Transition metal nitrides and oxynitrides exhibit catalytic properties that make them promising candidates as alternatives to noble metals. A series of high-surface-area chromium oxynitrides, CrOxN1-x (0.10 < x < 0.25), was synthesized from a cheap hydroxide precursor and investigated as unconventional heterogeneous catalysts for the Water-Gas Shift (WGS) reaction. Currently, this reaction is predominantly catalyzed by platinum. Replacing platinum with chromium oxynitrides could provide a more cost-effective and environmentally friendly solution.

An original synthesis route for tailoring the hydrogen evolution reaction (HER) activity of alpha-Mo2C-based catalysts is reported using soluble and air-stable halide precursors built from nanosized [Mo6Cl14]2- cluster units, namely (H3O)2[Mo6Cl14]7H2O and ((n-C4H9)4N)2[Mo6Cl14], combined with sucrose as a biosourced carbon source. The resulting catalysts consist of nanosized alpha-Mo2C crystallites embedded in residual carbon, with molybdenum preserved in the +2 oxidation state from the halide precursor to the final material. The chemical nature of the precursor strongly influences the phase composition, homogeneity, specific surface area, and morphology of the resulting alpha-Mo2C powders. Among the synthesized materials, the catalyst derived from ((n-C4H9)4N)2[Mo6Cl14] exhibits the highest HER performance in alkaline media, characterized by the lowest overpotential at 10 mA cm-2, the largest electrochemical surface area, and the smallest Tafel slope. Long-term electrochemical testing also reveals surface activation during operation, enhancing both activity and stability. These findings indicate that the catalytic behavior of alpha-Mo2C cannot be attributed solely to nanostructuring effects but arises from a subtle interplay between crystallite size, porosity, and surface chemistry. The use of Mo6 cluster-based precursors thus provides an effective and versatile approach to control the composition and molybdenum oxidation state of molybdenum carbides, enabling the design of advanced powder materials with optimized surface and electrocatalytic properties.

(Text in French)Dihydrogen: production by water electrolysis, molecular storage and conversion in a fuel cell. The production of dihydrogen (H2) by water electrolysis, its molecular storage and its use in fuel cells are strong research topics at ISCR, requiring complementary expertises in electrochemistry, molecular chemistry and materials chemistry. This know-how has been applied to elaborate and optimise structured catalytic electrode materials based on transition metals, primarily Ni, Mo and their derivatives, for the alkaline electrolysis of water at room temperature or near-room temperature. Innovative electrode materials are also being developed to convert this molecule into electricity in solid oxide fuel cells (SOFC), which have the advantage of operating at lower temperatures and for longer periods compared to conventional fuel cells. In addition to this work, the ISCR is also investigating the storage of H2 in small organic molecules that are liquid at room temperature, such as formic acid. Using ad-hoc organometallic catalysts, these small molecules can be efficiently dehydrogenated.

Correction for ‘From cluster halides to catalysts: nanostructured molybdenum carbides for efficient hydrogen evolution reaction’ by Guillaume Dubois et al. , J. Mater. Chem. A , 2026, 14 , 11332–11343, https://doi.org/10.1039/D5TA09668E.

The Ni 3 N@NF‖Ni 3 S 2 @NF (NF = Nickel Foil) electrode pair exhibited the highest electrocatalytic activity for H 2 production coupled with glucose oxidation (HER‖GOR) and excellent stability for more than 100 h at 100 mA cm −2 .

This study investigates the structural, thermal, and mechanical properties of Mg–Al–Si–O–N glasses. Six compositions with increasing nitrogen content from 1.7 to 6.2 at.% were synthesized by melting mixtures of high‐purity oxide and nitride precursors, followed by quenching and annealing. Structural analysis via X‐ray diffraction and Raman spectroscopy confirms the amorphous nature of the glasses and highlights distinct spectral features based on the Mg/Al ratios, providing insight into the changes of the Si‐O and Al‐O bond concentration with the nitrogen content. The effects of nitrogen incorporation on density, molar volume, atomic packing density, glass transition temperature, and thermal expansion were systematically examined, revealing strong correlations. Measurements of elastic moduli, hardness, and fracture toughness underscore the role of nitrogen and the Mg/Al ratio in enhancing the mechanical properties. The findings demonstrate that by increasing the nitrogen content, the glass becomes stiffer and denser, and the mechanical properties are improved.

Transition metal carbides and nitrides demonstrate very interesting electrocatalytic properties, close to those of noble metals. Indeed,platinum being a scarce and expensive element, carbides and nitrides could be an interesting alternative to make this technology economically viable. Recently, different authors reported promising (electro)catalytic properties of molybdenum carbides and nitrides. Herein we report the synthesis of Mo nitrides and carbides from original routes using transition metal cluster-based precursors or laser pyrolysis. The resulting nitrides and carbides were characterized by several complementary techniques (XRD, BET, SEM, etc.). These innovative modes of synthesis afford nanostructured compounds and the evaluation of Mo5N6 for the WGS reaction is reported.

Due to their high electronic conductivity, high catalytic activity, and superior chemical stability, nickel nitrides and sulfides have been demonstrated to be cost-effective and robust electrocatalysts for achieving HER under alkaline conditions. Herein, we report on a simple and optimized approach to directly grow single-phase nickel nitride (Ni3N) and nickel sulfide (Ni3S2) on a flat nickel substrate. Different preparation conditions are tested in order to achieve materials exhibiting the best electrocatalytic efficiency for HER. The optimized Ni3N and Ni3S2 on nickel are obtained at 700 degrees C for 30 min under ammonia gas flow and at 350 degrees C for 1 h in 10% H2S/H2 gas mixture, respectively. Ni3N operate HER in 1 M KOH more efficiently than Ni3S2, as supported by overpotential values of 0.189, 0.291, and 0.342 V measured at 10, 100, and 200 mA cm-2, respectively, which are lower than those measured for Ni3S2, i.e., 0.204, 0.351, and 0.417 V. Remarkably, it is worth noticing that its HER activity competes with that of Pt for current densities higher than 200 mA cm-2. Its superior catalytic activity is corroborated by additional cyclic voltammetry (Tafel slopes) and electrochemical impedance spectroscopy measurements. Moreover, Ni3N and Ni3S2 are found to be stable over 45 h of electrolysis at 10 mA cm-2 with a potential change of only 24 and 31 mV, respectively. To gain further understanding on the electrocatalytic HER activities of both materials, density functional theory (DFT) calculations and an in situ bubble dynamics study are performed. Owing to the more hydrophilic character of Ni3N, smaller H2 bubbles form and detach more rapidly from the surface which leads to a fast renewal of the active surface for HER. In contrast, for Ni3S2, both the bubble size and the retention time increase, leading to the adverse blockage of the active sites and requiring higher overpotential for HER. This observation perfectly aligns with DFT calculations, which show that H2O adsorption is predominantly favored on the Ni3N surface. Our work highlights that the use of a planar electrocatalyst support instead of a foam-type porous one is essential to evaluate the alone contribution of the electrocatalyst on the electrogenerated gas bubble dynamics and consequently the impact on the catalytic performance.

CrN-based thin films are emerging as thermoelectric materials for energy harvesting. Their thermoelectric properties depend on phase composition and stoichiometry, necessitating control over the nitrogen content and how it affects the phase composition. Here, the effect of high-temperature ammonia annealing on the thermoelectric properties as well as crystal structure of thin films of Cr-N on c-plane sapphire (Al2O3(0001)) was investigated. Single-phase (cubic CrN) and mix-phase (cubic CrN + hexagonal-Cr2N) Cr-N films were annealed in ammonia, converting any secondary phase of hexagonal Cr2N to cubic CrN. The thermoelectric properties of the films that contained a secondary phase of hexagonal (CrN)-N-2 greatly improved upon annealing, with an increase of 900% to 0.5 x 10-3 W m(-1) K-2 for the film annealed at 800 degrees C for 2 h. Annealing of single-phase films of cubic CrN resulted in films with near-insulating electrical properties. For the thermoelectric applications of CrN, ammonia annealing can be beneficial over meticulous deposition control.

Hydrogen (H2) is considered a clean and sustainable alternative energy carrier to fossil fuels for meeting future energy demands.1 Electrocatalytic water splitting is a promising approach to producing eco-friendly H2 involving a hydrogen evolution reaction (HER) at the cathode and an oxygen evolution reaction (OER) at the anode.2 However, during these electrochemical gas evolution reactions, gas bubbles evolving at the surface of the electrocatalyst may result in undesired blockage of active sites and can influence the performance of the electrocatalytic process.3 In this study, we optimized the direct growth of single-phase nickel sulfide and nitride (Ni3S2@NF and Ni3N@NF) on metallic nickel foil (NF) and investigated the influence of surface hydrophilicity or hydrophobicity on electrochemical HER through in situ hydrogen bubble dynamics. Contact angle measurements revealed that metallic NF, Ni3S2@NF, and Ni3N@NF electrodes followed a trend of decreasing contact angle in an alkaline solution, indicating that Ni3N@NF exhibited the highest hydrophilicity/aerophobicity.4 In situ bubble visualization demonstrated that hydrophilic/aerophobic Ni3N@NF led to smaller and faster bubble departure, offering more active sites and a lower overpotential. Conversely, decreasing hydrophilicity or aerophobicity resulted in larger bubbles and longer retention times, leading to the unwanted blockage of the active sites and requiring high overpotential for HER. This highlights the significant impact of surface-wetting properties and hydrophilicity on electron and mass transfer during hydrogen generation, particularly at higher current densities. References Lewis, N. S.; Nocera, D. G. Natl. Acad. Sci. U. S. A. 2006, 103, 15729. Turner, J. A. Science 2004, 305, 972. Angulo, A.; van der Linde, P.; Gardeniers, H.; Modestino, M.; Fernández Rivas, D. Joule 2020, 4, 555. Tyagi, C.; Fabre, B.; Jullien, M.-C.; Bouquet, V.; Tessier, F. submitted. Figure 1

Tungsten carbide (WC) has been exploredas a cost-effectiveandEarth-abundant alternative electrocatalyst for the hydrogen evolutionreaction (HER) in both acid and alkaline conditions, due to its electronicstructure comparable to that of platinum. Herein, we report on a simpleand convenient approach for depositing the carbon-embedded WC electrocatalyston nickel foam from the thermal reduction of a sucrose-impregnatedself-deposited tungsten trioxide (WO3) precursor. Differentsucrose concentrations (between 20 and 80% aqueous solution) and reductiontemperatures (between 600 and 1000 degrees C) are tested to achievean optimized material exhibiting the best electrocatalytic efficiencyfor HER. The optimized material is obtained from the precursor impregnatedwith 50% sucrose and thermally reduced at 800 degrees C. It can operateHER with overpotential values measured at 10 and 100 mA cm(-2) of 0.124 and 0.232 V, respectively, at pH 14, and 0.208 and 0.333V at pH 0.3, respectively. Furthermore, these electrodes are foundto be stable in both media during controlled-current density electrolysistests over a period of 40 h. The presence of excess amorphous carbonembedding WC is beneficial to improve the conductivity and dispersibilityof the electrocatalyst and consequently its HER activity. These findingsdemonstrate that robust and efficient WC-based binder-free HER electrocatalystscan be produced easily from spontaneously deposited WO3 film and sucrose as the carbon source.

Germanium nitride, having cubic spinel structure, γ-Ge3N4, is a wide band-gap semiconductor with a large exciton binding energy that exhibits high hardness, elastic moduli and elevated thermal stability up to approximately 700°C. Experimental data on its bulk and shear moduli (B0 and G0, respectively) are strongly limited, inconsistent and, thus, require verification. Moreover, earlier first-principles density functional calculations provided significantly scattering B0 values but consistently predicted G0 much higher than the so far available experimental value. Here, we examined the elasticity of polycrystalline γ-Ge3N4, densified applying high pressures and temperatures, using the techniques of laser ultrasonics (LU) and Brillouin light scattering (BLS) and compared with our extended first-principles calculations. From the LU measurements, we obtained its longitudinal- and Rayleigh wave sound velocities and, taking into account the sample porosity, derived B0 = 322(44) GPa and G0 = 188(7) GPa for the dense polycrystalline γ-Ge3N4. While our calculations underestimated B0 by approximately 17%, most of the predicted G0 matched well with our experimental value. Combining the LU- and BLS data and taking into account the elastic anisotropy, we determined the refractive index of γ-Ge3N4 in the visible range of light to be n = 2.4, similarly high as that of diamond or GaN, and matching our calculated value. This article is part of the theme issue 'Exploring the length scales, timescales and chemistry of challenging materials (Part 1)'.

The modification of porosity and surface silanization are efficient methods to improve physicochemical and biological properties of bioactive glass. For sol-gel-derived glasses, the use of surfactant in the synthesis medium allows to pattern porosity and may significantly impact their in vitro bioactivity. Additionally, surface functionalization by silanization may be a key method for grafting drugs or biomolecules to the glass surface. In this work, we realized a comparative study of the effect of porosity modification and surface silanization on in vitro bioactivity of sol-gel-derived bioactive glasses. The materials characterization by FTIR spectroscopy, XRD analysis, ICP-OES spectroscopy, and SEM-EDS, before and after soaking in SBF, showed that the ordered porosity increases significantly the kinetics of hydroxyl-carbonate apatite formation and induces a control of the mineralization at the glass surface. The results show also that the glass remains bioactive after silanization. The present work shows that porosity structuring improves the in vitro bioactivity of our glass and increases the silanization rate of the glass surface.

This short communication reports on the facile and scalable synthesis and characterization of molybdenum carbides/carbon nanocomposites prepared by laser pyrolysis in a one-step process. Water and commercial molybdenum oxide were used as low-cost environmentally friendly precursors. The nanocomposites are mainly composed of two types of carbides with different apparent crystallite sizes, 21 ± 1 nm and 9 ± 1 nm for Mo2C and MoC1−x, respectively. Thanks to a simple annealing at 500 °C under argon, it was possible to increase the specific surface area around 50 m2/g without changing the morphology of the nanocomposite.

In this paper, ferroelectric ceramics with (Sr2Ta2O7)(100)(-x)(La2Ti2O7)(x) (STLTO) compositions have been investigated and their dielectric properties have been characterized in wide frequency band (from few kHz to few GHz); their integration in Dielectric Resonator Antennas (DRA) was conducted. The dense STLTO ceramics have been obtained by high temperature sintering of powders synthetized by solid state chemistry route. STLTO crystalline cell parameters and volume vary linearly as a function of the chemical composition (x) thus demonstrating an ideal solid solution domain for 0 <= x <= 3. Dielectric characterizations highlight that the permittivity and the dielectric loss vary according to the composition (x) and that the lowest losses are obtained for x< 1.65 compositions. The latter corresponds to the transition between the ferroelectric and paraelectric compositions of the STLTO material at room temperature. A low profile DRA structure was realized using a cylindrical paraelectric STLTO resonator (with x = 0) with a permittivity of 83 and losses tan delta = 5 x 10(-3)@3.3 GHz. The DRA prototype was simulated, produced and tested. It exhibits a hybrid HEM11 delta mode, with a resonant frequency at 5.80 GHz, a 4.9% bandwidth and a gain of 6.4 dB. These features confirm the potential of the paraelectric STLTO compositions in compact antennas radiating at frequencies below 6 GHz. (C) 2021 Elsevier B.V. All rights reserved.

Structural and dielectric properties of thin films produced by reactive radiofrequency sputtering of a (Sr2Ta2O7)(100-x) (La2Ti2O7)(x) target with x = 1.65 were studied. The chemical composition characterization shows Sr/Ta ratios ranging between 0.49 and 0.56, thus pointing out the deposition of strontium deficient films, belonging to the tetragonal tungsten bronze family. The highest permittivities and tunabilities, associated with the lowest dielectric losses, are obtained when films are pure and fully textured. This is achieved for a 900 nmthick film deposited at T-s = 850 degrees C: epsilon' = 116, tan delta = 0.007 and tunability T = 14.5% at 340 kV/cm and 100 kHz.

Electronic band structure in germanium nitride having spinel structure, γ-Ge3N4, was examined using two spectroscopic techniques, cathodoluminescence and synchrotron-based photoluminescence. The sample purity was confirmed by x-ray diffraction and Raman analyses. The spectroscopic measurements provided first experimental evidence of a large free exciton binding energy De≈0.30 eV and direct interband transitions in this material. The band gap energy Eg = 3.65 ± 0.05 eV measured with a higher precision was in agreement with that previously obtained via XES/XANES method. The screened hybrid functional Heyd–Scuseria–Ernzerhof (HSE06) calculations of the electronic structure supported the experimental results. Based on the experimental data and theoretical calculations, the limiting efficiency of the excitation conversion to light was estimated and compared with that of w-GaN, which is the basic material of commercial light emitting diodes. The high conversion efficiency, very high hardness and rigidity combined with a thermal stability in air up to ~ 700 °C reveal the potential of γ-Ge3N4 for robust and efficient photonic emitters.

In this study, the influence of the degree of crystallization and thickness of films was correlated with the photoelectrochemical performance of SrTaO2N semiconductor films for O-2 evolution reaction under visible light irradiation. Oxynitride films were deposited on various substrates using the sputtering in Ar + N-2 reactive atmosphere from a home-made SrTaO2N target. Films with stoichiometric composition were obtained at a high temperature (T-s = 800 degrees C) with reduced bandgap. The different substrates led to diverse degrees of film crystallization, from weakly crystallized to fully c-axis oriented. The photoelectrochemical performance was improved by improving the film crystallinity and the thickness. For further improvement of the photoelectrochemical performance, the following three limiting factors are identified: 1) low absorption coefficient, especially in the visible domain from 500 to 600 nm; 2) short lifetimes of excited charge carriers; and 3) permittivity with only moderate values lower than 10 in the visible-light domain.