An Ultrastable Low-Temperature Na Metal Battery Enabled by Synergy between Weakly Solvating Solvents

The low ionic conductivity and high desolvation barrier are the main challenges for organic electrolytes in rechargeable metal batteries, especially at low temperatures. The general strategy is to couple strong-solvation and weak-solvation solvents to give balanced physicochemical properties. However, the two challenges described above cannot be overcome at the same time. Herein, we combine two different kinds of weakly solvating solvents with a very low desolvation energy. Interestingly, the synergy between the weak-solvation solvents can break the locally ordered structure at a low temperature to enable higher ionic conductivity compared to those with individual solvents. Thus, facile desolvation and high ionic conductivity are achieved simultaneously, significantly improving the reversibility of electrode reactions at low temperatures. The Na metal anode can be stably cycled at 2 mA cm–2 at −40 °C for 1000 h. The Na||Na3V2(PO4)3 cell shows the reversible capacity of 64 mAh g–1 at 0.3 C after 300 cycles at −40 °C, and the capacity retention is 86%. This strategy is applicable to other sets of weak-solvation solvents, providing guidance for the development of electrolytes for low-temperature rechargeable metal batteries

Boosting Formate Production in Electrocatalytic CO₂ Reduction over Wide Potential Window on Pd Surfaces

Facile interconversion between CO₂ and formate/formic acid (FA) is of broad interest in energy storage and conversion and neutral carbon emission. Historically, electrochemical CO₂ reduction reaction to formate on Pd surfaces was limited to a narrow potential range positive of −0.25 V (vs RHE). Herein, a boron-doped Pd catalyst (Pd–B/C), with a high CO tolerance to facilitate dehydrogenation of FA/formate to CO₂, is initially explored for electrochemical CO₂ reduction over the potential range of −0.2 V to −1.0 V (vs RHE), with reference to Pd/C. The experimental results demonstrate that the faradaic efficiency for formate (η_HCOO^–) reaches ca. 70% over 2 h of electrolysis in CO₂-saturated 0.1 M KHCO₃ at −0.5 V (vs RHE) on Pd–B/C, that is ca. 12 times as high as that on homemade or commercial Pd/C, leading to a formate concentration of ca. 234 mM mg^–1 Pd, or ca. 18 times as high as that on Pd/C, without optimization of the catalyst layer and the electrolyte. Furthermore, the competitive selectivity η_HCOO^–/η_CO on Pd–B/C is always significantly higher than that on Pd/C despite a decreases of η_HCOO^– and an increases of the CO faradaic efficiency (η_CO) at potentials negative of −0.5 V. The density functional theory (DFT) calculations on energetic aspects of CO₂ reduction reaction on modeled Pd(111) surfaces with and without H-adsorbate reveal that the B-doping in the Pd subsurface favors the formation of the adsorbed HCOO*, an intermediate for the FA pathway, more than that of *COOH, an intermediate for the CO pathway. The present study confers Pd–B/C a unique dual functional catalyst for the HCOOH ↔ CO₂ interconversion

Alkyne-Modulated Surface-Enhanced Raman Scattering-Palette for Optical Interference-Free and Multiplex Cellular Imaging

The alkyne tags possess unique interference-free Raman emissions but are still hindered for further application in the field of biochemical labels due to its extremely weak spontaneous Raman scattering. With the aid of computational chemistry, herein, an alkyne-modulated surface-enhanced Raman scattering (SERS) palette is constructed based on rationally designed 4-ethynylbenzenethiol derivatives for spectroscopic signature, Au@Ag core for optical enhancement and an encapsulating polyallylamine shell for protection and conjugation. Even for the pigment rich plant cell (e.g., pollen), the alkyne-coded SERS tag can be highly discerned on two-dimension distribution impervious to strong organic interferences originating from resonance-enhanced Raman scattering or autofluorescence. In addition, the alkynyl-containing Raman reporters contribute especially narrow emission, band shift-tunable (2100–2300 cm^–1) and tremendously enhanced Raman signals when the alkynyl group locates at para position of mercaptobenzene ring. Depending on only single Raman band, the suggested alkyne-modulated SERS-palette potentially provides a more effective solution for multiplex cellular imaging with vibrant colors, when the hyperspectral and fairly intense optical noises originating from lower wavenumber region (<1800 cm^–1) are inevitable under complex ambient conditions

Theoretical Study of Quantum Conductance of Conjugated and Nonconjugated Molecular Wire Junctions

Electron transport through molecular junctions has been widely investigated experimentally and theoretically. Unfortunately, there exists discrepancy on the single molecular conductance between theoretical calculations and experimental measurements. In this paper, first-principle density functional theory combined with nonequilibrium Green’s function approach is employed; we studied electronic structures, molecular lengths, and interfacial interactions of three kinds of molecular junctions, alkanedithiols, oligo­(1,4-phenylene-ethynylene)­s, and 1,4-benzene-di­(<i>n</i>-alkylthiol) (BD<i>n</i>T), embedding in nanogaps of gold electrodes. First, our approach can accurately describe the binding interaction between the thiol group and gold electrode so that the conductance of alkanedithiol in a gold junction can be well predicted. We found that a previous underestimation of HOMO–LUMO gaps in the junction system leads to the overestimated conductance for conjugate molecules with sulfur atoms binding to gold electrodes. In the study of BD<i>n</i>T molecular wires with a phenyl ring, our results show that the HOMO–LUMO gap reaches a constant with molecular length increasing. Moreover, a larger predicted conductance can be attributed to the overlapping between the nonbonding lone-paired orbital of sulfur atoms and the delocalized π electrons of the phenyl ring. Finally, we found that the conductance of molecules with short length or conjugated electronic structure greatly relies on the interfacial configuration. We proposed that these findings can give a clear understanding of electron transport in junction systems and open a promising theoretical study of molecular electronics

In Situ Probing the Structure Change and Interaction of Interfacial Water and Hydroxyl Intermediates on Ni(OH)₂ Surface over Water Splitting

There is growing acknowledgment that the properties of the electrochemical interfaces play an increasingly pivotal role in improving the performance of the hydrogen evolution reaction (HER). Here, we present, for the first time, direct dynamic spectral evidence illustrating the impact of the interaction between interfacial water molecules and adsorbed hydroxyl species (OHad) on the HER properties of Ni(OH)2 using Au/core-Ni(OH)2/shell nanoparticle-enhanced Raman spectroscopy. Notably, our findings highlight that the interaction between OHad and interfacial water molecules promotes the formation of weakly hydrogen-bonded water, fostering an environment conducive to improving the HER performance. Furthermore, the participation of OHad in the reaction is substantiated by the observed deprotonation step of Au@2 nm Ni(OH)2 during the HER process. This phenomenon is corroborated by the phase transition of Ni(OH)2 to NiO, as verified through Raman and X-ray photoelectron spectroscopy. The significant redshift in the OH-stretching frequency of water molecules during the phase transition confirms that surface OHad disrupts the hydrogen-bond network of interfacial water molecules. Through manipulation of the shell thickness of Au@Ni(OH)2, we additionally validate the interaction between OHad and interfacial water molecules. In summary, our insights emphasize the potential of electrochemical interfacial engineering as a potent approach to enhance electrocatalytic performance

Revealing the Role of Interfacial Properties on Catalytic Behaviors by <i>in Situ</i> Surface-Enhanced Raman Spectroscopy

Insightful understanding of how interfacial structures and properties affect catalytic processes is one of the most challenging issues in heterogeneous catalysis. Here, the essential roles of Pt–Au and Pt−oxide−Au interfaces on the activation of H₂ and the hydrogenation of para-nitrothiophenol (pNTP) were studied at molecular level by <i>in situ</i> surface-enhanced Raman spectroscopy (SERS) and shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS). Pt–Au and Pt–oxide–Au interfaces were fabricated through the synthesis of Pt-on-Au and Pt-on-SHINs nanocomposites. Direct spectroscopic evidence demonstrates that the atomic hydrogen species generated on the Pt nanocatalysts can spill over from Pt to Au via the Pt–Au and Pt–TiO₂–Au interfaces, but would be blocked at the Pt–SiO₂–Au interfaces, leading to the different reaction pathways and product selectivity on Pt-on-Au and Pt-on-SHINs nanocomposites. Such findings have also been verified by the density functional theory calculation. In addition, it is found that nanocatalysts assembled on pinhole-free shell-isolated nanoparticles (Pt-on-pinhole-free-SHINs) can override the influence of the Au core on the reaction and can be applied as promising platforms for the <i>in situ</i> study of heterogeneous catalysis. This work offers a concrete example of how SERS/SHINERS elucidate details about <i>in situ</i> reaction and helps to dig out the fundamental role of interfaces in catalysis

Plasmon-Enhanced Ultrasensitive Surface Analysis Using Ag Nanoantenna

Raman scattering and fluorescence spectroscopy permeate analytic science and are featured in the plasmon-enhanced spectroscopy (PES) family. However, the modest enhancement of plasmon-enhanced fluorescence (PEF) significantly limits the sensitivity in surface analysis and material characterization. Herein, we report a Ag nanoantenna platform, which simultaneously fulfills very strong emission (an optimum average enhancement of 10⁵-fold) and an ultrafast emission rate (∼280-fold) in PES. For applications in surface science, this platform has been examined with a diverse array of fluorophores. Meanwhile, we utilized a finite-element method (FEM) and time-dependent density functional theory (TD-DFT) to comprehensively investigate the mechanism of largely enhanced radiative decay. PES with a shell-isolated Ag nanoantenna will open a wealth of advanced scenarios for ultrasensitive surface analysis