Publications related to Nanochemistry Laboratory for Energy

Tandem electrocatalytic CO2 reduction with Fe-porphyrins and Cu nanocubes enhances ethylene production

Raffaella Buonsanti, Anna Loiudice, Min Wang

Copper-based tandem schemes have emerged as promising strategies to promote the formation of multi-carbon products in the electrocatalytic CO2 reduction reaction. In such approaches, the CO-generating component of the tandem catalyst increases the local concentration of CO and thereby enhances the intrinsic carbon-carbon (C-C) coupling on copper. However, the optimal characteristics of the CO-generating catalyst for maximizing the C-2 production are currently unknown. In this work, we developed tunable tandem catalysts comprising iron porphyrin (Fe-Por), as the CO-generating component, and Cu nanocubes (Cucub) to understand how the turnover frequency for CO (TOFCO) of the molecular catalysts impacts the C-C coupling on the Cu surface. First, we tuned the TOFCO of the Fe-Por by varying the number of orbitals involved in the pi-system. Then, we coupled these molecular catalysts with the Cu-cub and assessed the current densities and faradaic efficiencies. We discovered that all of the designed Fe-Por boost ethylene production. The most efficient Cu-cub/Fe-Por tandem catalyst was the one including the Fe-Por with the highest TOFCO and exhibited a nearly 22-fold increase in the ethylene selectivity and 100 mV positive shift of the onset potential with respect to the pristine Cu-cub. These results reveal that coupling the TOFCO tunability of molecular catalysts with copper nanocatalysts opens up new possibilities towards the development of Cu-based catalysts with enhanced selectivity for multi-carbon product generation at low overpotential.

ROYAL SOC CHEMISTRY2022

Structural characterisation of nanoalloys for (photo)catalytic applications with the Sapphire library

Kevin Rossi

A non-trivial interplay rules the relationship between the structure and the chemophysical properties of a nanoparticle. In this context, characterization experiments, molecular dynamics simulations and electronic structure calculations may allow the variables that determine a given property to be pinpointed. Conversely, a rigorous computational characterization of the geometry and chemical ordering of metallic nanoparticles and nanoalloys enables discrimination of which descriptors could be linked with their stability and performance. To this end, we introduce a modular and open-source library, Sapphire, which may classify the structural characteristics of a given nanoparticle through several structural analysis techniques and order parameters. A special focus is geared towards using geometrical descriptors to make predictions on a given nanoparticle's catalytic activity.

ROYAL SOC CHEMISTRY2022

2022 roadmap on low temperature electrochemical CO2 reduction

Etienne Boutin, Raffaella Buonsanti, Sophia Haussener, Xuan Liu, Ming Ma, Ludmilla Steier, Xiaoyan Wang

Electrochemical CO2 reduction (CO2R) is an attractive option for storing renewable electricity and for the sustainable production of valuable chemicals and fuels. In this roadmap, we review recent progress in fundamental understanding, catalyst development, and in engineering and scale-up. We discuss the outstanding challenges towards commercialization of electrochemical CO2R technology: energy efficiencies, selectivities, low current densities, and stability. We highlight the opportunities in establishing rigorous standards for benchmarking performance, advances in in operando characterization, the discovery of new materials towards high value products, the investigation of phenomena across multiple-length scales and the application of data science towards doing so. We hope that this collective perspective sparks new research activities that ultimately bring us a step closer towards establishing a low- or zero-emission carbon cycle.

IOP Publishing Ltd2022

High-Throughput Sizing, Counting, and Elemental Analysis of Anisotropic Multimetallic Nanoparticles with Single-Particle Inductively Coupled Plasma Mass Spectrometry

Ayush Agarwal, Natalia Gasilova, Cedric David Koolen, Mo Li, Wen Luo, Andreas Züttel

Nanoparticles (NPs) have wide applications in physical and chemical processes, and their individual properties (e.g., shape, size, and composition) and ensemble properties (e.g., distribution and homogeneity) can significantly affect the performance. However, the extrapolation of information from a single particle to the ensemble remains a challenge due to the lack of suitable techniques. Herein, we report a high-throughput single-particle inductively coupled plasma mass spectrometry (SP-ICP-MS)-based protocol to simultaneously determine the size, count, and elemental makeup of several thousands of (an)isotropic NPs independent of composition, size, shape, and dispersing medium with atomistic precision in a matter of minutes. By introducing highly diluted nebulized aqueous dispersions of NPs directly into the plasma torch of an ICP-MS instrument, individual NPs are atomized and ionized, resulting in ion plumes that can be registered by the mass analyzer. Our proposed protocol includes a phase transfer step for NPs synthesized in organic media, which are otherwise incompatible with ICP-MS instruments, and a modeling tool that extends the measurement of particle morphologies beyond spherical to include cubes, truncated octahedra, and tetrahedra, exemplified by anisotropic Cu NPs. Finally, we demonstrate the versatility of our method by studying the doping of bulk-dilute (

2022

Solid-state synthesis of a MOF/polymer composite for hydrodeoxygenation of vanillin

Vikram Vinayak Karve, Wendy Lee Queen, Dragos-Constantin Stoian, Olga Trukhina

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

Tandem effect of Ag@C@Cu catalysts enhances ethanol selectivity for electrochemical CO2 reduction in flow reactors

Youngdon Ko, Cedric David Koolen, Mo Li, Wen Luo, Thi Ha My Pham, Jie Zhang, Liping Zhong, Andreas Züttel

CO-selective metals (e.g., Ag) on Cu catalysts improve the selec-tivity of multi-carbon (C2+) products in electrochemical CO2 reduc-tion. However, the origin of the improvement remains unclear due to the convolution of tandem and interface effects. Here, Ag@C@Cu core-shell catalysts were synthesized, in which the thin carbon interlayer inhibited the direct interaction between Ag and Cu while still allowing the reduction of CO2 on Ag, thus isolating the tandem effect from other effects. This catalyst produced higher ratios of ethanol to ethylene relative to the monometallic Cu catalyst, demonstrating that the locally increased CO concentration promoted the ethanol pathway over the ethylene pathway. Further, the selectivity of ethanol was optimized by tuning the thickness of the Cu shell. This work provides a rational approach to design core-shell catalysts for understanding structure-performance relationships and demonstrates the key role of the tandem effect in tuning the selectivity of C2+ products.

ELSEVIER2022

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

Accelerating the theoretical study of Li-polysulfide adsorption on single-atom catalysts via machine learning approaches

Kevin Rossi

Li-S batteries are a promising alternative to Li-ion batteries, offering large energy storage capacity and wide operating temperature range. However, their performance is heavily affected by the Li-polysulfide (LiPS) shuttling. Computational screening of LiPS adsorption on single-atom catalyst (SAC) substrates is of great aid to the design of Li-S batteries which are robust against the LiPS shuttling from the cathode to the anode and the electrolyte. To facilitate this process, we develop a machine learning (ML) protocol to accelerate the systematic mapping of dominant local energy minima found with calculations based on the density functional theory (DFT), and, in turn, fast screening of LiPS adsorption properties on SACs. We first validate the approach by probing the potential energy surface for LiPS adsorbed on graphene decorated with a Fe-N-4-C SAC. We identify minima whose binding energies are better or on par with the one previously reported in the literature. We then move to analyze the adsorption trends on Zn-N-4-C SAC and observe similar adsorption strength and behavior with the Fe-N-4-C SAC, highlighting the good predictive power of our protocol. Our approach offers a comprehensive and computationally efficient alternative to conventional approaches studying LiPS adsorption.

WILEY2022

Electrochemical reduction of carbon dioxide is a promising approach to decrease the amount of anthropogenic CO2 being released into the atmosphere, provided that a surplus of renewable electrical energy is available. Copper based materials are at the center of attention as a catalyst to this reaction. The exact atomic arrangement of the Cu surface determines the selectivity and activity of the electrochemical reaction. However, recent evidence reports morphology changes of the Cu catalyst surface during the course the reaction. This thesis investigates the operational stability of Cu catalysts with various in-situ techniques, particularly liquid cell TEM, which was adapted to electrochemical CO2 reduction reaction so that it provides morphological and structural information on the catalyst in real-time. Two distinct stages contributing to the reconstruction of Cu catalysts are identified. In the first stage, the catalyst dissolves and spontaneously oxidizes during its contact with the reaction environment. As the reducing potential is applied, the initially dissolved Cu deposits back onto the working electrode. In the second stage, during the catalyst operation at reducing potentials, the dissolution/redeposition continues in the close vicinity of the catalyst surface. Formation of transient [CuCO]+ complexes is identified as the major process responsible for the operational dissolution of Cu catalysts. The provided mechanistic understanding of Cu catalyst (in)stability during electrochemical reduction of CO2 rationalizes the efforts in designing catalysts and electrolyzers with long-term stable operation and motivates further investigation on how to control the operational redeposition of Cu to continuously refresh the active surface motives.

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