Journal: Small Structures

Abbreviation

Small Struct.

Publisher

Wiley-VCH

Journal Volumes

ISSN

2688-4062

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2023 - 20256
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Publications 1 - 6 of 6
  • Template-Free Synthesis of Highly Porous Metal Nitride Architectures for Electronics and Molecular Sensing
    Item type: Journal Article
    Baut, Adrien; Pereira Martins, Michael; Güntner, Andreas (2025)
    Small Structures
    Metal nitrides (MN) possess exceptional catalytic, electronic, and physical properties making them widely used in (opto-)electronics and as hard coatings. When used as films in surface-active applications, however, their performance remains limited by poor mass transfer and reduced accessibility of reactive sites. This is associated to compact film architecture yielded by conventional deposition techniques (e.g., sputtering). Herein, a template-free method for the design of highly porous (≥84%) MN films with high compositional versatility, as shown for Cu3N, W2N, MoNx, and TiN, is demonstrated. These are obtained by conversion of fractal-like metal oxide (MOx) agglomerated films through dry nitridation. In case of Cu3N, monocrystalline oxide nanoparticles are converted to polycrystalline nitrides, as traced by X-ray diffraction and electron microscopy. Such films feature consistently lower resistances than their MOx counterparts, as well as high reactivity and mass transfer. This is exploited exemplarily for molecular sensing of NO2 at only 75 °C temperature, leading to up to a fivefold higher response with faster response time over more compact spin-coated films. As a result, this approach overcomes critical mass transfer performance limitations of MN films that are also relevant for other applications like electrocatalysis and energy storage.
  • Droplet-Based Microfluidics Platform for the Synthesis of Single-Atom Heterogeneous Catalysts
    Item type: Journal Article
    Moragues, Thomas; Mitchell, Sharon; Faust Akl, Dario; et al. (2023)
    Small Structures
    Wet chemical approaches are among the most versatile and scalable strategies for preparing single-atom heterogeneous catalysts (SACs). However, despite their broad application, the synthesis of SACs via these routes remains largely ad hoc, with limited attention to the effect of different synthetic parameters on the stabilization of metal species. As a proof of concept, herein, a microfluidic platform is demonstrated for short-timescale (<10 s), systematic syntheses of SACs via wet impregnation using a range of metal precursor-carrier combinations. The microfluidic environment within rapidly mixed, nanoliter droplets ensures precise control of the concentrations and residence times of the support particles in the metal precursor solutions. This enables the rapid assessment of the influence of the metal precursor concentration on the uptake and dispersion of the adsorbed metal species, as demonstrated for the synthesis of palladium and platinum SACs based on a high-surface form of graphitic carbon nitride (C3N4). Extension to SACs based on other metals (Ni) and relevant carriers (N-doped carbon, gamma-alumina) confirms the generality of the synthesis method. The microfluidic approach opens possibilities for high-throughput parameter screening and mechanistic studies in the design of heterogeneous single-atom catalysts.
  • The Role of Phosphate Functionalization on the Oxygen Evolution Reaction Activity of Cobalt-Based Oxides at Different pH Values
    Item type: Journal Article
    Yoshimune, Wataru; Falqueto, Juliana B.; Clark, Adam H.; et al. (2023)
    Small Structures
    Cobalt-based oxides have attracted attention as active electrocatalysts for the oxygen evolution reaction (OER) in alkaline electrolytes. However, highly OER active catalysts at near-neutral pHs are also desired for practical applications. Herein, a dry phosphate functionalization process is presented to enhance the OER activity of different cobalt-based catalysts at near-neutral pHs. Electrochemical evaluations show that the P-functionalization can effectively improve the OER activity at near-neutral pHs for La0.2Sr0.8CoO3-d , La0.2Sr0.8Co0.8Fe0.2O3-d , and CoOx catalysts, but not for La0.5Sr1.5CoO4-d . Bulk and surface sensitive X-ray absorption spectroscopy and X-ray photoelectron spectroscopy unveil the influence of P incorporated in the order of ppm on the electronic state, local structure, and surface composition of the investigated catalysts. The P-functionalization reduces the Co oxidation state in La0.2Sr0.8CoO3-d and La0.5Sr1.5CoO4-d , but the latter also presents significant Sr-based segregations on the surface-inhibiting OER activity at near-neutral pHs. Differently, La0.2Sr0.8CoO3-d , and to a lesser extent La0.2Sr0.8Co0.8Fe0.2O3-d and CoOx , shows improved OER activity at neutral pH after the P-functionalization. The findings disclose that P-functionalization successfully enhances OER activity at near-neutral pHs and that both phosphate ion assistance in the OER mechanism and catalyst Co oxidation state can play a role in the enhanced OER activity.
  • Size- and Temperature-Dependent Lattice Anisotropy and Structural Distortion in CsPbBr₃ Quantum Dots by Reciprocal Space X-ray Total Scattering Analysis
    Item type: Journal Article
    Bertolotti, Federica; Dengo, Nicola; Cervellino, Antonio; et al. (2024)
    Small Structures
    Lead halide perovskite nanocrystals (NCs) have emerged as next-generation semiconductors capable of unifying superior photoemission properties, facile and inexpensive preparation, compositional and structural versatility. Among them, CsPbBr₃ is a model system in theoretical and experimental studies owing to its intrinsic chemical stability. Nonetheless, knowledge of the precise magnitude and the size- and temperature-dependent lattice and structural distortions is lacking, and the static/dynamic nature of disorder in NCs remains an open question. Herein, robust reciprocal space X-ray total scattering analysis is applied and accurate lattice distortions, Pb-Br bond distances, and Pb-Br-Pb angles versus NCs size are extracted. The lattice anisotropy increases upon expansion on downsizing while, upon contraction on cooling, the lattice distortion behaves differently at intermediate (9 nm) and ultrasmall (5 nm) sizes and from the bulk. Bond distances (stretched by ≈1%) do not show any size dependence, whereas equatorial and axial angles denote more symmetric octahedral arrangements in the smallest sizes, where they differ by ≈2° compared to ≈8° in the bulk. Anomalously high atomic displacement parameters of axial bromine ions persisting down to cryogenic temperatures suggest statically disordered octahedral tilts. These results provide insights having important implications on size-dependent emission properties and the exciton fine structure.
  • Anisotropic, Strong, and Thermally Insulating 3D-Printed Nanocellulose–PNIPAAM Aerogels
    Item type: Journal Article
    Nagel, Yannick; Sivaraman, Deeptanshu; Neels, Antonia; et al. (2023)
    Small Structures
    Cellulose is a promising candidate for the fabrication of superinsulating materials, which would be of great interest for thermal management applications as well as for the scientific community. Until now, the production of strong cellulose-based aerogels has been dominated by traditional manufacturing processes, which have limited the possibilities to achieve the structural control and mechanical properties seen in natural materials such as wood. In this work, we show a simple but versatile method to fabricate cellulose aerogels in intricate geometries. We take advantage of the 3D printing technique direct ink writing to control both the shape and the thermal-mechanical properties of the printed cellulose-based hydrogel inks. Moreover, the shear forces involved in the extrusion process allow us to impart an anisotropic nanostructure to the printed samples. By solvent exchange and supercritical drying, the hydrogel parts are then transformed into stable aerogels. Using X-ray diffraction analysis, mechanical tests and thermal conductivity tests, our 3D printed aerogels are shown to exhibit directionally dependent thermal-mechanical properties higher than those reported for earlier cellulose-based aerogels. These characteristics enable us to fabricate customized structures that can be precisely tailored for their application as load-bearing insulating materials for thermal management.
  • Planar [Cu-S]-Organic Framework for Selective and Low-Overpotential CO₂ Reduction to Formate
    Item type: Journal Article
    Roohi, Khatereh; Soleimani, Mohammad; Khossossi, Nabil; et al. (2025)
    Small Structures
    The development of advanced catalysts with innovative nanoarchitectures is critical for addressing energy and environmental challenges such as the electrochemical CO₂ reduction reaction (CO₂ RR). Herein, the synthesis of an innovative copper–sulfur planar structure, Cu–S–BDC, within a metal–organic framework (MOF) catalyst is presented, which demonstrates 100% selectivity toward formate as the sole carbon product. Structural analysis and surface characterizations reveal that Cu–S–BDC exhibits quasi-2D inorganic building units, with Cu bonded to two S-CH₃ groups and one BDC linker, while carboxylate groups adopt a bridging coordination mode. This unique arrangement not only imparts remarkable structural stability but also enhances the electronic properties of the MOF, as evidenced by a narrow bandgap of 1.203 eV that facilitates efficient charge transfer and increased electrochemical current density in CO₂RR. Notably, it offers a Faradaic efficiency of 92% for formate at an overpotential as low as −0.4 V versus the reversible hydrogen electrode (RHE) in an aqueous electrolyte of 1 M KOH, as well as a current density of −25.8 mA cm² at −0.9 V versus RHE, averaged over 24 h of electrolysis. This study highlights a fresh perspective in the field of MOF electrocatalysts by demonstrating that engineering the metal coordination environment can significantly enhance the electronic properties and consequently improve the electrocatalytic performance of these materials.
Publications 1 - 6 of 6