Lithium manganese oxide (LiMn2O4, LMO) is a promising cathode material for Li-ion batteries owing to its high energy density, low cost, and environmental benignity. However, its practical use is limited by severe capacity fading, primarily caused by the Jahn-Teller distortion associated with Mn3+ and the dissolution of Mn into the electrolyte. In this study, we explore a multidoping strategy to overcome these drawbacks by synthesizing multicomponent oxides of formula LiCrxFeyMn2-x-y-zTizO4 via a facile sol-gel method. Three compositions with varying transition metal ratios were investigated to evaluate the effects of cationic substitution on electrochemical behavior and structural stability. The best performance was achieved for compositions containing all four transition metals (Cr, Fe, Mn, and Ti). Ex situ and operando X-ray diffraction and X-ray absorption spectroscopy revealed excellent structural stability, with no evidence of phase separation or Jahn-Teller-induced distortion even after 60 cycles. Manganese was identified as the sole electrochemically active element, undergoing a reversible Mn4+/Mn3+ redox process through an intercalation/deintercalation mechanism. These results demonstrate that multidoping effectively enhances the structural and electrochemical stability of spinel-type cathodes, providing a viable pathway toward the design of Co-free and Ni-free electrodes for next-generation Li-ion batteries.

Submarine alkaline hydrothermal vents (SAVs) are geological structures considered plausible sites for life emergence, here a life-like thermodynamic disequilibrium is generated by the presence of two fluids with different pH and composition across opposite surfaces of a mineral membrane. The redox potential generated can drive the formation of organic molecules by coupling CO2 reduction with H2 oxidation. In this work, we propose a novel electrochemical model for SAVs, treating them as short-circuited fuel cells. Using two iron sulfide electrodes exposed to the different environments, we measured the potential difference (Uc) generated in the cell by the pH and redox gradients, namely the open circuit potential difference between two electrodes. Short-circuiting the electrodes equalized their potential, i.e. the mixed potential (Em) and allowed a current to flow and thus two or more redox reactions to proceed. Under far-from-equilibrium conditions, spontaneous current generation was observed for the first time ever, leading to the formation of formic acid. Our results show the active role of the mineral barrier as the site where geochemical energy is dissipated and converted into the very first protobiotic chemistry. Submarine hydrothermal vents are among the most compelling candidates for where life on Earth began, their mineral walls dissipate the redox and pH gradients to drive primitive chemistry. Here, researchers introduce an electrochemistry-grounded model that treats these vents as a short-circuited fuel cell, building iron sulfide electrodes to capture spontaneous potential and current generation in real time — and catch CO2 being converted into formic acid, an early building block of life.

Bimetallic NiCu co-catalysts are consistently reported to be more active than monometallic Ni and Cu counterparts for photocatalytic H2 evolution. There is consensus in the literature that this effect is due to the NiCu electronic structure, which provides an optimal adsorption/desorption energy landscape for faster H2 evolution kinetics compared to monometallic co-catalysts. Less is known, however, about the oxidation state of Ni and Cu co-catalysts under photocatalytic conditions, both in the case of mono- and bi-metallic systems. Red-ox dynamics for Ni and Cu are particularly complex in liquid aqueous media where, in addition to changes in oxidation state induced by photogenerated charge carriers, Ni and Cu can undergo dissolution, redeposition and surface reconstruction. Several diverging hypotheses on Ni and Cu oxidation states have been formed in recent years, most of which were based primarily on results of ex situ characterization techniques. Herein, we use in situ X-ray Absorption Spectroscopy to investigate red-ox dynamics in Ni-, Cu-, and NiCu-TiO2 photocatalysts in plain water and water/methanol solutions under hydrogen evolution conditions. This enables us to monitor changes in Ni and Cu oxidation state over time and identify the active phase of Ni and Cu co-catalysts “at work”. It is proposed that the observed synergy in NiCu-TiO2 arises from a division of roles, where Cu serves as an efficient electron sink for hydrogen evolution, while Ni acts as a dynamic hole buffer through reversible oxidation, thereby enhancing charge separation and suppressing self-deactivation pathways.

Ni 2+ single atoms on PHI photocatalyze the selective semi-hydrogenation of alkynes, using water as the proton source.

We employ several X-ray based techniques, including X-ray diffraction, absorption and resonant inelastic scattering, to disentangle the contributions of individual chemical species to the structural, electronic and magnetic properties of high-entropy oxides. In the benchmark compound Mg0.2Co0.2Ni0.2Cu0.2Zn0.2O and related systems, we unambiguously resolve a sizable Jahn-Teller distortion at the Cu sites, more pronounced in the absence of Ni2+ and Mg2+, suggesting that these ions promote positional order, whereas Cu2+ ions act to destabilize it. Moreover, we detect magnetic excitations and estimate the strength of the interactions between pairs of different magnetic elements. Our results provide valuable insights into the role of the various chemical species in shaping the physical properties of high-entropy oxides.

A set of rock-salt oxides was prepared starting from the high entropy oxide Mg0.2Co0.2Ni0.2Cu0.2Zn0.2O (HEO5) by progressively reducing the number of components, while preserving the native rock-salt structure. The obtained medium entropy oxides were Co0.2Ni0.4Cu0.2Zn0.2O (MEO4) and Ni0.6Cu0.2Zn0.2O (MEO3). The performance of the prepared materials towards the selected prototypical probe reaction (CO oxidation) was investigated and correlated with structural and spectroscopic features. The catalytic activity was evaluated over a wide temperature range (50-400 degrees C). The medium entropy oxide with three cations (MEO3) exhibited the best catalytic performance and became active at low temperature (50 degrees C). All the materials achieved complete conversion (99.9%) with full selectivity to the desired product (CO2 selectivity 99.9%) at medium-high temperatures (250 degrees C < T < 300 degrees C). We demonstrated that the catalyst surfaces could exhibit different local compositions, with metal enrichment and re-organization induced by the experimental conditions, leading to the formation of novel potentially active surface species. Configurational entropy is a stabilizing term, whose decrease enhances the catalytic activity of the materials, promoting a progressive destabilization of Ni(II) in favor of reduced Ni species on MEO3.

This work presents the first systematic investigation of Ruthner-derived hematite recovered from steelmaking waste streams as a functional precursor for the synthesis of black ceramic pigments. A sustainable approach for the synthesis of black ceramic pigments by substituting conventional Fe sources with recycled hematite derived from steelwork waste. The investigated pigment composition (Cr0.4Fe0.35Co0.25)3O4, was prepared via solid-state synthesis at 1300 degrees C, 1200 degrees C, and 1100 degrees C and compared to a reference one prepared with goethite. Characterization by XRD, SEM-EDS, XAS and SCI colorimetric analysis, revealed that recovered hematite promotes the formation of more rounded and uniformly distributed crystallites, promoting the development of a dark hue, while the incorporation of the pigment into a transparent ceramic glaze showed that recovered-hematite-based pigments provide darker and more saturated black tones with improved optical performance compared to goethite-derived pigments. These findings demonstrate that industrial waste-derived secondary raw materials can effectively reduce the reliance on primary and critical raw materials, enabling lower-temperature, energy-efficient synthesis of high-performance black pigments for ceramic decoration. This approach contributes to reducing the environmental impact of pigment production while maintaining industrially relevant properties.

Since their appearance on the scene, MXenes have been recognized as promising anode materials for rechargeable batteries, thanks to the combination of structural and electronic features. The layered structure with a suitable interlayer distance, good electronic conductivity, and moldability in composition makes MXenes exploitable both as active and support materials for the fabrication of nanocomposites providing both capacitive and Faradaic contributions to the final capacity. Although a variety of possibilities has been explored, the fundamental mechanism of the electrode reaction is still hazy. We herein report the investigation of Ti3C2T x MXenes, the benchmark composition for application in energy storage, through the combined operando X-ray absorption spectroscopy (XAS) and Raman analysis supported by density functional theory (DFT) calculations with the aim of clarifying the origin and nature of capacity when the material was cycled vs Na. The electrode reaction determined was Ti3C2X2 + 1Na → Na1Ti3C2X2, defining the theoretical capacity.

High entropy oxides are a novel class of materials, where multiple cations can be incorporated in a single-phase structure. Since the discovery of the prototypical compound Co0.2Cu0.2Mg0.2Ni0.2Zn0.2O, the research on these materials has shown an impressive boost. This compound adopts a rock-salt structure, even if CuO and ZnO are usually stable as tenorite and wurtzite. The attainment of a single phase is usually ascribed to the substantial value of configurational entropy that counterbalances unfavourable enthalpy terms. Here, we reconsider the effective role of configurational entropy in the stabilization in view of the solubility and redox equilibria involved. A careful examination of the high-temperature solubility limit of CuO in each native rock salt oxide proves to be useful to predict the phase stability. However, when the number of components is high, the behaviour becomes, at least to some extent, distinct from that of the constituent rock-salt oxides and difficult to predict.

It is well-known that ceria nanoparticles (CNPs) exhibit significant antioxidant activity, offering potential applications in the treatment of ROS-related pathologies. This activity of CNPs as a nanozyme is typically interpreted by considering Ce(III)/Ce(IV) equilibria on the nanoparticles' surface. However, the validity of this mechanism has never been directly proven in a biological context. Furthermore, it is often overlooked that after endocytosis, CNPs are compartmentalized within endolysosomes, while ROS are primarily located in the cytoplasm, making their direct interaction difficult. This study presents chemical and biological evidence supporting an alternative mechanism of action. By utilizing synchrotron μXRF and μXANES analysis on individual cells, the study shows that the amount of Ce(III), the species responsible for the antioxidant activity, increases linearly with time within the endolysosomes, where CNPs are accumulated, and in their vicinity. Such an increase can be explained by the release of Ce3+ ions resulting from a partial reductive dissolution of CNPs in the acidic environment of the endolysosomes. The Ce3+ ions can then cross the endolysosomal membrane, reaching the cytosol, where they can exert their reducing activity on ROS. In fact, neutralizing the acidic endolysosomal pH results in a complete inhibition of the CNP activity. Consequently, CNP antioxidant activity should be regarded as the result of redox processes that extend beyond the nanoparticles surface but involve complex dissolution equilibria.

Synthesis of substituted anilines upon nucleophilic addition of secondary amines to cyclohexanone derivatives followed by aromatization of the enamine by employing a combination of Ir-polypyridine complex as a photoredox catalyst and cobaloxime as H2-evolution catalyst is developed recently by Leonori et al. In this work, the homogeneous photoredox catalyst is replaced by a heterogeneous and metal-free mesoporous graphitic carbon nitride (mpg-CN). Substituted aromatic amine and H2 are formed simultaneously. Combination of X-ray spectroscopies reveals charge transfer from cobaloxime to mpg-CN in the dark. Illumination of the catalytic system with visible light induces electron transfer from mpg-CN to cobaloxime and formation of persistent Co(II) species. The results of density functional theory modeling suggest that the studied reaction is strongly endothermic and endergonic. Thus, energy of photons is stored in the reaction products-H2 and the aromatic amine.

Spinels like Co3O4 have acquired relevance because of their photocatalytic, electrocatalytic, optical and magnetic properties. In this context, we investigated the defect structure evolution of compounds synthetized using the nitrate precursor method and after annealing cycles at temperatures ranging from 260 to 650 °C by means of thermogravimetric analysis (TGA), neutron powder diffraction (NPD), X-ray powder diffraction (XRPD) coupled to Pair Distribution Function (PDF) analysis, and Density Functional Theory (DFT) calculations. Deuterated and hydrogenated precursors were adopted to produce the samples for NPD and XRPD experiments, respectively. TGA measurements displayed weight losses, the extent of which increased on lowering the preparation annealing temperature, suggesting that the adopted wet synthesis introduces structural water in the sample. Both XRPD and NPD revealed the presence of vacancies in tetrahedral cobalt sites (VCo1″) whose concentration at RT decreases on raising the annealing temperatures, while octahedral cobalt and oxygen sites were fully occupied in all the samples. In addition, the VCo1″ presence induces a shrinking of the volume of the CoO4 tetrahedra. The combination of DFT calculation and diffraction revealed that deuterium/hydrogen ions (Di•/Hi•), introduced during the synthesis by the nitrate precursor balanced the VCo1″. Finally, DFT calculations revealed that (Di•/Hi•) in Co3O4 forms hydroxyl groups.

We present here a new design for an electrochemical cell that allows grazing incidence X-ray absorption spectroscopy (XAS) experiments to be performed. The idea is to have a laminar flow of electrolyte in front of the working electrode. In this way, the thickness of the electrolyte layer can be kept small enough to cope with the penetration depth of X-rays at the K-edges of 3d metals. The laminar flow is achieved by letting the electrolyte flow by gravity over a flat surface of the cell, where the working electrode is positioned. In this way, surface sensitivity can be achieved on bulk electrodes, as demonstrated by performing the water splitting reaction on nickel wires, which are the materials used in industrial conditions. The cell is easy to use and can be easily installed in an experimental hutch of an XAS beamline, the only requirement being to have enough space.

Photoelectrochemical energy conversion is a promising solution for sustainable energy production by harnessing solar energy to produce clean fuels like hydrogen (H2). H2, as a clean and renewable energy vector, can be produced from water using solar energy in one step. In this work, CuxO electrode was synthesized by thermal treatment and used as photocathode, after the deposition on metallic Cu to improve the PEC water splitting performance. The synthesized photocathodes were characterized by XRD, SEM, XAS and then their electrochemical performances were investigated. Two CuxO electrodes were alternatively used as working electrode (WE) and counter electrode (CE), recording the photocurrent of the WE in each switching process. This procedure has been applied with the aim of improving the lifetime of the CuxO electrode, since CuxO is easily reduced during the PEC water splitting. Interestingly, the cathode photocurrent increases in the third switching process, reaching a maximum and then decreases. Therefore, operando X-ray absorption near edge structure spectrum (XANES) was used to track the effective composition of the photocathodes during the hydrogen production, applying a sequence of polarization potentials in order to mimic the described switching process during PEC water splitting. This work provides a method to investigate the semiconductors behaviour during their role of photoanode/photocathode, including possible photocorrosion phenomena.