The importance of nanoscale confinement to electrocatalytic performance

Electrocatalytic nanoparticles that mimic the three-dimensional geometric architecture of enzymes where the reaction occurs down a substrate channel isolated from bulk solution, referred to herein as nanozymes, were used to explore the impact of nano-confinement on electrocatalytic reactions. Surfactant covered Pt–Ni nanozyme nanoparticles, with Ni etched from the nanoparticles, possess a nanoscale channel in which the active sites for electrocatalysis of oxygen reduction are located. Different particle compositions and etching parameters allowed synthesis of nanoparticles with different average substrate channel diameters that have varying amounts of nano-confinement. The results showed that in the kinetically limited regime at low overpotentials, the smaller the substrate channels the higher the specific activity of the electrocatalyst. This is attributed to higher concentrations of protons, relative to bulk solution, required to balance the potential inside the nano-confined channel. However, at higher overpotentials where limitation by mass transport of oxygen becomes important, the nanozymes with larger substrate channels showed higher electrocatalytic activity. A reaction-diffusion model revealed that the higher electrocatalytic activity at low overpotentials with smaller substrate channels can be explained by the higher concentration of protons. The model suggests that the dominant mode of mass transport to achieve these high concentrations is by migration, exemplifying how nano-confinement can be used to enhance reaction rates. Experimental and theoretical data show that under mass transport limiting potentials, the nano-confinement has no effect and the reaction only occurs at the entrance of the substrate channel at the nanoparticle surface.

Nanoparticles mimicking the three-dimensional architecture of enzymes where the reaction occurs down a channel isolated from bulk solution, referred here as nanozymes, were used to explore the impact of nano-confinement on electrocatalytic reactions.     

The etching strategy of zinc anode to enable high performance zinc-ion batteries

Zinc-ion batteries(ZIBs) are considered to be one of the most promising candidates to replace lithium-ion batteries(LIBs) due to the high theoretical capacity, low cost and intrinsic safety. However, zinc dendrites, hydrogen evolution reaction, surface passivation and other side reactions will inevitably occur during the charging and discharging process of Zn anode, which will seriously affect the cycle stability of the battery and hinder its practical application. The etching strategy of Zn ano...     

Selective nitrogen doping on carbon cloth to enhance the performance of zinc anode

Metallic zinc is attractive anode material of rechargeable aqueous Zn-based batteries due to its ambient stability,high volumetric capacity,and abundant reserves.Nonetheless,Zn anodes suffer from issues such as low coulombic efficiency(CE),large polarization and dendrite formation.Herein,uniform Zn electrodeposition is reported on carbon substrates by selective nitrogen doping.Combined experimental and theoretical investigations demonstrate that pyrrolic and pyridinic nitrogen doped in carbon play beneficial effect as zinc-philic sites to direct nucleation and growth of metallic Zn,while negligible effect is observed for graphite nitrogen in Zn plating.The carbon cloth with modified amount of doped pyrrolic and pyridinic nitrogen stabilizes Zn plating/stripping with 99.3% CE after 300 cycles and significantly increases the deliverable capacity at high depth of charge and discharge compared to undoped carbon substrate and Zn foil.This work provides a better understanding of heteroatom doping effect in design and preparation of stable 3 D carbon-supported zinc anode.     

A new organic carbon detector for size exclusion chromatography

A novel organic carbon detector (OCD) for size exclusion chromatography (SEC), and its application to the characterisation of aquatic natural organic matter (NOM) in natural and treated potable water samples, is described. The instrument uses a conventional UV-persulfate oxidation technique to convert organic carbon to CO(2). The novelty of the technique is detection of the evolved CO(2) using a sensitive Fourier transform infrared (FTIR) spectroscopy 'lightpipe' detector originally designed for detection of analytes after gas chromatographic separation. With the exception of the lightpipe, the OCD system was constructed using simple, inexpensive, readily available components. The system was designed to minimise deadvolume, allowing for use of smaller sample sizes and smaller columns, substantially shortening analysis time, while maintaining chromatographic integrity through the OCD system. Downscaling resulted in some loss of separation but it was shown that this was caused by the lower separation efficiency of the smaller capacity column, rather than from sample dispersion within the OCD system.     

Application of a high-performance liquid chromatography fluorescence detector as a nephelometric turbidity detector following Field-Flow Fractionation to analyse size distributions of environmental colloids

A new operation mode for HPLC-type fluorescence detectors is presented and evaluated using synthetic and environmental particles in the colloidal size range. By applying identical wavelengths for excitation and emission a nephelometric turbidity or single angle light scattering detector is created which can be easily coupled to flow or sedimentation Field-Flow Fractionation (Flow FFF or Sed FFF) for the analysis of colloidal dispersions. The results are compared with standard UV-vis detection methods. Signals obtained are given as a function of particle size and selected detection wavelength. Conclusions can be drawn which affect the current practice of FFF but also for other techniques as groundwater sampling and laboratory column experiments when turbidity is measured in nephelometric mode and in small sample volumes or at low flow rates.     

电化学法改性阳极对MFC性能的影响

采用不同质量分数的NH_4NO_3和(NH_4)_2S_2O_8溶液作为电解液,对双室微生物燃料电池的阳极炭布进行改性。以餐厨废水作为阳极底物,以K_3[Fe(CN)_6]和NaCl混合溶液为阴极液,考察不同电解液改性阳极条件下微生物燃料电池的产电性能及污水处理效果。结果表明,采用NH_4NO_3或(NH_4)_2S_2O_8改性炭布作为阳极的微生物燃料电池的发电性能和水处理效果均有改善。其中,采用质量分数为4%的(NH_4)_2S_2O_8溶液作为阳极改性电解液时,微生物燃料电池系统的产电性能达到最佳,其稳态电流密度约为60 m A/m~2,COD去除率约为42.5%。     

Improved SOFC performance with continuously graded anode functional layer

Continuously graded anode functional layers (CG-AFLs) were fabricated on the Ni–YSZ anode substrates by electrophoretic co-deposition (EPD) technique. The microstructure and composition of the CG-AFLs were investigated. The result showed that uniform and graded structure in AFL was obtained. The single cells were constructed on the basis of CG-AFLs, with a maximum output power density greater than 1.10 W cm^?2 obtained at 800 °C for the cell with 9.8 μm-thick CG-AFL. Electrochemical impedance spectroscopy (EIS) indicated that the excellent cell performance was contributed to the enlargement of triple phase boundary (TPB) by adding the CG-AFL.     

Cycling performance and temperature stability of a tin-borate glass anode

The thermal stability and cycling performance for a new glass material, SnB₂O₄, of interest for use as anode material in Li-ion batteries, have been examined. Both the potential range and the electrolyte composition were varied to investigate their impact on the cycling stability. It was found that the SnB₂O₄ glass exhibits an upper charge limit of 0.8 V for good cycling stability. No such limit was found for the discharge potential. When cycled in the (0.01–0.8) V range, a capacity of around 530 mAh/g was achieved for at least 40 cycles. The cycling performance was almost unaffected by changes in the electrolyte composition. Differential scanning calorimetry (DSC) measurements on the glass anode revealed a high thermal stability that exceeds that of graphite, regardless of the potential range or the specific electrolytes investigated.     

Improved electrode fabrication method to enhance performance and stability of MoS2-based lithium-ion battery anode

Choice of binder and the electrode-making process play a pivotal role in the electrochemical performance of MoS₂, when used as lithium-ion battery anode. In this work, MoS₂ nanorods are prepared by gas phase synthesis method using molybdenum trioxide (MoO₃) nanobelts and sulfur as starting materials. It has been observed that by tuning the reaction conditions, morphology and yield of the final product can be controlled. Carboxymethyl cellulose (CMC) is used as binder to fabricate the MoS₂ electrode, and its electrochemical performance is tested against Li/Li⁺. The performance of electrode can be further improved by incorporating heat treatment to the active material and conductive carbon mixture prior to electrode fabrication. The electrochemical data shows that the optimum temperature for heat treatment is 700 °C. In the current report, we would like to elucidate a detailed study based on electrode fabrication process and their impact on the electrochemical performance.     

Electrolyte additive maintains high performance for dendrite-free lithium metal anode

Because of their high capacity and low potential, lithium metal anodes are considered to be promising candidates for next generation electrode materials. However, the safety concerns and limited cycling life associated with uncontrollable dendrite growth hamper practical applications. In this work, the acidified cellulose ester, which is a mixed fiber microporous membrane film, was used as a novel electrolyte additive that effectively improves the cycle stability of the lithium metal anode and inhibits dendrite growth. The focus of this paper is on inhibiting the formation and growth of lithium dendrites. The coulombic efficiency of a Li|Cu battery with this acidified cellulose ester additive remains stable at 99% after 500 cycles under a current density of 1 mA/cm². Symmetric batteries also remain stable after 500 cycles (1000 h) under a current density of 1 mA/cm². These superior properties can be ascribed to the induced nucleation and the uniform distribution of lithium ion flux. This study uncovers an approach for effectively enabling stable cycling of dendrite-free lithium metal anodes.     

The importance of ion size and electrode curvature on electrical double layers in ionic liquids

Room-temperature ionic liquids (ILs) are an emerging class of electrolytes for supercapacitors. We investigate the effects of ion size and electrode curvature on the electrical double layers (EDLs) in two ILs 1-butyl-3-methylimidazolium chloride [BMIM][Cl] and 1-butyl-3-methylimidazolium hexafluorophosphate [BMIM][PF(6)], using a combination of molecular dynamics (MD) and quantum density functional theory (DFT) simulations. The sizes of the counter-ion and co-ion affect the ion distribution and orientational structure of EDLs. The EDL capacitances near both planar and cylindrical electrodes were found to follow the order: [BMIM][Cl] (near the positive electrode) > [BMIM][PF(6)] (near the positive electrode) ≈ [BMIM][Cl] (near the negative electrode) ≈ [BMIM][PF(6)] (near the negative electrode). The EDL capacitance was also found to increase as the electrode curvature increases. These capacitance data can be fit to the Helmholtz model and the recently proposed exohedral electrical double-cylinder capacitor (xEDCC) model when the EDL thickness is properly parameterized, even though key features of the EDLs in ILs are not accounted for in these models. To remedy the shortcomings of existing models, we propose a "Multiple Ion Layers with Overscreening" (MILO) model for the EDLs in ILs that takes into account two critical features of such EDLs, i.e., alternating layering of counter-ions and co-ions and charge overscreening. The capacitance computed from the MILO model agrees well with the MD prediction. Although some input parameters of the MILO model must be obtained from MD simulations, the MILO model may provide a new framework for understanding many important aspects of EDLs in ILs (e.g., the variation of EDL capacitance with the electrode potential) that are difficult to interpret using classical EDL models and experiments.     

Electrochemical performance of lithium titanate anode fabricated using a water-based binder

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Electrochemical performance of graphene nanosheets as anode material for lithium-ion batteries

Graphene nanosheets (GNSs) were prepared from artificial graphite by oxidation, rapid expansion and ultrasonic treatment. The morphology, structure and electrochemical performance of GNSs as anode material for lithium-ion batteries were systematically investigated by high-resolution transmission electron microscope, scanning electron microscope, X-ray diffraction, Fourier transform infrared spectroscopy and a variety of electrochemical testing techniques. It was found that GNSs exhibited a relatively high reversible capacity of 672 mA h/g and fine cycle performance. The exchange current density of GNSs increased with the growth of cycle numbers exhibiting the peculiar electrochemical performance.     

A selenium-doped carbon anode of high performance for lithium ion batteries

Journal of Solid State Electrochemistry - The strong demand on high-performance lithium ion batteries has brought up an attention upsurge in the research society and the commercial market. Carbon...     

Lithium storage performance of Sn-MOF-derived SnO2 nanospheres as anode material

Journal of Solid State Electrochemistry - In this work, a spherical Sn-MOF precursor was synthesized through hydrothermal method using 1,3,5-benzenetricarboxylic acid (H3BTC) as the organic ligand....     

Critical importance of current collector property to the performance of flexible electrochemical power sources

The property of current collector is significant to the performance of flexible power supply.     

A contactless conductivity detector for capillary electrophoresis: effects of the detection cell geometry on the detector performance

The effect of the gap between the electrodes and of their width on the behavior of a capacitively wired contactless conductivity detector was studied. The results obtained have indicated that the detector response can be qualitatively described by a model based on the concept of the effective electrode width which is a complex parameter determined by the gap between the electrodes, the frequency of the input signal and the conductivity of the test solution. The detector sensitivity and the effect on the separation efficiency depend on the difference between the effective and geometric electrode widths. Higher detection sensitivities have been attained for detectors with wide electrodes operating at lower frequencies, however, better separation efficiencies have been achieved using detectors with narrow electrodes and higher operational frequencies. The noise increases with decreasing gap between the electrodes and increasing frequency, especially with detectors employing narrow electrodes.