Disclosing the Interfacial Electrolyte Structure of Na-Insertion Electrode Materials: Origins of the Desolvation Phenomenon

Computational tasks were performed using resources from GENCI-IDRIS (Grants 2022-A0120910463 and 2023-A0140910463) and from the MeSU supercomputer of Sorbonne University.International audienceAmong a variety of promising cathode materials for Na-ion batteries, polyanionic Na-insertion compounds are among the preferred choices due to known fast sodium transfer through the ion channels along their framework structures. The most interesting representatives are Na3V2(PO4)3 (NVP) and Na3V2(PO4)2F3 (NVPF), which display large Na+ diffusion coefficients (up to 10–9 m2 s–1 in NVP) and high voltage plateaux (up to 4.2 V for NVPF). While the diffusion in the solid material is well-known to be the rate-limiting step during charging, already being thoroughly discussed in the literature, interfacial transport of sodium ions from the liquid electrolyte toward the electrode was recently shown to be important due to complex ion desolvation effects at the surface. In order to fill the blanks in the description of the electrode/electrolyte interface in Na-ion batteries, we performed a molecular dynamics study of the local nanostructure of a series of carbonate-based sodium electrolytes at the NVP and the NVPF interfaces along with careful examination of the desolvation phenomenon. We show that the tightness of solvent packing at the electrode surface is a major factor determining the height of the free energy barrier associated with desolvation, which explains the differences between the NVP and the NVPF structures. To rationalize and emphasize the remarkable properties of this family of cathode materials, a complementary comparative analysis of the same electrolyte system at the carbon electrode interface was also performed

Synthesis of carbon nanofibers/poly(para-phenylenediamine)/nickel particles nanocomposite for enhanced methanol electrooxidation

International audienceSeveral studies have been conducted on direct methanol fuel cells (DMFCs) to resolve major issues such as the high cost of the catalyst and the poisoning of the electrode. Herein, a low-cost catalyst based on nickel particles (NiPs), carbon nanofibers (CNF) and poly(para-phenylenediamine) (PpPD) was carried out using a simple electrochemical method. The morphology and structure of the nanocomposite electrodes are characterized by field-emission gun scanning electron microscopy coupled with an energy dispersive X-ray detector, X-ray diffraction, Fourier transform infrared spectroscopy and Raman spectroscopy. The effects of various parameters such as the PpPD film thickness and the NiPs content on the electrocatalytic performance of CPE/CNF/PpPD/NiPs are evaluated which lead to the optimized composition. The results of the methanol electrooxidation reaction at room temperature showed that the optimized CPE/CNF/PpPD/NiPs nanocomposite exhibits a high catalytic activity (Ip = 38.11 mA cm−2), good stability and durability for more than 6 h in comparison with CPE/CNF/NiPs. These findings truly highlight the synergetic effect of CNF/PpPD in enhancing the electrochemical activity and stability and the vast potential of CPE/CNF/PpPD/NiPs as low-cost catalyst and electrodes for DMFCs

Hydrothermal synthesis of a graphene‐based composite enabling the fabrication of a current collector‐free microsupercapacitor with improved energy storage performance

Herein, the development and the characterization of an all-solid state symmetrical and current collector-free microsupercapacitor based on a new reduced graphene oxide-polydopamine (rGO-PDA) composite are reported. The rGO-PDA composite is synthesized by a facile, ecofriendly and scalable hydrothermal approach in the presence of dopamine which can not only contribute to the oxygen functional groups removal from graphene oxide but also polymerize onto the rGO sheets reducing their restacking and improving the wettability of the electrode. The optimized rGO-PDA composite material exhibits excellent capacitance and cycling stability as well as an improved rate capability compared to the pristine rGO in Na2SO4 solution. This performance enhancement can be linked to the higher transfer kinetic and lower transfer resistance values of the ions involved in the charge storage process of rGO-PDA, as determined by ac-electrogravimetry. Furthermore, an all-solid-state microsupercapacitor was prepared employing the optimized rGO-PDA composite as electrode material. Interdigitated electrodes were obtained thanks to a CO2 laser and a Na2SO4/PVA hydrogel was employed, no current collector was used. This device achieves a noteworthy energy density of 6.2mWh•cm-3 at a power density of 0.22W•cm-3. Moreover, it exhibits exceptional cycling stability, retaining 104% of its initial capacity even after undergoing 10,000 cycles at 2V•s-1

Original Fuel-Cell Membranes from Crosslinked Terpolymers via a ‘‘Sol–gel'' Strategy

International audienceHybrid organic/inorganic membranes that include a functionalized (-SO3H), interconnected silica network, a non-porogenic organic matrix, and a -SO3Hfunctionalized terpolymer are synthesized through a sol–gel-based strategy. The use of a novel crosslinkable poly(vinylidene fluoride-ter-perfluoro(4- methyl-3,6-dioxaoct-7-ene sulfonyl fluoride)-ter-vinyltriethoxysilane) (poly(VDF-ter-PFSVE-ter-VTEOS)) terpolymer allows a multiple tuning of the different interfaces to produce original hybrid membranes with improved properties. The synthesized terpolymer and the composite membranes are characterized, and the proton conductivity of a hybrid membrane in the absence of the terpolymer is promising, since 8mS cm1 is reached at room temperature, immersed in water, with an experimental ion-exchange-capacity (IECexp) value of 0.4 meq g1. Furthermore, when the composite membranes contain the interfaced terpolymer, they exhibit both a higher proton conductivity (43mS cm1 at 65 -C under 100% relative humidity) and better stability than the standard hybrid membrane, arising from the occurrence of a better interface between the inorganic silica and the poly[(vinylidene fluoride)- co-hexafluoropropylene] (poly(VDF-co-HFP)) copolymer network. Accordingly, the hybrid SiO2-SO3H/terpolymer/poly(VDF-co-HFP) copolymer membrane has potential use as an electrolyte in a polymer-electrolytemembrane fuel cell operating at intermediate temperatures

Design, Synthesis, Structural and Textural Characterization, and Electrical Properties of Mesoporous Thin Films Made of Rare Earth Oxide Binaries

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Unveiling the Ionic Exchange Mechanisms in Vertical Graphene Nanosheet Supercapacitor Electrodes by Using AC-Electrogravimetry

International audienceVertically oriented graphene nanosheets (VOGNs) have recently shown a great potential aselectrodes for electrochemical double layer capacitors due to their peculiar characteristics suchas high conductivity, ion access facility and open structure with high surface area [1, 2].This work presents, for the first time, the electrochemicalquartz crystal microbalance (EQCM) results obtained onVOGNs using various organic electrolytes. Themeasurements were performed on VOGNs grown on goldpatterned GaPO4 piezoelectric resonator electrodesaccording to our previous experimental conditions (Fig. 1a)[2]. In this direction, EQCM measurements provide fruitfulinsights derived from mass variations concerning thebehavior of ions upon cycling (Fig. 1b).A more advanced electrogravimetric technique, acelectrogravimetry, combines electrochemical impedancespectroscopy with mass measurements to obtain specificdynamic attributes for each species exchanged at theelectrode surface (Fig. 1c).This unique technique was used on VOGNs to attain thedeconvolution of the global EQCM outcome intoindividual dynamic responses for each species exchangedat the electrode-electrolyte interface [3]. Depending on thenature of cations and anions, the energy storage mechanismwas driven by different species from the electrolyte. Thefundamental insight obtained in this study paves the way tobetter understand the supercapacitor’s key mechanisms forenergy storage, which is crucial for further developingnew electrode designs.References[1] Z. Bo, S. Mao, Z.J. Han, K. Cen, J. Chen,K.K. Ostrikov, Chem. Soc. Rev. 2015, 44, 2108–2121.[2] D. Aradilla, M. Delaunay, S. Sadki, J.M. Gérard, G. Bidan, J. Mater. Chem. A. 2015,3, 19254–19262.[3] H. Goubaa, F. Escobar-Teran, I. Ressam, W. Gao, A.E. Kadib, I.T. Lucas, M.Raihane, M. Lahcini, H. Perrot, O. Sel, J. Phys. Chem. C. 2017, 121, 9370–9380

Unveiling the ionic exchange mechanisms in vertical graphene nanosheet supercapacitor electrodes with ac-electrogravimetry

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