ACS Physical Chemistry Au最新文献

This study investigates the effect of anion composition on the performance of supercapacitors (SCs) using hydrated ionic liquids and graphene electrodes, focusing on comparing pure and mixed electrolytes. Systems containing [bmim] paired with NO₃ ^-, ClO₄ ^-, and Br^- were evaluated to assess their impact on electric double layer (EDL) formation and electrochemical behavior. Molecular dynamics (MD) simulations were performed under varying surface polarization, focusing on interaction energies, species distribution, capacitance, and projected energy density. Capacitance values ranged from 2.30 to 2.55 μF/cm², while energy densities varied between 5.03 and 5.58 J/g, depending on electrolyte composition. The results show that small, mobile anions like Br^- promote more compact EDLs and higher capacitance, even with weak electrode interactions. NO₃ ^- contributes to interfacial organization through hydrogen bonding with water. Mixed anion systems demonstrated competitive performance, with the best results obtained by combining high ion mobility and structural organization. This suggests that hybrid electrolytes are a promising strategy for optimizing energy storage in ionic liquid-based SCs.

Measuring nanoscale local temperatures, particularly in vertically integrated and multicomponent systems, remains challenging. Spectroscopic techniques like X-ray absorption and core-loss electron energy-loss spectroscopy (EELS) are sensitive to lattice temperature, but understanding thermal effects is nontrivial. This work explores the potential for nanoscale and element-specific core-loss thermometry by comparing the Si L_2,3 edge's temperature-dependent redshift against plasmon energy expansion thermometry (PEET) in a scanning TEM. Using density functional theory (DFT), time-dependent DFT, and the Bethe-Salpeter equation, we ab initio model both the Si L_2,3 and plasmon redshift. We find that the core-loss redshift occurs due to bandgap reduction from electron-phonon renormalization. Our results indicate that despite lower core-loss signal intensity compared to plasmon features, core-loss thermometry has key advantages and can be more accurate through standard spectral denoising. Specifically, we show that the Varshni equation easily interprets the core-loss redshift for semiconductors, which avoids plasmon spectral convolution for PEET in complex junctions and interfaces. We also find that core-loss thermometry is more accurate than PEET at modeling thermal lattice expansion in semiconductors, unless the specimen's temperature-dependent dielectric properties are fully characterized. Furthermore, core-loss thermometry has the potential to measure nanoscale heating in multicomponent materials and stacked interfaces with elemental specificity at length scales smaller than the plasmon's wave function.

We have performed Quantum Monte Carlo (QMC) simulations on Na-intercalated bilayer graphene to study the evolution of electronic and optical properties upon Na intercalation into hard carbon layers. The objective was to model the optimal configuration of Na intercalation into a hard carbon matrix containing graphene regions. Our study showed that Na intercalation can be energetically stabilized at large interlayer distances (over 6 Å) in both AA- and AB-stacked bilayer graphene. In the QMC results, we found a significant band gap opening at the equilibrium interlayer distance of Na-intercalated bilayer graphene, while corresponding density functional theory (DFT) results showed no gap. This difference between DFT and QMC results indicates that the gap opening induced by Na intercalation into a hard carbon is underestimated within the DFT framework. In addition, a zigzag configuration of Na atoms was found to be energetically stable at interlayer distances up to 10 Å, leading us to predict the existence of a local minimum of Na intercalation at large interlayer distance. These computation and modeling results can provide guidance on how to synthesize and optimize hard carbon with bilayer graphene regions that permit a zigzag intercalation configuration that will maximize and stabilize sodium hosting.