Fast electrodeposition of zinc onto single zinc nanoparticles.

The zinc deposition reaction onto metallic zinc has been investigated at the single particle level through the electrode-particle collision method in neutral solutions, and in respect of its dependence on the applied potential and the ionic strength of a sulphate-containing solution. Depending on the concentration of sulphate ions in solution, different amounts of metallic zinc were deposited on the single Zn nanoparticles. Specifically, insights into the electron transfer kinetics at the single particles were obtained, indicating an electrically early reactant-like transition state, which is consistent with the rate-determining partial de-hydration/de-complexation process. Such information on the reaction kinetics at the nanoscale is of vital importance for the development of more efficient and long-lasting nanostructured Zn-based negative electrodes for Zn-ion battery applications.

Tannic acid capped gold nanoparticles: capping agent chemistry controls the redox activity.

We report the key role of the capping agent in the detection of metal cations using tannic acid (TA) capped gold nanoparticles at both ensembles (using cyclic voltammetry) and with individual particles (using oxidative and reductive nanoimpacts). The results show that the capping agent complexes with Zn2+ and Hg2+ in a reversible and Langmuirian manner in both cases. The sensitivity of detection is determined by the amount of capping agent present on the nanoparticles with similar values seen for both oxidation and reduction reactions. The optimisation of the capping agent loading is therefore key to metal ion detection.

Understanding gold nanoparticle dissolution in cyanide-containing solution via impact-chemistry.

The electrochemical dissolution of citrate-capped gold nanoparticles (AuNPs) was studied in cyanide (CN-) containing solutions. It was found that the gold nanoparticles exhibited different dissolution behaviours as ensembles compared to the single particles. At the single particle level, a nearly complete oxidation of 60 nm AuNPs was achieved at concentrations greater than or equal to 35.0 mM CN- and at a potential of 1.0 V. Mechanistic insights and rate data are reported.

Electrochemical Behavior of Single CuO Nanoparticles: Implications for the Assessment of their Environmental Fate.

The electrochemical behavior of copper oxide nanoparticles is investigated at both the single particle and at the ensemble level in neutral aqueous solutions through the electrode-particle collision method and cyclic voltammetry, respectively. The influence of Cl- and NO3- anions on the electrochemical processes occurring at the nanoparticles is further evaluated. The electroactivity of CuO nanoparticles is found to differ between the two types of experiments. At the single-particle scale, the reduction of the CuO nanoparticles proceeds to a higher extent in the presence of chloride ion than of nitrate ion containing solutions. However, at the multiparticle scale the CuO reduction proceeds to the same extent regardless of the type of anions present in solution. The implications for assessing realistically the environmental fate and therefore the toxicity of metal-based nanoparticles in general, and copper-based nanoparticles in particular, are discussed.

Revealing the electronic character of the positive electrode/electrolyte interface in lithium-ion batteries.

High voltage operating active materials are among the most promising components for positive electrodes of future high energy lithium-ion batteries. However, the operating potential range of such materials often exceeds anodically the thermodynamic stability window of the electrolyte. A surface layer is therefore formed, which is supposed to be one of the reasons for the high irreversible charge loss of these electrodes. The electronic character of such a surface layer formed at the electrode/electrolyte interface of LiNi0.5Mn1.5O4 (LNM), stoichiometric (x = 0) and overlithiated (x = 0.1) Li1+x(Ni1/3Mn1/3Co1/3)1-xO2 (NMC) based paste electrodes was investigated in situ using feedback-mode scanning electrochemical microscopy (SECM). The role in the formation of an electronically insulating layer of a conductive carbon additive-based electrode and of the Al current collector was explored as well. The surface layers formed on all oxide based paste electrodes and on conductive carbon additive based electrodes showed unexpectedly an electronic conducting behavior, while the Al current collector formed an electronically insulating layer which was found to be influenced by the electrolyte.

Potassium (De-)insertion Processes in Prussian Blue Particles: Ensemble versus Single Nanoparticle Behaviour.

Potassium (de-)insertion from Prussian blue (PB) is investigated at the single and multi-particle scale. The electrochemical behaviour is found to differ between the two measurement types. At the single particle level, oxidation of the PB nanoparticles with concomitant K+ deinsertion occurs more readily than the associated reduction, relating to K+ insertion. In contrast, the cyclic voltammetry of PB in a composite electrode containing conductive additives and polymeric binder suggests the opposite behaviour. Implications for assessing battery materials are discussed.

Lithium-Ion-Transfer Kinetics of Single LiMn2 O4 Particles.

A stochastic investigation of lithium deinsertion from individual 200-nm-sized particles of LiMn2 O4 reveals the rate-determining step at high overpotentials to be the transfer of the cation across the particle-electrolyte interface. Measurement of the (electro)chemical behavior of the spinel is undertaken without forming a conductive composite electrode. The kinetics of the interfacial ion transfer defines a theoretical upper limit for the discharge rates of batteries using LiMn2 O4 in an aqueous environment.

Solid Electrolyte Interphase (SEI) at TiO2 Electrodes in Li-Ion Batteries: Defining Apparent and Effective SEI Based on Evidence from X-ray Photoemission Spectroscopy and Scanning Electrochemical Microscopy.

The high (de)lithiation potential of TiO2 (ca. 1.7 V vs Li/Li+ in 1 M Li+) decreases the voltage and, thus, the energy density of a corresponding Li-ion battery. On the other hand, it offers several advantages such as the (de)lithiation potential far from lithium deposition or absence of a solid electrolyte interphase (SEI). The latter is currently under controversial debate as several studies reported the presence of a SEI when operating TiO2 electrodes at potentials above 1.0 V vs Li/Li+. We investigate the formation of a SEI at anatase TiO2 electrodes by means of X-ray photoemission spectroscopy (XPS) and scanning electrochemical microscopy (SECM). The investigations were performed in different potential ranges, namely, during storage (without external polarization), between 3.0-2.0 V and 3.0-1.0 V vs Li/Li+, respectively. No SEI is formed when a completely dried and residues-free TiO2 electrode is cycled between 3.0 and 2.0 V vs Li/Li+. A SEI is detected by XPS in the case of samples stored for 6 weeks or cycled between 3.0 and 1.0 V vs Li/Li+. With use of SECM, it is verified that this SEI does not possess the electrically insulating character as expected for a "classic" SEI. Therefore, we propose the term apparent SEI for TiO2 electrodes to differentiate it from the protecting and effective SEI formed at graphite electrodes.

Fluorescence Monitored Voltammetry of Single Attoliter Droplets.

The lipid soluble fluorophore Nile Red (9-diethylamino-5-benzo[α]phenoxazinone) is used to fluorescently and electrochemically label an organic-in-water emulsion, where the organic phase is an ionic liquid [P6,6,6,14][FAP]/toluene mixture. The optical detection of the individual droplets is enabled facilitating the in situ tracking and sizing of the suspended particles (average diameter = 530 nm, interquartile range = 180 nm). Through the use of a combined thin-layer optical/electrochemical cell, the irreversible accumulation of the droplets at an optically opaque carbon fiber electrode (diameter ∼7.5 µm) can be monitored. Potentiostatic control of the system enables the fluorescence of the surface bound particles to be electrochemically switched via control of the redox state of the dye. Subsequent measurements of the individual particle fluorescence intensities as a function of the applied electrode potential enables construction of an effective, dynamically recorded cyclic voltammogram of an individual particle. The confined volume voltammetry (∼tens of attoliters) yields insight into the asymmetry of the kinetics of the redox switching process, where it is proposed that the reformation of the fluorescent Nile Red becomes chemically "gated" in the organic phase.

Wet Nanoindentation of the Solid Electrolyte Interphase on Thin Film Si Electrodes.

The solid electrolyte interphase (SEI) film formed at the surface of negative electrodes strongly affects the performance of a Li-ion battery. The mechanical properties of the SEI are of special importance for Si electrodes due to the large volumetric changes of Si upon (de)insertion of Li ions. This manuscript reports the careful determination of the Young's modulus of the SEI formed on a sputtered Si electrode using wet atomic force microscopy (AFM)-nanoindentation. Several key parameters in the determination of the Young's modulus are considered and discussed, e.g., wetness and roughness-thickness ratio of the film and the shape of a nanoindenter. The values of the Young's modulus were determined to be 0.5-10 MPa under the investigated conditions which are in the lower range of those previously reported, i.e., 1 MPa to 10 GPa, pointing out the importance of the conditions of its determination. After multiple electrochemical cycles, the polymeric deposits formed on the surface of the SEI are revealed, by force-volume mapping in liquid using colloidal probes, to extend up to 300 nm into bulk solution.

In situ visualization of Li-ion intercalation and formation of the solid electrolyte interphase on TiO2 based paste electrodes using scanning electrochemical microscopy.

Scanning electrochemical microscopy (SECM) inside a glove box was used for the in situ visualization of solid electrolyte interphase (SEI) formation as well as Li-ion intercalation and de-intercalation on anatase TiO2 based paste electrodes.