysis. For PEM electrolysis in particular, key components that determine the stack cost are the titanium-based contact elements, such as the bipolar plates (BPP) and the current collectors (CC), and the high iridium loading of electrocatalyst for the OER in state of art membrane electrode assemblies (MEA). However, the cost structure depends on the specific design of the electrolyser. This presentation will discuss strategies for cost reduction by synthesizing novel electrocatalyst with the aim of lowering the high Ir loading. Our concept can be applied to supported and alloy electrocatalysts. The supports need to be highly stable and exhibit sufficient electronic conductivity. The enhancement of activity achieved with improved electrocatalyst reaches a factor of about 15 with respect to the best commercially available electrocatalyst. Additionally, the cost reduction achieved by a titanium coating for stainless steel BPPs or CCs for PEM electrolysis will be discussed. We use vacuum plasma spraying (VPS) to coat either dense coatings for corrosion protection of stainless steel components or build up titanium diffusion layers with defined porosity as contact elements for the MEA. The conductivity of the titanium coating can be improved by well-known Pt or Au additions; however, we have also developed promising non-noble conductivity enhancement elements. Furthermore, the VPS coating and production procedure is adaptable to large-scale industrial production. Acknowledgements The research leading to these results has received funding from the European Union’s Seventh Framework Program (FP7/ 2007-2013) for the Fuel Cells and Hydrogen Joint Technology Initiative under grant n° 621237, “ INSIDE- In -situ Diagnostics in Water Electrolyzers“ and from national projects “LastElSys” and “WESpe” by Federal Ministry for Economic Affairs and Energy. Figure 1

International audience; The use of high amounts of iridium in industrial proton exchange membrane water electrolyzers (PEMWE) could hinder their widespread use for the decarbonization of society with hydrogen. Nonthermally oxidized Ir nanoparticles supported on antimony-doped tin oxide (SnO2:Sb, ATO) aerogel allow decreasing the use of the precious metal by more than 70% while enhancing the electrocatalytic activity and stability. To date, the origin of these benefits remains unknown. Here, we present clear evidence of the mechanisms that lead to the enhancement of the electrochemical properties of the catalyst. Operando near-ambient pressure X-ray photoelectron spectroscopy on membrane electrode assemblies reveals a low degree of Ir oxidation, attributed to the oxygen spill-over from Ir to SnO2:Sb. Furthermore, the formation of highly unstable Ir(III) species is mitigated, while the decrease of Ir dissolution in Ir/SnO2:Sb is confirmed by inductively coupled plasma mass spectrometry. The mechanisms that lead to the high activity and stability of Ir catalysts supported on SnO2:Sb aerogel for PEMWE are thus unveiled.

The fluctuating behavior of renewable energy sources hinders the widespread integration of those in a reliable electricity grid. Presumably, the wide operation range and rapid response of proton exchange membrane (PEM) electrolyzers can stabilize the grid, yet the degradation effects are not fully understood. The results presented here show no negative effect of dynamic operation at current 0.8, 1.6, 2.5 and 3.3 A cm-2, on commercial membrane electrode assemblies (MEA) with two different catalyst loadings. Conversely, the reduction of the loading of precious metal in the MEA leads to a cell voltage increase by 100 mV at 3.3 A cm-2. In addition, stack temperature correction of industrial facilities is necessary for proper comparison of cell potential and analysis of degradation mechanisms.

The anode side catalyst is one of the key parts for sustainable hydrogen production via proton exchange membrane (PEM) electrolysis. An optimized synthesis of the oxygen evolution reaction (OER) catalysts may lead to a cost efficient production, promoting the commercialization of new catalyst materials. This work compares the electrochemical characteristics of Ir nanoparticles synthetized in different purities of ethanol and deionized (DI) water as solvents. The use of cetyltrimethyl ammonium bromide (CTAB) as a surfactant is discussed as well. In general, the absence of the surfactant and use of either low ethanol purity or water is detrimental for electrocatalytic properties of the materials. Changes in the Tafel slope are observed, while the analysis of the specific exchange current can be misleading. The active sites from the IrIII/IrIV oxidation peak do not correlate exactly with the OER activities, while the capacitive current provides more meaningful information.

Progress in the development of proton exchange membrane (PEM) water electrolysis technology requires decreasing the anode overpotential, where the sluggish multistep oxygen evolution reaction (OER) occurs. This calls for an understanding of the nature of the active OER sites and reaction intermediates, which are still being debated. In this work, we apply synchrotron radiation-based near-ambient pressure X-ray photoelectron and absorption spectroscopies under operando conditions in order to unveil the nature of the reaction intermediates and shed light on the OER mechanism on electrocatalysts most widely used in PEM electrolyzers—electrochemical and thermal iridium oxides. Analysis of the O K-edge and Ir 4f spectra backed by density functional calculations reveals a universal oxygen anion red–ox mechanism regardless of the nature (electrochemical or thermal) of the iridium oxide. The formation of molecular oxygen is considered to occur through a chemical step from the electrophilic OI– species, which itself is formed in an electrochemical step.

We have developed a highly active nanostructured iridium catalyst for anodes of proton exchange membrane (PEM) electrolysis. Clusters of nanosized crystallites are obtained by reducing surfactant-stabilized IrCl3 in water-free conditions. The catalyst shows a five-fold higher activity towards oxygen evolution reaction (OER) than commercial Ir-black. The improved kinetics of the catalyst are reflected in the high performance of the PEM electrolyzer (1 mg(Ir) cm(-2)), showing an unparalleled low overpotential and negligible degradation. Our results demonstrate that this enhancement cannot be only attributed to increased surface area, but rather to the ligand effect and low coordinate sites resulting in a high turnover frequency (TOF). The catalyst developed herein sets a benchmark and a strategy for the development of ultra-low loading catalyst layers for PEM electrolysis.

Proton exchange membrane fuel cells (PEMFC) systems are efficient generators to supply electricity from the electrochemical reaction between hydrogen and oxygen. These devices use bipolar plates (BPP) that serve to distribute the reactive gases, manage the produced water and collect the generated electrons [1]. The BPPs of a PEMFC stack are usually made of composite graphitic carbon. However the plates are thick, brittle, and corrode at high potentials. Stainless steel (ss) can be used as alternative, but it has to be protected with a highly conductive and corrosion resistant coating [2]. Vacuum plasma spraying (VPS) is a suitable technique for producing dense Ti coatings for BPPs of PEM electrolyzers [3]. In this work we coat stainless steel PEMFC electrode holders (EH) with Ti by VPS technique. Several parameters such as the type of plasma torch nozzle, the powder feeding rate, and the plasma gas flow rates of Ar, N2 and H2 are varied. The surface of the VPS coating is subsequently modified with Au by electrodeposition to reduce passivation. The same layer is applied directly on stainless steel substrates for comparison purposes. The coatings were characterized by scanning electron microscopy (SEM), x-ray diffraction (XRD) and x-ray photoelectron spectroscopy (XPS) techniques. SEM images show that the thickness of the Au/Ti coating is 62 µm with a roughness factor of 0.7. The presence of TiO2 between Ti and Au is negligible as confirmed by XRD and XPS techniques. Potentiodynamic characteristics in O2-saturated 0.5 M H2SO4 show that Au/Ti/ss has comparable corrosion currents to Au/ss but higher corrosion potentials. The interfacial contact resistance (ICR) of Au/Ti/ss is 8.6 mΩ cm2 under a compaction pressure of 140 N cm-2, thus meeting the US Department of Energy (DOE) requirement for this parameter. The cell voltage-current characteristics of PEMFCs with Au and Au/Ti coated EHs are shown in Fig. 1a. The performances of the PEMFCs above 0.75 V are almost identical. However, at 0.6 V the PEMFC with the Au/Ti coatings produces almost 30% more current. By keeping the cell voltage (Ecell) constant at 0.6 V, the Au/Ti coating allows reducing the current instabilities of the PEMFC operating under strong flooding conditions, see Fig. 1b. The periodic spikes and oscillations in the generated current of the PEMFC with the Au coating are produced as result of water droplets that find difficulty to flow through channels of the flow field [4]. Finally, the same phenomenon occurs in the cathode pressure, confirming the unique property of the Au/Ti coating for reducing flooding. Thus, the thermally sprayed coatings protect the stainless bipolar plates from corrosion, increase the ICR and improve the water management in a PEMFC. References [1] R. Taherian, J. Power Sources 265 (2014) 370. [2] R.A. Antunes, M.C.L. Oliveira, G. Ett, V. Ett, Int. J. Hydrogen Energy 35 (2010) 3632. [3] A.S. Gago, A.S. Ansar, P. Gazdzicki, N. Wagner, J. Arnold, K.A. Friedrich, ECS Trans. 64 (2014) 1039. [4] D.G. Sanchez, D.G. Diaz, R. Hiesgen, I. Wehl, K.A. Friedrich, J. Electroanal. Chem. 649 (2010) 219. Figure 1

Electroceramic support materials can help reducing the noble-metal loading of iridium in the membrane electrodes assembly (MEA) of proton exchange membrane (PEM) electrolyzers. Highly active anodes containing Ir-black catalyst and submicronic Ti4O7 are manufactured through screen printing technique. Several vehicle solvents, including ethane-1,2-diol; propane-1,2-diol and cyclohexanol are investigated. Suitable functional anodic layer with iridium loading as low as 0.4 mg cm−2 is obtained. Surface properties of the deposited layers are investigated by atomic force microscopy (AFM). The most homogeneous coating with the highest electronic conductivity is obtained using cyclohexanol. Tests in PEM electrolyzer operating at 1.7 V and 40 °C demonstrate that the CCM with anode coated with cyclohexanol presents a 1.5-fold higher Ir-mass activity than that of the commercial CCM.

Chalcogenide electrocatalysts are highly active for the oxygen reduction reaction (ORR) in electrolytes containing small organics, such as methanol (CH3OH) and formic acid (HCOOH), thanks to its tolerance to poisoning. This property allows using them as tolerant cathodes of fuel cells that use highly concentrated liquid fuel. In this review a comprehensive discussion about the mechanism of ORR and tolerance of the chalcogenide electrocatalysts to small organic molecules is provided. Some aspects of the chemical synthesis and physical structure are also discussed. Chalcogenide-based cathodes of direct methanol fuel cell and novel membrane-less fuel cells can overcome the problem of the formation of a mixed potential due to the fuel crossover. Special attention is given to the use of tolerant cathodes to the laminar flow fuel cell and other membrane-less microsystems.

Cost reduction and high efficiency are the mayor challenges for sustainable H2 production via proton exchange membrane (PEM) electrolysis. Titanium-based components such as bipolar plates (BPP) have the largest contribution to the capital cost. This work proposes the use of stainless steel BPPs coated with Nb and Ti by magnetron sputtering physical vapor deposition (PVD) and vacuum plasma spraying (VPS), respectively. The physical properties of the coatings are thoroughly characterized by scanning electron, atomic force microscopies (SEM, AFM); and X-ray diffraction, photoelectron spectroscopies (XRD, XPS). The Ti coating (50 μm) protects the stainless steel substrate against corrosion, while a 50-fold thinner layer of Nb decreases the contact resistance by almost one order of magnitude. The Nb/Ti-coated stainless steel bipolar BPPs endure the harsh environment of the anode for more than 1000 h of operation under nominal conditions, showing a potential use in PEM electrolyzers for large-scale H2 production from renewables.

Hydrogen produced by water splitting is a promising solution for a sustained economy from renewable energy sources. Proton exchange membrane (PEM) electrolysis is the utmost suitable technology for this purpose, although the quest for low cost, highly active and durable catalysts is persistent. Here we develop a nanostructured iridium catalyst after electrochemically leaching ruthenium from metallic iridium-ruthenium, Ir0.7Ru0.3Ox (EC), and compare its physical and electrochemical properties to the thermally treated counterpart: Ir0.7Ru0.3O2 (TT). Ir0.7Ru0.3Ox (EC) shows an unparalleled 13-fold higher oxygen evolution reaction (OER) activity compared to the Ir0.7Ru0.3O2 (TT). PEM electrolyzer tests at 1 A cm−2 show no increase of cell voltage for almost 400 h, proving that Ir0.7Ru0.3Ox (EC) is one of the most efficient anodes so far developed.

International audience; Low Ir loading oxygen evolution reaction (OER) catalysts with superior activity and durability for proton exchange membrane (PEM) electrolyzers are an important topic in industry and academia. One possible strategy for addressing this challenge is the use of support materials that are stable under highly corrosive acidic environments at a high working potential (>1.4 V). Moreover, highly porous structure is another key criteria for OER catalyst support to achieve a high electrochemical surface area. Here, we report a novel Ir supported on a SnO2:Sb aerogel OER catalyst (Ir/SnO2:Sb-mod-V), which was prepared under ambient pressure by using vanadium additives. It shows an unrivaled activity and enhanced stability, on which vanadium does not play any active role but demonstrates the influences that changes the porosity of the aerogel support and affects the impurity content of the chlorine. By taking advantage of the high porosity of the aerogel substrate, Ir/SnO2:Sb-mod-V allows a decrease of more than 70 wt% for precious metal usage in the catalyst layer while keeping a similar OER activity compared to its unsupported counterpart.

Proton exchange membrane (PEM) electrolysis is a promising technology for large H 2 production from surplus electricity from renewable sources. However, the electrolyser stack is costly due to the manufacture of bipolar plates (BPP). Stainless steel can be used as an alternative, but it must be coated. Herein, dense titanium coatings are produced on stainless steel substrates by vacuum plasma spraying (VPS). Further surface modification of the Ti coating with Pt (8 wt% Pt/Ti) deposited by physical vapour deposition (PVD) magnetron sputtering reduces the interfacial contact resistance (ICR). The Ti and Pt/Ti coatings are characterised by scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD), and X-ray photoelectron microscopy (XPS). Subsequently, the coatings are evaluated in simulated and real PEM electrolyser environments, and they managed to fully protect the stainless steel substrate. In contrast, the absence of the thermally sprayed Ti layer between Pt and stainless steel leads to pitting corrosion. The Pt/Ti coating is tested in a PEM electrolyser cell for almost 200 h, exhibiting an average degradation rate of 26.5 μV h −1 . The results reported here demonstrate the possibility of using stainless steel as a base material for the stack of a PEM electrolyser.

Current energy policies require the urgent replacement of fossil energy carriers by carbon neutral ones, such as hydrogen. The backing or micro-porous layer plays an important role in the performance of hydrogen proton exchange membrane (PEM) fuel cells, reducing contact resistance and improving reactant/product management. Such carbon-based coating cannot be used in PEM electrolysis since it oxidizes to CO2 at high voltages. A functional titanium macro-porous layer (MPL) on the current collectors of a PEM electrolyzer is developed by thermal spraying. It improves the contact with the catalyst layers by ca. 20 mΩ cm2, increasing significantly the efficiency of the device when operating at high current densities.

PEM water electrolysis has recently emerged as one of the most promising technologies for large H2 production from a temporal surplus of renewable electricity; yet it is expensive, partly due to the use of large amounts of Ir present in the anode. Here we report the development and characterization of a cost-effective catalyst, which consists of metallic Ir nanoparticles supported on commercial Ti4O7. The catalyst is synthesized by reducing IrCl3 with NaBH4 in a suspension containing Ti4O7, cetyltrimethylammonium bromide (CTAB) and anhydrous ethanol. No thermal treatment was applied afterwards in order to preserve the high conductivity of Ti4O7 and the metallic properties of Ir. Electron microscopy images show an uniform distribution of mostly single Ir particles covering the electro-ceramic support, although some agglomerates are still present. X-ray diffraction (XRD) analysis reveals a cubic face centered structure of Ir nanoparticles with a crystallite size of ca. 1.8 nm. According to X-ray photoelectron spectroscopy (XPS), the ratio of metallic Ir and Ir-oxide, identified as Ir(3+), is 3 : 1 after the removal of surface contamination. Other surface properties such as primary particle size distribution and surface potential were determined by atomic force microscopy (AFM). Cyclic and linear voltammetric measurements were conducted to study the electrochemical surface and kinetics of Ir-black and Ir/Ti4O7. The developed catalyst outperforms the commercial Ir-black in terms of mass activity for the oxygen evolution reaction (OER) in acid medium by a factor of four, measured at 0.25 V overpotential and room temperature. In general, the Ir/Ti4O7 catalyst exhibits improved kinetics and higher turnover frequency (TOF) compared to Ir-black. The developed Ir/Ti4O7 catalyst allows reducing the precious metal loading in the anode of a PEM electrolyzer by taking advantage of the use of an electro-ceramic support.

Given its rapid response to fluctuating currents and wide operation range, proton exchange membrane (PEM) water electrolysis is utmost suitable for generation of hydrogen from renewable power. However, it is still hindered by the high cost of the stack components compared to those used in the alkaline technology. In particular, the titanium bipolar plates (BPP) are an issue and the replacement of this metal by stainless steel is a challenge, due to the highly corrosive environment inside PEM electrolyzer stack. Herein, we coat stainless steel BPPs with 50–60 μm Ti and 1.5 μm Pt coatings by vacuum plasma spraying (VPS) and magnetron sputtering physical vapor deposition (PVD), respectively. The BPPs are evaluated at constant 1 A cm−2 for more than 1000 h. The thermally sprayed Ti coatings fully protect the stainless steel substrate during this period of time, and the Pt surface modification allows achieving a cell performance comparable to the baseline.

High efficiencies, wide operation range and rapid response time have motivated the recent interest in proton exchange membrane (PEM) electrolysis for hydrogen generation with surplus electricity. However, degradation at high current densities and the associated mechanism has not been thoroughly explored so far. In this work, membrane electrode assemblies (MEA) from different suppliers are aged in a commercial PEM electrolyzer (2.5 N m3 H2 h1 ), operating up to 4 A cm2 for more than 750 h. In all cases, the cell voltage (Ecell) decreases during the testing period. Interestingly, the cells with Ir-black anodes exhibit the highest performance with the lowest precious metal loading (1 mg cm-2). Electrochemical impedance spectroscopy (EIS) shows a progressive decrease in the specific exchange current, while the ohmic resistance decreases when doubling the nominal current density. This effect translates into an enhancement of cell efficiency at high current densities. However, Ir concurrently leaches out and diffuses into the membrane. No decrease in membrane thickness is observed at the end of the tests. High current densities do not lead to lowering the performance of the PEM electrolyzer over time, although MEA components degrade, in particular the anode.

This review covers topics related to the synthesis of nanoparticles, the anodic and cathodic electrochemical reactions and low temperature electrochemical energy devices. The thermodynamic aspects of nucleation and growth of nanoparticles are discussed. Different methods of chemical synthesis such as w/o microemulsion, Bönnemann, polyol and carbonyl are presented. How the electrochemical reactions take place on the surface of the catalytic nanoparticles and the importance of the substrate is put in evidence. The use of nanomaterials in low temperature energy devices such as H2/O2 polymer electrolyte or proton exchange membrane fuel cell (PEMFC) and micro-direct methanol fuel cell (μDMFC), as well as recent progress and durability, is discussed. Special attention is given to the novel laminar flow fuel cell (LFFC). This review starts with the genesis of catalytic nanoparticles, continues with the surface electrochemical reactions that occur on them, and finally it discusses their application in electrochemical energy devices such as low temperature fuel cells or Li-air batteries.