Chemical engineering of 2D materials for electrochemical energy storage

L'attractivité des supercondensateur réside dans leur complémentarité avec les batteries, en particulier en termes de durée de vie et de puissance. Leur densité d'énergie plus faible reste un inconvénient qui peut être dépassé en travaillant sur les matériaux d'électrode. Au cours e cette thèse, divers matériaux 2D ont permis la formulation d'électrodes présentant de meilleures densités d'énergie. L'intercalation de Cu2+ dans delta-MnO2 par une méthode hydrothermale a conduit à une amélioration fdes performances. Des effets synergiques ont été observés dans des composites à base de MnO2 et Ti3C2-MXene. Ils ont été attribués à l'amélioration de la conductivité électronique apportée par le composant MXene. Pour éviter le ré- empilement des Mxenes exfoliés, des méthodes de templating ont conduit à des matériaux expansés et des mousses. Une couche de MXene à la surface de fibres de carbone modifiée par physisorption de molécules rédox-actives a augmenté fortement la cyclabilité de l'électrode.Supercapacitors attractiveness lies in their complementarity with batteries, especially in terms of expended lifespan and greater power density. Their lower energy density however remains a drawback and the electrode material design and composition play a crucial role to address it. During this thesis work, various 2D materials were used to fabricate electrodes with enhanced energy densities. An hydrothermal method was explored using delta-MnO2 for Cu2+ intercalation leading to performance improvement. Attractive synergistic effects were evidenced in composite materials based on 2D pseudocapacitive MnO2 and Ti3C2-MXene. They have been assigned to electronic conductivity improvement from MXene component. To prevent the restacking of exfoliated MXene, template-assisted syntheses led to expanded MXene and foam. An MXene coating was deposited at the surface of carbon fibers modified by physisorbed redox-active organic salts, promoting efficient charge storage and stabilizing the assemble

Most Modern Supercapacitor Designs Advanced Electrolyte and Interface

Electrolyte plays a key and significant role in supercapacitors. The interaction of an electrode and a chosen electrolyte has a significant effect on the parameters., i.e., ionic conductivity, stable potential range, and charge transfer coefficient, therefore determining the corresponding performance. The captivating interface between electrode and electrolyte is also pushing the intensive research. In this chapter, we focus on two kinds of electrolytes, including water-in-salt electrolytes and redox-ionic liquid. Water-in-salt electrolyte is drawing continuous attention thanks to the formed hydrophobic layer on the positive electrode and solid electrolyte interphase (SEI) on the negative side, preventing water splitting. On the other side, redox-ionic liquid, taking advantage of the broad and stable working window, on the interface, the redox shuttle passes and targets the suitable electrode bulk, leading to redox reactions to highlight capacitance and energy

MIMO-Based Forward-Looking SAR Imaging Algorithm and Simulation

Multiple-input multiple-output (MIMO) radar imaging can provide higher resolution and better sensitivity and thus can be applied to targets detection, recognition, and tracking. Missile-borne forward-looking SAR (MFL-SAR) is a new and special MIMO radar mode. It has advantage of two-dimensional (2D) imaging capability in forward direction over monostatic missile-borne SAR and airborne SAR. However, it is difficult to obtain accurate 2D frequency spectrum of the target echo signal due to the high velocity and descending height of this platform, which brings a lot of obstacles to imaging algorithm design. Therefore, a new imaging algorithm for MFL-SAR configuration based on the method of series reversion is proposed in this paper. This imaging method can implement range compression, secondary range compression (SRC), and range cell migration correction (RCMC) effectively. Finally, some simulations of point targets and comparison results confirm the efficiency of our proposed algorithm

JNK pathway promotes hepatocyte apoptosis by inhibiting Bcl-2 and upregulating expressions of Bim, caspase-3 and caspase-9 after cardiopulmonary bypass

Purpose: To study the effect of Jun N-terminal kinase (JNK) signaling pathway on hepatocyte apoptosis in vivo and in vitro, and to elucidate the mechanism of action. Methods: TdT-mediated dUTP Nick-End Labeling (TUNEL) method was used to determine apoptosis in control and cardiopulmonary bypass (CPB) groups at 0, 3 and 6 hours after rat surgery. The expressions of JNK and p-c-Jun in liver tissues at 0, 3 and 6 h after surgery, and the levels of p-c-Jun, Bcl-2 and Bim following overexpression of JNK, were determined using Western blot assay. Human liver cell line HL-7702 was cultured and transfected with over-expressed JNK plasmid and empty plasmid. Proliferation of HL-7702 cells after JNK over-expression was assessed by Cell Counting Kit-8 (CCK-8), while quantitative real-time polymerase chain reaction (RT-qPCR) was employed to evaluate mRNA expression levels of caspase-3 and caspase-9 mRNA after JNK over-expression. Apoptosis of the cells was determined by flow cytometry (FC) after JNK over-expression. Results: FC results showed that the number of apoptotic hepatocytes increased after JNK overexpression in hepatocytes while TUNEL assay results demonstrated that hepatocyte apoptosis increased in CPB group, when compared to control group; furthermore, the number of apoptotic cells gradually increased within 6 h after surgery. The expressions of JNK and p-c-Jun were higher in CPB group than in control group, and increased gradually in both groups within 6 h after surgery. Overexpression of JNK decreased the proliferation of hepatocytes, and also lowered protein expression levels of p-c-Jun and Bim; on the other hand, the protein expression levels of Bcl-2 fell, while mRNA expression levels of caspase-3 and caspase-9 mRNA increased. Conclusion: JNK pathway promotes hepatocyte apoptosis after cardiopulmonary bypass by inhibiting Bcl-2 pathway and promoting the expressions of Bim caspase-3 and caspase-9. Keywords: Cardiopulmonary bypass, Apoptosis, JNK pathway, Bim, caspase-3 and caspase-

Self-assembled Ni/NiO/RGO heterostructures for high-performance supercapacitors

A nano-sized nickel/nickel oxide/RGO (Ni/NiO/RGO) nano-hybrid was generated successfully by using a facile and green sol-gel approach, with the reduced graphene oxide as an effective component, for developing a high-efficiency electrode material with super-capacitance. In the novel hierarchical nano-composite, the combination of metallic nickel interfaced with the nickel oxide was created by the reduction of a nickel nitrate precursor with the carbon of the reduced graphene oxide surface, during the thermal treatment in nitrogen. The electrochemical performances of the Ni/NiO/RGO composite were measured through cyclic voltammetry tests and galvanostatic charge-discharges, as a supercapacitor material. Due to the higher conductivity and synergistic effect, the new hybrid delivered a high specific capacitance of 1027.27 F g-1 at the charge/discharge current density of 2 A g-1, and 720 F g-1 at 20 A g-1. After 1000 uninterrupted cycles at 5 A g-1, the high specific capacitance value can be still stabilized, and kept at 92.95% of the initial value of the specific capacitance for Ni/NiO/RGO. This new nano composite with RGO and Ni/NiO exhibits great promise as an electrode material for supercapacitors

Atomic Structure Evolution of Pt–Co Binary Catalysts: Single Metal Sites versus Intermetallic Nanocrystals

Due to their exceptional catalytic properties for the oxygen reduction reaction (ORR) and other crucial electrochemical reactions, PtCo intermetallic nanoparticle (NP) and single atomic (SA) Pt metal site catalysts have received considerable attention. However, their formation mechanisms at the atomic level during high-temperature annealing processes remain elusive. Here, the thermally driven structure evolution of Pt–Co binary catalyst systems is investigated using advanced in situ electron microscopy, including PtCo intermetallic alloys and single Pt/Co metal sites. The pre-doping of CoN4 sites in carbon supports and the initial Pt NP sizes play essential roles in forming either Pt3Co intermetallics or single Pt/Co metal sites. Importantly, the initial Pt NP loadings against the carbon support are critical to whether alloying to L12-ordered Pt3Co NPs or atomizing to SA Pt sites at high temperatures. High Pt NP loadings (e.g., 20%) tend to lead to the formation of highly ordered Pt3Co intermetallic NPs with excellent activity and enhanced stability toward the ORR. In contrast, at a relatively low Pt loading (<6 wt%), the formation of single Pt sites in the form of PtC3N is thermodynamically favorable, in which a synergy between the PtC3N and the CoN4 sites could enhance the catalytic activity for the ORR, but showing insufficient stability

Chemical engineering of 2D materials for electrochemical energy storage

Supercapacitors attractiveness lies in their complementarity with batteries, especially in terms of expended lifespan and greater power density. Their lower energy density however remains a drawback and the electrode material design and composition play a crucial role to address it. During this thesis work, various 2D materials were used to fabricate electrodes with enhanced energy densities. An hydrothermal method was explored using delta-MnO2 for Cu2+ intercalation leading to performance improvement. Attractive synergistic effects were evidenced in composite materials based on 2D pseudocapacitive MnO2 and Ti3C2-MXene. They have been assigned to electronic conductivity improvement from MXene component. To prevent the restacking of exfoliated MXene, template-assisted syntheses led to expanded MXene and foam. An MXene coating was deposited at the surface of carbon fibers modified by physisorbed redox-active organic salts, promoting efficient charge storage and stabilizing the assemble.L'attractivité des supercondensateur réside dans leur complémentarité avec les batteries, en particulier en termes de durée de vie et de puissance. Leur densité d'énergie plus faible reste un inconvénient qui peut être dépassé en travaillant sur les matériaux d'électrode. Au cours e cette thèse, divers matériaux 2D ont permis la formulation d'électrodes présentant de meilleures densités d'énergie. L'intercalation de Cu2+ dans delta-MnO2 par une méthode hydrothermale a conduit à une amélioration fdes performances. Des effets synergiques ont été observés dans des composites à base de MnO2 et Ti3C2-MXene. Ils ont été attribués à l'amélioration de la conductivité électronique apportée par le composant MXene. Pour éviter le ré- empilement des Mxenes exfoliés, des méthodes de templating ont conduit à des matériaux expansés et des mousses. Une couche de MXene à la surface de fibres de carbone modifiée par physisorption de molécules rédox-actives a augmenté fortement la cyclabilité de l'électrode

Ingénierie chimique des matériaux 2D pour le stockage de l'énergie électrochimique

L'attractivité des supercondensateur réside dans leur complémentarité avec les batteries, en particulier en termes de durée de vie et de puissance. Leur densité d'énergie plus faible reste un inconvénient qui peut être dépassé en travaillant sur les matériaux d'électrode. Au cours e cette thèse, divers matériaux 2D ont permis la formulation d'électrodes présentant de meilleures densités d'énergie. L'intercalation de Cu2+ dans delta-MnO2 par une méthode hydrothermale a conduit à une amélioration fdes performances. Des effets synergiques ont été observés dans des composites à base de MnO2 et Ti3C2-MXene. Ils ont été attribués à l'amélioration de la conductivité électronique apportée par le composant MXene. Pour éviter le ré- empilement des Mxenes exfoliés, des méthodes de templating ont conduit à des matériaux expansés et des mousses. Une couche de MXene à la surface de fibres de carbone modifiée par physisorption de molécules rédox-actives a augmenté fortement la cyclabilité de l'électrode.Supercapacitors attractiveness lies in their complementarity with batteries, especially in terms of expended lifespan and greater power density. Their lower energy density however remains a drawback and the electrode material design and composition play a crucial role to address it. During this thesis work, various 2D materials were used to fabricate electrodes with enhanced energy densities. An hydrothermal method was explored using delta-MnO2 for Cu2+ intercalation leading to performance improvement. Attractive synergistic effects were evidenced in composite materials based on 2D pseudocapacitive MnO2 and Ti3C2-MXene. They have been assigned to electronic conductivity improvement from MXene component. To prevent the restacking of exfoliated MXene, template-assisted syntheses led to expanded MXene and foam. An MXene coating was deposited at the surface of carbon fibers modified by physisorbed redox-active organic salts, promoting efficient charge storage and stabilizing the assemble