Formation of unexpectedly active Ni–Fe oxygen evolution electrocatalysts by physically mixing Ni and Fe oxyhydroxides

We present an unusual, yet facile, strategy towards formation of physically mixed Ni–Fe(OxHy) oxygen evolution electrocatalysts. We use in situ X-ray absorption and UV-vis spectroscopy, and high-resolution imaging to demonstrate that physical contact between two inferior Ni(OH)2 and Fe(OOH) catalysts self-assemble into atomically intermixed Ni–Fe catalysts with unexpectedly high activity

Experimental Activity Descriptors for Iridium-based Catalysts for the Electrochemical Oxygen Evolution Reaction (OER)

Recent progress in the activity improvement of anode catalysts for acidic electrochemical water splitting was largely achieved through empirical studies of iridium-based bimetallic oxides. However, practical, experimentally accessible, yet general predictors of catalytic OER activity are lacking. This study investigates iridium and iridium-nickel thin film model electrocatalysts for the OER and identifies a set of general ex situ properties that allow the reliable prediction of their OER activity. Well defined Ir-based catalysts of various chemical nature and composition were synthesized by magnetron sput-tering. Correlation of physico-chemical and electrocatalytic properties revealed two experimental OER activity descriptors that are able to predict trends in the OER activity of unknown Ir based catalyst systems. More specifically, our study demonstrates that the IrIII+ and OH-surface concentration of the oxide catalyst constitute closely correlated, and generally applicable OER activity predictors. Based on these, an experimental volcano relationship of Ir-based OER electrocatalysts is presented and discussed

Mesenchymal Stem Cell Graft Improves Recovery after Spinal Cord Injury in Adult Rats through Neurotrophic and Pro-Angiogenic Actions

Numerous strategies have been managed to improve functional recovery after spinal cord injury (SCI) but an optimal strategy doesn't exist yet. Actually, it is the complexity of the injured spinal cord pathophysiology that begets the multifactorial approaches assessed to favour tissue protection, axonal regrowth and functional recovery. In this context, it appears that mesenchymal stem cells (MSCs) could take an interesting part. The aim of this study is to graft MSCs after a spinal cord compression injury in adult rat to assess their effect on functional recovery and to highlight their mechanisms of action. We found that in intravenously grafted animals, MSCs induce, as early as 1 week after the graft, an improvement of their open field and grid navigation scores compared to control animals. At the histological analysis of their dissected spinal cord, no MSCs were found within the host despite their BrdU labelling performed before the graft, whatever the delay observed: 7, 14 or 21 days. However, a cytokine array performed on spinal cord extracts 3 days after MSC graft reveals a significant increase of NGF expression in the injured tissue. Also, a significant tissue sparing effect of MSC graft was observed. Finally, we also show that MSCs promote vascularisation, as the density of blood vessels within the lesioned area was higher in grafted rats. In conclusion, we bring here some new evidences that MSCs most likely act throughout their secretions and not via their own integration/differentiation within the host tissue

Struktur-Aktivität-Stabilität und in situ Raman spektroskopische Untersuchungen von Sauerstoffevolutionskatalysatoren in sauren Elektrolyten

Water electrolysis emerges as key technology for the long-term storage of electricity from renewable sources which is essential to overcome their intermittent availability. In this context, proton exchange membrane (PEM) electrolyzers constitute the most promising technology. Considering PEM electrolyzers, the main catalytic efficiency losses (overpotentials) and stability problems are related to the noble metal based anode catalyst, were the oxygen evolution reaction (OER) proceeds. This work aims to establish a more profound understanding of the electrocatalytic OER and the related catalysts under acidic conditions to facilitate the knowledge based improvement of the catalyst's activity and stability and, additionally, to lower its noble metal content. Initially, an appropriate model catalyst for the fundamental investigation of PEM-OER catalysts was contrived, which allows for microkinetic studies and the investigation of catalyst-substrate interactions. In this context, thermally prepared thin homogenous oxide films were found to constitute an adequate model system. Based on this model system, first Ir oxide was studied. Thereby, two chemically distinct Ir oxides with distinctly different catalytic properties were identified as a function of calcination temperature. The amorphous low temperature Ir oxide provided a considerably higher OER activity but, unfortunately, a lower Ir stability than the crystalline Ir oxide formed at higher calcination temperatures. Catalyst-substrate interactions between the Ir oxide layer and the Ti substrate were solely identified at the highest investigated calcination temperature of 550°C and decreased the OER activity of the catalyst. Although indications for the OER activity and stability determining material properties were obtained in the study of pure Ir oxides, a more detailed investigation of this aspect was performed based on Ir-Ni mixed oxides. Considering Ir-Ni mixed oxides, the OER activity and the Ir stability can be varied continuously, which allows the identification of the material properties relevant for the OER activity and stability as well as their optimization. Based on Ir-Ni mixed oxides the Ir mass based OER activity could be increased by a factor of ~20 compared to a similarly prepared pure Ir oxide reference sample. Furthermore, this study revealed that the oxide surface termination critically determines the OER activity of Ir-Ni oxides. Hereby, the fraction of surface hydroxyl groups was found to be correlated to the surface specific OER activity of the oxide. The surface processes occurring during the OER were studied by in-situ surface enhanced Raman spectroscopy (SERS) on a Ru oxide catalyst. In order to provide the required surface enhancement a recent approach called shell-isolated nanoparticle-enhanced Raman spectroscopy was adapted to PEM-OER catalysts and its applicability for SERS studies of OER catalysts was demonstrated. In this study an OHx species was identified which appeared exclusively during the OER.Die Wasserelektrolyse stellt eine Schlüsseltechnologie für die Speicherung von überschüssiger Elektrizität aus erneuerbaren Quellen dar. Protonen Austausch Membran (engl.: proton exchange membrane - PEM) Elektrolyseure sind die vielversprechendste Technologie in diesem Zusammenhang. Im Bereich der PEM Elektrolyseure sind die größten katalytischen Effizienzeinbußen und Stabilitätsprobleme mit dem edelmetallbasierten Anodenkatalysator verbunden, an dem die elektrokatalytische Sauerstoffevolutionsreaktion (engl.: oxygen evolution reaction - OER) abläuft. Ziel dieser Arbeit ist ein tiefer gehendes Verständnis der elektrokatalytischen OER und des dafür eingesetzten Katalysators im stark sauren Milieu zu entwickeln, um die Aktivität und Stabilität des Katalysators gezielt zu steigern und den Edelmetallgehalt zu senken. Als Modellkatalysator für diese Untersuchung wurden dünne thermisch synthetisierte Oxidfilme ausgewählt, die sich hervorragend für mikrokinetische Studien und die Untersuchung von Katalysator-Substrat-Wechselwirkungen eignen. Auf Grundlage dieses Modellsystems wurde zunächst reines Iridiumoxid untersucht. Dabei wurden zwei chemisch unterschiedliche Iridiumoxide in Abhängigkeit von der Kalzinierungstemperatur nachgewiesen. Das bei niedrigen Kalzinierungstemperaturen entstandene amorphe Iridiumoxid zeigte eine größere Aktivität aber eine geringere Stabilität in der OER als das kristalline Iridiumoxid, das bei höheren Kalzinierungstemperaturen entstand. Katalysator-Substrat-Wechselwirkungen zwischen Iridiumoxid und Titansubstrat konnten ausschließlich bei der höchsten Kalzinierungstemperatur von 550°C festgestellt werden und verringerten die OER-Aktivität des Katalysators. Obschon die Untersuchung von reinem Iridiumoxid Hinweise auf die aktivitäts- und stabilitätsbestimmenden Materialeigenschaften lieferte, wurden diese auf Basis von Iridium-Nickel-Mischoxiden genauer untersucht. Iridium-Nickel-Mischoxide erlauben eine kontinuierliche Variation der OER-Aktivität und Iridium-Stabilität, und somit deren Optimierung, durch Änderung des Ir:Ni Verhältnisses. Durch gleichzeitige umfassende Charakterisierung der Materialeigenschaften des Mischoxids konnten die für die OER-Aktivität und Iridium-Stabilität maßgeblichen Materialeigenschaften identifiziert werden. Die OER-Aktivität wurde dabei maßgeblich von der Oberflächenterminierung des Oxids bestimmt. Durch Optimierung des Ir:Ni Verhältnisses konnte die auf die Iridium Masse normierte OER-Aktivität um den Faktor 20 gesteigert werden. Die Oberflächenprozesse während der OER wurden in-situ mittels oberflächenverstärkter Ramanspektroskopie auf einem Rutheniumoxidkatalysator untersucht. Um die benötigte Oberflächenverstärkung bereitzustellen wurde eine neue Technik namens shell-isolated nanoparticle-enhanced Raman spectroscopy angewendet und deren Einsetzbarkeit für OER-Untersuchungen demonstriert. Im Rahmen der ramanspektroskopischen Untersuchung wurde eine OHx Spezies identifiziert, die ausschließlich während der OER zu beobachten war

Oxide-supported Ir nanodendrites with high activity and durability for the oxygen evolution reaction in acid PEM water electrolyzers

Reducing the noble-metal catalyst content of acid Polymer Electrolyte Membrane (PEM) water electrolyzers without compromising catalytic activity and stability is a goal of fundamental scientific interest and substantial technical importance for cost-effective hydrogen-based energy storage. This study presents nanostructured iridium nanodendrites (Ir-ND) supported on antimony doped tin oxide (ATO) as efficient and stable water splitting catalysts for PEM electrolyzers. The active Ir-ND structures exhibited superior structural and morphological properties, such as particle size and surface area compared to commercial state-of-art Ir catalysts. Supported on tailored corrosion-stable conductive oxides, the Ir-ND catalysts exhibited a more than 2-fold larger kinetic water splitting activity compared with supported Ir nanoparticles, and a more than 8-fold larger catalytic activity than commercial Ir blacks. In single-cell PEM electrolyzer tests, the Ir-ND/ATO outperformed commercial Ir catalysts more than 2-fold at technological current densities of 1.5 A cm(-2) at a mere 1.80 V cell voltage, while showing excellent durability under constant current conditions. We conclude that Ir-ND/ATO catalysts have the potential to substantially reduce the required noble metal loading, while maintaining their catalytic performance, both in idealized three-electrode set ups and in the real electrolyzer device environments.DFG, SPP 1613, Regenerativ erzeugte Brennstoffe durch lichtgetriebene Wasserspaltung: Aufklärung der Elementarprozesse und Umsetzungsperspektiven auf technologische Konzept

Stability of nanostructured iridium oxide electrocatalysts during oxygen evolution reaction in acidic environment

The electrochemical stability of thermally prepared Ir oxide films is investigated using a scanning flow cell (SFC)–inductively coupled plasma mass-spectrometer (ICP-MS) setup under transient and stationary potential and/or current conditions. Time-resolved dissolution rates provide important insights into critical conditions for material breakdown and a fully quantitative in-situ assessment of the electrochemical stability during oxygen evolution reaction (OER) conditions. In particular, the results demonstrate that stability and OER activity of the IrOx catalysts strongly depend on the chemical and structural nature of Ir oxide species and their synthesis conditions. Keywords: Oxygen evolution, Energy conversion, Iridium oxide, IrO2, Dissolution, Corrosio

Tuning the Catalytic Activity and Selectivity of Cu for CO₂ Electroreduction in the Presence of Halides

In the present study we demonstrate that the activity and selectivity of copper during CO₂ electrochemical reduction can be tuned by simply adding halides to the electrolyte. Comparing the production rate and Faradaic selectivity of the major products as a function the working potential in the presence of Cl^–, Br^–, and I^–, we show that the activity and selectivity of Cu depends on the concentration and nature of the added halide. We find that the addition Cl^– and Br^– results in an increased CO selectivity. On the contrary, in the presence of I^– the selectivity toward CO drops down and instead methane formation is enhanced up to 6 times compared with the halide-free electrolyte. Even though Br^– and I^– can induce morphology changes of the surface, the modification in the catalytic performance of Cu is mainly attributed to halides adsorption on the Cu surface. We hypothesizes that the adsorption of halides alters the catalytic performance of Cu by increasing the negative charge on the surface according to the following order: Cl^– < Br^– < I^–. In the case of adsorbed I^–, the induced negative charge has a remarkably positive effect favoring the protonation of CO. These results present an easy way to enhance CH₄ production during the CO2RR on Cu. Furthermore, understanding this effect can contribute to the design of new and more efficient catalysts

Quantifying the density and utilization of active sites in non-precious metal oxygen electroreduction catalysts

Carbon materials doped with transition metal and nitrogen are highly active, non-precious metal catalysts for the electrochemical conversion of molecular oxygen in fuel cells, metal air batteries, and electrolytic processes. However, accurate measurement of their intrinsic turn-over frequency and active-site density based on metal centres in bulk and surface has remained difficult to date, which has hampered a more rational catalyst design. Here we report a successful quantification of bulk and surface-based active-site density and associated turn-over frequency values of mono-and bimetallic Fe/N-doped carbons using a combination of chemisorption, desorption and Fe-57 Mossbauer spectroscopy techniques. Our general approach yields an experimental descriptor for the intrinsic activity and the active-site utilization, aiding in the catalyst development process and enabling a previously unachieved level of understanding of reactivity trends owing to a deconvolution of site density and intrinsic activity

Demographic change and urban transformation: the challenges of residents' attitudes

Due to copyright restrictions, the access to the full text of this article is only available via subscription.ities around different regions of the world have been subject to important social and cultural alterations due to ever increasing affects of globalization process. The cities in Turkey are no exception to this urban transformation with different physical and social structures emerging as a result of the economical, political, socio-cultural and technological developments. Especially during the last thirty years, the increased linkage of the country to the global world has been even felt in smaller cities in the form of new local developmental opportunities in different sectors including industry, international trade, tourism and real estate. Ever since the 1950s, one of the major components of urban transformation in Turkey has been the migration of masses that changed the socio-cultural and economic structure of the cities and eventually led to rapid transformation of the existing physical environment and created new spatial formations. As such, the topic of the urban transformation of cities while protecting both its physical as well as socio-cultural values, which is also intricately linked to sustainable regeneration and architectural identity issues, has been a hot topic of recent architectural discourse. The ongoing demographic change due to relocation process from rural to urban areas and from smaller to bigger cities, as well as due to industrialization and increasing concentration of people in urban areas, have accelerated socio-cultural and spatial differentiation and diversity, while bringing about some continuity and development trends in urban housing environments. This situation concerning housing environments show a dramatic transition procedure from past to future, from tradition to contemporary while at the same time living through changes in the residents’ perception of home and urban environments with different perceptions for people from different backgrounds. In this context, the city of Istanbul is a good example to observe and evaluate the physical reflections of a mutual interaction between the architectural identity of the city and its social structure and dynamism. Cultural synthesis is more in evidence here than in most other Turkish cities. However, the concepts of social, cultural, spatial diversity and complexity especially in housing environments differ in smaller scale Anatolian cities such as Balikesir where the city center, which always included major housing stock of the city as well, has kept its location and prominence as the only center while the city boundaries has been constantly growing and expanding. In recent years, the city started to change with an ever increasing rate causing the city to have a multi-centered organization while the historic city center is becoming more deteriorated with each day. The housing stock in the center has become a derelict area causing it to be the home for the people migrated from small villages around with low socio-economic status, which is a major threat for the restoration and renovation and later on protection of the cultural heritage of the city