Innovative materials
Operando Soft X-ray Absorption of LaMn1–xCoxO3 Perovskites for CO Oxidation
Abstract We employed operando soft X-ray absorption spectroscopy (XAS) to monitor the changes in the valence states and spin properties of LaMn1–xCoxO3 catalysts subjected to a mixture of CO and O2 at ambient pressure. Guided by simulations based on charge transfer multiplet theory, we quantitatively analyze the Mn and Co 2p XAS as well as the oxygen K-edge XAS spectra during the reaction process. The Mn sites are particularly sensitive to the catalytic reaction, displaying dynamics in their oxidation state. When Co doping is introduced (x ≤ 0.5), Mn oxidizes from Mn2+ to Mn3+ and Mn4+, while Co largely maintains a valence state of Co2+. In the case of LaCoO3, we identify high-spin and low-spin Co3+ species combined with Co2+. Our investigation underscores the importance to consider the spin and valence states of catalyst materials under operando conditions. Authors Qijun Che, Mahnaz Ghiasi, Luca Braglia, Matt LJ Peerlings, Silvia Mauri, Piero Torelli, Petra de Jongh, Frank MF de Groot Journal ACS Catalysis Date 12/07/2024 Consult the paper
Low-Temperature Methane Activation Reaction Pathways over Mechanochemically-Generated Ce4+/Cu+ Interfacial Sites
Abstract Methane is a valuable resource and its valorization is an important challenge in heterogeneous catalysis. Here it is shown that CeO2/CuO composite prepared by ball milling activates methane at a temperature as low as 250 °C. In contrast to conventionally prepared catalysts, the formation of partial oxidation products such as methanol and formaldehyde is also observed. Through an in situ Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) and operando Near Edge X-Ray Absorption Fine Structure Spectroscopy (NEXAFS) approach, it can be established that this unusual reactivity can be attributed to the presence of Ce4+/Cu+ interfaces generated through a redox exchange between Ce3+ and Cu2+ atoms facilitated by the mechanical energy supplied during milling. DFT modeling of the electronic properties confirms the existence of a charge transfer mechanism. These results demonstrate the effectiveness and distinctiveness of the mechanical approach in creating unique and resilient interfaces thereby enabling the optimization and refining of CeO2/CuO catalysts in methane activation reactions. Authors Silvia Mauri, Rudy Calligaro, Carlo Federico Pauletti, Matteo Farnesi Camellone, Marta Boaro, Luca Braglia, Stefano Fabris, Simone Piccinin, Piero Torelli, Alessandro Trovarelli Journal Small Date 11/06/2024 Consult the paper
On the origin of the improved hydrogen evolution reaction in Mn-and Co-doped MoS 2
Abstract In the field of hydrogen production, MoS2 demonstrates good catalytic properties for the hydrogen evolution reaction (HER) which improve when doped with metal cations. However, while the role of sulfur atoms as active sites in the HER is largely reported, the role of metal atoms (i.e. molybdenum or the dopant cations) has yet to be studied in depth. To understand the role of the metal dopant, we study MoS2 thin films doped with Co and Mn ions. We identify the contribution of the electronic bands of the Mn and Co dopants to the integral valence band of the material using in situ resonant photoemission measurements. We demonstrate that Mn and Co dopants act differently: Mn doping favors the shift of the S–Mo hybridized band towards the Fermi level, while in the case of Co doping it is the less hybridized Co band that shifts closer to the Fermi level. Doping with Mn increases the effectiveness of S as the active site, thus improving the HER, while doping with Co introduces the metallic site of Co as the active site, which is less effective in improving HER properties. We therefore clarify the role of the dopant cation in the electronic structure determining the active site for hydrogen adsorption/desorption. Our results pave the way for the design of efficient materials for hydrogen production via the doping route, which can be extended to different catalytic reactions in the field of energy applications. Authors Pasquale Orgiani, Luca Braglia, Vincent Polewczyk, Zhiwei Nie, Francesco Lavini, Shyni Punathum Chalil, Sandeep Kumar Chaluvadi, Piu Rajak, Floriana Morabito, Edvard Dobovičnik, Vittorio Foglietti, Piero Torelli, Elisa Riedo, Regina Ciancio, Nan Yang, Carmela Aruta Journal Nanoscale Date 25/05/2024 Consult the ppaer
Advanced Electrode Materials Based on Brownmillerite Calcium Ferrite for Li-Ion Batteries
Abstract Iron-based materials are considered potential anode materials for lithium-ion batteries thanks to their low cost, abundancy, non-flammability, good safety, environmental benignity, and high specific capacity. Here, a series of calcium iron oxides materials having brownmillerite structure (i. e., Ca2Fe2-xMxO5, where M=Mn, Ni and Cu and x=0 and 0.1) has been extensively studied for their use as conversion anodes in lithium cell. In particular, a mechanochemical approach has been used either to synthesize the samples and to prepare electrodes for the tests in lithium cell. Ca2Fe2O5 based electrodes proved excellent performance in lithium cell, approaching the theoretical capacity and being stable upon prolonged cycling (529 mAh g−1 at C/10 and a capacity retention of 81 % after 100 cycles). Through the use of ex-situ diffraction measurements, we have analyzed the conversion mechanism and proved the partial reversibility of its electrochemical reaction. Also, the incorporation of dopants into the structure of calcium iron oxide resulted in further improvement of its electrochemical performance as is the case of Mn doped sample that show a considerable specific capacity of 567 mAh g−1 and the capacity retention is almost 99 % after 100 cycles. Authors Guido Spanu, Arcangelo Celeste, Francesco Bozza, Emanuele Serra, Piero Torelli, Luca Braglia, Sergio Brutti, Priscilla Reale, Laura Silvestri Journal Batteries & Supercaps Date 18/05/2024 Consult the paper
Pulsed Laser Deposition using high-power Nd:YAG laser source operating at its first harmonics: recent approaches and advances
Abstract We report on the progress of Pulsed Laser Deposition growth of thin films by using a high-power Nd:YAG laser source. We demonstrate that by using the fundamental wavelength at 1064 nm, the congruent ablation of a large number of materials can be successfully achieved. Even if the infra-red radiation of the fundamental harmonics of Nd:YAG lasers – corresponding to impinging photons with energy of about 1.16 eV – is unexpectedly proved to be also absorbed by insulating materials characterized by a large value of the band-gap (e.g. 3.0 eV for rutile TiO2). Combined investigation of structural properties by transmission electron microscopy and scanning electron microscopy provides evidence of the very high-quality thin films grown by Nd:YAG lasers with no trace of precipitates and droplets over a scale of tens of micrometers. Authors S. K. Chaluvadi, S. Punathum Chalil, F. Mazzola, P. Rajak, P. Banerjee, D. Knez, R. Ciancio, G. Rossi, P. Orgiani Journal Proceedings of SPIE – The International Society for Optical Engineering Date 11/04/2024 Consult the paper
Nickel-and/or iron-based ceria-supported catalysts for CO oxidation in combustion exhaust gases
Abstract We present a series of Ni, Fe, and mixed NiFe-based catalysts, deposited onto ceria prepared with either soft templated (with CTAB) or hard templated (with SBA-15) syntheses. The prepared materials were thoroughly characterized with SEM, HRTEM, EDX, ICP-MS, PXRD, and N2 adsorption techniques, to fully comprehend their physicochemical properties. All catalysts were then tested for carbon monoxide oxidation reaction at different temperatures, aiming to reach temperature and feed composition conditions typical of combustion exhausts from industrial and power plants (350–400 °C, in the presence of competitive species such as CO2 and H2O in the feed). Advanced reaction tests highlighted outstanding materials (especially NiFe catalyst deposited onto hard-templated ceria), displaying catalytic performances able to compete with those typical of noble metal–based catalysts. Such catalysts were further investigated by means of Raman, NEXAFS, H2–TPR, and CO@FT-IR, unraveling their surface and reduction properties, which make them excellent candidates for replacing more costly noble metal-based catalysts currently employed for CO oxidation reaction. Authors Andrea Lazzarini, Luciano Atzori, Matteo Signorile, Luca Braglia, Francesco Ferella, Maria Giorgia Cutrufello, Elisabetta Rombi, Marcello Crucianelli Journal Journal of Catalysis Date 24/01/2024 Consult the paper
Peptide Stereochemistry Effects from pKa-Shift to Gold Nanoparticle Templating in a Supramolecular Hydrogel
Abstract The divergent supramolecular behavior of a series of tripeptide stereoisomers was elucidated through spectroscopic, microscopic, crystallographic, and computational techniques. Only two epimers were able to effectively self-organize into amphipathic structures, leading to supramolecular hydrogels or crystals, respectively. Despite the similarity between the two peptides’ turn conformations, stereoconfiguration led to different abilities to engage in intramolecular hydrogen bonding. Self-assembly further shifted the pKa value of the C-terminal side chain. As a result, across the pH range 4–6, only one epimer predominated sufficiently as a zwitterion to reach the critical molar fraction, allowing gelation. By contrast, the differing pKa values and higher dipole moment of the other epimer favored crystallization. The four stereoisomers were further tested for gold nanoparticle (AuNP) formation, with the supramolecular hydrogel being the key to control and stabilize AuNPs, yielding a nanocomposite that catalyzed the photodegradation of a dye. Importantly, the AuNP formation occurred without the use of reductants other than the peptide, and the redox chemistry was investigated by LC–MS, NMR, and infrared scattering-type near field optical microscopy (IR s-SNOM). This study provides important insights for the rational design of simple peptides as minimalistic and green building blocks for functional nanocomposites. Authors Simone Adorinni, Serena Gentile, Ottavia Bellotto, Slavko Kralj, Evelina Parisi, Maria C. Cringoli, Caterina Deganutti, Giuliano Malloci, Federica Piccirilli, Paolo Pengo, Lisa Vaccari, Silvano Geremia, Attilio V. Vargiu, Rita De Zorzi, Silvia Marchesan Journal ACS Nano Publication date 18/01/2024 Consult the publication
Synthesis, characterization, functional testing and ageing analysis of bifunctional Zn-air battery GDEs, based on α-MnO2 nanowires and Ni/NiO nanoparticle electrocatalysts
Abstract Electrically rechargeable alkaline zinc air batteries (RZAB) – currently still at the R&D stage –, have great potential for stationary, as well as prospectively mobile, electrochemical energy storage applications. Their chief appeal is that they are made of abundant, environmentally friendly, intrinsically safe, and cheap materials, with established recycling concepts and auspicious life-cycle costs. One of the key weak points of present-generation RZAB programs is the air gas-diffusion electrode (GDE). In fact, on the one hand, GDE fabrication and testing are generally based on poorly understood protocols, and, on the other hand, performance is challenged by efficiency and durability issues. This work is centred on the fabrication of a novel bifunctional GDE for the air side of RZABs, on the assessment of its electrochemical performance and on the identification of factors impacting its efficiency and durability. The electrocatalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are α-MnO2 nanowires and Ni/NiO nanoparticles, respectively. The composition of the active layer was optimized with rotating ring-disc electrode (RRDE) electrocatalysts tests. The GDEs were fabricated by spray-coating an ink, formulated with the electrocatalysts and the PTFE binder in an aqueous matrix. Fabrication and functional performance of GDEs – in pristine form and after ageing under realistic RZAB conditions – are rationalized on the basis of Scanning Electron Microscopy (SEM), Scanning Transmission X-ray SpectroMicroscopy (STXSM) at the Mn l-edge and Transmission Electron Microscopy (TEM) analyses. Imaging and spectral imaging disclosed the morphological and chemical-state evolution, brought about by electrochemical cycling. Special attention was devoted to the understanding of the role played by the presence of zincate in the electrolyte on the performance and ageing of the reversible air electrodes. Authors Salman Y., Waseem S., Alleva A., Banerjee P., Bonanni V., Emanuele E., Ciancio R., Gianoncelli A., Kourousias G., Li Bassi A., Macrelli A, Marini E., Rajak P., Bozzini B., Journal Electrochimica Acta Date 20/11/2023 Consult the paper
Unveiling the Electronic Structure of Pseudotetragonal WO3 Thin Films
Abstract WO3 is a 5d compound that undergoes several structural transitions in its bulk form. Its versatility is well-documented, with a wide range of applications, such as flexopiezoelectricity, electrochromism, gating-induced phase transitions, and its ability to improve the performance of Li-based batteries. The synthesis of WO3 thin films holds promise in stabilizing electronic phases for practical applications. However, despite its potential, the electronic structure of this material remains experimentally unexplored. Furthermore, its thermal instability limits its use in certain technological devices. Here, we employ tensile strain to stabilize WO3 thin films, which we call the pseudotetragonal phase, and investigate its electronic structure using a combination of photoelectron spectroscopy and density functional theory calculations. This study reveals the Fermiology of the system, notably identifying significant energy splittings between different orbital manifolds arising from atomic distortions. These splittings, along with the system’s thermal stability, offer a potential avenue for controlling inter- and intraband scattering for electronic applications. Authors Mazzola F., Hassani H., Amoroso D., Chaluvadi S.K., Fujii J., Polewczyk V., Rajak P., Koegler M. Ciancio R., Partoens B., Rossi G., Vobornik I., Ghosez P. and Orgiani P. Journal Journal of Physical Chemistry Letters Date 08/08/2023 Consult the paper
The Interaction of Amines with Gold Nanoparticles
Abstract Here, we present an integrated ultra-high-vacuum (UHV) apparatus for the growth of complex materials and heterostructures. The specific growth technique is the Pulsed Laser Deposition (PLD) by means of a dual-laser source based on an excimer KrF ultraviolet and solid-state Nd:YAG infra-red lasers. By taking advantage of the two laser sources—both lasers can be independently used within the deposition chambers—a large number of different materials—ranging from oxides to metals, to selenides, and others—can be successfully grown in the form of thin films and heterostructures. All of the samples can be in situ transferred between the deposition chambers and the analysis chambers by using vessels and holders’ manipulators. The apparatus also offers the possibility to transfer samples to remote instrumentation under UHV conditions by means of commercially available UHV-suitcases. The dual-PLD operates for in-house research as well as user facility in combination with the Advanced Photo-electric Effect beamline at the Elettra synchrotron radiation facility in Trieste and allows synchrotron-based photo-emission as well as x-ray absorption experiments on pristine films and heterostructures. Authors Yanchao Lyu, Lucia Morillas Becerril, Mirko Vanzan, Stefano Corni, Mattia Cattelan, Gaetano Granozzi, Marco Frasconi, Piu Rajak, Pritam Banerjee, Fabrizio Mancin, Paolo Scrimin Journal Advanced Materials Date 23/03/2023 Consult the paper
Evidence of silicide at the Ni/ β-Si3N4(0001)/Si(111) interface
Abstract We present a study of a sub-nanometre interlayer of crystalline silicon nitride at the Ni/Si interface. We performed transmission electron microscopy measurements complemented by energy dispersive X-ray analysis to investigate to what extent the nitride layer act as a barrier against atom diffusion. The results show that discontinuous silicide areas can form just below the nitride layer, whose composition is compatible with that of the nickel disilicide. The Ni–Si reaction is tentatively attributed to the thermal strain suffered by the interface during the deposition of Ni at low temperature. Authors Piu Rajak, Regina Ciancio, Antonio Caretta, Simone Laterza, Richa Bhardwaj, Matteo Jugovac, Marco Malvestuto, Paolo Moras, Roberto Flammini Journal Applied Surface Science Date 13/03/2023 Consult the paper
Nd:YAG infrared laser as a viable alternative to excimer laser: YBCO case study
Abstract We report on the growth and characterization of epitaxial YBa2Cu3O7−δ (YBCO) complex oxide thin films and related heterostructures exclusively by Pulsed Laser Deposition (PLD) and using first harmonic Nd:Y3Al5O12 (Nd:YAG) pulsed laser source (λ = 1064 nm). High-quality epitaxial YBCO thin film heterostructures display superconducting properties with transition temperature ∼ 80 K. Compared with the excimer lasers, when using Nd:YAG lasers, the optimal growth conditions are achieved at a large target-to-substrate distance d. These results clearly demonstrate the potential use of the first harmonic Nd:YAG laser source as an alternative to the excimer lasers for the PLD thin film community. Its compactness as well as the absence of any safety issues related to poisonous gas represent a major breakthrough in the deposition of complex multi-element compounds in form of thin films. Authors Sandeep Kumar Chaluvadi, Shyni Punathum Chalil, Federico Mazzola, Simone Dolabella, Piu Rajak, Marcello Ferrara, Regina Ciancio, Jun Fujii, Giancarlo Panaccione, Giorgio Rossi & Pasquale Orgiani Journal Scientific Reports Date 08/03/2023 Consult the paper