James Richard Pankhurst

Related publications (10)

Modulating the Reactivity of Liquid Ga Nanoparticle Inks by Modifying Their Surface Chemistry

Raffaella Buonsanti, Laia Castilla Amorós, Tzu-Chin Chang Chien, James Richard Pankhurst

Micro- and nanosized particles of liquid metals, particularly Ga-based alloys, are attracting increasing attention for applications in several fields. The surface functionalization of Ga-based nanoparticles (NPs) with organic ligands renders easily processable inks. However, little is known about the interaction of these molecules with the native oxide skin, which regulates many properties of liquid metal NPs. Here, we investigate the impact of selected capping ligands on the native oxide thickness of Ga NPs and on their chemical reactivity, choosing the galvanic replacement reaction (Go) as one example. We demonstrate that amines and carboxylic acids promote thicker oxide shells while thiols and phosphines hinder the oxide growth. Upon pondering thermodynamics and kinetics factors, we conclude the affinity of the anchoring group toward the metal core being the major driver in determining the oxide thickness. We go on to prove that thicker shells foster the formation of Cu-Ga nanodimers following the reaction of the Ga NPs with a copper-amine complex. In contrast, thinner oxides lead to formation of isolated Cu NPs. This study reveals the importance of the choice of ligand when studying Ga-based metal NPs for different applications since both their surface chemistry and reactivity are largely affected by this decision.

AMER CHEMICAL SOC2022

Copper Nanocrystal Morphology Determines the Viability of Molecular Surface Functionalization in Tuning Electrocatalytic Behavior in CO2 Reduction

Raffaella Buonsanti, Pranit Srinivas Iyengar, Valery Okatenko, James Richard Pankhurst

Molecular surface functionalization of metallic catalysts is emerging as an ever-developing approach to tuning their catalytic performance. Here, we report the synthesis of hybrid catalysts comprising copper nanocrystals (CuNCs) and an imidazolium ligand for the electrochemical CO2 reduction reaction (CO2RR). We show that this organic modifier steers the selectivity of cubic CuNCs toward liquid products. A comparison between cubic and spherical CuNCs reveals the impact of surface reconstruction on the viability of surface functionalization schemes. Indeed, the intrinsic instability of spherical CuNCs leads to ejection of the functionalized surface atoms. Finally, we also demonstrate that the more stable hybrid nanocrystal catalysts, which include cubic CuNCs, can be transferred into gas-flow CO2RR cells for testing under more industrially relevant conditions.

AMER CHEMICAL SOC2021

Theory-Guided Enhancement of CO2 Reduction to Ethanol on Ag-Cu Tandem Catalysts via Particle-Size Effects

Raffaella Buonsanti, Pranit Srinivas Iyengar, James Richard Pankhurst

In the CO2 reduction reaction, the design of electrocatalysts that selectively promote alcohols over hydrocarbons (e.g., ethanol over ethylene) hinges on the understanding of the pathways and specific sites that form alcohols. Herein, theoretical considerations guide state-of-the-art synthesis of well-defined catalysts to show that higher selectivity toward ethanol is achieved on Cu(110) edge sites compared to Cu(100) terraces. Specifically, we study the catalytic behavior of Cu nano-cubes (Cu-cub) of different sizes in the framework of tandem catalysis with CO-producing Ag nano-spheres. We predict and experimentally find that the smaller Cu-cub possess higher selectivity for ethanol in view of their larger edge-to-faces ratio and of the fact that ethylene is produced at terraces while ethanol is selectively produced at step edges. These results call for synthetic developments toward Cu nanostructures exposing only edge sites, such as hollow cubic nanocages, to further increase ethanol selectivity. More generally, this study encourages the application of well-defined nano catalysts as a bridge between theory and experiments in electrocatalysis.

AMER CHEMICAL SOC2021

Colloidal Synthesis of Cu-M-S (M = V, Cr, Mn) Nanocrystals by Tuning the Copper Precursor Reactivity

Raffaella Buonsanti, Valeria Mantella, James Richard Pankhurst, Seyedehbehnaz Varandili

New ternary and higher order inorganic materials are needed for a large variety of applications, yet their synthesis still represents a chemistry challenge. Herein, we focus on the synthesis of Cu-M-S nanocrystals (where M = V, Cr, Mn) via a wet-chemistry route and investigate their formation mechanisms. We reveal that the interplay between the copper precursor and the thiophilicity of the transition metal M is the key for the synthesis of pure phase Cu-M-S nanocrystals under the same reaction conditions. In particular, we observe that the interdiffusion kinetics of the intermediate species is crucial, and the extent of nucleation of the ternary product can be controlled by the copper precursor reactivity. The insights provided by this work contribute to open up new avenues toward the design of improved synthesis strategies to multinary nanocrystalline compounds.

AMER CHEMICAL SOC2020

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

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

Insights into Reaction Intermediates to Predict Synthetic Pathways for Shape-Controlled Metal Nanocrystals

Raffaella Buonsanti, Shubhajit Das, Pranit Srinivas Iyengar, Anna Loiudice, Valeria Mantella, James Richard Pankhurst, Michal Stanislaw Strach

Understanding nucleation phenomena is crucial across all branches of physical and natural sciences. Colloidal nanocrystals are among the most versatile and tunable synthetic nanomaterials. While huge steps have been made in their synthetic development, synthesis by design is still impeded by the lack of knowledge of reaction mechanisms. Here, we report on the investigation of the reaction intermediates in high temperature syntheses of copper nanocrystals by a variety of techniques, including X-ray absorption at a synchrotron source using a customized in situ cell. We reveal unique insights into the chemical nature of the reaction intermediates and into their role in determining the final shape of the metal nanocrystals. Overall, this study highlights the importance of understanding the chemistry behind nucleation as a key parameter to predict synthetic pathways for shape-controlled nanocrystals.

AMER CHEMICAL SOC2019

Molecular tunability of surface-functionalized metal nanocrystals for selective electrochemical CO2 reduction

Raffaella Buonsanti, Yannick Thomas Guntern, Mounir Driss Mensi, James Richard Pankhurst

Organic ligands are used in homogeneous catalysis to tune the metal center reactivity; in contrast, clean surfaces are usually preferred in heterogeneous catalysis. Herein, we demonstrate the potential of a molecular chemistry approach to develop efficient and selective heterogeneous catalysts in the electrochemical CO2 reduction reaction (CO2RR). We have tailor-made imidazolium ligands to promote the CO2RR at the surface of hybrid organic/inorganic electrode materials. We used silver nanocrystals for the inorganic component to obtain fundamental insights into the delicate tuning of the surface chemistry offered by these ligands. We reveal that modifying the electronic properties of the metal surface with anchor groups along with the solid/liquid interface with tail groups is crucial in obtaining selectivities (above 90% FE for CO), which are higher than the non-functionalized Ag nanocrystals. We also show that there is a unique dependency of the CO2RR selectivity on the length of the hydrocarbon tail of these ligands, offering a new way to tune the interactions between the metal surface with the electrolyte and reactants.

ROYAL SOC CHEMISTRY2019

Nanocrystal/Metal–Organic Framework Hybrids as Electrocatalytic Platforms for CO2 Conversion

Raffaella Buonsanti, Yannick Thomas Guntern, Valeria Mantella, Mounir Driss Mensi, James Richard Pankhurst, Pascal Alexander Schouwink, Jan Vávra

The tunable chemistry linked to the organic/inorganic components in colloidal nanocrystals (NCs) and metal–organic frameworks (MOFs) offers a rich playground to advance the fundamental understanding of materials design for various applications. Herein, we combine these two classes of materials by synthesizing NC/MOF hybrids comprising Ag NCs that are in intimate contact with Al‐PMOF ([Al2(OH)2(TCPP)]) (tetrakis(4‐carboxyphenyl)porphyrin (TCPP)), to form Ag@Al‐PMOF. In our hybrids, the NCs are embedded in the MOF while still preserving electrical contact with a conductive substrate. This key feature allows the investigation of the Ag@Al‐PMOFs as electrocatalysts for the CO2 reduction reaction (CO2RR). We show that the pristine interface between the NCs and the MOFs accounts for electronic changes in the Ag, which suppress the hydrogen evolution reaction (HER) and promote the CO2RR. We also demonstrate a minor contribution of mass‐transfer effects imposed by the porous MOF layer under the chosen testing conditions. Furthermore, we find an increased morphological stability of the Ag NCs when combined with the Al‐PMOF. The synthesis method is general and applicable to other metal NCs, thus revealing a new way to think about rationally tailored electrocatalytic materials to steer selectivity and improve stability.

2019