Deposition-dissolution Cycles Research Articles

Hybrid Solid Electrolyte Interphases Enabled Ultralong Life Ca-Metal Batteries Working at Room Temperature.

Currently, the application of calcium metal anodes is challenged by rapidly degenerated plating/stripping electrochemistry without suitable solid electrolyte interphases (SEIs) capable of fast Ca2+ transport kinetics and superior ability to resist anion oxidation. Here, through in situ evolved Na/Ca hybrid SEIs, symmetrical Ca//Ca batteries readily remain stable for more than 1000 h deposition-dissolution cycles (versus less than 60 h for those with pure Ca SEIs under the same condition). Coupled with a specially designed freestanding lattice-expanded graphitic carbon fiber membrane and tailored operation voltages, the proof-of-concept Ca-metal batteries reversibly run for almost 1900 cycles with ≈83% capacity retention and a high average discharge voltage of 3.16V. The good performance not only benefits from the stable SEIs at the Ca metal surface which affords free Ca2+ transports and prohibits out-of-control fluridation of Ca (forming CaF2 ion-/electron-insulating layer) but is also attributed to reversible relay insertion/extraction electrochemistry in the cathode. This work sheds new light on durable metal battery technology.

Silver isotope analysis of gold nuggets: An appraisal of instrumental isotope fractionation effects and potential for high-resolution tracing of placer gold

We describe a technique for high-precision analysis of 109Ag/107Ag ratios in natural and archaeological gold (1.0–120 mg/g Ag) with particular emphasis on the control of Ag yield and effects of instrumental mass bias. After dissolution of mg-sized gold samples in aqua regia and conversion to chlorides, a miniature column filled with the anion exchange resin AG@1-X8 was used for removal of Au from the sample solutions. In a second miniature column made of the Triskem TBP resin Ag was converted from the chloride to the nitrate form. Isotopic analyses on the MC-ICP-MS employed the combination of Pd-doping and standard bracketing and considering the measurements of replicate dissolutions and chromatographic separations for SRM978a and CEZAg reference solutions, the combined analytical uncertainty (2 s) of the analytical method is better than 0.016‰. A solution prepared from several gold nuggets was characterised isotopically (CEZAg with δ109Ag = 0.043 ± 0.015‰) for use as a silver-in‑gold reference material in Ag isotope studies of natural and processed gold.Results for gold nuggets from three continents indicate a wide variation in Ag concentrations (5 to 123 mg/g) and this is matched by an equally wide range in isotopic compositions (δ109Ag −0.58 to +0.83‰). This is larger than the variation found so far in in native gold from primary deposits (−0.42 to +0.5‰). Although small isotopic effects to lower δ109Ag during strong Ag loss are possible within a single grain, most analysed nuggets are internally isotopically homogeneous. This suggests preservation of the primary δ109Ag in the supergene environment and that gold was sourced from several distinct gold deposits in the catchment. Recent studies, however, indicate that even single primary deposits may be isotopically heterogeneous implying that Ag isotope fractionation is caused by numerous deposition-dissolution cycles in hydrothermal systems. Fine-grained detrital gold from three placers along the Rhine river in Germany show only small differences in δ109Ag (−0.005 ± 0.047 to +0.124 ± 0.007‰, despite being distributed along 480 km of river length. This may indicate thorough mixing of gold grain populations during transport.The small sample size required for Ag isotope work on gold opens the way for detailed micro-sampling approaches. These may be used to further examine the potential for within-grain isotopic variability related to fluviatile processing and can be used to correlate the composition of the placers with that of grains from primary sources.

New sample preparation procedure for effective improvement on surface-enhanced Raman scattering effects

As shown in the literature, molecules located between two metallic nanoparticles (NPs) can display the greatest surface-enhanced Raman scattering (SERS) enhancement. Thus many methods have been developed to increase these hot spots on SERS-active substrates. Generally, SERS-active substrates were first prepared. Then probe molecules were adsorbed on the prepared substrates to examine the corresponding SERS effects. In this work, we employ a newly developed pathway to prepare SERS-active substrates with Au NPs by sonoelectrochemical deposition-dissolution cycles (SEDDCs). In preparation probe molecules were added in electrolytes to produce SERS-active substrates with analytes-adsorbed Au NPs by one-step. Encouragingly, based on this strategy, the SERS intensity of cation-type dye of model probe molecules of Rhodamine 6G (R6G) with 2×10−6M in preparation can be increased by more than 20-fold of magnitude, as compared with that of R6G adsorbed on the already-prepared SERS-active substrates by using a general procedure for preparation of SERS samples. This strategy for improved SERS effect is also effective for probe molecules of 4-mercaptopyridine (4-MPy) with 1×10−4M. Moreover, the improved SERS effect is successfully explained from the viewpoint of electromagnetic (EM) enhancement.

Surfactant-assisted preparation of surface-enhanced Raman scattering-active substrates

As shown in the literature, cationic surfactant hexadecyltrimethylammonium bromide (CTAB) has been predominantly employed in the shape-controlled synthesis of Au nanoparticles (NPs) in solution to produce the corresponding shape-dependent Au NP catalysts. Among the different techniques used to obtain rough metal substrates with surface-enhanced Raman scattering (SERS) activities, controllable and reproducible surface roughness can be generated using an electrochemical process. In this work, innovative SERS-active substrates with Au NPs are prepared for the first time using sonoelectrochemical deposition-dissolution cycles (SEDDCs) in CTAB-containing electrolytes. Encouragingly, the SERS intensity for both the model probe molecule Rhodamine 6G (R6G) and the general example molecule 4-mercaptopyridine (4-MPy) adsorbed onto the developed substrates are higher by more than one order of magnitude compared with R6G and 4-MPy adsorbed onto SERS-active substrates prepared in solutions in the absence of CTAB. Moreover, the limits of detection (LOD) recorded for the developed SERS-active substrates are as low as 2 × 10−15 and 1 × 10−10 M for R6G and 4-MPy, respectively.

Surface-enhanced Raman scattering-active silver nanostructures with two domains

Generally, a controllable and reproduced surface roughness for surface-enhanced Raman scattering (SERS) studies can be generated through control of the electrochemical oxidation–reduction cycles (ORC) procedure. In this work, we propose a new sonoelectrochemical approach to prepare SERS-active substrates with two domain-Ag nanostructures. The method is based on a strategy of deposition–dissolution cycles (DDCs) by using a cathodic overpotential and an anodic overpotential from open circuit potential (OCP) in turn under sonication. The prepared SERS-active substrate demonstrates large Raman scattering enhancement for adsorbed Rhodamine 6G (R6G) with an enhancement factor of 2.3 × 10 8 and a limit of detection of 2 × 10 −13 M. The improved SERS performances can be successfully explained from the viewpoints of electromagnetic (EM) and chemical (CHEM) enhancements.

New electrochemical method to deposit surface-enhanced Raman scattering-active silver nanoparticles on metal substrates

As shown in the literature, many methods have been developed to improve the signal, reproducibility and stability of surface-enhanced Raman scattering (SERS) for its reliable application. However, the fabrication needed is laborious. In this work, we propose an effective method to prepare SERS-active substrates with Ag nanoparticles (NPs) by a new electrochemical strategy of deposition–dissolution cycles (DDCs). This electrochemical method is based on a cathodic potential of 0.25 V and an anodic potential of 1.05 V vs.Ag/AgCl, which are applied in turn under sonication. The prepared SERS-active substrate demonstrates a large Raman scattering enhancement for adsorbed Rhodamine 6G (R6G). The practical detection limit for polypyrrole deposited on this substrate is 0.1 μC cm−2. Moreover, the prepared SERS-active substrates exhibit satisfactory reproducibility and thermal stability. The SERS spectrum of R6G on the newly developed substrate still performs well at a high temperature of 250 °C.

A new strategy to prepare surface-enhanced Raman scattering-active substrates by electrochemical pulse deposition of gold nanoparticles

In this communication, we develop a simple pathway to prepare SERS-active substrates with Au nanoparticles (NPs) by an electrochemical strategy of deposition-dissolution cycles (DDCs). The prepared SERS-active substrates demonstrate large Raman scattering enhancement for Rhodamine 6G (R6G) with a detection limit of 2 × 10(-12) M and an enhancement factor of 5.8 × 10(7).

A short review on the comparison between Li battery systems and rechargeable magnesium battery technology

An active metal that should be considered as an anode material in high energy density batteries is definitely magnesium. It is relatively cheap, much safer to use and handle than lithium, and its compounds are usually non-toxic. Similar to lithium, magnesium is covered by surface films in any ‘inert’ atmosphere that contains atmospheric contaminants, and in most of the relevant electrolyte solutions for batteries. In contrast to lithium where the surface films covering the active metal are Li-ion conductors, surface films formed similarly on magnesium cannot conduct the bivalent Mg 2+ ions. We developed new electrolyte solutions based on ethers of the ‘glyme’ family and magnesium aluminates whose electrochemical window is 2.5 V wide. The efficiency of Mg deposition–dissolution cycles in these solutions is higher than 99%. We also showed that it is possible to construct rechargeable Mg batteries using these electrolyte solutions and cathodes of the Mg x MoS y type (chevrel phase), which operate at 1–1.5 V, and can deliver more than 1000 charge–discharge cycles. Some technical details of these battery systems are discussed.