Dragos-Constantin Stoian

Related publications (10)

Alloying as a Strategy to Boost the Stability of Copper Nanocatalysts during the Electrochemical CO2 Reduction Reaction

Anastasia Blokhina, Raffaella Buonsanti, Anna Loiudice, Valery Okatenko, Kevin Rossi, Dragos-Constantin Stoian

2023

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A new solid-state method was used to introduce a furan-thiourea polymer into the pores of a MOF, Cr-BDC. Next, the activity of the new MOF-polymer composite containing Pd was assessed in the catalytic hydrodeoxygenation of vanillin, a biomass derived chemical.

ROYAL SOC CHEMISTRY2022

The native oxide skin of liquid metal Ga nanoparticles prevents their rapid coalescence during electrocatalysis

Raffaella Buonsanti, Laia Castilla Amorós, Anna Loiudice, Valery Okatenko, Dragos-Constantin Stoian, Jan Vávra

Liquid metals (LMs) have been used in electrochemistry since the 19th century, but it is only recently that they have emerged as electrocatalysts with unique properties, such as inherent resistance to coke-poisoning, which derives from the dynamic nature of their surface. The use of LM nanoparticles (NPs) as electrocatalysts is highly desirable to enhance any surface-related phenomena. However, LM NPs are expected to rapidly coalesce, similarly to liquid drops, which makes their implementation in electrocatalysis hard to envision. Herein, we demonstrate that liquid Ga NPs drive the electrochemical CO2 reduction reaction (CO2RR) while remaining well-separated from each other. The combination of electrochemical, microscopic and spectroscopic techniques, including operando X-Ray absorption, indicates that the unique properties of the native oxide skin of the Ga NPs account for their resistance to coalescence during operation. This discovery provides an avenue for future development of Ga-based LM NPs as a new class of electrocatalysts.

2022

A metal-organic framework/polymer derived catalyst containing single-atom nickel species for electrocatalysis

Mehrdad Asgari, Ilia Kochetygov, Wen Luo, Emadeddin Oveisi, Li Peng, Wendy Lee Queen, Dragos-Constantin Stoian, Daniel Teav Sun, Olga Trukhina, Shuliang Yang, Jie Zhang

While metal-organic frameworks (MOF) alone offer a wide range of structural tunability, the formation of composites, through the introduction of other non-native species, like polymers, can further broaden their structure/property spectrum. Here we demonstrate that a polymer, placed inside the MOF pores, can support the collapsible MOF and help inhibit the aggregation of nickel during pyrolysis; this leads to the formation of single atom nickel species in the resulting nitrogen doped carbons, and dramatically improves the activity, CO selectivity and stability in electrochemical CO(2)reduction reaction. Considering the vast number of multifarious MOFs and polymers to choose from, we believe this strategy can open up more possibilities in the field of catalyst design, and further contribute to the already expansive set of MOF applications.

ROYAL SOC CHEMISTRY2020

Exploring the Chemical Reactivity of Gallium Liquid Metal Nanoparticles in Galvanic Replacement

Raffaella Buonsanti, Laia Castilla Amorós, James Richard Pankhurst, Dragos-Constantin Stoian, Seyedehbehnaz Varandili

Micron/nanosized particles of liquid metals possess intriguing properties and are gaining popularity for applications in various research fields. Nevertheless, the knowledge of their chemistry is still very limited compared to that of other classes of materials. In this work, we explore the reactivity of Ga nanoparticles (NPs) toward a copper molecular precursor to synthesize bimetallic Cu-Ga NPs. Anisotropic Cu-Ga nanodimers, where the two segregated domains of the constituent metals share an interface, form as the reaction product. Through a series of careful experiments, we demonstrate that a galvanic replacement reaction (GRR) between the Ga seeds and a copper-amine complex takes place. We attribute the final morphology of the bimetallic NPs, which is unusual for a GRR, to the presence of the native oxide shell around the Ga NPs and their liquid nature, via a mechanism that resembles the adhesion of bulk Ga drops to solid conductors. On the basis of this new knowledge, we also demonstrate that sequential GRRs to include more metal domains are possible. This study illustrates a new approach to the synthesis of Ga-based metal nanoparticles and provides the basis for its extension to many more systems with increased levels of complexity.

AMER CHEMICAL SOC2020

Ligand-mediated formation of Cu/metal oxide hybrid nanocrystals with tunable number of interfaces

Raffaella Buonsanti, James Richard Pankhurst, Dragos-Constantin Stoian, Seyedehbehnaz Varandili, Jan Vávra

Combining domains of different chemical nature within the same hybrid material through the formation of heterojunctions provides the opportunity to exploit the properties of each individual component within the same nano-object; furthermore, new synergistic properties will often arise as a result of unique interface interactions. However, synthetic strategies enabling precise control over the final architecture of multicomponent objects still remain scarce for certain classes of materials. Herein, we report on the formation of Cu/MOx (M = Ce, Zn and Zr) hybrid nanocrystals with a tunable number of interfaces between the two domains. We demonstrate that the organic ligands employed during the synthesis play a key role in regulating the final configuration. Finally, we show that the synthesized nanocrystals serve as materials platforms to investigate the impact of the Cu/metal oxide interfaces in applications by focusing on the electrochemical CO2 reduction reaction as one representative example.

2020

Nanocrystals as Precursors in Solid-State Reactions for Size- and Shape-Controlled Polyelemental Nanomaterials

Raffaella Buonsanti, Laia Castilla Amorós, Chethana Janardhana Gadiyar, Pranit Srinivas Iyengar, Anna Loiudice, Valeria Mantella, Emadeddin Oveisi, Dragos-Constantin Stoian

Solid-state reactions between micrometer-size powders are among the oldest, simplest, and still widely used methods for the fabrication of inorganic solids. These reactions are intrinsically slow because, although the precursorsare "well mixed" at the macroscale, they are highly inhomogeneous at the atomic level. Furthermore, their products are bulk powders that are not suitable for device integration. Herein, we substitute micrometersize particles with nanocrystals. Scaling down the size of the precursors reduces the reaction time and temperature. More importantly, the final products are nanocrystals with controlled size and shape that can be used as active materials in various applications, including electro- and photocatalysis. The assembly of the nanocrystal precursors as ordered close-packed superlattices enables microscopy studies that deepen the understanding of the solid-state reaction mechanism. We learn that having only one of the two nanocrystal precursors dissolving and diffusing toward the other is crucial to obtain a final nanocrystalline product with homogeneous size and shape. The latter are regulated by the nanocrystal precursor that is the most stable at the reaction temperature. Considering the variety of controlled nanocrystals available, our findings open a new avenue for the synthesis of functional and tunable polyelemental nanomaterials.

AMER CHEMICAL SOC2020

Polymer Lamellae as Reaction Intermediates in the Formation of Copper Nanospheres as Evidenced by In Situ X-ray Studies

Raffaella Buonsanti, Kilian Frank, Chethana Janardhana Gadiyar, Valeria Mantella, James Richard Pankhurst, Dragos-Constantin Stoian, Michal Stanislaw Strach

The classical nucleation theory (CNT) is the most common theoretical framework used to explain particle formation. However, nucleation is a complex process with reaction pathways which are often not covered by the CNT. Herein, we study the formation mechanism of copper nanospheres using in situ X-ray absorption and scattering measurements. We reveal that their nucleation involves coordination polymer lamellae as pre-nucleation structures occupying a local minimum in the reaction energy landscape. Having learned this, we achieved a superior monodispersity for Cu nanospheres of different sizes. This report exemplifies the importance of developing a more realistic picture of the mechanism involved in the formation of inorganic nanoparticles to develop a rational approach to their synthesis.

WILEY-V C H VERLAG GMBH2020

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Size, morphology, and surface sites of electrocatalysts have a major impact on their performance. Understanding how, when, and why these parameters change under operating conditions is of importance for designing stable, active, and selective catalysts. Herein, we study the reconstruction of a Cu-based nanocatalysts during the startup phase of the electrochemical CO2 reduction reaction by combining results from electrochemical in situ transmission electron microscopy with operando X-ray absorption spectroscopy. We reveal that dissolution followed by redeposition, rather than coalescence, is the mechanism responsible for the size increase and morphology change of the electrocatalyst. Furthermore, we point out the key role played by the formation of copper oxides in the process. Understanding of the underlying processes opens a pathway to rational design of Cu electro (re)deposited catalysts and to stability improvement for catalysts fabricated by other methods.

WILEY-V C H VERLAG GMBH2020

We compare two reactor setups commonly used to make operando measurements of catalyst behavior using X-rays in terms of the degree to which they may be considered to yield radial and axial isothermality. We use axial and radial Cu K-edge XANES mapping of copper containing zeolites after high temperature activation (773 K) in oxygen and subsequent exposure to methane (473 K), to demonstrate the ease with which it is possible to enter into substantially non isothermal situations using air blower systems of a type commonly utilized. The implications of these observations for the attainment of non-representative structure-function relations are discussed. We further show, using this chemistry and infrared imaging, how this unwanted situation can be ameliorated by adopting a different type of reactor and point out that, even in this case isothermality should not be taken for granted and should be actively verified prior to experimental investigation.

ROYAL SOC CHEMISTRY2019