Suchergebnisse

Co3O4 nanocubes are evaluated concerning their intrinsic electrocatalytic activity towards the oxygen evolution reaction (OER) by means of single-entity electrochemistry. Scanning electrochemical cell microscopy (SECCM) provides data on the electrocatalytic OER activity from several individual measurement areas covering one Co3O4 nanocube of a comparatively high number of individual particles with sufficient statistical reproducibility. Single-particle-on-nano-electrode measurements of Co3O4 nanocubes provide an accelerated stress test at highly alkaline conditions with current densities of up to 5.5 Acm-2, and allows to derive TOF values of up to 2.8 X104 s-1 at 1.92 V vs. RHE for surface Co atoms of a single cubic nanoparticle. Obtaining such high current densities combined with identical-location transmission electron microscopy allows monitoring the formation of an oxy(hydroxide) surface layer during electrocatalysis. Combining two independent single-entity electrochemistry techniques provides the basis for elucidating structure–activity relations of single electrocatalyst nanoparticles with well-defined surface structure. ; This research obtained funding from the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) within the collaborative research centre/transregio 247 "Heterogeneous Oxidation Catalysis in the Liquid Phase" TRR 247 [388390466] (projects A2 and C3) as well as under Germany's Excellence Strategy-EXC 2033-390677874-RESOLV. This project has received funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (grant agreement CasCat [833408]). The mechanical workshop team at the faculty of chemistry and biochemistry, Ruhr University Bochum, is acknowledged for the contribution in designing and building the nanoelectrode TEM holder. We acknowledge Prof. Patrick Unwin from the University of Warwick for providing the initial control software (WEC-SPM) for our SECCM experiments. Open Access funding enabled and organized by ...

Eine SEM‐gesteuerte Mikromanipulatortechnik wird vorgeschlagen, um einzelne Co3O4‐Nanopartikel aufzunehmen und auf der modifizierten Oberfläche einer Kohlenstoff‐Nanoelektrode zu platzieren. Damit kann die intrinsische Sauerstoffentwicklungsaktivität des Nanopartikels bei industriell relevanter Stromdichte ohne Film‐ und Ensemble‐Effekte bestimmt werden. Post‐elektrochemische TEM‐Analysen geben Einblick in die Strukturtransformationen während der Elektrokatalyse. ; Die Arbeiten wurden von der DFG im Rahmen des SFB/Transregio 247 "Heterogene Oxidationskatalyse in der Flüssigphase" TRR 247 [388390466] sowie im Rahmen der Deutschen Exzellenzstrategie – EXC 2033‐390677874 – RESOLV gefördert. Weiterhin wurden die Arbeiten vom ERC im Rahmen des European Union's Horizon 2020 Forschungs‐ und Innovationsprograms (CasCat [833408]) unterstützt. H.B.A. bedankt sich bei der Alexander von Humboldt‐Stiftung für ein Postdoc‐Stipendium. P.W. bedankt sich beim Fonds der chemischen Industrie e.V. (VCI) für die Unterstützung durch ein Doktorandenstiopendium. Open Access Veröffentlichung ermöglicht und organisiert durch Projekt DEAL.

Nano‐electrochemical tools to assess individual catalyst entities are critical to comprehend single‐entity measurements. The intrinsic electrocatalytic activity of an individual well‐defined Co3O4 nanoparticle supported on a carbon‐based nanoelectrode is determined by employing an efficient SEM‐controlled robotic technique for picking and placing a single catalyst particle onto a modified carbon nanoelectrode surface. The stable nanoassembly is microscopically investigated and subsequently electrochemically characterized. The hexagonal‐shaped Co3O4 nanoparticles demonstrate size‐dependent electrochemical activity and exhibit very high catalytic activity with a current density of up to 11.5 A cm−2 at 1.92 V (vs. RHE), and a turnover frequency of 532±100 s−1 at 1.92 V (vs. RHE) towards catalyzing the oxygen evolution reaction. ; This research was funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) within the collaborative research centre/transregio 247 "Heterogeneous Oxidation Catalysis in the Liquid Phase" TRR 247 [388390466] as well as under Germany's Excellence Strategy—EXC 2033‐390677874—RESOLV. The project has received funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation program (grant agreement CasCat [833408]). H.B.A. acknowledges the Alexander von Humboldt foundation for a Postdoc fellowship. P.W. is grateful to the Association of the Chemical Industry e.V. (VCI) for funding of the PhD fellowship. Open access funding enabled and organized by Projekt DEAL.

GaN nanorods, essentially free from crystal defects and exhibiting very sharp band-edge luminescence, have been grown by reactive direct-current magnetron sputter epitaxy onto Si (111) substrates at a low working pressure of 5 mTorr. Upon diluting the reactive N2 working gas with a small amount of Ar (0.5 mTorr), we observed an increase in the nanorod aspect ratio from 8 to ~35, a decrease in the average diameter from 74 to 35 nm, and a two-fold increase in nanorod density. With further dilution (Ar = 2.5 mTorr), the aspect ratio decreased to 14, while the diameter increased to 60 nm and the nanorod density increased to a maximum of 2.4 × 109 cm−2. Yet, lower N2 partial pressures eventually led to the growth of continuous GaN films. The observed morphological dependence on N2 partial pressure is explained by a change from N-rich to Ga-rich growth conditions, combined with reduced GaN-poisoning of the Ga-target as the N2 gas pressure is reduced. Nanorods grown at 2.5 mTorr N2 partial pressure exhibited a high intensity 4 K photoluminescence neutral donor bound exciton transitions (D0XA) peak at ~3.479 eV with a full-width-at-half-maximum of 1.7 meV. High-resolution transmission electron microscopy corroborated the excellent crystalline quality of the nanorods. ; Funding agencies: Swedish Research Council (VR) [621-2013-5360, 621-2012-4420, 2016-04412]; Swedish Government Strategic Research Area Grant in Materials Science AFM-SFO MatLiU [2009-00971]; Knut and Alice Wallenberg Foundation

The number of active sites and their intrinsic activity are key factors in designing high-performance catalysts for the oxygen evolution reaction (OER). The synthesis, properties, and in-depth characterization of a homogeneous CoNiFeCu catalyst are reported, demonstrating that multimetal synergistic effects improve the OER kinetics and the intrinsic activity. In situ carbon corrosion and Cu leaching during the OER lead to an enhanced electrochemically active surface area, providing favorable conditions for improved electronic interaction between the constituent metals. After activation, the catalyst exhibits excellent activity with a low overpotential of 291.5 ± 0.5 mV at 10 mA cm−2 and a Tafel slope of 43.9 mV dec−1. It shows superior stability compared to RuO2 in 1 m KOH, which is even preserved for 120 h at 500 mA cm−2 in 7 m KOH at 50 °C. Single particles of this CoNiFeCu after their placement on nanoelectrodes combined with identical location transmission electron microscopy before and after applying cyclic voltammetry are investigated. The improved catalytic performance is due to surface carbon corrosion and Cu leaching. The proposed catalyst design strategy combined with the unique single-nanoparticle technique contributes to the development and characterization of high-performance catalysts for electrochemical energy conversion. ; This research was funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) within the collaborative research center/transregio 247 "Heterogeneous Oxidation Catalysis in the Liquid Phase" TRR 247 [388390466] as well as under Germanys Excellence Strategy—EXC 2033-390677874—RESOLV. The project has received funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation program (Grant Agreement CasCat [833408]). J.Z. acknowledges the Chinese Scholarship Council for a Ph.D. fellowship. This work was supported by the "Center for Solvation Science ZEMOS" funded by the German Federal Ministry of Education and ...

Rational design of highly active electrocatalysts for the oxygen evolution reaction (OER) is critical to improving overall electrochemical water splitting efficiency. This study suggests hollow CeO2@Co2N nanosheets synthesized using Co-ZIF-L as a precursor, followed by a hydrothermal reaction and a nitridation process as very attractive OER catalysts. The increased activity is supposed to be due to nitridation and strong electronic interaction between CeO2 and Co2N that contribute to the formation of active CoOOH phase. The synthesized CeO2@Co2N exhibits low overpotentials of 219 and 345 mV at OER current densities of 10 and 100 mA cm–2, respectively, as well as a long-term durability of 30 h at a comparatively high current density of 100 mA cm−2. ; This research was funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) within the collaborative research center/ transregio 247 "Heterogeneous Oxidation Catalysis in the Liquid Phase" TRR 247 (388390466). The project received funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation program (grant agreement CasCat (833408)). J.Z. acknowledges the Chinese Scholarship Council for a Ph.D. fellowship. Open access funding enabled and organized by Projekt DEAL.

Cu-based catalysts have shown structural instability during the electrochemical CO2 reduction reaction (CO2RR). However, studies on monometallic Cu catalysts do not allow a nuanced differentiation between the contribution of the applied potential and the local concentration of CO as the reaction intermediate since both are inevitably linked. We first use bimetallic Ag-core/porous Cu-shell nanoparticles, which utilise nanoconfinement to generate high local CO concentrations at the Ag core at potentials at which the Cu shell is still inactive for the CO2RR. Using operando liquid cell TEM in combination with ex situ TEM, we can unequivocally confirm that the local CO concentration is the main source for the Cu instability. The local CO concentration is then modulated by replacing the Ag-core with a Pd-core which further confirms the role of high local CO concentrations. Product quantification during CO2RR reveals an inherent trade-off between stability, selectivity and activity in both systems. ; W. S. is grateful for financial support by the Deutsche Forschungsgemeinschaft under Germany's Excellence Strategy – EXC 2033 – 390677874 – RESOLV and the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (CasCat; grant agreement No. 833408). This work was supported by the DAAD in the framework of the PPP project 57446293 as well as the Ruhr University Research School PLUS through a research stay of P. W. at UNSW. This research was financially supported by the Australian Research Council of Centre of Excellence in Convergent Bio-Nano Science and Technology (CE140100036), the ARC Laureate Fellowship (FL150100060) and the Discovery Project (DP190102659). The Mark Wainwright Analytical Centre (MWAC) at UNSW. This work used the facilities supported by Microscopy Australia at the Electron Microscope Unit at UNSW. Wei Xia is acknowledged for his contribution to the CO measurements. P. B. O'M. acknowledges the Australian Government Research Training Program Scholarship for ...