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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
Electrochemical Performance of Tisub.3Csub.2Tsub.x MXenes During Structural Evolution
MXenes, with a high surface area, abundant active sites, and excellent ion transport properties, have demonstrated excellent electrochemical performance. However, systematic comparisons of the structural evolution process and electrochemical performance for MXene are lacking. In this study, multilayer MXene (M-Ti[sub.3]C[sub.2]T[sub.x]) was successfully fabricated by in situ etching. During the subsequent centrifugation process, the thicker and heavier multilayer sheets settled due to their faster sedimentation rate, while the lighter, surface-functionalized monolayer sheets remained colloidally stable in the supernatant due to solvation and electrostatic repulsion, thereby achieving separation and obtaining delaminated MXene (D-Ti[sub.3]C[sub.2]T[sub.x]). Structural analysis indicates that the removal of the aluminum layer synergizes with the exfoliation of the nanosheets, significantly increasing the interlayer spacing and making the sheet structure more pronounced, and the pore structure is more abundant. Especially, in three-electrode and two-electrode systems at an identical mass loading of 5 mg on carbon paper, D-Ti[sub.3]C[sub.2]T[sub.x] delivered a higher specific capacitance, more pronounced pseudocapacitive behavior, and a superior rate capability compared to Ti[sub.3]AlC[sub.2] and M-Ti[sub.3]C[sub.2]T[sub.x]. Such excellent electrochemical performance of D-Ti[sub.3]C[sub.2]T[sub.x] is due to the shortened ion diffusion path in the delaminated structure, which enables rapid ion migration, an extremely large specific surface area, and a mesoporous structure that provides abundant active sites. This study underscores the significant potential of D-Ti[sub.3]C[sub.2]T[sub.x] in emerging energy storage systems and offers insights into guiding MAX phase synthesis during its preparation.
Journal Article
P2-type Na.sub.0.67Mn.sub.0.6Ni.sub.0.3Ti.sub.0.1O.sub.2 as cathode material for sodium-ion batteries: solid electrolyte versus liquid electrolyte
P2-type Na.sub.0.67Mn.sub.0.6Ni.sub.0.3Ti.sub.0.1O.sub.2 is synthesized via a sol-gel method and its electrochemical performance is investigated as a cathode material for sodium-ion batteries (SIBs) employing both a Na.sub.3Zr.sub.2Si.sub.2PO.sub.12 solid electrolyte and an organic liquid electrolyte. In the liquid electrolyte cells, the Na.sub.0.67Mn.sub.0.6Ni.sub.0.3Ti.sub.0.1O.sub.2 cathode exhibits a high discharge capacity of 87.5 mAh g.sup.-1, with a capacity retention of 73.2% after 500 cycles at 0.1 C (10 mA g.sup.-1), while in the solid electrolyte cells, a higher discharge capacity of 94.5 mAh g.sup.-1 at 0.1 C and an improved high-rate capacity of 70.8 mAh g.sup.-1 at 2 C are demonstrated. Moreover, stable charge/discharge cycles are observed in the solid electrolyte cells, with a discharge capacity of 75.3 mAh g.sup.-1 and a retention of 60.7% over 100 cycles at 1 C. This work highlights the substantial effect of the electrolyte conditions on the performance of layered oxide cathode materials, providing potential strategies to overcome current challenges for high-performance SIBs.
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