Machine learning accelerates materials discovery by suggesting targets, yielding exceptionally complex biphasic nanoparticles.
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Heteroanionic materials exhibit great structural diversity with adjustable electronic, magnetic, and optical properties that provide immense opportunities for materials design. Within this material family, perovskite oxynitrides incorporate earth-abundant nitrogen with differing size, electronegativity, and charge into oxide, enabling a unique approach to tuning metal-anion covalency and energy of metal cation electronic states, thereby achieving functionality that may be inaccessible from their perovskite oxide counterparts, which have been widely studied as electrocatalysts. However, it is very challenging to directly obtain such materials due to the poor thermal stability of late transition metals coordinated with N and/or at high valence states. Herein, we introduce an effective strategy to prepare a perovskite oxynitride with a small fraction of sites substituted with Ir and adopt it as the first electrocatalyst in this material family, thereby enabling high activity and efficient utilization of precious metal content. From a series of characterization techniques, including X-ray absorption spectroscopy, atomic resolution electron microscopy, X-ray photoelectron spectroscopy, and X-ray diffraction, we prove the successful incorporation of Ir into a strontium tungsten oxynitride perovskite structure and discover the formation of a unique Ir–N/O coordination structure. Benefitting from this, the material exhibits a high activity toward the hydrogen evolution reaction, which exhibits an ultralow overpotential of only 8 mV to reach 10 mA/cm2 geo in 0.5 M H2SO4 and 4.5-fold enhanced mass activity compared to commercial Pt/C. This work opens a new avenue for oxynitride material synthesis as well as pursuit of a new class of high-performance electrocatalysts.
Corrosion is a significant problem for the stability of structural metals and potentially for functional nanomaterials in operating environments. When two metals with different electrochemical potentials form a junction, galvanic corrosion occurs, resulting in the sacrificial dissolution of the metal with a higher oxidation potential (lower electrode potential). Here, it is shown that bimetallic hetero-nanostructures composed of phase-segregated metals undergo galvanic corrosion in aqueous environments. Such selective etching of the sacrificial metal in heterojunction particles leads to the formation of unusual and kinetically stabilized half-spheroid particles. By using a fluid cell and in situ scanning transmission electron microscopy, a two-stage corrosion process can be observed where the Cu experiences a fractal breakdown before the Ag corrodes due to the lack of a protective oxide layer. However, when treated with a mild Ar plasma, the stability of these structures against corrosion is enhanced due to the conversion of the amorphous native oxide to a denser, thin layer of CuO on the Cu surface. Taken together, this work highlights the importance of considering the effects of galvanic corrosion on the stability of multicomponent nanoparticles, and it shows how mass transport in a nanoscale system is influenced by redox processes.
We report a general nanopatterning strategy that takes advantage of the dynamic coordination bonds between polyphenols and metal ions (e.g., Fe 3+ and Cu 2+ ) to create structures on surfaces with a range of properties. With this methodology, under acidic conditions, 29 metal−phenolic complex-based precursors composed of different polyphenols and metal ions are patterned using scanning probe and large-area cantilever free nanolithography techniques, resulting in a library of deposited metal−phenolic nanopatterns. Significantly, post-treatment of the patterns under basic conditions (i.e., ammonia vapor) triggers a change in coordination state and results in the in situ generation of more stable networks firmly attached to the underlying substrates. The methodology provides control over feature size, shape, and composition, almost regardless of substrate (e.g., Si, Au, and silicon nitride). Under reducing conditions (i.e., H 2 ) at elevated temperatures (180−600 °C), the patterned features have been used as nanoreactors to synthesize individual metal nanoparticles. At room temperature, the ammonia-treated features can reduce Ag + to form metal nanostructures and be modified with peptides, proteins, and thiolated DNA via Michael addition and/or Schiff base reaction. The generality of this technique should make it useful for a wide variety of researchers interested in modifying surfaces for catalytic, chemical and biological sensing, and template-directed assembly purposes.
A versatile approach for synthesizing Yb 3+ -and Er 3+ -doped NaYF 4 upconversion nanoparticle (UCNP) arrays is presented. The nanoparticles are positioned at precisely defined locations through the tip-directed deposition of polyol nanoreactors and subsequent thermal conversion. This method is based on conducting a solution-phase polyol synthesis in nanometerscale reactors, which provide isolated and confined reaction vessels for the thermal decomposition of a fluoride precursor and the coarsening of fluoride nanoparticles. When the nanoreactors are annealed at 350 °C, the polyol degrades, and the nanoparticles, which exhibit upconversion properties, crystallize. Single nanoparticles are attained in each nanoreactor by tuning the precursor concentration, nanoreactor size, and temperature ramping rate. This strategy enhances the scope of nanostructures that can be synthesized by tip-directed routes and, when combined with massively parallel pen approaches such as polymer pen lithography, provides a generalizable platform for the high-throughput synthesis, screening, and discovery of nanomaterials for photonics and other applications.
Inspired by the scanning probe block copolymer lithography process, hollow silica shells were loaded with polymermetal ink mixtures and investigated as solution-based nanoreactors for the synthesis of gold nanoparticles. The incorporation of poly(ethylene oxide) (PEO) into these hollow silica nanoreactors (approximately 40 nm in size) and the use of a two-step reductive annealing process (first at 200 °C and then at 600 °C) results in a high yield (76%) of larger (∼6 nm) single nanoparticles; when the polymer is not used, smaller (∼3 nm) particles dominate, and the yield of single particles is only 6%. It was determined that particle coarsening mostly occurs in the temperature range where the polymer is present and not degraded (i.e., <400 °C for PEO), as indicted by correlative in situ scanning/transmission electron microscopy in a reductive gas-phase environment. Thus, polymer incorporation in this nanoreactor system, which is amenable to scale up, drives the complete conversion of nanoreactor contents without excessive metal loss, highlighting the impact of nanoreactor composition and structural design on particle synthesis.
Megalibraries are centimeter-scale chips containing millions of materials synthesized in parallel using scanning probe lithography. As such, they stand to accelerate how materials are discovered for applications spanning catalysis, optics, and more. However, a long-standing challenge is the availability of substrates compatible with megalibrary synthesis, which limits the structural and functional design space that can be explored. To address this challenge, thermally removable polystyrene films were developed as universal substrate coatings that decouple lithography-enabled nanoparticle synthesis from the underlying substrate chemistry, thus providing consistent lithography parameters on diverse substrates. Multi-spray inking of the scanning probe arrays with polymer solutions containing metal salts allows patterning of >56 million nanoreactors designed to vary in composition and size. These are subsequently converted to inorganic nanoparticles via reductive thermal annealing, which also removes the polystyrene to deposit the megalibrary. Megalibraries with mono-, bi-, and trimetallic materials were synthesized, and nanoparticle size was controlled between 5 and 35 nm by modulating the lithography speed. Importantly, the polystyrene coating can be used on conventional substrates like Si/SiOx, as well as substrates typically more difficult to pattern on, such as glassy carbon, diamond, TiO2, BN, W, or SiC. Finally, high-throughput materials discovery is performed in the context of photocatalytic degradation of organic pollutants using Au–Pd–Cu nanoparticle megalibraries on TiO2 substrates with 2,250,000 unique composition/size combinations. The megalibrary was screened within 1 h by developing fluorescent thin-film coatings on top of the megalibrary as proxies for catalytic turnover, revealing Au0.53Pd0.38Cu0.09-TiO2 as the most active photocatalyst composition.
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