Colloidal bimetallic platinum–ruthenium nanoparticles in ordered mesoporous carbon films as highly active electrocatalysts for the hydrogen evolution reaction

Hydrogen features a very high specific energy density and is therefore a promising candidate for clean fuel from renewable resources. Water electrolysis can convert electrical energy into storable and transportable hydrogen gas. Under acidic conditions, platinum is the most active and stable monometallic catalyst for the hydrogen evolution reaction (HER). Yet, platinum is rare and needs to be used efficiently. Here, we report a synthesis concept for colloidal bimetallic platinum–ruthenium and rhodium–ruthenium nanoparticles (PtRuNP, RhRuNP) and their incorporation into ordered mesoporous carbon (OMC) films. The films exhibit high surface area, good electrical conductivity and well-dispersed nanoparticles inside the mesopores. The nanoparticles retain their size, crystallinity and composition during carbonization. In the hydrogen evolution reaction (HER), PtRuNP/OMC catalyst films show up to five times higher activity per Pt than Pt/C/Nafion® and PtRu/C/Nafion® reference catalysts.TU Berlin, Open-Access-Mittel - 2020European Metrology Research Programme (EMRP), 16ENG0, Hybrid metrology for thin films in energy applications (HyMET)BMBF, 03VP05390, Nanostrukturierte Elektroden der nächsten Generation für eine energieeffiziente Produktion von Chlor - Next-Gen-ChlorBMBF, 03EK3009, Design hocheffizienter Elektrolysekatalysatore

Fabrication of an efficient vanadium redox flow battery electrode using a free-standing carbon-loaded electrospun nanofibrous composite

Vanadium redox flow batteries (VRFBs) are considered as promising electrochemical energy storage systems due to their efficiency, flexibility and scalability to meet our needs in renewable energy applications. Unfortunately, the low electrochemical performance of the available carbon-based electrodes hinders their commercial viability. Herein, novel free-standing electrospun nanofibrous carbon-loaded composites with textile-like characteristics have been constructed and employed as efficient electrodes for VRFBs. In this work, polyacrylonitrile-based electrospun nanofibers loaded with different types of carbon black (CB) were electrospun providing a robust free-standing network. Incorporation of CBs (14% and 50% weight ratio) resulted in fibers with rough surface and increased mean diameter. It provided higher BET surface area of 83.8 m2 g−1 for as-spun and 356.7 m2 g−1 for carbonized fibers compared to the commercial carbon felt (0.6 m2 g−1). These loaded CB-fibers also had better thermal stability and showed higher electrochemical activity for VRFBs than a commercial felt electrode

Mesoporous WCx Films with NiO‐Protected Surface: Highly Active Electrocatalysts for the Alkaline Oxygen Evolution Reaction

Metal carbides are promising materials for electrocatalytic reactions such as water electrolysis. However, for application in catalysis for the oxygen evolution reaction (OER), protection against oxidative corrosion, a high surface area with facile electrolyte access, and control over the exposed active surface sites are highly desirable. This study concerns a new method for the synthesis of porous tungsten carbide films with template-controlled porosity that are surface-modified with thin layers of nickel oxide (NiO) to obtain active and stable OER catalysts. The method relies on the synthesis of soft-templated mesoporous tungsten oxide (mp. WOx) films, a pseudomorphic transformation into mesoporous tungsten carbide (mp. WCx), and a subsequent shape-conformal deposition of finely dispersed NiO species by atomic layer deposition (ALD). As theoretically predicted by density functional theory (DFT) calculations, the highly conductive carbide support promotes the conversion of Ni2+ into Ni3+, leading to remarkably improved utilization of OER-active sites in alkaline medium. The obtained Ni mass-specific activity is about 280 times that of mesoporous NiOx (mp. NiOx) films. The NiO-coated WCx catalyst achieves an outstanding mass-specific activity of 1989 A gNi−1 in a rotating-disc electrode (RDE) setup at 25 °C using 0.1 m KOH as the electrolyte.BMBFDFG SPP 2080 priority programPeer Reviewe

Mesoporous WCx Films with NiO‐Protected Surface: Highly Active Electrocatalysts for the Alkaline Oxygen Evolution Reaction

Metal carbides are promising materials for electrocatalytic reactions such as water electrolysis. However, for application in catalysis for the oxygen evolution reaction (OER), protection against oxidative corrosion, a high surface area with facile electrolyte access, and control over the exposed active surface sites are highly desirable. This study concerns a new method for the synthesis of porous tungsten carbide films with template‐controlled porosity that are surface‐modified with thin layers of nickel oxide (NiO) to obtain active and stable OER catalysts. The method relies on the synthesis of soft‐templated mesoporous tungsten oxide (mp. WOx) films, a pseudomorphic transformation into mesoporous tungsten carbide (mp. WCx), and a subsequent shape‐conformal deposition of finely dispersed NiO species by atomic layer deposition (ALD). As theoretically predicted by density functional theory (DFT) calculations, the highly conductive carbide support promotes the conversion of Ni2+ into Ni3+, leading to remarkably improved utilization of OER‐active sites in alkaline medium. The obtained Ni mass‐specific activity is about 280 times that of mesoporous NiOx (mp. NiOx) films. The NiO‐coated WCx catalyst achieves an outstanding mass‐specific activity of 1989 A gNi−1 in a rotating‐disc electrode (RDE) setup at 25 °C using 0.1 m KOH as the electrolyte.BMBF, 03EK3052A, Verbundvorhaben ATO-KAT: Atomar dünn beschichtete poröse Elektroden als neuartige Katalysatoren für die Wasser-Elektrolyse: - leitfähige Träger und Elektrochemie -BMBF, 03EK3052C, Verbundvorhaben ATO-KAT: Quantenchemische Berechnung beschichteter dotierter Metalloxide als Katalysatoren für die OER.DFG,358713534, SPP 2080: Katalysatoren und Reaktoren unter dynamischen Betriebsbedingungen für die Energiespeicherung und -wandlun

Edelmetallnanopartikel in geordneten mesoporösen Kohlenstoffschichten als effiziente Elektrokatalysatoren für die Wasserstoffevolutionsreaktion

Hydrogen has the highest gravimetric energy density of all chemical substances. Accordingly, hydrogen is a promising candidate as a fuel or for energy storage. One efficient way to produce hydrogen is the electrolytic splitting of water molecules. Water electrolysis requires electrode coatings with high catalytic activity. Platinum efficiently catalyzes the hydrogen evolution reaction (HER) in acidic environments but is also a rare and expensive metal. The activity achieved per metal atom can be increased when small Pt-containing particles are dispersed onto electrically conductive, accessible and stable support materials. However, the addition of Nafion, a typical binder material can decrease catalytic activity via blocking of pores and active surface sites. This thesis reports two new synthesis approaches for highly active Nafion-free catalyst films consisting of small nanoparticles supported in a conductive mesoporous carbon matrix. One approach relies on the co-deposition of suitable noble metal ions together with carbon precursors in the presence of polymer micelles, which act as pore templates. The other approach employs preformed colloidal nanoparticles as noble metal precursors. Carbonization in inert atmosphere produces porous ordered mesoporous carbon films with defined structural properties like film thickness, pore size, nanoparticle composition and metal loading. The films were tested for catalytic activity: Pt-containing catalyst films exhibited the highest activity in the HER and clearly outperform Nafion-based Pt/C catalysts in particular at high current densities. Bimetallic RuPt catalyst films showed a four times higher activity per Pt compared to conventional Pt/C reference catalysts. Pd-containing mesoporous carbon films were also tested as catalysts in the selective gas-phase hydrogenation of butadiene. The obtained catalysts provided significantly higher space-time-yields than all reported Pd/C catalysts. The optimal conditions for carbonization were identified as well as necessary properties of the employed metal for a successful synthesis. Synthetic aspects like the influence of high weight loadings of the metal and kinetic aspects like the rate-determining step during the HER were studied. Generally, the syntheses represent generic approaches to ordered mesoporous carbon coatings containing metal nanoparticles. Further improvements in the composition can lead to even higher activity and lower costs for catalyst production. The catalysts developed in this work can help to make water electrolyzers more efficient and cheaper.Wasserstoff besitzt die höchste massenspezifische Energiedichte aller chemischen Substanzen und erfährt daher zunehmende Bedeutung als Treibstoff oder als Energiespeicher. Die saure Wasserelektrolyse ist eine effiziente Methode um Wasserstoff herzustellen. Um Überpotentiale bei der Wasserelektrolyse zu reduzieren, werden katalytisch aktive Elektrodenbeschichtungen eingesetzt. Platin ist der aktivste Katalysator für die Wasserstoffevolutionsreaktion (englisch hydrogen evolution reaction HER), jedoch ist es selten und teuer. Um die Massenaktivität des eingesetzten Platins zu erhöhen, werden üblicherweise kleine Pt-Nanopartikel auf elektrisch leitfähigem Kohlenstoff gebracht. Dieses Material sollte sowohl eine hohe Zugänglichkeit der aktiven Zentren sowie eine hohe Stabilität aufweisen. Nafion, welches typischerweise als Binder eingesetzt wird, kann jedoch die katalytische Aktivität reduzieren, indem es Poren sowie aktive Zentren blockiert. Diese Arbeit beschreibt zwei neue Syntheseansätze für hochaktive Nafion-freie mesoporöse Katalysatorschichten. Diese bestehen aus kleinen Edelmetallnanopartikeln, verteilt in leitfähigem Kohlenstoff. Im ersten Syntheseansatz wurden lösliche ionische Edelmetall-Präkursoren verwendet, die zusammen mit einem Kohlenstoff-Präkursor sowie Blockcopolymeren, welche als Porentemplate dienten, abgeschieden wurden. Der zweite Syntheseansatz nutzte vorgeformte kolloidale Nanopartikel als Edelmetall-Präkursoren. Karbonisierung führte zu porösen Katalysatorfilmen mit kontrollierbaren Eigenschaften wie Filmdicke, Porengröße und Verteilung sowie Zusammensetzung der Nanopartikel. Die Katalysatorschichten wurden auf ihre katalytische Aktivität hin untersucht: Pt-haltige Schichten zeigten eine deutlich höhere Aktivität in der HER als vergleichbare Nafion-haltige Pt/C Schichten insbesondere bei hohen Stromdichten. RuPt Katalysatoren zeigten eine vierfach höhere Aktivität pro eingesetztem Platin. Darüber hinaus wurden Pd-haltige Schichten in der Hydrierung von Butadien untersucht. Sie zeigten eine signifikant höhere Raum-Zeit-Ausbeute als alle bisher veröffentlichten Pd/C Katalysatoren. Es gelang die optimalen Karbonisiertemperaturen der Schichten sowie notwendige Eigenschaften der einsetzbaren Metalle zu identifizieren. Synthetische Aspekte, wie der Einfluss einer hohen Metallbeladung und kinetische Aspekte, wie der geschwindigkeitsbestimmende Schritt der HER wurden untersucht. Die präsentierten Syntheseansätze sind generisch und es lassen sich Kohlenstofffilme mit verschiedenen Edelmetallen herstellen. Durch weitere Verbesserungen der Zusammensetzung könnten noch aktivere und kostengünstigere Katalysatoren entwickelt werden, die dabei helfen Wasserelektrolyseure effizienter und preiswerter zu machen.BMBF, 03EK3009, ELYKAT - Design hocheffizienter Elektrolysekatalysatore

Versatile control over size and spacing of small mesopores in metal oxide films and catalytic coatings via templating with hyperbranched core-multishell polymers

Controlling the pore structure of metal oxide films and supported catalysts is an essential requirement for tuning their functionality and long-term stability. Typical synthesis concepts such as “Evaporation Induced Self Assembly” rely on micelle formation and self assembly. These processes are dynamic in nature and therefore strongly influenced by even slight variations in the synthesis conditions. Moreover, the synthesis of very small mesopores (2–5 nm) and independent control over the thickness of pore walls are very difficult to realize with micelle-based approaches. In this contribution, we present a novel approach for the synthesis of mesoporous metal oxide films and catalytic coatings with ordered porosity that decouples template formation and film deposition by use of hyperbranched core–multishell polymers as templates. The approach enables independent control of pore size, wall thickness and the content of catalytically active metal particles. Moreover, dual templating with a combination of hyperbranched core–multishell polymers and micelles provides facile access to hierarchical bimodal porosity. The developed approach is illustrated by synthesizing one of the most common metal oxides (TiO2) and a typical supported catalyst (PdNP/TiO2). Superior catalyst performance is shown for the gas-phase hydrogenation of butadiene. The concept provides a versatile and general platform for the rational optimization of catalysts based e.g. on computational prediction of optimal pore structures and catalyst compositions.BMBF, 03EK3009, Design hocheffizienter Elektrolysekatalysatore

Bridging experiment and theory: enhancing the electrical conductivities of soft-templated niobium-doped mesoporous titania films

Theoretical calculations suggest a strong dependence of electrical conductivity and doping concentration in transition-metal doped titania. Herein, we present a combined theoretical and experimental approach for the prediction of relative phase stability and electrical conductivity in niobium-doped titania as model system. Our method paves the way towards the development of materials with improved electrical properties.TU Berlin, Open-Access-Mittel – 2021BMBF, 03EK3052A, Verbundvorhaben ATO-KAT: Atomar dünn beschichtete poröse Elektroden als neuartige Katalysatoren für die Wasser-Elektrolyse: - leitfähige Träger und Elektrochemie

Antireflective Coatings with Adjustable Refractive Index and Porosity Synthesized by Micelle-Templated Deposition of MgF₂ Sol Particles

Minimizing efficiency losses caused by unwanted light reflection at the interface between lenses, optical instruments and solar cells with the surrounding medium requires antireflective coatings with adequate refractive index and coating thickness. We describe a new type of antireflective coating material with easily and independently tailorable refractive index and coating thickness based on the deposition of colloidal MgF₂ nanoparticles. The material synthesis employs micelles of amphiphilic block copolymers as structure directing agent to introduce controlled mesoporosity into MgF₂ film. The coatings thickness can be easily adjusted by the applied coating conditions. The coatings refractive index is determined by the materials porosity, which is controlled by the amount of employed pore template. The refractive index can be precisely tuned between 1.23 and 1.11, i.e., in a range that is not accessible to nonporous inorganic materials. Hence, zero reflectance conditions can be established for a wide range of substrate materials