Hydrothermal synthesis of anisotropic alkali and alkaline earth vanadates

In the course of a systematic field study, anisotropic alkali and alkaline earth vanadates have been accessed through a straightforward, one-step hydrothermal process. They are formed quantitatively from V2O5 and alkali- or alkaline earth halide solutions after a few days of autoclave treatment in the temperature range between 100 and 220 °C. The presence of ionic additives leads to an interplay between the formation of isotropic crystalline phases and the production of fibrous oxide materials, such as a novel magnesium vanadate. The influence of the hydrothermal parameters and of the alkali/alkaline earth halides on the emerging phases and morphologies has been investigated in the course of a systematic study. The results are compared with other vanadate- and transition metal oxide-based hydrothermal systems, and the emerging trends are discussed with respect to the development of predictive synthetic concepts for nanostructured vanadium oxide

In the footsteps of Alfred Werner: The institute of Inorganic Chemistry at the University of Zurich

Inorganic chemistry has a long-standing tradition at the University of Zurich starting with Carl Jacob Lowig, the first professor of chemistry. The influence of Nobel Prize winner Alfred Werner in coordination, organometallic, and bioinorganic chemistry extends right up to the present day as can be seen in many of the research fields of the current professors and young research scientists. With all due respect for the long tradition in inorganic chemistry the Institute of Inorganic Chemistry is also looking forwards to define its role to meet the challenges of the future

Tailoring C─N containing compounds into carbon nanomaterials with tunable morphologies for electrocatalytic applications

Carbon materials with unique sp2-hybridization are extensively researched for catalytic applications due to their excellent conductivity and tunable physicochemical properties. However, the development of economic approaches to tailoring carbon materials into desired morphologies remains a challenge. Herein, a convenient “bottom-up” strategy by pyrolysis of graphitic carbon nitride (g-C3N4) (or other carbon/nitrogen (C, N)-enriched compounds) together with selected metal salts and molecules is reported for the construction of different carbon-based catalysts with tunable morphologies, including carbon nano-balls, carbon nanotubes, nitrogen/sulfur (S, N) doped-carbon nanosheets, and single-atom catalysts, supported by carbon layers. The catalysts are systematically investigated through various microscopic, spectroscopic, and diffraction methods and they demonstrate promising and broad applications in electrocatalysis such as in the oxygen reduction reaction and water splitting. Mechanistic monitoring of the synthesis process through online thermogravimetric-gas chromatography-mass spectrometry measurements indicates that the release of C─N-related moieties, such as dicyan, plays a key role in the growth of carbon products. This enables to successfully predict other widely available precursor compounds beyond g-C3N4 such as caffeine, melamine, and urea. This work develops a novel and economic strategy to generate morphologically diverse carbon-based catalysts and provides new, essential insights into the growth mechanism of carbon nanomaterials syntheses

Tailoring C─N Containing Compounds into Carbon Nanomaterials with Tunable Morphologies for Electrocatalytic Applications

Carbon materials with unique sp2-hybridization are extensively researched for catalytic applications due to their excellent conductivity and tunable physicochemical properties. However, the development of economic approaches to tailoring carbon materials into desired morphologies remains a challenge. Herein, a convenient “bottom-up” strategy by pyrolysis of graphitic carbon nitride (g-C3N4) (or other carbon/nitrogen (C, N)-enriched compounds) together with selected metal salts and molecules is reported for the construction of different carbon-based catalysts with tunable morphologies, including carbon nano-balls, carbon nanotubes, nitrogen/sulfur (S, N) doped-carbon nanosheets, and single-atom catalysts, supported by carbon layers. The catalysts are systematically investigated through various microscopic, spectroscopic, and diffraction methods and they demonstrate promising and broad applications in electrocatalysis such as in the oxygen reduction reaction and water splitting. Mechanistic monitoring of the synthesis process through online thermogravimetric-gas chromatography-mass spectrometry measurements indicates that the release of C─N-related moieties, such as dicyan, plays a key role in the growth of carbon products. This enables to successfully predict other widely available precursor compounds beyond g-C3N4 such as caffeine, melamine, and urea. This work develops a novel and economic strategy to generate morphologically diverse carbon-based catalysts and provides new, essential insights into the growth mechanism of carbon nanomaterials synthese

Mechanistically Driven Control over Cubane Oxo Cluster Catalysts

Predictive and mechanistically driven access to polynuclear oxo clusters and related materials remains a grand challenge of inorganic chemistry. We here introduce a novel strategy for synthetic control over highly sought-after transition metal {M4O4} cubanes. They attract interest as molecular water oxidation catalysts that combine features of both heterogeneous oxide catalysts and nature’s cuboidal {CaMn4O5} center of photosystem II. For the first time, we demonstrate the outstanding structure-directing effect of straightforward inorganic counteranions in solution on the self-assembly of oxo clusters. We introduce a selective counteranion toolbox for the controlled assembly of di(2-pyridyl) ketone (dpk) with M(OAc)2 (M = Co, Ni) precursors into different cubane types. Perchlorate anions provide selective access to type 2 cubanes with the characteristic {H2O-M2(OR)2-OH2} edge-site, such as [Co4(dpy-C{OH}O)4(OAc)2(H2O)2](ClO4)2. Type 1 cubanes with separated polar faces [Co4(dpy-C{OH}O)4(L2)4]n+ (L2 = OAc, Cl, or OAc and H2O) can be tuned with a wide range of other counteranions. The combination of these counteranion sets with Ni(OAc)2 as precursor selectively produces type 2 Co/Ni-mixed or {Ni4O4} cubanes. Systematic mechanistic experiments in combination with computational studies provide strong evidence for type 2 cubane formation through reaction of the key dimeric building block [M2(dpy-C{OH}O)2(H2O)4]2+ with monomers, such as [Co(dpy-C{OH}O)(OAc)(H2O)3]. Furthermore, both experiments and DFT calculations support an energetically favorable type 1 cubane formation pathway via direct head-to-head combination of two [Co2(dpy-C{OH}O)2(OAc)2(H2O)2] dimers. Finally, the visible-light-driven water oxidation activity of type 1 and 2 cubanes with tuned ligand environments was assessed. We pave the way to efficient design concepts in coordination chemistry through ionic control over cluster assembly pathways. Our comprehensive strategy demonstrates how retrosynthetic analyses can be implemented with readily available assembly directing counteranions to provide rapid access to tuned molecular materials

The h‐SbxWO3+2x Oxygen Excess Antimony Tungsten Bronze

We describe the previously unreported oxygen excess hexagonal antimony tungsten bronze with composition Sb0.5W3O10, in the following denoted as h‐SbxWO3+2x with x=0.167, to demonstrate its analogy to classical AxWO3 tungsten bronzes. This compound forms in a relatively narrow temperature range between 580 °C<T<620 °C. It was obtained as a dark‐blue polycrystalline powder, and as thin, needle‐shaped, blue single crystals. h‐SbxWO3+2x crystallizes in the hexagonal space group P6/mmm with the cell parameters a=7.4369(4) Å and c=3.7800(2) Å. The antimony and excess oxygen occupy the hexagonal channels within the network of corner‐sharing WO6 octahedra. h‐SbxWO3+2x has a resistivity of ρ300 K≈1.28 mΩ cm at room temperature, with little if any temperature‐dependence on cooling. DFT calculations on a simplified model for this compound find a metallic‐like electronic structure with the Fermi level falling within rather flat bands, especially around the Γ point

Modulating Carrier Kinetics in BiVO4 Photoanodes through Molecular Co4O4 Cubane Layers

Understanding the role and immobilization of molecular catalysts on photoelectrodes is essential to use their full potential for efficient solar fuel generation. Here, a CoII4O4 cubane with proven catalytic performance and an active H2O─Co2(OR)2─OH2 edge-site moiety is immobilized on BiVO4 photoanodes through a versatile layer-by-layer assembly strategy. This delivers a photocurrent of 3.3 mA cm−2 at 1.23 VRHE and prolonged stability. Tuning the thickness of the Co4O4 layer has remarkable effects on photocurrents, dynamic open circuit potentials, and charge carrier behavior. Comprehensive-time and frequency-dependent perturbation techniques are employed to investigate carrier kinetics in transient and pseudo-steady-state operando conditions. It is revealed that the Co4O4 layer can prolong carrier lifetime, unblock kinetic limitations at the interface by suppressing recombination, and enhance charge transfer. Additionally, its flexible roles are identified as passivation/hole trapping/catalytic layer at respective lower/moderate/higher potentials. These competing functions are under dynamic equilibrium, which fundamentally defines the observed photocurrent trends

Copper(II) defect-cubane water oxidation electrocatalysts: from molecular tetramers to oxidic nanostructures

We report on the synthesis and spectroscopic evidence for a sequence of structural transformations of a new defect-cubane type copper complex, [Cu4(pyalk)4(OAc)4](ClO4)(HNEt3), which acts as a pre-catalyst for water oxidation. In situ and post-catalytic studies showed that the tetrameric complex undergoes a structural transformation into dimeric and monomeric species, induced by water molecules and carbonate anions, respectively. Further, the observed electrocatalytic water oxidation activity has been confirmed to arise from in situ-generated Cu(II) oxidic nanostructures at the electrode interface

Photoinduced Oxygen Evolution Catalysis Promoted by Polyoxometalate Salts of Cationic Photosensitizers

The insoluble salt Cs15K[Co9(H2O)6(OH)3(HPO4)2(PW9O34)3] (CsCo9) is tested as heterogeneous oxygen evolution catalyst in light-induced experiments, when combined with the homogeneous photosensitizer [Ru(bpy)3]2+ and the oxidant Na2S2O8 in neutral pH. Oxygen evolution occurs in parallel to a solid transformation. Post-catalytic essays indicate that the CsCo9 salt is transformed into the corresponding [Ru(bpy)3]2+ salt, upon cesium loss. Remarkably, analogous photoactivated oxygen evolution experiments starting with the [Ru(bpy)3](5+x)K(6−2x)[Co9(H2O)6(OH)3(HPO4)2(PW9O34)3]·(39+x)H2O (RuCo9) salt demonstrate much higher efficiency and kinetics. The origin of this improved performance is at the cation-anion, photosensitizer-catalyst pairing in the solid state. This is beneficial for the electron transfer event, and for the long-term stability of the photosensitizer. The latter was confirmed as the limiting process during these oxygen evolution reactions, with the polyoxometalate catalyst exhibiting robust performance in multiple cycles, upon addition of photosensitizer, and/or oxidant to the reaction mixture