Yahdi Bin Rus

Résumé : Des feuillets de graphène fonction-nalisés FGSx avec un rapport C/O~x ont été post-fonctionnalisés avec des dérivés de tétrazine (3,6-bis(2-pyridyl)-1,2,4,5-tétrazine) par cycloa-ddition de Diels-Alder à demande inverse. Des applications potentielles de ces graphènes fonctionnalisés ont été explorées sur le stockage d'énergie (supercondensateur) et l’électrocatalyse (réaction de réduction de l'oxygène).Pour les applications de supercondensateurs, des nanocomposites constitués de FGS20 fonction-nalisé et de polypyrrole ont été synthétisés en deux étapes en incorporant d’abord les fonctions pyridine-pyridazine à la surface du FGS20 par cycloaddition suivie de l’électropolymérisation du pyrrole dans l’acétonitrile. La capacité spéci-fique du matériau a été mesurée par des cycles de charge-décharge galvanique et la stabilité au cyclage a été étudiée dans divers milieux électro-lytiques (acétonitrile, liquide ionique, eau acide et eau neutre) et les résultats comparés par rapport au FGS20 non fonctionnalisé avec ou sans polypyrrole. Alors que l'acétonitrile révèle un comportement capacitif pur pour tous les matériaux étudiés, l'eau acide est le milieu où les valeurs de capacité sont les plus élevées et, de manière surprenante, où les nanocomposites contenant du polypyrrole présentent une meilleure rétention de capacité lors du cyclage que le graphène seul. Un impact positif de la fonctionnalisation du graphène avant l'électropoplymérisation a été mis en évidence dans tous les milieux électrolytiques (pertes de capacité limitées à moins de 8% après 1500 cycles dans tous les milieux sauf l'eau neutre), soulignant l'intérêt du contrôle d'interface dans ce type de nanocomposites.

Incorporating graphene into Ni-rich cathode materials, such as the LiNi_0.815Co_0.15Al_0.035O₂ (NCA) cathode, has been frequently reported as an effective strategy to improve the performance of lithium-ion batteries. However, the influence of the oxidation degree of graphene on the electrochemical performance of the mixed NCA/graphene cathode remains largely unexplored. In this work, the oxidation degree of graphene was tuned by varying the electrolyte concentration during the electrochemical exfoliation process, and its impact on the performance of NCA/graphene cathodes was evaluated. The results show that the exfoliated graphene (EG) synthesized using 0.3 M (NH₄)₂SO₄ (denoted as EG 0.3) possesses the lowest oxidation degree among all the samples, which leads to the highest electrical conductivity and the lowest moisture content. When incorporated into the NCA cathode, EG 0.3 produced a composite (NCA/EG 0.3) with the best rate capability and cycling stability owing to the low degree of cation mixing and the lowest charge-transfer resistance in the resulting cathode. Electrochemical measurements revealed that the NCA/EG 0.3 cathode delivers the highest specific capacity of 191.32 mA h g⁻¹ at 0.1C, 67.72% capacity retention rate at 5C compared with 0.1C, and good cycling stability (85.13% capacity retention after 100 cycles at 0.2C), which outperformed other composite cathodes. This study demonstrates that the oxidation degree of graphene can govern the cation mixing degree and charge-transfer resistance in Ni-rich cathodes, offering insights into the design of graphene-based additives and protective layers for lithium-ion battery cathodes.

Additive engineering in tin-based perovskite solar cells. Insight from the experiment and computational.

A new and versatile method to prepare Ag nanoparticles on functionalized graphene sheets is described. In a first step, pyridine‐pyridazine units are introduced on graphene sheets by cycloaddition reaction with a tetrazine derivative. Then the material is coated on an electrode and electrodeposition is carried out to generate silver nanoparticles in a one‐step electroreduction process. The applied potential signal is shown to influence the size and dispersity of the particles in the composite. While larger particles are active in improving sensitivity of Surface‐Enhanced Raman Spectroscopy, smaller ones can be efficiently used in electrocatalysis, like for oxygen reduction. Both effects are demonstrated to highlight the versatility of the applications of these easily prepared nanocomposites.

LiFePO₄ is commonly used as cathode material for Li-ion batteries due to its stable operational voltage and high specific capacity. However, it suffers from certain disadvantages such as low intrinsic electronic conductivity and low ionic diffusion. This study was conducted to analyse the effect of reduced graphene oxide (rGO) on the electrochemical properties of LiFePO₄/Li₂SiO₃ composite. This composite was synthesized by a hydrothermal method. Fourier transform infrared spectroscopy measurement identified the O–P–O, Fe–O, P–O, and O–Si–O⁻ bands in the LiFePO₄/Li₂SiO₃ composite. X-ray diffraction measurement confirmed the formation of LiFePO₄. Meanwhile, Raman spectroscopy confirmed the number of rGO layers. Further, scanning electron microscopy images showed that rGO was distributed around the LiFePO₄/Li₂SiO₃ particles. Finally, the electrochemical impedance spectroscopy results showed that the addition of 1 wt% of rGO to the LiFePO₄/Li₂SiO₃ composite reduced charge transfer resistance. It may be concluded that the addition of 1 wt% rGO to LiFePO₄/Li₂SiO₃ composite can enhance its electrochemical performance as a cathode material.

A reduced graphene oxide/nickel (rGO/Ni) composite has been succesfully synthesized using a combination of Marcano’s method for synthesizing graphene oxide (GO), subsequently followed by a facile microwave assisted reduction method. X-ray diffraction results show the presence of graphene and nickel on the prepared samples. In addition, the Fourier Tansform Infrared Spectroscopy measurement showed that the absorption peaks of O-H, C=O, C-OH, and C-O only appear in the GO sample. A Scanning Electron Microscope photograph shows that the morphology of the rGO samples contain nano-layered forms. A Raman spectroscopy characterization of the prepared rGO samples show a peak of G band’s wave number at 1586.5 cm^-1. From the calculation of the G band’s wave number, the average number of graphene layers is 1.15.