Cation Dynamics as Structure Explorer in Hybrid Perovskites-The Case of MAPbI3.

Hybrid organic-inorganic perovskites exhibit remarkable potential as cost-effective and high-efficiency materials for photovoltaic applications. Their exceptional chemical tunability opens further routes for optimizing their optical and electronic properties through structural engineering. Nevertheless, the extraordinary softness of the lattice, stemming from its interconnected organic-inorganic composition, unveils formidable challenges in structural characterization. Here, by focusing on the quintessential methylammonium lead triiodide, MAPbI3, we combine first-principles modeling with high-resolution neutron scattering data to identify the key stationary points on its shallow potential energy landscape. This combined experimental and computational approach enables us to benchmark the performance of a collection of semilocal exchange-correlation functionals and to track the local distortions of the perovskite framework, hallmarked by the inelastic neutron scattering response of the organic cation. By conducting a thorough examination of structural distortions, we introduce the IKUR-PVP-1 structural data set. This data set contains nine mechanically stable structural models, each manifesting a distinct vibrational response. IKUR-PVP-1 constitutes a valuable resource for assessing thermal behavior in the low-temperature perovskite phase. In addition, it paves the way for the development of accurate force fields, enabling a comprehensive understanding of the interplay between the structure and dynamics in MAPbI3 and related hybrid perovskites.

Temperature and pH Stimuli-Responsive System Delivers Location-Specific Antimicrobial Activity with Natural Products.

Smart materials with controlled stimuli-responsive functions are at the forefront of technological development. In this work, we present a generic strategy that combines simple components, physicochemical responses, and easy fabrication methods to achieve a dual stimuli-responsive system capable of location-specific antimicrobial cargo delivery. The encapsulated system is fabricated by combining a biocompatible inert polymeric matrix of poly(dimethylsiloxane) (PDMS) and a bioactive cargo of saturated fatty acids. We demonstrate the effectiveness of our approach to deliver antimicrobial activity for the model bacteria Escherichia coli. The system responds to two control variables, temperature and pH, delivering two levels of antimicrobial response under distinct combinations of stimuli: one response toward the planktonic media and another response directly at the surface for sessile bacteria. Spatially resolved Raman spectroscopy alongside thermal and structural material analysis reveals that the system not only exhibits ON/OFF states but can also control relocation and targeting of the active cargo toward either the surface or the liquid media, leading to different ON/OFF states for the planktonic and sessile bacteria. The approach proposed herein is technologically simple and scalable, facing low regulatory barriers within the food and healthcare sectors by using approved components and relying on fundamental chemical processes. Our results also provide a proof-of-concept platform for the design and easy fabrication of delivery systems capable of operating as Boolean logic gates, delivering different responses under different environmental conditions.

Influence of Vacancies in Manganese Hexacyanoferrate Cathode for Organic Na-Ion Batteries: A Structural Perspective.

Manganese hexacyanoferrates (MnHCF) are promising positive electrode materials for non-aqueous batteries, including Na-ion batteries, due to their large specific capacity (>130 mAh g-1 ), high discharge potential and sustainability. Typically, the electrochemical reaction of MnHCF associates with phase and structural changes, due to the Jahn-Teller (JT) distortion of Mn sites upon the charge process. To understand the effect of the MnHCF structure on its electrochemical performance, two MnHCF materials with different vacancies content are investigated herein. The electrochemical results show that the sample with lower vacancy content (4 %) exhibits relatively higher capacity retention of 99.1 % and 92.6 % at 2nd and 10th cycles, respectively, with respect to 97.4 % and 79.3 % in sample with higher vacancy content (11 %). Ex-situ X-ray absorption spectroscopy (XAS) and ex situ X-ray diffraction (XRD) characterization results show that a weaker cooperative JT-distortion effect and relatively smaller crystal structure modification occurred for the material with lower vacancies, which explains the better electrochemical performance in cycled electrodes.

CO2 Separation by Imide/Imine Organic Cages.

Invited for the cover of this issue are the groups of Valeria Amendola at the University of Pavia, Mariolino Carta at the University of Swansea, and Johannes C. Jansen at the CNR-ITM. The image depicts one of the novel imide/imine organic cages that were employed as fillers in mixed-matrix membranes for the selective separation of CO2 from N2 and CH4 . Read the full text of the article at 10.1002/chem.202201631.

CO2 Separation by Imide/Imine Organic Cages.

Two novel imide/imine-based organic cages have been prepared and studied as materials for the selective separation of CO2 from N2 and CH4 under vacuum swing adsorption conditions. Gas adsorption on the new compounds showed selectivity for CO2 over N2 and CH4 . The cages were also tested as fillers in mixed-matrix membranes for gas separation. Dense and robust membranes were obtained by loading the cages in either Matrimid® or PEEK-WC polymers. Improved gas-transport properties and selectivity for CO2 were achieved compared to the neat polymer membranes.

Robust coherent spin centers from stable azafullerene radicals entrapped in cycloparaphenylene rings.

Molecular entities with robust spin-1/2 are natural two-level quantum systems for realizing qubits and are key ingredients of emerging quantum technologies such as quantum computing. Here we show that robust and abundant spin-1/2 species can be created in situ in the solid state from spin-active azafullerene C59N cages supramolecularly hosted in crystals of [10]cycloparaphenylene ([10]CPP) nanohoops. This is achieved via a two-stage thermally-assisted homolysis of the parent diamagnetic [10]CPP⊃(C59N)2⊂[10]CPP supramolecular complex. Upon cooling, the otherwise unstable C59N˙ radical is remarkably persistent with a measured radical lifetime of several years. Additionally, pulsed electron paramagnetic resonance measurements show long coherence times, fulfilling a basic condition for any qubit manipulation, and observed Rabi oscillations demonstrate single qubit operation. These findings together with rapid recent advances on the synthesis of carbon nanohoops offer the potential to fabricate tailored cycloparaphenylene networks hosting C59N˙ centers, providing a promising platform for building complex qubit circuits.

Structure-Tailored Non-Noble Metal-based Ternary Chalcogenide Nanocrystals for Pt-like Electrocatalytic Hydrogen Production.

A facile microwave-assisted strategy was employed to synthesize Ni3 Bi2 S2 nanocrystals. Variation in the synthesis conditions tuned the composition of monoclinic and orthorhombic phases of Ni3 Bi2 S2 . The electrochemical hydrogen evolution activity of the catalyst with highest percentage of monoclinic phase demonstrated a negligible onset potential of only 24 mV close to that of state-of-the-art Pt/C with an overpotential as low as 88 mV. Density functional theory calculations predicted the monoclinic phase exhibit the lowest adsorption free energy corresponding to hydrogen adsorption ( Δ G ads H * ) and, therefore, the highest hydrogen evolution activity amongst the considered phases. The quasi-2D structure of monoclinic phase facilitated an increased charge-transfer between Ni and Bi, favoring the downward shift of the d-band center to enhance the catalytic activity.

Dynamics & Spectroscopy with Neutrons-Recent Developments & Emerging Opportunities.

This work provides an up-to-date overview of recent developments in neutron spectroscopic techniques and associated computational tools to interrogate the structural properties and dynamical behavior of complex and disordered materials, with a focus on those of a soft and polymeric nature. These have and continue to pave the way for new scientific opportunities simply thought unthinkable not so long ago, and have particularly benefited from advances in high-resolution, broadband techniques spanning energy transfers from the meV to the eV. Topical areas include the identification and robust assignment of low-energy modes underpinning functionality in soft solids and supramolecular frameworks, or the quantification in the laboratory of hitherto unexplored nuclear quantum effects dictating thermodynamic properties. In addition to novel classes of materials, we also discuss recent discoveries around water and its phase diagram, which continue to surprise us. All throughout, emphasis is placed on linking these ongoing and exciting experimental and computational developments to specific scientific questions in the context of the discovery of new materials for sustainable technologies.

Large scale synthesis of copper nickel alloy nanoparticles with reduced compressibility using arc thermal plasma process.

Among the various methods employed in the synthesis of nanostructures, those involving high operating temperature and sharp thermal gradients often lead to the establishment of new exotic properties. Herein, we report on the formation of Cu-Ni metallic alloy nanoparticles with greatly enhanced stiffness achieved through direct-current transferred arc-thermal plasma assisted vapour-phase condensation. High pressure synchrotron X-ray powder diffraction (XRPD) at ambient temperature as well as XRPD in the temperature range 180 to 920 K, show that the thermal arc-plasma route resulted in alloy nanoparticles with much enhanced bulk modulus compared to their bulk counterparts. Such a behaviour may find an explanation in the sudden quenching assisted by the retention of a large amount of local strain due to alloying, combined with the perfect miscibility of the elemental components during the thermal plasma synthesis process.

In-Operando Diffraction and Spectroscopic Evaluation of Pure, Zr-, and Ce-Doped Vanadium Dioxide Thermochromic Films Derived via Glycolate Synthesis.

Pure and doped vanadia (VO2, V0.98Zr0.02O2, V0.98Ce0.02O2) samples were prepared by wet chemistry synthesis from vanadyl glycolate intermediate phase and tape casted into films. Combining in-operando grazing incidence synchrotron X-ray diffraction and Raman spectroscopy, we studied the structural evolution of the films under isothermal conditions. The setup allowed assessment of the thermochromic functionality with continuous monitoring of the monoclinic to tetragonal transition in pure and doped vanadia phases, responsible for the transmission and reflection of light in the infrared part of the solar spectrum. The materials characterisation by X-ray diffraction beamline (MCX) goniometer demonstrated ideal performance, combining flexible geometry, high resolution, and the potential to accommodate the multi-channel equipment for in-operando characterisation. This method proved viable for evaluating the relevant structural and physical, and thereof functional properties of these systems. We revealed that dopants reduce the transition temperature by 5 °C on average. The synthetic route of the films was held responsible for the observed phase separation. The more favourable behaviour of cerium-doped sample was attributed to cerium alkoxide behaviour. In addition, structural, microstructural, thermal, and spectroscopic characterisation on powder samples was performed to gain more insight into the development of the phases that are responsible for thermochromic features in a broader range of doping ratios. The influence of the dopants on the extent of the thermochromic transition (transmission to reflection hysteresis) was also evaluated using (micro) structural, thermal and spectroscopic methods of powder samples. Characterisations showed that zirconium doping in 2, 4, and 6 mol% significantly influenced the phase composition and morphology of the precursor. Vanadium oxides other than VO2 can easily crystallise; however, a thermal treatment regime that allowed crystallisation of VO2 as a single phase was established.

Titanium-based potassium-ion battery positive electrode with extraordinarily high redox potential.

The rapid progress in mass-market applications of metal-ion batteries intensifies the development of economically feasible electrode materials based on earth-abundant elements. Here, we report on a record-breaking titanium-based positive electrode material, KTiPO4F, exhibiting a superior electrode potential of 3.6 V in a potassium-ion cell, which is extraordinarily high for titanium redox transitions. We hypothesize that such an unexpectedly major boost of the electrode potential benefits from the synergy of the cumulative inductive effect of two anions and charge/vacancy ordering. Carbon-coated electrode materials display no capacity fading when cycled at 5C rate for 100 cycles, which coupled with extremely low energy barriers for potassium-ion migration of 0.2 eV anticipates high-power applications. Our contribution shows that the titanium redox activity traditionally considered as "reducing" can be upshifted to near-4V electrode potentials thus providing a playground to design sustainable and cost-effective titanium-containing positive electrode materials with promising electrochemical characteristics.

Optimal hydrogen storage in sodium substituted lithium fullerides.

Through the substitution of Li with Na in Li6C60, we synthesized a series of mixed alkali cluster intercalated fullerides, NaxLi6-xC60. These compounds share lattices of Na6C60 and Li6C60 with a cubic parameter linearly dependent on x. H2 absorption and desorption were studied by means of charge/discharge kinetic measurements and coupled calorimetric-manometric evaluation. By varying the stoichiometry, we found the best compromise among the absorption rate, temperature and amount of hydrogen for x = 0.5 and 1. Small concentrations of Na substituted to Li significantly lower the absorption temperature of Li6C60, improving the hydrogenation capacity, the kinetics, and the dehydrogenation enthalpy, the latter being 43.8 kJ mol-1 H2 for x = 1. This study moves further toward the utilization of intercalated fullerides for hydrogen storage applications.

Mechanisms of Sodium Insertion/Extraction on the Surface of Defective Graphenes.

Two chemically synthesized defective graphene materials with distinctly contrasting extended structures and surface chemistry are used to prepare sodium-ion battery electrodes. The difference in electrode performance between the chemically prepared graphene materials is qualified based on correlations with intrinsic structural and chemical dissimilarities. The overall effects of the materials' physical and chemical discrepancies are quantified by measuring the electrode capacities after repeated charge/discharge cycles. Solvothermal synthesized graphene (STSG) electrodes produce capacities of 92 mAh/g in sodium-ion batteries after 50 cycles at 10 mA/g, while thermally exfoliated graphite oxide (TEGO) electrodes produce capacities of 248 mAh/g after 50 cycles at 100 mA/g. Solid-state 23Na nuclear magnetic resonance spectroscopy is employed to locally probe distinct sodium environments on and between the surface of the graphene layers after charge/discharge cycles that are responsible for the variations in electrode capacities. Multiple distinct sodium environments of which at least 3 are mobile during the charge-discharge cycle are found in both cases, but the majority of Na is predominantly located in an immobile site, assigned to the solid electrolyte interface (SEI) layer. Mechanisms of sodium insertion and extraction on and between the defective graphene surfaces are proposed and discussed in relation to electrode performance. This work provides a direct account of the chemical and structural environments on the surface of graphene that govern the feasibility of graphene materials for use as sodium-ion battery electrodes.

Hydrogen motions in defective graphene: the role of surface defects.

Understanding the mobility of H at the surface of carbon nanostructures is one of the essential ingredients for a deep comprehension of the catalytic formation of H2 in interstellar clouds. In this paper, we combine neutron vibrational spectroscopy with DFT molecular dynamics simulations to study the local environment of H structures chemisorbed at the surface of disordered graphene sheets. At 5 K, the ground state is composed of large clusters of hydrogen chemisorbed at sp2 carbon sites, on the edges and in voids of the graphene sheets. At temperatures of ∼300 K, a high degree of dispersion of the clusters is observed, involving the breaking and reforming of covalent bonds which, at low temperatures, is mediated by incoherent tunnelling of hydrogen.

Structural rearrangements induced by acid-base reactions in metal carbonyl clusters: the case of [H(3-n)Co15Pd9C3(CO)38]n- (n = 0-3).

The new bimetallic [HCo15Pd9C3(CO)38](2-) tri-carbide carbonyl cluster has been obtained from the reaction of [H2Co20Pd16C4(CO)48](4-) with an excess of acid in CH2Cl2 solution. The mono-hydride di-anion can be reversibly protonated and deprotonated by means of acid-base reactions leading to closely related [H(3-n)Co15Pd9C3(CO)38](n-) (n = 0-3) clusters. The crystal structures of the three anionic and the neutral clusters have been determined as their H3Co15Pd9C3(CO)38·2thf, [NEt4][H2Co15Pd9C3(CO)38]·0.5C6H14, [NMe3(CH2Ph)]2[HCo15Pd9C3(CO)38]·C6H14 and [NEt4]3[Co15Pd9C3(CO)38]·thf salts. They are composed of a Pd9(µ3-CO)2 core stabilised by three Co5C(CO)12 organometallic fragments. The poly-hydride nature of these clusters has been indirectly inferred via chemical, electrochemical and magnetic measurements. Besides, cyclic voltammetry shows that the [H(3-n)Co15Pd9C3(CO)38](n-) (n = 1-3) anions are multivalent, since they undergo two or three reversible oxidations. SQUID measurements of [HCo15Pd9C3(CO)38](2-) indicate that this even electron cluster is paramagnetic with two unpaired electrons, giving further support to its hydride nature. Finally, structural studies show that the Pd9 core of [H(3-n)Co15Pd9C3(CO)38](n-) (n = 0,1) is a tri-capped octahedron, which becomes a tri-capped trigonal prism in the more charged [H(3-n)Co15Pd9C3(CO)38](n-) (n = 2,3) anions. Such a significant structural rearrangement of the metal core of a large carbonyl cluster upon protonation-deprotonation reactions is unprecedented in cluster chemistry, and suggests that interstitial hydrides may have relevant stereochemical effects even in large carbonyl clusters.