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Molten Salt Synthesis and Electrochemical Evaluation of Na/Ag-Containing Mnsub.xOsub.y Composites for Pseudocapacitor Applications
Different composites of manganese oxides (Mn[sub.x]O[sub.y]) containing sodium (Na) and silver (Ag) were synthesized by the molten salt method with various MnSO[sub.4]·H[sub.2]O/NaNO[sub.3] (M/N) molar ratios (between 0.3 and 1), and different AgNO[sub.3] and NaOH amounts, obtaining two groups of materials: without the addition of AgNO[sub.3] (labeled as M/N) and with AgNO[sub.3] (labeled as M/N-A). As for the M/N group, the system with the lowest M/N ratio yielded the highest specific capacitance (160.5 F g[sup.−1]), attributed to the formation of Mn[sub.3]O[sub.4] and sodium birnessite. In the M/N-A group, the 1 M/N-0.5A system, produced with M/N ratio of 1 and addition of 0.5 g of AgNO[sub.3], exhibited the highest specific capacitance (229.1 F g[sup.−1]), associated with the presence of Mn[sub.2]O[sub.3], silver hollandite, and metallic Ag. This enhancement is attributed to the synergistic effects of Na[sup.+] and Ag[sup.+] ions, which improve charge transfer kinetics and electrochemical performance. It was demonstrated that decreasing the MnSO[sub.4]·H[sub.2]O/NaNO[sub.3] ratio in the M/N group and increasing AgNO[sub.3] content in the M/N-A group enhances the electrochemically active surface area. Galvanostatic charge–discharge (GCD) and electrochemical impedance spectroscopy (EIS) techniques confirmed that the 1 M/N-0.5A system exhibited the best performance, characterized by high energy retention, stable cycling behavior, and low capacitance dispersion, indicating its strong potential as an active material for pseudocapacitor applications.
Journal Article
The Design of the Nisub.3N/Nbsub.4Nsub.5 Heterostructure as Bifunctional Adsorption/Electrocatalytic Materials for Lithium–Sulfur Batteries
Lithium–sulfur (Li-S) batteries are hindered by the sluggish electrochemical kinetics and poor reversibility of lithium polysulfides (LiPSs), which limits their practical energy density and cycle life. In order to address this issue, a novel Ni[sub.3]N/Nb[sub.4]N[sub.5] heterostructure was synthesized via electrospinning and nitridation as a functional coating for polypropylene (PP) separators. Adsorption experiments were conducted in order to ascertain the heterostructure’s superior affinity for LiPSs, thereby effectively mitigating their shuttling. Studies of Li[sub.2]S nucleation demonstrated the catalytic role of the substance in accelerating the deposition kinetics of Li[sub.2]S. Consequently, Li-S cells that employed the Ni[sub.3]N/Nb[sub.4]N[sub.5]-modified separator were found to achieve significantly enhanced electrochemical performance, with the cells delivering an initial discharge capacity of 1294.4 mAh g[sup.−1] at 0.2 C. The results demonstrate that, after 150 cycles, the cells retained a discharge capacity of 796.2 mAh g[sup.−1], corresponding to a low capacity decay rate of only 0.25% per cycle. In addition, the rate capability of the cells was found to be improved in comparison to control cells with NiNb[sub.2]O[sub.6]-modified or pristine separators.
Journal Article
Concepts and tools for mechanism and selectivity analysis in synthetic organic electrochemistry
As an accompaniment to the current renaissance of synthetic organic electrochemistry, the heterogeneous and space-dependent nature of electrochemical reactions is analyzed in detail. The reactions that follow the initial electron transfer step and yield the products are intimately coupled with reactant transport. Depiction of the ensuing reactions profiles is the key to the mechanism and selectivity parameters. Analysis is eased by the steady state resulting from coupling of diffusion with convection forced by solution stirring or circulation. Homogeneous molecular catalysis of organic electrochemical reactions of the redox or chemical type may be treated in the same manner. The same benchmarking procedures recently developed for the activation of small molecules in the context of modern energy challenges lead to the establishment and comparison of the catalytic Tafel plots. At the very opposite, redox-neutral chemical reactions may be catalyzed by injection (or removal) of an electron from the electrode. This class of reactions has currently few, but very thoroughly analyzed, examples. It is likely that new cases will emerge in the near future.
Journal Article
Three-dimensional network of Mn.sub.3O.sub.4/reduced graphene oxide aerogel with improved electrochemical performances of sodium-ion batteries
It is widely known that transition-metal oxides, including Mn.sub.3O.sub.4, suffer from volume expansion and poor conductivity and thus, result in unsatisfactory cycling stability in the sodium-ion batteries. One approach to overcome these issues is to use reduced graphene oxide (rGO) aerogels as a potential matrix to support the Mn.sub.3O.sub.4 electrode during the sodiation/desodiation process. In this study, Mn.sub.3O.sub.4/rGO aerogels are prepared by the hydrothermal process, followed by the freeze-drying process without further heat treatment. The reduction of graphite oxide, deposition of Mn.sub.3O.sub.4 nanoparticles, and formation of a three-dimensional network of rGO nanosheets can all occur concurrently during the synthesis process, ensuring an even distribution of Mn.sub.3O.sub.4 nanoparticles on the rGO sheet. The Mn.sub.3O.sub.4/rGO aerogels exhibit a good electrochemical sodium storage performance when tested as an anode material. In the initial cycle, the Mn.sub.3O.sub.4/rGO aerogels delivered a high discharge capacity of 947 mAh g.sup.-1 and sustained a capacity of 283 mAh g.sup.-1 at a current density of 0.1 A g.sup.-1 after 100 cycles, with a large Coulombic efficiency of ~ 99%. The excellent cycling stability and improved discharge capacity of the electrode could be due to the hierarchical structures of rGO with nanosized Mn.sub.3O.sub.4, which can expedite more ion and electron transporting channels from various directions, provide high interfacial sodium storage, and prevent the structure from collapsing. The electrochemical results indicate that the Mn.sub.3O.sub.4/rGO aerogels can be further explored for the development of sodium-ion batteries and the synergistic effect contributed by both rGO aerogel and Mn.sub.3O.sub.4 nanoparticles offers an alternative strategy to mitigate the issues associated with Mn.sub.3O.sub.4.
Journal Article
Synergy of Oxygen Vacancy and Surface Modulation Endows Hollow Hydrangea-like MnCosub.2Osub.4.5 with Enhanced Capacitive Performance
Surface chemistry and bulk structure jointly play crucial roles in achieving high-performance supercapacitors. Here, the synergistic effect of surface chemistry properties (vacancy and phosphorization) and structure-derived properties (hollow hydrangea-like structure) on energy storage is explored by the surface treatment and architecture design of the nanostructures. The theoretical calculations and experiments prove that surface chemistry modulation is capable of improving electronic conductivity and electrolyte wettability. The structural engineering of both hollow and nanosheets produces a high specific surface area and an abundant pore structure, which is favorable in exposing more active sites and shortens the ion diffusion distance. Benefiting from its admirable physicochemical properties, the surface phosphorylated MnCo[sub.2]O[sub.4.5] hollow hydrangea-like structure (P-MnCoO) delivers a high capacitance of 425 F g[sup.−1] at 1 A g[sup.−1], a superior capability rate of 63.9%, capacitance retention at 10 A g[sup.−1], and extremely long cyclic stability (91.1% after 10,000 cycles). The fabricated P-MnCoO/AC asymmetric supercapacitor achieved superior energy and power density. This work opens a new avenue to further improve the electrochemical performance of metal oxides for supercapacitors.
Journal Article