Supracrystals are highly symmetrical ordered superstructures built up from nanoparticles (NPs) via self‐assembly. While the NP assembly has been intensively investigated, the formation mechanism is still not understood. To shed some light onto the formation mechanism, one of the most common supracrystal morphologies, the trigonal structures, as a model system is being used to investigate the formation process in solution. To explain the formation of the trigonal structures and determining the size of the supracrystal seeds formed in solution, the concept of substrate‐affected growth is introduced. Furthermore, the influence of the NP concentration on the seed size is shown and our investigations from Ag toward Au are extended.
Abstract Supercrystals (SCs) offer the opportunity to integrate nanoparticles into current technologies without losing their unique and designable properties. In the past two decades, much research has been conducted, allowing the synthesis of differently shaped nanoparticles of various materials. Employing those building units, several methods have been developed enabling the preparation of an increasing number of different superstructures. In this review, an overview is given of the large versatility of surfactant molecules used for SC preparation. While SCs with uncharged organic ligands are by far the largest group, the use of charged or uncommon ligands allows the preparation of unique SCs and superlattices. Additionally, the influence of the ligands on the self‐assembly and properties of the resulting SCs is highlighted.
State-of-the-art electrocatalysts for the H 2 -oxidation and O 2 -reduction reactions (HOR and ORR, respectively) taking place inside polymer electrolyte fuel cells (PEFCs) consist of Pt-nanoparticles supported on a high-surface area carbon black (Pt/C). This support grants the large extents of Pt-nanoparticle dispersion and reactant/product-transport required to achieve optimum PEFC-performance, but also suffers from severe corrosion during the potential cycles intrinsic to the device’s operation, compromising its reliability and commercial feasibility [1]. One approach to overcome this issue relies on the development of unsupported electrocatalysts, which can be prepared, e.g., following a nanoparticle destabilization and gelation procedure [2-6]. The resulting, highly dispersed (≈ 100 m metal 2 ∙g metal -1 ) aerogels can be synthesized both in mono- and bimetallic compositions that, in the case of PtPd-alloys, display a ≈ 5-fold improvement in mass-specific ORR-activity over commercial Pt/C-catalysts [4]. Additionally, these unsupported materials also demonstrate better stability upon potential cycling, at least within the potential window of 0.5 – 1 V RHE assessed in Ref. 4. Nevertheless, the latter study [4] did not provide any insight on the durability of these aerogels upon potential excursions up to 1.5 V RHE concomitant to PEFC-start/stop, or on the detailed mechanisms of catalyst degradation at play in these tests. Motivated by this lack of understanding, we have studied the stability of the monometallic Pt-aerogel under various PEFC-relevant potential-holding and -cycling conditions. More precisely, these stability tests were performed in a three-electrode, rotating disk electrode (RDE) setup, cycling the potential between 0.5 − 1.0 V RHE or 0.5 − 1.5 V RHE , or holding the potential at 1.5 V RHE for a given time. The first of these protocols is intended to mimic the cathode potential profile during high- and low-power operation, while the other two emphasize the corrosion of Pt nanoparticles and of the carbon support upon PEFC-start/stop [7]. Beyond the use of RDE-voltammetry to assess the changes in electrochemical surface area and ORR-activity, we performed CO-stripping voltammetry [8] and transmission electron microscopy to study the evolution of the particles’ morphology and size during these tests. Additionally, the use of a low volume (≈ 12 cm 3 ) electrochemical cell allowed us to quantify the extent of Pt-dissolution by analyzing the electrolyte with inductively coupled plasma/optical emission spectrometry. Considering that the Pt-aerogel consists of interconnected nanoparticles with an average diameter of 2.5 – 3 nm (Fig. 1), the results obtained with these techniques were compared to those acquired on a commercial catalyst with a similar particle size and electrochemical surface area (TKK’s 47 % Pt/C, with ≈ 80 m Pt 2 ∙g Pt -1 ) [9]. In summary, this contribution will provide detailed insight into the potential-induced degradation mechanisms at play on a commercially relevant Pt/C-catalyst and an unsupported Pt-aerogel, which ultimately benefits from the absence of a carbon support. Moreover, the results obtained with the latter material will serve as a benchmark for our ongoing studies on bimetallic aerogels based on the combination of Pt with other inexpensive transition metals like Ni or Fe. Figure 1. Transmission electron micrographs of the Pt-aerogel. Acknowledgements Funding from the Swiss National Science Foundation (contract 20001E_151122/1), the Alexander von Humboldt Foundation, the European Research Council (ERC-2013-AdG AEROCAT) and the Deutsche Forschungsgemeinschaft (grant Nr. EY 16/10-1 and -2, RTG 1401, cfAED, and EY 16/18-1) is greatly acknowledged. References [1] A. Rabis, P. Rodríguez, and T. J. Schmidt, ACS Catal. , 2 , 864 (2012). [2] N. C. Bigall, A. K. Herrmann, M. Vogel, M. Rose, P. Simon, W. Carrillo-Cabrera, D. Dorfs, S. Kaskel, N. Gaponik, and A. Eychmüller, Angew. Chem. , 48 , 9731 (2009). [3] W. Liu, A.-K. Herrmann, D. Geiger, L. Borchardt, F. Simon, S. Kaskel, N. Gaponik, and A. Eychmüller, Angew. Chem. , 51 , 5743 (2012). [4] W. Liu, P. Rodríguez, L. Borchardt, A. Foelske, J. Yuan, A.-K. Herrmann, D. Geiger, Z. Zheng, S. Kaskel, N. Gaponik, R. Kötz, T. J. Schmidt, and A. Eychmüller, Angew. Chem. , 52 , 9849 (2013). [5] A.-K. Herrmann, P. Formanek, L. Borchardt, M. Klose, L. Giebeler, J. Eckert, S. Kaskel, N. Gaponik, and A. Eychmüller, Chem. Mater ., 26 , 1074 (2014). [6] W. Liu, A.-K. Herrmann, N. C. Bigall, P. Rodríguez, D. Wen, M. Özaslan, T. J. Schmidt, N. Gaponik, and A. Eychmüller, Acc. Chem. Res. , 48 , 154 (2015). [7] C. A. Reiser, L. J. Bregoli, T. W. Patterson, J. S. Yi, J. D. Yang, M. L. Perry, and T. D. Jarvi, Electrochem. Solid-State Lett. , 8 , A273 (2005). [8] F. Maillard, S. Pronkin, and E. R. Savinova, in Handbook of Fuel Cells: Fundamentals, Technology and Applications , Vol. 5, W. Vielstich, H. A. Gasteiger, and H. Yokokawa, Editors, p. 91, John Wiley & Sons, New York (2009). [9] H. A. Gasteiger, S. S. Kocha, B. Sompalli, and F. T. Wagner, Appl. Catal. B , 56 , 9 (2005). Figure 1
Developing electrocatalysts with low cost, high activity, and good durability is urgently demanded for the wide commercialization of fuel cells. By taking advantage of nanostructure engineering, we fabricated PtAg nanotubular aerogels (NTAGs) with high electrocatalytic activity and good durability via a simple galvanic replacement reaction between the in situ spontaneously gelated Ag hydrogel and the Pt precursor. The PtAg NTAGs have hierarchical porous network features with primary networks and pores from the interconnected nanotubes of the aerogel and secondary networks and pores from the interconnected thin nanowires on the nanotube surface, and they show very high porosities and large specific surface areas. Due to the unique structure, the PtAg NTAGs exhibit greatly enhanced electrocatalytic activity toward formic acid oxidation, reaching 19 times higher metal-based mass current density as compared to the commercial Pt black. Furthermore, the PtAg NTAGs show outstanding structural stability and electrochemical durability during the electrocatalysis. Noble metal-based NTAGs are promising candidates for applications in electrocatalysis not only for fuel cells, but also for other energy-related systems.
Abstract Tri(pyrazolyl)phosphane werden als alternative kostengünstige und weniger toxische Phosphorquelle in der Synthese von InP/ZnS‐Quantenpunkten (QDs) eingesetzt. Ausgehend von ihnen können langzeitstabile (>6 Monate) P(OLA) 3 ‐Stammlösungen (OLAH=Oleylamin) synthetisiert werden, aus denen sich die entsprechenden Pyrazole einfach zurückgewinnen lassen. P(OLA) 3 fungiert in der Synthese von stark emittierenden InP/ZnS‐QDs sowohl als Phosphorquelle als auch als Reduktionsmittel. Die erhaltenen Kern/Schale‐Partikel zeichnen sich durch hohe Photolumineszenz‐Quantenausbeuten von 51–62 % in einem Spektralbereich von 530–620 nm aus. Die Verarbeitung und Anwendung dieser InP/ZnS‐QDs als Farbkonversionsschicht wurde anhand des Einsatzes in einer weißen Leuchtdiode demonstriert.
Abstract Wir stellen in dieser Arbeit eine effiziente Anordnungsstrategie verschiedener elektrostatisch stabilisierter Halbleiternanokristalle (NK) vor, welche sich über geeignete Ionen zu einem mehrfach verzweigten Gelnetzwerk verbinden. Diese rein anorganischen, ungeordneten 3D‐Strukturen profitieren von starken interpartikulären Wechselwirkungen, was in einem verbesserten Ladungstransport zwischen verschiedenen NK, mit unterschiedlichen Morphologien, Zusammensetzungen, Größen sowie funktionalisierten Liganden resultiert. Darüber hinaus weisen die erhaltenen getrockneten Gelmonolithe (Aerogelen) eine hochporöse Netzwerkstruktur auf, ohne dass dabei die Quantenbeschränkung der Baueinheiten beeinträchtigt wird. Insbesondere anorganische Halbleiteraerogele, wie hier aus kolloidalen, 4.5 nm großen CdSe‐NK aufgebaut, die anschließend mit Iodidliganden modifiziert und über Cd 2+ ‐Ionen verbrückt wurden, zeigen eine große spezifische Oberfläche von 146 m 2 g −1 .
Tri(pyrazolyl)phosphanes (5R1,R2 ) are utilized as an alternative, cheap and low-toxic phosphorus source for the convenient synthesis of InP/ZnS quantum dots (QDs). From these precursors, remarkably long-term stable stock solutions (>6 months) of P(OLA)3 (OLAH=oleylamine) are generated from which the respective pyrazoles are conveniently recovered. P(OLA)3 acts simultaneously as phosphorus source and reducing agent in the synthesis of highly emitting InP/ZnS core/shell QDs. These QDs are characterized by a spectral range between 530-620 nm and photoluminescence quantum yields (PL QYs) between 51-62 %. A proof-of-concept white light-emitting diode (LED) applying the InP/ZnS QDs as a color-conversion layer was built to demonstrate their applicability and processibility.
A controlled assembly of natural beta-cyclodextrin modified Au NPs mediated by dopamine is demonstrated. Furthermore, a simple and sensitive colorimetric detection for dopamine is established by the concentration-dependent assembly. As a service to our authors and readers, this journal provides supporting information supplied by the authors. Such materials are peer reviewed and may be re-organized for online delivery, but are not copy-edited or typeset. Technical support issues arising from supporting information (other than missing files) should be addressed to the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.
Abstract We report an efficient approach to assemble a variety of electrostatically stabilized all‐inorganic semiconductor nanocrystals (NCs) by their linking with appropriate ions into multibranched gel networks. These all‐inorganic non‐ordered 3D assemblies benefit from strong interparticle coupling, which facilitates charge transport between the NCs with diverse morphologies, compositions, sizes, and functional capping ligands. Moreover, the resulting dry gels (aerogels) are highly porous monolithic structures, which preserve the quantum confinement of their building blocks. The inorganic semiconductor aerogel made of 4.5 nm CdSe colloidal NCs capped with I − ions and bridged with Cd 2+ ions had a large surface area of 146 m 2 g −1 .
