Laia Castilla Amorós

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

Galvanic replacement reactions of Ga and In with Cu for the synthesis of bimetallic nanoparticles

Laia Castilla Amorós

The need for efficient and selective catalysts, capable of driving important conversions to build a more sustainable society, encourages the development of synthetic approaches towards new nanomaterials. Cu-based bimetallic nanoparticles (NPs) promise to fulfill this gap by selectively producing energy-dense products via CO2 electroreduction (CO2RR). However, as small variations in its composition and configuration can enormously affect the catalyst performance, the vast diversity of bimetallic NPs challenges systematic catalyst evaluation. Colloidal bimetallic NPs serve as an ideal platform for the exploration of composition-configuration-property relationships, necessary for rational catalyst design. Although an extensive library of noble metal bimetallic NPs exists, much less has been done regarding non-noble Cu-based bimetallic NPs despite their potential as catalysts for CO2RR. The aim of this thesis is to advance in the synthesis of Cu-based NPs, with focus on Cu-Ga and Cu-In, which have been predicted or demonstrated to possess interesting catalytic properties.The thesis starts with an introduction on bimetallic NPs and the different colloidal approaches to synthesize them. Galvanic replacement reactions (GRRs) are discussed more in details, as they are the synthetic approach of choice for the Cu-Ga and Cu-In NPs. Ga and In belong to a family of liquid metals; thus, information on their general properties is also provided. The first two experimental chapters focus on the reactivity and surface chemistry of Ga NPs. Chapter 3 demonstrates that Ga NPs react with a copper-amine complex to form anisotropic Cu-Ga nanodimers (NDs). Mechanistic studies reveal that a GRR takes place. Yet, the ND morphology differs from the more typical hollow core@shell structures obtained from GRRs. This unusual morphology is attributed to the liquid nature of Ga NPs and to the presence of a native oxide shell. This discovery fostered a follow up study, which is discussed in Chapter 4. The effect of the chemical nature of the capping ligand on the oxide thickness and reactivity of the Ga NPs is investigated. The thickness of the oxide skin is found to greatly depend on the ligands. Specifically, amines and carboxylic acids promote thicker oxide shells while thiols and phosphines hinder its growth. The reaction between Ga NPs with different oxide thickness and the copper precursor leads to a surprising result, while thicker oxides cause the formation of NDs, isolated Cu NPs form with thinner oxides.Chapter 5 turns towards Cu-In NPs. Following the same synthetic scheme, In NPs with different sizes are exploited as sacrificial seeds for the GRR. Cu-In NPs with an unprecedented variety of morphologies and elemental distributions are obtained: spherical Cu11In9 intermetallic and patchy phase-segregated Cu-In NPs, as well as Cu-Cu11In9 and Cu-In NDs. Segregation of the two metals occurs as the GRR progresses, with time or with higher copper precursor concentration. Comparing the obtained results with the Cu-In phase diagram reveals that the bigger seeds stabilize the bulk-like Cu-Cu11In9 configuration before their complete segregation into Cu-In NDs. Aiding in the development of more predictive synthetic approaches.Finally, Chapter 6 concludes by summarizing the significance of the achievements, which advance the knowledge on underexplored bimetallic NPs and on the GRR when applied beyond noble metals. An outlook on future developments is also provided.

EPFL2022

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

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

Galvanic replacement reactions of Ga and In with Cu for the synthesis of bimetallic nanoparticles

Laia Castilla Amorós

EPFL2022