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CaB12H12: A promising salt for aprotic electrolytes in calcium-based secondary batteries
No full textInternational audienceCalcium dodecaborate, CaB12H12, is introduced and successfully tested as a promising salt for aprotic electrolytes in calcium-based batteries. The synthesis protocol for this innovative salt is both cost-effective and scalable, paving the way for environmentally safe and efficient manufacturing. The salt was incorporated into novel aprotic electrolyte formulations aimed at improving the reversibility of calcium plating and stripping, addressing a key challenge in calcium battery technology. Among the various tested formulations, a 0.25 M solution of CaB12H12 in N-methyl pyrrolidone exhibits superior performance, enabling reversible calcium plating/stripping at room temperature with overpotentials below 0.5 V at a current density of 0.1 mAcm−2
Unveiling photoinduced electron transfers in photosensitized polyoxometalates for solar energy conversion
No full textInternational audienceArtificial photosynthesis faces the challenge of developing visible-light-driven strategies for converting and storing solar energy in the form of fuels and high-value chemicals. In such an approach, selective fuel production often depends on the accumulation of multiple electrons at a catalytic site. However, this process is constrained by the rapid recombination of photogenerated charges and the inherently slow kinetics of multi-electron catalytic reactions, which hinder efficient charge buildup and utilization. Polyoxometalates (POMs), a tunable class of nanoscale metal oxides, have emerged as promising multi-electron acceptors due to their redox versatility and stability. Their electron storage capabilities make them attractive as both reservoirs and catalysts. In most cases, their UV-limited absorption necessitates pairing of the POM with visible-light-absorbing antennas. Advances in photosensitized POM derivatives—via electrostatic assembly, covalent bonding, or band-gap engineering—are herein detailed. Covalent hybrids, in particular, allow precise control over electron transfer. Still, a detailed understanding of photoinduced electron transfer kinetics remains limited. This perspective article explores the potential applications of POMs in solar fuel generation, emphasizing the need for kinetic insight to design efficient, visible-light-driven photocatalysts and photoelectrochemical devices
Controlled HPHT annealing of SiV-doped nanodiamonds at SOLEIL synchrotron: structural and optical investigations
No full textInternational audienceDiamonds and nanodiamonds (NDs) containing quantum color centers, such as nitrogen-vacancy (NV) centers, have been widely studied in recent years for their promising applications across various fields, including cryptography and telecommunications, medical sciences, and sensing. In the context of sensing, recent studies on color centers such as silicon-vacancy (SiV) and germanium-vacancy (GeV) centers have shown great potential for measuring physical quantities like magnetic fields, temperature, and strain. This is due to their intense zero-phonon line (ZPL) optical signal, about 80% of their total luminescence, which is characteristic of group-IV color centers (G4V) [1]. In our recent papers, we demonstrated that as-grown CVD NDs containing SiV and GeV centers, featuring luminescent ZPLs and excellent photostability at room temperature, can function effectively as nanosensors of high stress and pressure conditions (up to 180 GPa) [2, 3]. To advance our research, in this work we investigate the optical properties of SiV centers in as-grown NDs at cryogenic temperatures. For SiV centers, which have spin 1/2, the fine structure should become accessible through the Jahn-Teller effect, which lifts the degeneracy at cryogenic temperatures (< 20 K). However, experiments on our as-grown NDs reveal significant spectral broadening even at around 9 K, caused by lattice strain, which prevents access to the optically addressable electronic spin states of the SiV center. To overcome this limitation, we propose an original post-treatment involving high-pressure and high-temperature (HPHT) annealing using the Paris–Edinburgh press. In fact, the gradual increase of temperature and pressure allows for control over the undesired diamond-to-graphite phase transition. HPHT annealing experiments were conducted at the PSICHE beamline of Synchrotron SOLEIL [4], where X-ray diffraction and tomography analyses enabled precise monitoring of P,T parameters and made it possible for the first time to access single fine-structure transitions of the in such SiV-NDs.References[1] C. Bradac, et al., Nat. Commun. 10, 1 (2019). [2] B. Vindolet, et al., Phys. Rev. B 106, 214109 (2022).[3] M. De Feudis, et al., Adv. Mater. Interfaces 7, 1901408 (2019).[4] L. Henry et al., J. Synchrotron Rad. 29 (2022)
Improved cycling stability of ferrocene intercalated layered double hydroxides electrodes in aqueous electrolytes
No full textInternational audienceThrough two redox molecules, mono- and dicarboxylic ferrocene anions (FcMono and FcDi, respectively), interleaved between the lamellae of a layered double hydroxide Mg2Al(OH)6 (LDH), have been synthesized and investigated as electrode materials inwater in salt electrolyte using lithium bis-(trifluoromethanesulfonyl)-imide Li+[N(SO2CF3)2]- (LiTFSI) mixed in different amount of H2O. The redox activities of the composite electrode materials including Mg2Al(OH)6[FcMono]1.0 and Mg2Al(OH)6[FcDi]0.5 suffer from the dissolution of the active redox species migrating out of the host structure in water based electrolyte when low molalities are used. However, while increasing the molality of the electrolyte solution Mg2Al(OH)6[FcDi]0.5 electrode material performs better than Mg2Al(OH)6[FcMono]1.0 ones according to the cycling stability For Mg2Al(OH)6[FcDi]0.5, an optimum behavior is observed for a concentration of LITFSI of at least of 10 m. The electrode exhibits a stable capacity of 25 mAh g-1 which is maintained after more than 100 cycles with 100 % coulombic efficiency. Such stability during cycling is explained by two complementary processes: the preservation of the lamellar structure of Mg2Al(OH)6[FcDi]0.5, FcDi molecule being tethered by its two ends (unlike FcMono tethered at one end only), in connection with the high concentration of the electrolyte in LiTFSI, which helps slowing down the migration of the interleaved redox species out of the structure. This opens the route to re-evaluate LDH-based hybrid materials for water-based energy storage devices
Toward Complete CO2 Electroconversion: Status, Challenges, and Perspectives
No full textInternational audienceElectrocatalytic conversion of carbon dioxide (CO2) into valuable carbon-based fuels and chemicals represents a promising approach to closing the carbon cycle and setting a circular economy. Nevertheless, for current electrocatalytic CO2 reduction reaction (ECO2 RR) systems, realizing 100% CO2 conversion with simultaneously high overall CO2 conversion rate (i.e., single-pass conversion) and high Faradaic efficiency (FE) remains a significant challenge. Enhancing CO2 conversion rate often results in a decrease in FE, conversely, improving FE may limit the CO2 conversion rate. Metal-CO2 (M-CO 2 ) batteries with CO2 conversion functions face similar challenges, particularly for reversible M-CO2 batteries, which do not accomplish net CO2 reduction because nearly all of CO2 RR products are reoxidized to CO2 during subsequent charging process. Such electrocatalytic CO2 conversion system for carbon neutrality poses substantial challenges. This perspective provides an in-depth analysis of state-of-the-art ECO2 RR systems and M-CO2 batteries, alongside the main strategies employed to address their respective challenges. The critical importance of achieving both a high CO2conversion rate and high Faradaic efficiency is underscored for practical applications and to effectively close the carbon cycle. Furthermore, a strategic roadmap that outlines future research directions is presented, thereby facilitating the advancement of comprehensive CO2 electroconversion technologies
Introduction of a Phosphine Group onto the Ferrocene Moiety in Ferrociphenol Opens Access to New Heterobimetallic Complexes with Anticancer Activity
No full textInternational audienceFerrocene analogs of biologically active compounds often exert favorable properties, as demonstrated by ferrocifens derived from the selective estrogen receptor modulator tamoxifen. This contribution reports an original approach to modify the structure of one of the first ferrocifens, namely ferrociphenol, by means of a diphenylphosphinyl moiety appended to the unsubstituted cyclopentadienyl ring of the ferrocene unit. The phosphine‐substituted ferrociphenol 1 is synthesized by two alternative routes and fully characterized including structure determination. Compound 1 is converted to the corresponding phosphonium salt 1 ·MeI and used to prepare a series of bimetallic (arene)metal and chloridogold(I) complexes. The biological evaluation reveals a relatively lower antiproliferative activity of the newly synthesized compounds compared to the parent ferrociphenol and [AuCl(FcPPh 2 ‐κ P )] (Fc = ferrocenyl) toward both tumorigenic and nontumorigenic cells. All the compounds exhibit complicated redox behavior due to chemical steps that follow the initial, ferrocene‐centered oxidation. Overall, the collected data indicate that the introduced phosphine substituent affects the redox and biological properties of the resulting compounds and, very likely, their mode of action
In Situ Synthesis of Iron Oxide-Polyisobutylene Multifunctional Nanocomposites: Size Control, Magnetic and Mechanical Properties Enhancement
No full textInternational audiencePolymer nanocomposites with precisely controlled nanoparticle size and narrow polydispersity offer substantialpotential for multifunctional applications, particularly in energy and healthcare. In this study, we introduce an in situ synthesis approach for creating iron oxide nanoparticle-polyisobutylene nanocomposites, where the nanoparticle size distribution and spatial dispersion are finely tuned by adjusting the polymer concentration and molecular weight. This method allows us to investigate and control the growth dynamics of nanoparticleswithin the polymer solution, providing insights into how the polymer molecular weight and concentration influence nucleation, growth, and assembly. Beyond achieving precise size control, our approach enables the rational design of nanocomposites with significantly enhanced mechanical strength, evidenced by an increased storage modulus, while preserving their superparamagnetic behavior. This strategy advances the development of high-performance magnetic polymer nanocomposites and opens up possibilities for applications that require both robust mechanical properties and responsive magnetic features, marking a significant step forward in nanocomposite design and functionality
The intriguing role of L-cysteine in the modulation of chiroplasmonic properties of chiral gold nano-arrows
No full textInternational audienceDeveloping chiral plasmonic nanostructures represents a significant scientific challenge due to their multidisciplinary potential. Observations have revealed that the dichroic behavior of metal plasmons changes when chiral molecules are present in the system, offering promising applications in various fields such as nano-optics, asymmetric catalysis, polarization-sensitive photochemistry and molecular detection. In this study, we explored the synthesis of plasmonic gold nanoparticles and the role of cysteine in their chiroplasmonic properties. Specifically, we synthesized chiral gold nano-arrows using a seed-mediated-growth synthesis method, in which gold nanorods are used as seeds while incorporating L-cysteine into growth solution as a chiral ligand. Our results show clearly that the chiral molecule transfers chirality to gold nanocrystals and the morphology is controlled through kinetic growth. In addition, we demonstrate that the chiroplasmonic properties, such as the sign of circular dichroism, can be modulated using only one enantiomeric form in the growth solution. To understand the origin of such an effect, we conducted theoretical modelling using density functional theory. Our results point to the intermolecular cysteine interactions as a key factor in the dichroic properties of surface-molecule chiral systems
Sensibilisation des polyoxométallates à la lumière visible et ses applications dans la conversion de l'énergie solaire
No full textPolyoxometalates (POMs) are transition metal-oxo clusters exhibiting diverse architectures such as the Keggin and Dawson types. Their functional versatility enables precise tuning of intrinsic redox and photochemical properties, particularly through hybridization with visible-light-absorbing photosensitizers (PS). These PS-POM assemblies exhibit light-induced charge separation, a process central to solar energy conversion and photocatalysis. This thesis focuses on the design, synthesis, and characterization of metal-free PS-POM hybrids using combined electrochemical and photophysical methods. Covalent hybrids of Keggin and Dawson phosphotungstates with bodipy and push-pull dyes were synthesized via palladium-catalyzed Sonogashira coupling. These assemblies were investigated for their ability to accumulate multiple redox equivalents under visible-light irradiation—an essential feature for multi-electron solar fuel processes such as water splitting. One exciting potential of POM-PS hybrids is their capacity for light-drive charge accumulation - an essential feature for solar fuel production and water splitting which rely on the catalysis of multielectron, multiproton reactions. This was demonstrated for bodipy-POM hybrids in acetonitrile with triethylamine (TEA) as a sacrificial donor. Spectroscopic monitoring revealed that the bodipy-Dawson hybrid, (TBA)₆[P₂W₁₇O₆₁{O(SiC₃₁H₃₀N₂BF₂)₂}] (TBA⁺ = tetrabutylammonium), accumulated up to two electrons within minutes. The first reduction step occurred rapidly and efficiently, while the second proceeded more slowly via a complex, multi-pathway mechanism. Two-electron accumulation was enhanced by trifluoroacetic acid through proton-coupled electron transfer (PCET) and by dismutation of one-electron-reduced intermediates. Additionally, reduction could proceed via a light-independent route involving the reactive TEA radical, effectively rendering TEA a two-electron, one-proton donor. The stored redox equivalents in the reduced POM were shown to activate O₂ and participate in PCET with substrates such as benzoquinone, underscoring the relevance of PS-POM systems for solar fuel transformations. Extending beyond homogeneous systems, PS-POM hybrids were integrated into dye-sensitized photoelectrochemical (DS-PEC) devices. A bodipy derivative bearing a carboxylic acid anchoring group was covalently linked to Keggin and Dawson POMs and immobilized on mesoporous NiO films for use in p-type dye-sensitized solar cells (DSCs). Although photovoltaic performance was modest and the POMs did not enhance bodipy's output, transient absorption spectroscopy indicated that hole injection into NiO was efficient, while subsequent electron transfer from bodipy to POM was limited by the hybrid's electronic structure. Push-pull dye-POM hybrids were further explored to exploit directional electron transfer. These hybrids were grafted onto mesoporous NiO films, and photocurrent densities were measured in sodium acetate buffer (pH 3.75) using [Co(NH₃)₅Cl]²⁺ as a sacrificial acceptor. The covalently bound assemblies exhibited photocurrents five times higher than previously reported systems with non-covalent POM and dye co-grafting on nanostructured ITO. Moreover, the inclusion of POM doubled the photocurrent generated per mole of dye compared to the dye alone. Post-operation surface analysis by wavelength-dispersive X-ray spectroscopy (WDS) confirmed the hybrids' structural integrity and stability under photoelectrochemical conditions. Overall, this work demonstrates the design principles and mechanistic foundations of visible-light-active PS-POM hybrids capable of light-driven multi-electron accumulation. Their integration into photoelectrochemical architectures highlights both the challenges and opportunities for advancing molecular-level solar energy conversion using POM-based hybrid materials.Les polyoxométallates (POMs) sont des agrégats d'oxydes de métaux de transition présentant une grande diversité structurale, notamment les types Keggin et Dawson. Leur fonctionnalisation permet d'ajuster leurs propriétés redox et photophysiques, voire de leur conférer de nouvelles fonctions. L'hybridation des POMs avec des photosensibilisateurs (PS) absorbant dans le visible constitue un axe de recherche en plein essor, ces assemblages PS-POM étant capables de séparation de charges photo-induite, un phénomène clé pour la conversion de l'énergie solaire. Cette thèse vise à concevoir, synthétiser et caractériser de nouveaux hybrides PS-POM à l'aide de méthodes électrochimiques et photophysiques. Des hybrides covalents de phosphotungstates de Keggin et Dawson ont été obtenus avec des colorants bodipy et push-pull par couplage Sonogashira catalysé par le palladium. Ces assemblages ont été étudiés pour leur aptitude à accumuler plusieurs équivalents rédox sous irradiation visible, une propriété essentielle impliqués dans la production de carburants solaires, tels que la photolyse de l'eau. L'accumulation photo-induite de charges a été démontrée pour les hybrides bodipy-POM en acétonitrile, en présence de triéthylamine (TEA) comme donneur sacrificiel. Le suivi spectroscopique du bodipy-Dawson, (TBA)₆[P₂W₁₇O₆₁{O(SiC₃₁H₃₀N₂BF₂)₂}] (TBA⁺ = ion tétrabutylammonium), a révélé l'accumulation de deux électrons en quelques minutes. La première réduction est rapide et efficace, tandis que la seconde est plus lente et procède via un mécanisme complexe à voies multiples. L'accumulation biélectronique est favorisée par l'acide trifluoroacétique via un transfert proton-électron couplé (PCET) et par la dismutation de l'espèce monoréduite. Par ailleurs, une voie non photo-induite, impliquant le radical réactif issu de la TEA, contribue également à la réduction, faisant de la TEA un donneur global de deux électrons et un proton. Les équivalents rédox stockés dans le POM réduit ont montré leur capacité à activer l'oxygène et à participer à des processus de PCET avec des substrats tels que la benzoquinone, soulignant le potentiel des hybrides PS-POM pour les transformations liées aux carburants solaires. Au-delà des milieux homogènes, les hybrides PS-POM ont été intégrés dans des dispositifs photoélectrochimiques. Un dérivé de bodipy muni d'un bras fonctionnel carboxylique a été greffé de manière covalente sur les POMs de Keggin et Dawson, puis immobilisé sur des films de NiO mésoporeux pour la fabrication de cellules solaires sensibilisées de type p (DSC). Les performances photovoltaïques, bien que modestes, ont montré une injection rapide de trous dans le NiO, tandis que le transfert d'électrons du bodipy vers le POM restait limité par la structure électronique de l'hybride, comme révélé par spectroscopie d'absorption transitoire. Des hybrides à colorants push-pull ont également été étudiés afin de tirer parti d'un transfert d'électrons directionnel. Greffés sur des films de NiO, ils ont produit des densités de photocourant mesurées en tampon acétate de sodium (pH 3,75) avec [Co(NH₃)₅Cl]²⁺ comme accepteur sacrificiel. Ces assemblages covalents ont généré des photocourants cinq fois supérieurs à ceux observés pour les systèmes non covalents (POM et colorant co-greffés sur ITO nanostructuré). De plus, la présence du POM a doublé le photocourant (par mole de colorant) par rapport au colorant seul. L'analyse post-opération par spectroscopie de rayons X à dispersion de longueur d'onde (WDS) a confirmé la stabilité structurale des hybrides durant l'expérimentation. Dans l'ensemble, ce travail met en évidence les principes de conception et les mécanismes fondamentaux des hybrides PS-POM actifs sous lumière visible, capables d'accumuler plusieurs électrons. Leur intégration dans des architectures photoélectrochimiques illustre à la fois les défis et le potentiel de ces matériaux moléculaires pour la conversion de l'énergie solaire à base de POMs
Element-resolved electrochemical database: AESEC polarization curves of ZnAlMg alloy coating constituents
No full textInternational audienceAn element-resolved electrochemical database of a ZnAlMg alloy coating is presented, obtained via atomic emission spectroelectrochemistry (AESEC) linear sweep voltammetry (LSV). Nominally pure Zn, Al and Mg metals as well as MgZn 2 , ZnAl intermetallic phases, and commercial ZnAl alloy coatings were investigated using AESEC-LSV to understand the complex electrochemical response of multi-phase ZnAlMg alloys. The elemental dissolution rates extrapolated from AESEC-LSV curves showed a linear relationship with spontaneous elemental dissolution rates. This demonstrates the possible use of AESEC-LSV for determining long-term elemental corrosion rates, as well as the use of element-specific electrochemical data as input parameters for more accurate machine learning based corrosion resistant alloy design. Element-resolved electrochemistry reveals important corrosion phenomena not detectable in conventional electrochemistry such as cathodic dissolution, chemical dissolution, cathodic dealloying, negative correlation effects, and anomalous hydrogen evolution. These phenomena may be significant and should be taken into account in the rate equations used for numerical modeling