For the de-fossilization of sectors like chemicals, steel, and transportation, green H 2 generated via water electrolysis provides a path towards net-zero. The broad use of H 2 across hard-to-abate sectors confirms the urgent need for green hydrogen at scale. More and more projects are announced and actually reaching realization phases. Within water electrolysis, there are several competing technologies: the so-called solid oxide electrolysis cell (SOEC), alkaline water electrolysis (AEL), anion exchange membrane electrolysis (AEM EL) and proton exchange membrane electrolysis (PEM EL). Here, the latter shows significant benefits, such as high current density operation (> 3 A/cm 2 ) and thus a smaller footprint, highly dynamic operation mode, high gas purity, and generation of pressurized hydrogen. However, at present, PEM EL requires precious metal catalysts; in particular, the O 2 evolution on the anode currently relies on iridium, a metal which is rather scarce and expensive.[1] Other components are also consisting of a certain share of precious metals, which is also true for some of the other mentioned water electrolysis technologies. To meet the demand of iridium with respect to the announced increase in electrolyzer capacities in the multi-GW range, material innovation to reduce the use of this precious metal must be implemented. In this plenary talk we will present you a view on the precious metal market related to the hydrogen value chain, especially water electrolysis, as well as mitigation strategies to avoid material limitations and lower the cost burden. Moreover, we will show you from depicted projects – own and publicly reported ones – insights on fundamental as well as industrial level to highlight the tremendous progress in understanding and implementation of materials and components in PEM electrolyzer technology in the recent decade. Amongst other highlights, we for example successfully reduced the catalyst loading with our core-shell material IrOx on TiO 2 towards 0.25 mg Ir /cm 2 demonstrating within the project Kopernikus P2X and its successor IRIDIOS (part of the platform H2Giga) an operating load of less than 0.1 t/GW [2, 3]. Last but not least, we will have a brief look on recycling of precious metals, as another important pillar for a sustainable use of important components in PEM electrolyzers, as well as a key step to enable a technology implementation at multi-GW scale. References [1] “Iridium Quaterly Market Report“, SFA Oxford (2021) 31 [2] M. Bernt, A. Hartig-Weiß, M.F. Tovini, H.A. El-Sayed, C. Schramm, J. Schröter, C. Gebauer, H.A. Gasteiger, Chem. Ing. Tech. 92, 31 (2020) [3] M. Möckl, M.F. Ernst, M. Kornherr, F. Allebrod, M. Bernt, J. Byrknes, C. Eickes, C. Gebauer, A. Moskovtseva, H.A. Gasteiger, J. Electrochem. Soc. 169, 064505 (2022)

In recent years, there has been a notable focus shift within the hydrogen fuel cell (FC) market from passenger electric vehicles (PEVs) to heavy-duty vehicles (HDVs). This trend arises from the expectation that fuel cells for HDVs will facilitate a quicker market entry, driven by their scalability, reduced need for hydrogen refueling stations (HRS), and distinct advantages of FC-HDV over battery electric vehicles (BEVs) such as longer range and faster refueling times. However, the deployment of HDV fuel cells offers numerous technical challenges for the developers and manufacturers of the components within a membrane electrode assembly (MEA). The desired operational specifications - including a lifespan of 25,000 hours, an efficiency of 68 %, and a cost target of $80/kW by 2030 - emphasize that durability and efficiency are the major challenges [1]. From a catalyst design perspective, additional requirements emerge under the harsher operating conditions typical of HDV fuel cells, which often entail higher temperatures (> 95 °C) and lower humidity levels (RH < 80%) [2]. When these requirements are translated into catalyst design targets, it becomes evident that materials must be specifically tailored for HDV applications, integrating high intrinsic activity, exceptional stability, and the capability to accommodate higher platinum loadings simultaneously. Achieving these goals necessitates a perfect understanding of the interactions among platinum nanoparticles, carbon support and ionomer within the catalyst structure. Furthermore, the effective development of these materials highly depends on testing under conditions that are close to real-world HDV applications. In the past, various strategies have been devised to synthesize Pt/C and Pt-alloy/C catalysts that exhibit remarkable initial activities; however, these materials often fail to sustain high performance in long-term durability tests. Additionally, many of these innovative materials are produced through complex laboratory synthesis methods that involve multiple steps, complicating the scaling process to meet industry-level production volumes and cost-competitive standards. This work presents the evolution of different generations of Pt/C catalysts for HDV applications from an industry standpoint. This includes catalyst materials developed within the EU-funded project PEMTASTIC [3], which strives to meet the performance targets for HDV applications through an integrated approach that combines modeling, material development, and application-relevant testing. The research leading to these results was supported by the project PEMTASTIC (101101433) which is supported by the Clean Hydrogen Partnership and its members Hydrogen Europe and Hydrogen Europe Research. References: [1] DOE HFTO Program Record #19006 [2] PEMTASTIC Deliverable 1.3: Public report on definition of FC test protocols [3] https://pemtastic-project.eu/

For the de-fossilization of sectors like chemicals, steel, and transportation, green H 2 generated via water electrolysis provides a path towards net-zero. The broad use of H 2 across hard-to-abate sectors confirms the urgent need for green hydrogen at scale. Within water electrolysis, there are several competing technologies: the so-called solid oxide electrolysis cell (SOEC), alkaline water electrolysis (AEL) and polymer electrolyte membrane electrolysis (PEM EL). Here, the latter shows significant benefits, such as high current density operation (> 2 A/cm 2 ) and thus a smaller footprint, highly dynamic operation mode, high gas purity, and generation of pressurized hydrogen. However, at present, PEM EL requires precious metal catalysts; in particular, the O 2 evolution on the anode currently relies on iridium, a metal which is rather scarce and expensive [1]. To meet the demand of iridium with respect to the announced increase in electrolyzer capacities in the multi-GW range, material innovation to reduce the use of this precious metal must be implemented. Successful catalyst and electrode developments have already been demonstrated in the BMBF funded project Kopernikus P2X, whereby loadings of approx. 0.3 mg/cm 2 (< 0.1 g/kW 1 ) have been achieved without any significant losses in activity over time [2, 3]. Here, we present a material innovation in the form of Ru-based electrocatalysts with a significantly reduced Ir content. This ruthenium-iridium oxide can be adjusted in a wide range of Ir content down to less than 15 wt.% (Ir). Consequently, iridium-based electrode loadings of less than 0.1 mg/cm 2 and mass activities of about 3,500 A/g are feasible. Moreover, in accelerated degradation tests those mixed-oxides have demonstrated the often-missing stability by showing low degradation rates, similar to that of pure IrO 2 , in up to 30,000 potential-induced stress cycles. This achievement stems from a remarkable screening approach that combines synthesis, characterization and testing at the nanoscale at Mattiq, and on industrial scale in the multi-gram range at Heraeus Precious Metals GmbH & Co. KG. Remarkably the alignment of degradation testing on both scales showcases the power of the applied method, providing a blueprint for high throughput screening for future material developments, both within water electrolysis and beyond. References [1] “Iridium Quaterly Market Report“, SFA Oxford (2021) 31 [2] M. Bernt, A. Hartig-Weiß, M.F. Tovini, H.A. El-Sayed, C. Schramm, J. Schröter, C. Gebauer, H.A. Gasteiger, Chem. Ing. Tech. 92, 31 (2020) [3] M. Möckl, M.F. Ernst, M. Kornherr, F. Allebrod, M. Bernt, J. Byrknes, C. Eickes, C. Gebauer, A. Moskovtseva, H.A. Gasteiger, J. Electrochem. Soc. 169, 064505 (2022)

In fuel cell applications with long lifetime requirements, the management of stressing operating conditions—such as hydrogen starvation events—plays a pivotal role. Among other remedies, the incorporation of an OER-enhancing co-catalyst, is widely employed to improve the intrinsic stability of Pt/C-based anode catalyst layers in PEM fuel cells. The present study investigates several supported and unsupported Ir-based co-catalysts comprising different oxidation states of iridium: from metallic to oxidic character, both anhydrous rutile-type IrO 2 and hydrated amorphous form. Utilizing a single-cell setup, cell reversal experiments were conducted initially after break-in of the MEA and after seven days of continuous operation under reductive H 2 atmosphere at application-relevant conditions. The initial cell reversal tolerance was found to increase in the order metallic Ir < crystalline Ir oxide < amorphous Ir oxyhydroxide. By contrast, after continuous operation under H 2 the order changes drastically to amorphous Ir oxyhydroxide ∼ metallic Ir < crystalline Ir oxide. This led us to conclude that the amorphous Ir oxyhydroxide is likely reduced to metallic Ir during continuous H 2 operation, while IrO 2 provides a reasonable trade-off between initial OER activity, high structural and chemical stability at high anode potentials during H 2 starvation and low reducibility under prolonged H 2 operation.

Lowering the iridium loading at the anode of proton exchange membrane (PEM) water electrolyzers is crucial for the envisaged GW-scale deployment of PEM water electrolysis. Here, the durability of a novel iridium catalyst with a low iridium packing density, allowing for low iridium loadings without decreasing the electrode thickness, is being investigated in a 10-cell PEM water electrolyzer short stack. The anodes of the membrane electrode assemblies (MEAs) of the first five cells utilize a conventional iridium catalyst, at loadings that serve as benchmark for today's industry standard (2 mgIr cm−2). The last five cells utilize the novel catalyst at 8-fold lower loadings (0.25 mgIr cm−2). The MEAs are based on Nafion® 117 and are tested for 3700 h by load cycling between 0.2 and 2.0 A cm−2, with weekly polarization curves and impedance diagnostics. For both catalysts, the performance degradation at low current densities is dominated by an increase of the overpotential for the oxygen evolution reaction (OER), whereby the OER mass activity of the novel catalyst remains ≈4-fold higher after 3700 h. The temporal evolution of the OER mass activities of the two catalysts will be analyzed in order to assess the suitability of the novel catalyst for industrial application.

One of the building blocks to transition to a fully renewable energy supply is the utilization of hydrogen as a replacement of fossil fuels and as a chemical energy storage/carrier medium. This requires the economical and sustainable generation of hydrogen by water electrolysis, whereby proton exchange membrane (PEM) water electrolyzers would enable much higher power densities compared to conventional electrolyzers based on liquid alkaline electrolytes [1]. However, one of the short-comings of PEM water electrolyzers (PEMWEs) is the need for expensive and resource-limited iridium based catalysts for the oxygen evolution reaction (OER), so that the large-scale global deployment of PEMWEs would require a substantial reduction of the iridium loading from currently ~1-2 mg Ir /cm 2 elelctrode to below ~0.05 mg Ir /cm 2 elelctrode [2]. In this contribution, we will discuss the technical challenge to reduce the iridium loading using currently employed iridium catalysts, which is related to the high iridium packing density in the electrode (in units of g Ir /cm 3 electrode ), so that for iridium loadings below ~0.4 mg Ir /cm 2 the electrode becomes too thin to allow for a homogenous electrode with sufficient in-plane electrical conductivity [3]. We will then present a catalyst concept that results in much lower iridium packing densities and that thus enables lower iridium loadings [4]. While such a catalyst exhibits a lower electrical conductivity than a currently employed benchmark catalyst, this drawback can be mitigated by utilizing porous transport layers at the anode that have a highly conductive coating [4]. The long-term stability of this novel type of iridium based OER catalyst will be examined in a 30 cm 2 active area short-stack over ~3700 h; comparing the evolution of the OER mass activity and of the high frequency resistance corrected cell voltage with that of a benchmark catalyst that is evaluated in the same short-stack, which allows for mechanistic insights into the observed degradation rates [5]. References: [1] A. Buttler, H. Spliethoff; "Current status of water electrolysis for energy storage, grid balancing and sector coupling via power-to-gas and power-to-liquids: A review"; Renewable and Sustainable Energy Reviews 82 (2018) 2440. [2] M. Bernt, A. Weiß, M. Fathi Tovini, H. El-Sayed, C. Schramm, J. Schröter, C. Gebauer, H. A. Gasteiger; "Current Challenges in Catalyst Development for PEM Water Electrolyzers"; Chem. Ing. Tech. 92 (2020) 31. [3] M. Bernt, A. Siebel, H. A. Gasteiger; "Analysis of Voltage Losses in PEM Water Electrolyzers with Low Platinum Group Metal Loadings"; J. Electrochem. Soc. 165 (2018) F305. [4] M. Bernt, C. Schramm, J. Schröter, C. Gebauer, J. Byrknes, C. Eickes, H. A. Gasteiger; "Effect of the IrO x Conductivity on the Anode Electrode/Porous Transport Layer Interfacial Resistance in PEM Water Electrolyzers"; J. Electrochem. Soc. 168 (2021) 084513. [5] M. Möckl, M. Ernst, M. Kornherr, F. Allebrod, M. Bernt, J. Byrknes, C. Eickes, C. Gebauer, A. Moskovtseva, H. A. Gasteiger; "Durability investigation and benchmarking of a novel iridium catalyst in a PEM water electrolyzer at low iridium loading"; manuscript to be submitted. Acknowledgements: This work was conducted within the framework of the Kopernikus P2X project funded by the German Federal Ministry of Education and Research (BMBF).

The shared vision of a hydrogen economy, in which sustainable hydrogen covers a substantial fraction of a nation’s energy demand, unites supporters from science, industry, and politics to engage in cooperative exchange and collaborative work. Several publicly and privately funded initiatives support research and innovation activities on renewable hydrogen production, distribution and storage, as well as fuel cell technologies for transportation and stationary applications with the goal of achieving set climate neutrality goals and limit the impact of human-driven climate change [1]. In this context, proton exchange membrane (PEM) fuel cells are considered to play a pivotal role in the decarbonization of the mobility sector, as they allow a simple power scaling through a modular stack design, offer a refueling time and range comparable to conventional combustors, but in contrast, are pollutant- and emission-free when green hydrogen is used [2]. In applications with high lifetime requirements, the management of challenging operating conditions is of key importance. Recently, particular attention was paid to cell reversal events triggered by hydrogen starvation, which – without proper countermeasures – lead to a sharp decline in performance within seconds as the carbon-supported catalyst significantly corrodes at the anode [3]. Among other remedies, the incorporation of a co-catalyst, like iridium oxide [4], that favors the harmless oxygen evolution reaction (OER) of water over the destructive carbon oxidation reaction (COR) is broadly employed to improve the intrinsic stability of Pt/C-based anode catalysts. However, the scarcity of platinum and especially iridium makes sophisticated catalyst and electrode concepts indispensable to serve the stability requirements in a resource-saving way. Based on the latest findings and developments, we derived a wide range of material requirements and material adjustments, which in combination enhance the tolerance against hydrogen starvation induced degradation. Incremental improvements of the Pt/C-based anode catalyst form the foundation [5], which is further extended by a broad screening of several iridium-based co-catalysts under application-relevant conditions [6]. As will be emphasized, a careful selection of the anode catalyst system properties not only results in a significant increase in the initial cell reversal tolerance but is also crucial to maintaining this stability after operation under reductive H2 conditions. References [1] V. Masson-Delmotte et al., In Press, IPCC: Global Warming of 1.5°C (2018). [2] O. Gröger et al., J. Electrochem. Soc., 162 (14) A2605-A2622 (2015). [3] M. F. Tovini et al., J. Electrochem. Soc., 168 064521 (2021). [4] K. H. Lim et al., J. Electrochem. Soc., 164 (14) F1580-F1586 (2017). [5] R. Marić, C. Gebauer, F. Eweiner, and P. Strasser, to be submitted. [6] R. Marić, C. Gebauer, F. Eweiner, and P. Strasser, to be submitted.

To enable future large-scale generation of hydrogen via proton exchange membrane (PEM) electrolysis, utilization of scarce iridium-based catalysts required for the oxygen evolution reaction (OER) has to be significantly lowered. To address this question, the facile synthesis of a highly active TiO2 supported iridium oxide based OER catalyst with reduced noble metal content and an Ir-density of the catalyst powder as low as 0.05–0.08 gIr cm-3 is described in this work. A high surface area corrosion-resistant titania catalyst support homogeneously coated with a 1-2 nm thin layer of amorphous IrOOHx is oxidized in molten NaNO3 between 350-375°C. This procedure allows for a controllable phase transformation and crystallization to form a layer of interconnected IrO2 nanoparticles of ≈2 nm on the surface of the TiO2 support. The increase in crystallinity is thereby accompanied by a significant increase in conductivity of up to 11 S cm-1 for a 30 wt% Ir loaded catalyst. Oxidized samples further display a significantly increased stability with less detectable Ir dissolution under OER conditions. With a mass-based activity of 59 A g-1 at an overpotential of 300 mV, the electrocatalytic activity is maintained at the level of the highly active amorphous IrOOHx phase used as precursor and outperforms it at higher current densities through the increased conductivity. MEA measurements with catalyst loadings of 0.2-0.3 mg cm-2 further confirm the high catalytic activity and initial stability at industrially relevant current densities. The introduced synthesis approach therefore shows a path for the fabrication of novel highly active and atom-efficient oxide supported catalysts with complex nanostructures and thin homogenous nanoparticle coatings that allows a future large-scale application of PEM electrolysis technology without restrictions by the natural abundance of iridium.

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.

A broad scientific consensus exists that anthropogenic emissions are major factors fueling global warming and its potential impacts on the earth’s ecosystem. On the way to a sustainable and decarbonized energy supply, "green" hydrogen is an emission-free alternative to conventional energy carriers. In this context, proton exchange membrane fuel cells (PEMFCs) offer promising properties for the electromobility by a simple scalability of the performance through the modular design of fuel cell stacks, a refueling time and range comparable with conventional combustion engines and zero emissions if "green" hydrogen is used. Despite all scientific work on this field – performance, cost and durability issues still hamper the wide commercialization of PEMFCs. Concerning the durability, global fuel starvation causes destructive and irreversible degradation at the anode catalyst. A lack of fuel supply leads to the anode potential being raised to levels where the oxygen evolution reaction (OER) and carbon oxidation reaction (COR) take place instead of the hydrogen oxidation reaction (HOR). Thus, the overall cell voltage reverses compared to normal operation. In consequence, the widely employed carbon-supported anode catalyst corrodes and the overall cell performance is reduced if appropriate mitigation strategies are absent [1]. Among other remedies, incorporating a second catalyst component with an enhanced OER activity, such as IrO2 [2], is a promising material-specific strategy. Within this study we present a technical approach on single cell level (50 cm2 geo) to investigate and evaluate the impact of short-pulsed versus long-lasting fuel starvation events on the degradation of a reversal-tolerant anode catalyst layer comprising Pt/C and IrO2 [3]. By utilizing an on-line mass spectrometer, the anode exhaust gas stream is examined in terms of O2- and CO2-amounts to reveal the origin of the degrading effect. References: [1] T. Ioroi and K. Yasuda, J. Power Sources, 450, 227656 (2020). [2] K. H. Lim, W. H. Lee, Y. Jeong, and H. Kim, J. Electrochem. Soc., 164, F1580 (2017). [3] R. Marić, C. Gebauer, M. Nesselberger, F. Hasché, and P. Strasser, to be submitted.

Chemie Ingenieur TechnikVolume 91, Issue 12 p. 1898-1898 VorschauFree Access Vorschau: Chem. Ing. Tech. 1–2/2020 First published: 21 November 2019 https://doi.org/10.1002/cite.201971206AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume91, Issue12Special Issue: Von Campus Blasensäulen zu Campus MehrphasenreaktorenDecember 2019Pages 1898-1898 RelatedInformation

This work addresses current challenges in catalyst development for proton exchange membrane water electrolyzers (PEM-WEs). To reduce the amount of iridium at the oxygen anode to levels commensurate with large-scale application of PEM-WEs, high-structured catalysts with a low packing density are required. To allow an efficient development of such catalysts, activity and durability screening tests are essential. Rotating disk electrode measurements are suitable to determine catalyst activity, while accelerated stress tests on the MEA level are required to evaluate catalyst stability.

In order to learn more about the effect of H-2 fuel starvation on the degradation of Pt anode catalysts and in particular on the role of the support therein, we have investigated the impact of a simulated fuel starvation procedure on three different polymer electrolyte fuel cell anode catalysts, Pt/C, Pt/TiO2 and Pt/TiO2+C, by differential electrochemical mass spectrometry (DEMS) measurements. Monitoring the potential as well as the mass spectrometric signal transients of the possible reaction products CO2 (carbon oxidation reaction - COR) and O-2 (oxygen evolution reaction - OER) upon switching from H-2-saturated to N-2-saturated electrolyte under galvanostatic oxidation conditions, we find a rapid increase of the potential to values at about 1.75 V upon electrolyte exchange, together with the onset of CO2 formation and O-2 evolution, where the latter dominates at high potentials. The ratio of O-2 evolution and carbon support oxidation differs significantly for different catalyst supports, with the COR contributing more for the carbon-containing catalysts in the initial stage of the fuel starvation period, and the OER prevailing for the Pt/TiO2 catalyst over the whole starvation time. The complex interplay between different catalyst degradation processes during fuel starvation is discussed. (c) The Author(s) 2018. Published by ECS.

Aiming at Pt nanoparticle catalysts for application in polymer electrolyte membrane fuel cell (PEMFC) cathodes, which are highly active and more corrosion resistant under realistic mobile applications than common Pt/C catalysts, we have prepared and investigated Pt catalysts supported on highly stable, nanostructured composite materials containing carbon nanotubes (CNTs) and titania. TiO2@CNT composite materials are synthesized via sol-gel processing and subsequent Pt deposition. The physical and electrochemical properties as well as the stability of these catalysts, as determined by transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), rotating ring disk electrode (RRDE) measurements and accelerated degradation tests (ADTs), were compared with those of commercial Pt/C, Pt/TiO2 and Pt/CNT. The measurements reveal a high activity of the composite catalyst, comparable to that of the Pt/C catalyst, but an almost complete loss of ORR activity upon an ADT procedure simulating start-stop behavior. In contrast to carbon supported catalysts, where degradation is mainly associated with corrosion at high potentials, we find the titania supported catalysts to mainly suffer from the reductive treatment in the ADTs. Consequences for the use of Pt catalysts supported on reducible oxides such as TiO2 as cathode catalysts in fuel cell applications are discussed.

Aiming at a better understanding of metal–support interactions in oxide supported Pt electrocatalysts, we have prepared and characterized planar Pt/TiO2 model catalyst electrodes, which combine high conductivity and direct Pt–TiO2 interactions. These consist of a thin TiO2 film on a glassy carbon (GC) substrate and Pt nanoparticles on top. TiO2 films were deposited via a potential induced sol-gel process and subsequently functionalized by Pt nanoparticles, by electrochemical Pt deposition, by deposition of pre-formed Pt nanoparticles or by photoassisted local reduction of Pt ions. Scanning electron microscopy, transmission electron microscopy and X-ray photoelectron spectroscopy were employed for structural and electronic characterization of the model catalyst electrodes, cyclic voltammetry, electrooxidation of pre-adsorbed CO and O2 reduction for evaluating their electrochemical / electrocatalytic properties. The impact of the Pt deposition method, of particle size effects and of metal–support interactions on the electrochemical properties and the catalytic activity / selectivity of these systems is discussed.

The Inside Cover picture shows a Pt/TiO2/GC model electrode developed to mimic the electrochemical/-catalytic activity of a realistic porous Pt/TiO2 catalyst without being affected by electric conductivity (ohmic drop) problems, and the metal–support interactions identified by using XPS and through the electrooxidation of a saturated CO adlayer. More details can be found in the Full Paper by J. Behm and co-workers on page 1553 in Issue 10, 2016 (DOI: 10.1002/celc.201600218).

We report results of a detailed study on the activity and stability of titanium oxynitrides in the oxygen evolution reaction (OER) and their correlation with structure and (surface) composition of these materials, which had been reported as promising catalysts for this reaction and for the reverse oxygen reduction reaction (ORR). Combining electrochemical flow cell measurements with online mass spectrometry analysis (differential electrochemical mass spectrometry) allows us to separate catalytic O2 evolution from other electrochemical reactions such as catalyst oxidation. Materials with different nitridation levels were fabricated via thermal treatment of titanium oxide in gaseous ammonia. The resulting materials, which cover a wide range of O:N ratios, were characterized by X-ray diffraction, elemental carbon-hydrogen-nitrogen analysis, and X-ray photoelectron spectroscopy, yielding information about bulk crystallinity, chemical composition, and surface species present, respectively. They show increasing oxidation current densities starting at about 1.2V, with a peak maximum at 1.7V. Online mass spectrometry analysis, however, reveals that this current results from oxidation of the electrode surface rather than from O2 evolution, while O2 evolution occurs only at potentials >1.7V. Increasing nitride contents were found to increase the electrochemical electrode oxidation reaction, while the onset of O2 evolution is independent of the extent of nitridation. Consequences of these findings on the suitability of these materials as OER catalysts will be discussed.