10 Search Results

The platinum‐ruthenium (PtRu) system is highly active for hydrogen evolution reaction (HER) in alkaline media with both Pt and Ru playing active roles in the water dissociation step that generates adsorbed hydrogen atoms. Precise control of the arrangement of Pt atoms on Ru nanoparticles can maximize the Pt‐Ru sites for water dissociation and Pt‐Pt sites for hydrogen production and can considerably improve HER catalytic performance. By directing the growth and distribution of Pt on Ru hourglass nanoparticles, the arrangement of Pt on Ru is controlled into forming Pt islands, small Pt clusters, and strings of a few Pt atoms. Calculationsmore » show that the unique atomic string arrangements of Pt on Ru is the thermodynamically favorable configuration. Additionally, these strings have a favorable combination of Pt‐Ru and Pt‐Pt sites, making the Pt‐string on Ru the most active catalyst with a more than fivefold increase in turnover frequency for alkaline HER compared to the Pt‐island on Ru catalyst. The results show how controlling the Pt atomic arrangement on Ru nanoparticle surfaces for the tuning of Pt‐Pt and Pt‐Ru neighboring sites can direct toward a more efficient HER mechanism and thereby significantly enhancing HER performance.« less

Single Pt atom catalysts are key targets because a high exposure of Pt substantially enhances electrocatalytic activity. In addition, PtRu alloy nanoparticles are the most active catalysts for the methanol oxidation reaction. To combine the exceptional activity of single Pt atom catalysts with an active Ru support we must overcome the synthetic challenge of forming single Pt atoms on noble metal nanoparticles. In this report we demonstrate a process that grows and spreads Pt islands on Ru branched nanoparticles to create single-Pt-atom-on-Ru catalysts. By following the spreading process by in situ TEM, we found that the formation of a stablemore » single atom structure is thermodynamically driven by the formation of strong Pt–Ru bonds and the lowering of the surface energy of the Pt islands. The stability of the single-Pt-atom-on-Ru structure and its resilience to CO poisoning result in a high current density and mass activity for the methanol oxidation reaction over time.« less

Abstract Wir berichten über ein auf einem Polymer basierendes, elektroenzymatisches Stickstofffixierungssystem unter Verwendung eines metallfreien Redoxpolymers – mit Neutralrot modifiziertes Poly(glycidylmethacrylat‐ co ‐methylmethacrylat‐ co ‐poly(ethylenglycol)methacrylat), das ein niedriges Redoxpotential von −0.58 V vs. SCE besitzt. Die stabile und effiziente elektrische Kontaktierung der Nitrogenase innerhalb der Redoxpolymermatrix ermöglicht eine mediierte Bioelektrokatalyse von N ₃ ⁻ , NO ₂ ⁻ und N ₂ zu NH ₃ , die durch das MoFe‐Protein über die polymergebundenen Redoxeinheiten, die in der Polymermatrix verteilt sind, katalysiert wird. Elektrolyse produzierte 209±30 nmol NH ₃  nmol MoFe ⁻¹  h ⁻¹ durch N ₂ ‐Reduktion. Die biosynthetische N ₂ ‐Reduktion zu NH ₃more » wurde durch ¹⁵ N ₂ ‐Markierungsexperimente und NMR‐Analysen bestätigt.« less

Abstract We report an organic redox‐polymer‐based electroenzymatic nitrogen fixation system using a metal‐free redox polymer, namely neutral‐red‐modified poly(glycidyl methacrylate‐ co ‐methylmethacrylate‐ co‐ poly(ethyleneglycol)methacrylate) with a low redox potential of −0.58 V vs. SCE. The stable and efficient electric wiring of nitrogenase within the redox polymer matrix enables mediated bioelectrocatalysis of N ₃ ⁻ , NO ₂ ⁻ and N ₂ to NH ₃ catalyzed by the MoFe protein via the polymer‐bound redox moieties distributed in the polymer matrix in the absence of the Fe protein. Bulk bioelectrosynthetic experiments produced 209±30 nmol NH ₃  nmol MoFe ⁻¹  h ⁻¹ from N ₂ reduction. ¹⁵ Nmore » ₂ labeling experiments and NMR analysis were performed to confirm biosynthetic N ₂ reduction to NH ₃ .« less

Abstract Die Kontrolle der Bildung von verzweigten Nanopartikeln mit hoher Homogenität ist eine der größten Herausforderungen bei der Herstellung von Nanokatalysatoren mit verbesserter Aktivität und Stabilität. Mithilfe eines Mechanismus unter Nutzung eines kubischen Kerns und hexagonaler Verzweigung zur Bildung hochgradig monodisperser verzweigter Nanopartikel wurde die Länge der Nickelverzweigungen variiert. Es hat sich gezeigt, dass die Verlängerung der Nickelzweige mit ihrer hohen Bedeckung der aktiven Facetten die Aktivität für die elektrokatalytische Oxidation von 5‐Hydroxymethylfurfural (HMF) als Beispiel für die Umwandlung von Biomasse verbessert.

Thin-film material libraries in the ternary and quaternary metal oxide systems Fe–V–O, Cu–V–O, and Cu–Fe–V–O were synthesized using combinatorial reactive co-sputtering with subsequent annealing in air. Their compositional, structural, and functional properties were assessed using high-throughput characterization methods. Prior to the investigation of the quaternary system Cu–Fe–V–O, the compositions (Fe₆₁V₃₉)O_x and (Cu₅₂V₄₈)O_x with promising photoactivity were identified from their ternary subsystems Fe–V–O and Cu–V–O, respectively. Two Cu–Fe–V–O material libraries with (Cu_29-72Fe_4-27V_22-57)O_x and (Cu_11-55Fe_27-73V_12-34)O_x composition spread were investigated. Seven mixed ternary and quaternary phase regions were identified: I (α-Cu₃FeV₆O₂₆/FeVO₄), II (Cu₅V₂O₁₀/FeVO₄/α-Cu₃Fe₄V₆O₂₆), III (Cu₅V₂O₁₀), IV (Cu₅V₂O₁₀/FeVO₄, V (FeVO₄/γ-Cu₂V₂O₇/α-Cu₃Fe₄V₆O₂₆), VI (β-Cu₂V₂O₇/α-Cu₃Fe₄V₆O₂₆/FeVO₄), and VIImore » (β-Cu₃Fe₄V₆O₂₆/FeVO₄). Furthermore, in the investigated composition range, two photoactive regions, (Cu₅₃Fe₇V₄₀)O_x and (Cu₄₅Fe₂₁V₃₄)O_x, were identified, exhibiting 103 μA/cm² and 108 μA/cm² photocurrent density for the oxygen evolution reaction at 1.63 V vs reversible hydrogen electrode, respectively. The highest photoactive region (Cu₄₅Fe₂₁V₃₄)O_x comprises the dominant α-Cu₃Fe₄V₆O₂₄ phase and minor FeVO₄ phase. This photoactive region corresponds to having an indirect bandgap of 1.87 eV and a direct bandgap of 2.58 eV with an incident photon-to-current efficiency of 30% at a wavelength of 310 nm.« less

Ag–V–O thin-film materials libraries, with both composition (Ag_22-77V_23-78O_x) and thickness (123–714 nm) gradients were fabricated using combinatorial reactive magnetron co-sputtering aiming on establishing relations between composition, structure, and functional properties. As-deposited libraries were annealed in air at 300 °C for 10 h. High-throughput characterization methods of composition, structure and functional properties were used to identify photoelectrochemically active regions. The phases AgV₆O₁₅, Ag₂V₄O₁₁, AgVO₃, and Ag₄V₂O₇ were observed throughout the composition gradient. The photoelectrochemical properties of Ag–V–O films are dependent on composition and morphology. An enhanced photocurrent density (~300–554 μA/cm²) was obtained at 30 to 45 at.% Ag along the thicknessmore » gradient. Thin films of these compositions show a nanowire morphology, which is an important factor for the enhancement of photoelectrochemical performance. The photoelectrochemically active regions were further investigated by high-throughput synchrotron-X-ray diffraction and transmission electron microscopy (Ag₃₂V₆₈O_x) which confirmed the presence of Ag₂V₄O₁₁ as the dominating phase along with the minor phases AgV₆O₁₅ and AgVO₃. This enhanced photoactive region shows bandgap values of ~2.30 eV for the direct and ~1.87 eV for the indirect bandgap energies. Finally, the porous nanostructured films improve charge transport and are hence of interest for photoelectrochemical water splitting.« less

A bio-inspired O₂ sensitive nickel catalyst dispersed in a hydrophobic and redox-silent polymer matrix shows enhanced stability for catalytic H₂ oxidation as well as O₂ tolerance. A simple but efficient electrode design separates the catalyst into two different reaction layers to promote different reactivity on the catalyst. (1) close to the electrode surface, the catalyst can directly exchange electrons with the electrode and generate current from H₂ oxidation; and (2) at the outer film boundary, the electrolyte exposed layer is electrically isolated from the electrode, which enables the H₂ reduced Ni-complex to convert O₂ to H₂O and thus provides protectionmore » to the O₂-sensitive inner reaction layer. This strategy solves one of the biggest limitations of these otherwise outstanding catalysts and could be used to protect other similar catalysts whose wider application is currently limited by sensitivity towards oxygen.« less

The overriding obstacle to mass production of hydrogen from water as the premium fuel for powering our planet is the frustratingly slow kinetics of the oxygen evolution reaction (OER). Additionally, inadequate understanding of the key barriers of the OER is a hindrance to insightful design of advanced OER catalysts. This study presents ultrathin amorphous high‐surface area nickel boride (Ni _x B) nanosheets as a low‐cost, very efficient and stable catalyst for the OER for electrochemical water splitting. The catalyst affords 10 mA cm ⁻² at 0.38 V overpotential during OER in 1.0 m KOH, reducing to only 0.28 V atmore » 20 mA cm ⁻² when supported on nickel foam, which ranks it among the best reported nonprecious catalysts for oxygen evolution. Operando X‐ray absorption fine‐structure spectroscopy measurements reveal prevalence of NiOOH, as well as Ni‐B under OER conditions, owing to a Ni‐B core@nickel oxyhydroxide shell (Ni‐B@NiO _x H) structure, and increase in disorder of the NiO _x H layer, thus revealing important insight into the transient states of the catalyst during oxygen evolution.« less