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The electrocatalytic activity for the oxygen evolution reaction in alkaline electrolyte of hexagonal spinel Co₃O₄ nanoparticles derived using scanning electrochemical cell microscopy (SECCM) is correlated with scanning electron microscopy and atomic force microscopy images of the droplet landing sites. A unique way to deconvolute the intrinsic catalytic activity of individual crystal facets of the hexagonal Co₃O₄ spinel particle is demonstrated in terms of the turnover frequency (TOF) of surface Co atoms. The top surface exposing 111 crystal planes displayed a thickness-dependent TOF with a TOF of about 100 s−¹ at a potential of 1.8 V vs. RHE and a particle thickness of 100 nm. The edge of the particle exposing (110) planes, however, showed an average TOF of 270±68 s−¹ at 1.8 V vs. RHE and no correlation with particle thickness. The higher atomic density of Co atoms on the edge surface (2.5 times of the top) renders the overall catalytic activity of the edge planes significantly higher than that of the top planes. The use of a free-diffusing Os complex in the alkaline electrolyte revealed the low electrical conductivity through individual particles, which explains the thickness-dependent TOF of the top planes and could be a reason for the low activity of the top (111) planes.

Three-dimensional topological insulators (3D TI) exhibit conventional parabolic bulk bands and protected Dirac surface states. A thorough investigation of the different transport channels provided by the bulk and surface carriers using macroscopic samples may provide a path toward accessing superior surface transport properties. Bi₂Te₃ materials make promising 3D TI models; however, due to their complicated defect chemistry, these materials have a high number of charge carriers in the bulk that dominate the transport, even as nanograined structures. To partially control the bulk charge carrier density, herein the synthesis of Te-enriched Bi₂Te₃ nanoparticles is reported. The resulting nanoparticles are compacted into nanograined pellets of varying porosity to tailor the surface-to-volume ratio, thereby emphasizing the surface transport channels. The nanograined pellets are characterized by a combination of resistivity, Hall- and magneto-conductance measurements together with (THz) time-domain reflectivity measurements. Using the Hikami-Larkin-Nagaoka (HLN) model, a characteristic coherence length of ≈200 nm is reported that is considerably larger than the diameter of the nanograins. The different contributions from the bulk and surface carriers are disentangled by THz spectroscopy, thus emphasizing the dominant role of the surface carriers. The results strongly suggest that the surface transport carriers have overcome the hindrance imposed by nanoparticle boundaries.

The electrocatalytic activity for the oxygen evolution reaction in alkaline electrolyte of hexagonal spinel Co3O4 nanoparticles derived using scanning electrochemical cell microscopy (SECCM) is correlated with scanning electron microscopy and atomic force microscopy images of the droplet landing sites. A unique way to deconvolute the intrinsic catalytic activity of individual crystal facets of the hexagonal Co3O4 spinel particle is demonstrated in terms of the turnover frequency (TOF) of surface Co atoms. The top surface exposing 111 crystal planes displayed a thickness-dependent TOF with a TOF of about 100 s−1 at a potential of 1.8 V vs. RHE and a particle thickness of 100 nm. The edge of the particle exposing (110) planes, however, showed an average TOF of 270±68 s−1 at 1.8 V vs. RHE and no correlation with particle thickness. The higher atomic density of Co atoms on the edge surface (2.5 times of the top) renders the overall catalytic activity of the edge planes significantly higher than that of the top planes. The use of a free-diffusing Os complex in the alkaline electrolyte revealed the low electrical conductivity through individual particles, which explains the thickness-dependent TOF of the top planes and could be a reason for the low activity of the top (111) planes.

Transition metals (TMs) are highly investigated as nonprecious electrocatalysts for hydrogen evolution (HER) and oxygen evolution (OER) reactions. There is a strong demand for highly efficient and inexpensive catalysts for overall water splitting. Herein, the bimetallic CoxFey alloy nanoparticles encapsulated in a N‐doped graphene shell containing molybdenum carbide (Mo2C) nanoparticles are synthesized by the pyrolysis of cobalt ferrite (CoxFe3−xO4) nanoparticles coated by melamine‐formaldehyde resin cross‐linked with molybdic acid. Molybdic acid not only serves as precursor for the formation of highly dispersed Mo2C nanoparticles in the N‐doped graphene shell but also enhances the thermal stability of the organic shell, resulting in the formation of smaller CoxFey cores. The formation of Mo2C nanoparticles in the graphene shell is promoted by the CoxFe3−xO4 core. Interestingly, the synergistic presence of Mo2C nanoparticles not only enhances the HER activity of the material but also renders a partial breakage of the graphene shell, which increases the surface concentration of OER‐active Co and therefore enhances the OER activity. The as‐prepared TM‐based materials serve as bifunctional catalysts for the overall water splitting and exhibit improved electrocatalytic performances compared to standard cells based on precious metals, with the potentials of 1.53 and 1.60 V at 10 and 20 mA cm−2 in alkaline media, respectively.

The synthesis of phase-pure ternary solutions of tetradymite-type materials (BiₓSb₁−ₓ)₂Te₃ (x=0.25; 0.50; 0.75) in an ionic liquid approach has been carried out. The nanoparticles are characterized by means of energy-dispersive X-ray spectroscopy (EDX), powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), and transmission electron microscopy. In addition, the role of different processing approaches on the thermoelectric properties - Seebeck coefficient as well as electrical and thermal conductivity - is demonstrated. CA Schulz und CA extern (Schierning)

Three Lewis acid–base adducts t‐Bu3Ga–EPh3 (E = P 1, As 2, Sb 3) were synthesized by reactions of Ph3E and t‐Bu3Ga and characterized by heteronuclear NMR (1H, 13C (31P)) and IR spectroscopy, elemental analysis and single crystal X‐ray diffraction. Their structural parameters are discussed and compared to similar t‐Bu3Ga adducts. The strength of the donor‐acceptor interactions within 1–3 was investigated in solution by temperature‐dependent 1H NMR spectroscopy and by quantum chemical calculations.

Intramolecularly‐stabilized germanium, tin, and lead alkoxides of the type M(OCH2CH2NR2)2 [R = Et, M = Ge (1); R = Me, M = Sn (2); R = Me, M = Pb (3)] are suitable precursors for the synthesis of group 14 chalcogenides ME (M = Ge, Sn, Pb; E = S, Se, Te) in scrambling reactions with (Me3Si)2S and (Et3Si)2E (E = Se, Te) at moderate temperatures via hot injection method. The reactions proceed with elimination of the corresponding silylether as was proven by in situ 1H NMR spectroscopy. The solid‐state structures of the homoleptic complex 1 and the heteroleptic complex ClGe(OC2H4NEt2) (4) were determined by single‐crystal X‐ray diffraction, whereas the group 14 chalcogenides were characterized by XRD, SEM, and EDX. Dedicated to Prof. G. Schmid on the occasion of his 80th birthday.

Intramolecularly stabilized Sb(OCH2CH2NMe2)3 (1) and Bi(OCH2CH2NMe2)3 (2) readily react with (Me3Si)2S and (Et3Si)2E (E = Se, Te) at moderate temperatures (hot injection method) with elimination of the corresponding silyl ether and subsequent formation of the group 15 chalcogenides Sb2E3 and Bi2E3, which were characterized by XRD, SEM, and energy‐dispersive X‐ray spectroscopy (EDX). In addition, the solid‐state structure of 1 was determined by single‐crystal XRD.

Oxidative addition of diethyldichalcogenanes Et2E2 (E = S, Se, Te) to bis[bis(trimethylsilyl]amido]germylene and ‐stannylene M[N(SiMe3)2]2 (M = Ge, Sn) proceed with formation of the corresponding bis(ethylchalcogenato)germanes (Me3Si)2N)2Ge(EEt)2 [E = S (1), Se (2), Te (3)] and ‐stannanes (Me3Si)2N)2Sn(EEt)2 [E = S (4), Se (5), Te (6)]. The solid state structures of 1–6 were determined by single‐crystal X‐ray diffraction.

Crystalline Ga2O3 nanowires are synthesized via an Au‐catalyzed, as well as a self‐catalyzed, growth by a low‐temperature metal‐organic (MO)CVD process using tBu3Ga as a novel Ga source. Morphology, elemental composition, and crystallinity of the resulting nanowires are analyzed by scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), energy dispersive X‐ray spectroscopy (EDX), X‐ray diffraction (XRD), and selected area electron diffraction (SAED). Photoluminescence (PL) spectra of the Ga2O3 nanowires show efficient defect‐luminescence in the visible and UV ranges with blue and green emission peaks at 430 nm and 512 nm, respectively, at room temperature.

Highly active, structurally disordered CoFe2O4/CoO electrocatalysts are synthesized by pulsed laser fragmentation in liquid (PLFL) of a commercial CoFe2O4 powder dispersed in water. A partial transformation of the CoFe2O4 educt to CoO is observed and proposed to be a thermal decomposition process induced by the picosecond pulsed laser irradiation. The overpotential in the OER in aqueous alkaline media at 10 mA cm-2 is reduced by 23% compared to the educt down to 0.32 V with a Tafel slope of 71 mV dec-1. Importantly, the catalytic activity is systematically adjustable by the number of PLFL treatment cycles. The occurrence of thermal melting and decomposition during one PLFL cycle is verified by modelling the laser beam energy distribution within the irradiated colloid volume and comparing the by single particles absorbed part to threshold energies. Thermal decomposition leads to a massive reduction in particle size and crystal transformations towards crystalline CoO and amorphous CoFe2O4. Subsequently, thermal melting forms multi-phase spherical and network-like particles. Additionally, Fe-based layered double hydroxides at higher process cycle repetitions emerge as a byproduct. The results show that PLFL is a promising method that allows modification of the structural order in oxides and thus access to catalytically interesting materials. OA Förderung 2017

In dieser Arbeit wurde das Wachstum von (SbxBi1-x)2Te3-Dünnschichten mittels MOCVD unter Verwendung von single source- sowie dual-source-Precursoren demonstriert. Die hergestellten Dünnschichten wurden mittels REM, EDX, AES, TEM, XPS und hinsichtlich ihrer elektrischen Eigenschaften untersucht. . Die elektrischen Transporteigenschaften der Schichten in Abhängigkeit von dem Bismutgehalt wurden bestimmt, wobei eine ausgeprägte Abhängigkeit der elektrischen Leitfähigkeit, der Ladungsträgerkonzentration und -mobilität von der chemischen Zusammensetzung festgestellt wurde. Die Bandstruktur einer unsubstituierten Sb2Te3-Schicht wurde mittels ARPES bestimmt und ein topologischer Oberflächenzustand erstmalig für MOCVD gewachsene Sb2Te3-Filme nachgewiesen. Des Weiteren wurde das Wachstum von Ga2O3-Nanodrähten untersucht. Es konnte gezeigt werden, dass tBu3Ga ein geeigneter Galliumprecursor ist und sowohl das gold- als auch das selbstkatalysierte Wachstum von Ga2O3-Nanodrähten oberhalb einer Substrattemperatur von 450 ◦C auf Si(100)-Substraten ermöglicht. Die Nanodrähte wurden mittels REM, EDX, XRD und TEM charakterisiert. Für die Au-katalysiert gewachsenen Drähte wurde ein vom klassischen VLS-Mechanismus abweichender Wachtumsmodus gefunden, der möglicherweise das Wachstum von hochkristallinen Ga2O3-Nanodrähten bei niedrigen Temperaturen ermöglicht. Photolumineszenzspektren der goldkatalysierten Drähte zeigen eine ausgeprägte Photolumineszenz sowohl im sichtbaren Bereich mit blauen (430 nm) und grünen (521 nm) Emissionspeaks als auch im UV-Bereich. Durch die thermische Zersetzung von Metallacetylacetaten in Oleylamin bei Temperaturen zwischen 200 und 300 ◦C konnten sub-10 nm CoFe2O4-Nanopartikel sowie die kationensubstituierten Spinelle Co0.5M0.5Fe2O4 (M = Mn, Fe, Ni, Cu, Zn) und CoFe2–xMxO4 (M = V) hergestellt werden. Die synthetisierten Partikel wurden mittels EDX, TEM und 57Fe- Mössbauer-spektroskopie charakterisiert. Es konnte gezeigt werden, dass die Substitution mit Übergangsmetallen eine wesentliche Aktivitätssteigerung der Spinelle als Elektrokatalysatoren in der Sauerstoffentwickungsreaktion OER zur Folge hat. Zusätzlich wurde auch das Reaktionsverhalten der Bis[bis(trimethylsilyl]-mido]germylene and -stannylene [(Me3Si)2N]2Ge und [(Me3Si)2N]2Sn gegenüber den Diethyldichalkogeniden Et2E2 (E = S, Se, Te) untersucht. Bei diesen Reaktionen konnte die Bildung der Bis(ethylchalkogenato)germane (Me3Si)2N)2Ge(EEt)2 [E = S (1), Se (2), Te (3)] und -stannane (Me3Si)2N)2Sn(EEt)2 [E = S (4), Se (5), Te (6)] beobachtet werden. Im Gegensatz dazu kam es bei der Reaktion des zyklischen Germylens Me2Si(NtBu) 2Ge mit den Diethyldichalkogeniden Et2E2 (E = S, Se, Te) zu einem Produktgemisch bestehend aus den Bis(alkylchalkogeno)germanen Me2Si(NtBu)2Ge(EEt)2 (E = S 8, Se 9, Te 12) und dem Digermanen [Me2Si(NtBu)2Ge(EEt)]2 (E = S 10, Se 11). Für die Reaktion der Germylens mit Et2Te2 konnte die Bildung des Me2Si(NtBu)2Ge(TeEt)2 12 spektroskopisch nachgewiesen werden. 12 zerfällt jedoch in die Te-verbrückte Spezies [Me2Si(NtBu)2GeTe]2, die in Form dunkelroter Kristalle isoliert werden konnte. Alle Reaktionsprodukte wurden NMR-spektroskopisch charakterisiert und die Festkörperstrukturen der Verbindungen 1-11 durch Einkristalldiffraktometrie bestimmt. Dissertation, Universität Duisburg-Essen, 2017

Crystalline Sb2Se3 nanoparticles were prepared by reaction of SbCl3 with (Et3Si)2Se in the presence of oleylamine (OA) in the ionic liquids [C4C1Im]Cl, whereas the reaction of (Et3Si)2Se with [C4C1Im]3[BiCl6] 1, which was obtained from the reaction of BiCl3 with [C4C1Im]Cl and structurally characterized by single crystal X-ray diffraction, yielded Bi-rich Bi2Se3 nanoparticles. In contrast, the reaction of the reactive IL [C4C1Im]3[Bi3I12] with (Et3Si)2Se in the presence of oleylamine (OA) in [C4C1Im]I gava phase-pure Bi2Se3 nanoparticles. The chemical composition of the nanoparticles was investigated by EDX, while possible surface contaminations were studied by XPS and IR spectroscopy. The morphology of the nanoparticles was studied by SEM and TEM.