Electrolytic Environment Research Articles

Illuminating nanostructured gold electrode: surface plasmons or electron ejection?

Recently, the photoelectric effect in metals in electrolyte environments has aroused the interest of researchers. However, direct evidence for surface plasmons-enhanced electrochemical reactions involving classic outer-sphere reactions of reversible redoxcouples is seldom reported. We used a surface plasmons-active gold-mushroom-array as a working electrode and observed enhanced faradaic current from ferrocenemethanol following illumination with a xenon lamp. The photoelectric current behaved differently in the presence and absence of oxygen in the solution. The preliminary results are discussed with consideration of the possible mechanisms of electron transfer, although they are very complex, due to the lack of direct evidence. Some consideration was also taken of the research on photoelectrochemical reactions on metallic electrodes.

Characteristics of sliding bubble in aqueous electrolyte: In presence of an external magnetic field

An experment was carried out to examine the influence of an external magnetic field on a bubble in an aqueous electrolytic cell. In the electrolysis process, bubbles nucleate instateneously and the electrolytic flow is mostly caused by swarm of bubbles, which makes it difficult to quantify the impacts of various forces, in particular the magneto-hydrodynamic (MHD) and gravity forces in Hall-Héroult cells. In this paper, an aqueous-electrolytic cell was designed to allow a single bubble to slide underneath the inclinde anode in an electrolytic environment and in presence of an external magnetic field. Air was injected at a constant flow rate of 6.2ml/min through a 3mm diameter orifice into a quiescent conducting aqueous electyrolytic media. Experiments were conducted both with and without external-magnetic field for varying anode-inclinations ranging from θ=4°, 6° and 8° in order to quantify the order of magnitude of MHD force in comparison to the gravity force. The data clearly shows that, in presence of the magnetic field, the bubble changes its shape and orientation at the onset of nucleation, which in turn gives rise to a non-linear trajectory across the longitudinal axis of electrode establishing a large circulatory flow within the electrolytic cell. In general, the experimental data shows that the bulk velocity was found to be dominated by the MHD driven flow overshadowing the influence of gravity force.

Ion Transport and Competition Effects on NaTi2(PO4)3 and Na4Mn9O18 Selective Insertion Electrode Performance.

We evaluate the efficiency and capacity of electrochemically reversible insertion electrodes for use in targeted ion removal applications in aqueous solutions. The relative attributes of insertion material chemistry are evaluated by comparing the performance of two different sodium insertion materials, NaTi2(PO4)3 and Na4Mn9O18, in different electrolyte environments. We performed experiments over a range of solution compositions containing both sodium and other non-inserting ions, and we then developed mechanistic insight into the effects of solution concentration and composition on overpotential losses and round trip Coulombic efficiency. In dilute aqueous streams, performance was limited by the rate of ion transport from the bulk electrolyte region to the electrode interface. This leads to slow rates of ion removal, large overpotentials for ion insertion, parasitic charge loss due to water electrolysis, and lower round trip Coulombic efficiencies. This effect is particularly large for insertion electrodes with redox potentials exceeding the water stability window. In solutions with high background concentrations of non-inserting ions, the accumulation of non-inserting ions at the electrode interface limits inserting ion flux and leads to low ion removal capacity and round trip Coulombic efficiency.

Specific binding of antigen-antibody in physiological environments: Measurement, force characteristics and analysis

The specific recognition of the antigen by the antibody is the crucial step in immunoassays. Measurement and analysis of the specific recognition, including the ways in which it is influenced by external factors are of paramount significance for the quality of the immunoassays. Using prostate-specific antigen (PSA)/anti-PSA antibody and α-fetoprotein (AFP) /anti-AFP antibody as examples, we have proposed a novel solution for measuring the binding forces between the antigens and their corresponding antibodies in different physiological environments by combining laminar flow control technology and optical tweezers technology. On the basis of the experimental results, the different binding forces of PSA/anti-PSA antibody and AFP/anti-AFP antibody in the same phosphate-buffered saline (PBS) environments are analysed by comparing the affinity constant of the two antibodies and the number of antigenic determinants of the two antigens. In different electrolyte environments, the changes of the binding force of antigens-antibodies are explained by the polyelectrolyte effect and hydrophobic interaction. Furthermore, in different pH environments, the changes of binding forces of antigens-antibodies are attributed to the role of the denaturation of protein. The study aims to recognise the antigen-antibody immune mechanism, thus ensuring further understanding of the biological functions of tumour markers, and it promises to be very useful for the clinical diagnosis of early-stage cancer.

(Invited) Electrodeposition and Development of Mg and Ca Metal Anodes

Various metals have been used as battery anodes in electrochemical cells ever since the birth of batteries with Volta’s pile and also in the first commercialized primary (Zn/MnO2, Leclanché 1866) and secondary (Pb/acid, Planté 1859) batteries. The idea and prospects of building a technology based on lithium are much more recent, as it required moving away from aqueous electrolytes. However, the first Li-MoS2 cells with specific energy two or three times higher than the current Ni/Cd or Pb/acid cells were withdrawn from the market after safety difficulties were experienced with overheating on recharge related to dendrite growth. As an alternative, secondary Li-ion batteries avoiding the use of lithium metal anodes were commercialized by Sony in 1991. In contrast with Li metal anode, electrodeposition of Mg and Ca does not seem to be plagued with dendrite formation.1,2 In addition to the low cost of the raw materials ($5000/ton, $100/ton and $265/ton for Li2CO3, CaCO3 and MgO2, respectively), such alternative technologies would benefit from high standard reduction potentials (ca. -2.87 V and -2.37 V vs NHE for Ca and Mg, respectively, as compared to -3 V for Li) and high theoretical electrochemical capacities (both gravimetric and volumetric) for the metal electrode, while relying on the 5th (Ca) and 8th (Mg) most abundant elements on the Earth’s crust, respectively, whereas Li is the 25th. These metals are thus interesting candidates as anodes in rechargeable batteries. Pioneering research work by Aurbach et al.3,4 allowed to conclude that the electrochemical behavior of Ca and Mg metal anodes in conventional organic electrolytes is surface-film controlled, as is the case for Li, but Ca and Mg plating is virtually impossible, which was attributed to the lack of divalent cation transport through the passivation layer (solid electrolyte interphase or SEI). Therefore, research has been focusing on electrolyte formulation in which no SEI is formed. Recently Ca plating and stripping through a stable SEI layer has been demonstrated, setting out the basis for the development of new electrolytes for divalent cation based batteries with high resilience upon oxidation.2 The effect of several factors influencing the Ca deposition/stripping will be presented. Also, the reliability of the so called half-cell configuration in which Mg or Ca pseudo reference and counterelectrodes are used will be discussed and a systematic evaluation of the non-polarizability and stability in the electrolytic environment will be presented for these metal electrodes. Fig ure 1. Theoretical gravimetric and volumetric capacities for different anodes: metals and Li-ion.

Theoretical and experimental approach on the molecular interactions of the DL-Alanine with an electrolytic environment

The molecular interactions that promote the stability of proteins and amino acids in saline solutions is a central topic of molecular biophysics. However, a well-supported molecular picture of the phenomena has not been established yet. In this paper, we studied as model system the mix between DL-Alanine in aqueous solutions of STP (Na2S2O3·5H2O) at different temperatures, from volumetric and viscometric properties. The thermophysical properties obtained indicate the presence of a strong preferential solvation, structure-making action and a possible salt in effect. Quantum chemical calculations and molecular dynamic (MD) simulations provide a new insight to support these arguments.

Study of Transport in a Novel, Heteropoly Acid Hybrid Polymer Membrane Designed for Use in Flow Batteries

The energy storage and power density are decoupled for flow batteries, therefore they may be tailored to specific applications and offer promising potential for grid scale energy storage.1 For this new technology to make an impact on our energy landscape, cost must be reduced. Some suggested design criteria for the separator to reduce capital costs requirements an area specific resistance <0.3 ohm/cm2 and low parasitic crossover.2One mechanism of parasitic crossover is through diffusion within extensive water channels, a drawback to perfluorinated sulfonic acids. This research works at minimizing unwanted crossover through reduction of water channels. The approach taken is to use heteropoly acid (HPA) to crosslink a fluoroelastomer. When films are crosslinked, they are more restricted and less able to swell, thus reducing the channels for crossover to occur. The reason for using HPA it is has proven to have great conductivity with low water content.3 We will report on transport of a verity of species in different electrolyte environments and discuss how film synthesis and processing can lead to more selective separators with better power and selectivity than Nafion.

Mg-Based Spinel Nanocrystals: Phase, Size, Electrochemical Properties

Li-ion batteries are the top choice in electrochemical energy storage for portable devices and mobile vehicles. However, the limited storage capacities do not quite yet meet the emerging energy demands in transportation and grid markets. Multivalent batteries based on divalent cations have attracted wide attention with high energy density/capacity in different framework of oxide cathodes. For instance, spinel structure M2O4, has been theoretically predicted as one of the most suitable oxide cathode for the reversible intercalation with Mg2+ [1]. Further, reversible, yet sluggish Mg intercalation into Mn2O4 host, prepared from de-lithiated LiMn2O4 electrode, was reported in aqueous electrolyte environments [2]. In order to enhance kinetics, reduction of particles to the smallest possible sizes is desired. Further, spinel-type Mn­2O4 can only be prepared by delithiation of LiMn2O4. Therefore, the direct synthesis of the parent spinel oxide, MgMn2O4, in the form nanocrystals would be desirable to investigate the fundamental limits of Mg intercalation within the spinel oxide framework, preferably in non-aqueous electrolytes. Here, we report a series of Mg-based spinel nanocrystals with different phase (MgxMn3-xO4 and MgxCr3-xO4), size (5nm~50nm), and shape (cube and sheet) via a low temperature hydrothermal process, followed by calcination (Figure 1). All samples were characterized with X-ray diffraction and spectroscopy, as well as electron microscopy in order to define the products of electrochemical reactions in non-aqueous cells. Our goal was to explore spinel oxide nanocrystals with optimal size, phase, and shape and establish size-structure-property relationship for the experimental realization of Mg reversible intercalation in spinel oxide hosts. 1. Liu, M., et al., Energy Environ. Sci. 2015, 8, 964. 2. Kim, C. et al., Adv. Mater. 2015, 27, 3377. Figure 1 (a) Representative STEM image of 50nm MgMn­2O4 nanocubes (b) Representative STEM image of 2~5nm thickness MgMn­2O4 nanosheets Figure 1

A simple model for long‐time degradation of magnesium under physiological conditions

The present work applies the law of mass conservation toward an analytical model describing the long‐term degradation of Mg‐0.3Ca implant material in defined physiological electrolyte environments. The model takes into account surface conversion and degradation product deposition related changes of degradation rates by introducing an effective layer thickness. The analytical nature of the approach does not consider detailed chemical and electrochemical process. Thus, it simply declares an effective damping term. In this way it can be applied easily for the prediction of materials failure in the named environments. Restrictions of the approach will be discussed as well since validity relates to a number of aspects.

(Invited) Electrochemically Tuned Metamaterials: New Scenarios Navigated By Theory

The notion of metamaterials has emerged in this century, primarily in the context of new structures with unusual optical properties, such as specially designed plasmonic materials. But metamaterials can be considered much more broadly, in the context of what is alternatively called smart materials, or even more modetly functional materials which can perform different kind of novel functions at our will. N. Zheludev, opening a META-2014 congress in Singapore, made a provocative statement: “The time of metamaterials is over. It is the time of …tuneable metamaterials”. Electrochemistry, known to physicists as a “surface science with a joy stick — the potentiostat” (B.Ocko) is actually in a best position to deliver innovations on this front. It can be used to tune the properties of nano and micro- structures designed to be electrochemically controlled. In such structures, varying electrode potentials rearranges the ionic distributions, remarkably affecting system properties. In this keynote I will discuss few most recent examples of electroactive/electrotuneable materials, the study of many of which are still in progress, and the design of which has been navigated or strongly influenced by the theory. These are Electrovariable nanoplasmonic mirrors and trace analyte sensors [1-2].Electrotuneable friction [3]Ultrananoporous supercapacitors [4,5]Electroactuators [6]Reverse electroactuators — harvesters of mechanical energy, such as AC-current generating shoes [7]Electrochemical single molecule rectifiers [8] Looking pretty much applied, all this systems, however, rest on interesting physics, contain challenges for theory, themselves emerged as derivatives of knowledge that electrochemistry accumulated by now. [1] J. Edel, A.A. Kornyshev, A. Kucernak, M. Urbakh, “Fundamentals and applications of self-assembled plasmonic nanoparticles at interfaces”, Chemical Soc. Reviews (2016) - DOI: 10.1039/c5cs00576k. [2] J.B. Edel, A.A.Kornyshev, M.Urbakh. “Self-assembly of nanoparticle arrays for use as mirrors, sensors, and antennas”, ACS NANO, 7, 9526-9632 (2013). [3] O. Fajardo, F. Bresme, A.A. Kornyshev, M. Urbakh, Electrotunable lubricity with ionic liquid nanoscale films, Scientific Reports (NPG) 5 # 7698 (2015); “Electrotunable friction with ionic liquid lubricants: how important is the molecular structure of ions?” J.Phys.Chem.Lett. 6, 3998-4004 (2015). [4] M.V.Fedorov, A.A.Kornyshev, Ionic liquids at electrified interfaces, Chem.Rev. 114, 2978−3036 (2014). [5] S. Kondrat, A.A.Kornyshev, Pressing a spring: what does it take to maximize the energy storage in nanoporous supercapacitors? Nanoscael Horizons, B1, 45-52 (2016). [6] A. Lee, R. Colby, A.A. Kornyshev, “Electroactuation with single charge carrier ionomers: the roles of electrostatic pressure and steric strain”, Soft Matter 9,3767-3776 (2013). [7] A.B. Kolomeisky, A.A. Kornyshev, 2016, Current-generating 'double layer shoe' with a porous sole, J. Phys.Cond.Matter 28, ISSN: 0953-8984 (2016). [8] K.C.M. Cheung, X. Chen, T.Albrecht, A. A. Kornyshev, “Principles of a single-molecule rectifier in electrolytic environment”,J.Phys.Chem.C (2016) - DOI: 10.1021/acs.jpcc.5b10320.

Performance of Conducting Polymers Electropolymerized Under Various Conditions for Redox–Magnetohydrodynamics (R-MHD) Pumping

Poly(3,4-ethylene dioxythiophene), PEDOT, was electropolymerized under different electrochemical conditions onto electrodes from two different electrolytes, tetrabutylammonium hexafluorophosphate (TBAPF6) and lithium perchlorate (LiClO4) in propylene carbonate (PC). Films were characterized by cyclic voltammetry, chronoamperometry, chronopotentiometry, and electrochemical impedance to determine performance suitable for redox-magnetohydrodynamics (MHD) microfluidics. Scanning electrochemical microscopy revealed information about morphological features. Maximizing charge capacity and current density of such modified electrodes provides longer MHD pumping times and faster fluid speeds, respectively, which in turn allows for a wider range of possible lab-on-a-chip applications for this microfluidics method. MHD is a non-mechanical pumping approach where fluid flows between electrodes by a net body force ( FB ), generated by the equation FB = j × B, where j is ionic current density and B is magnetic flux density. 1,2 It offers unique advantages that complement other microfluidics methods, such as flat flow profiles, tunability, portability, circular flow, and low voltage requirements. 3 The electronic current or potential applied at the electrodes generates ionic current by oxidizing and reducing redox species in the cell. Contamination to analyte in the surrounding solution can be avoided by immobilizing redox species on the electrode surfaces, which also offers fast access of electrodes to high concentrations of charge and therefore high current and high fluid velocity. PEDOT has been used successfully by us for this purpose because it generates MHD flow in the presence of a magnetic field while maintaining good chemical stability, reversible doping states, and a low redox potential. 4,5 Its monomer, EDOT, is also commercially available. PEDOT performance can vary widely, depending on (1) the conditions under which it is electropolymerized and (2) electrolyte environments in which it is used for MHD pumping. Results will be presented that address both of these points. Electrochemical deposition was chosen because it requires a small amount of monomer, forms well adherent films, incorporates dopant ions as needed, and allows programmability of deposition time. 6 Film efficiency can be tuned by optimizing deposition factors, such as electrodeposition conditions (cycled or stepped potential or current, duration, and number of cycles), solvents, electrolytes, monomer types, and concentrations. 7,8 In this study, primarily cyclic voltammetry was investigated for deposition in organic solvents that dissolve monomers more easily than aqueous solutions, and which generate thick, well adherent, and highly conductive films. 9 PEDOT was deposited on gold microband electrodes (1.5 cm × 650 μm × 0.250 μm) for MHD experiments and electrochemical characterization. Additional studies involving potentiostatic and galvanostatic electrodeposition of other viable thiophene based monomers (e.g. ProDOT (3,4-Propylenedioxythiophene) and hydroxymethyl-EDOT) will also be described for charge and current maximization. Propylene carbonate (PC) has been shown to be a suitable solvent for EDOT electrodeposition. Its high boiling point, compared to other organic solvents (e.g acetonitrile), avoids evaporation, and therefore maintains a stable monomer concentration in small volumes for long periods of time. Maximum current densities (acquired in the same aqueous electrolyte solution) for films electrodeposited from different electrolytes (LiClO4 and TBAPF6) in PC were within error of each other, but the charge densities depended on the potential range of electrodeposition. In MHD experiments, this performance of the polymers translated into similar fluid speeds and different pumping durations. The maximum achievable current density depended greatly on the type and ionic strength of the electrolyte solution in which the films were characterized having the following increasing order: 0.1 M NaCl (x) < 0.01 M PBS (1.36x) < 0.1 M PBS (5x). Poly-ProDOT films deposited from TBAPF6in PC exhibited lower current density and lower charge density in aqueous electrolytes than their PEDOT counterparts by factors of 1.65 and 2.55 times, respectively. References Grant, K. M.; Hemmert, J. W.; White, H. S. J. Am. Chem. Soc. 2002, 124, 462−467. Leventis, N.; Gao, X. R. Anal. Chem. 2001, 73, 3981−3992. Sahore, V.; Fritsch, I. Anal. Chem . 2013, 85 (24), 11809–11816. Nash, C.K.; Fritsch, I. Anal. Chem. 2016, 88 (3), 1601–1609. Poverenov, E.; Li, M.; Bitler, A.; Bendikov, M. Chem.Mater. 2010, 22, 4019-4025. Groenendaal, L., Zotti, G., Aubert, P.-H., Waybright, S.M.;Reynolds, J.R. Adv. Mater. 2003, 15, 855–879. Vorotyntsev, M. A.; Zinovyeva, V. A.; Konev, D.V. Electropolymerization: Concepts, Materials and Applications, WILEY-VCH, 2010, 27-50. Kayinamura, Y.P.;Ovadia, M.; Zavitz,D.; Rubinson, J.F. ACS Appl. Mater. Interfaces, 2010, 2, 2653-2662. Huang, J.H.; kekuda, D.; Che, C.W.; Ho, K.C. J. Mater. Chem. 2009, 19, 3704-3712.

Hydrothermal vs electrodeposition: How does deposition method affect the electrochemical capacitor performance of manganese dioxide?

Abstract Hydrothermal and electrodeposition are widely utilized methods in the preparation of MnO 2 nanomaterials for electrochemical capacitor application. In this paper, these two approaches were applied to synthesize nanoscale MnO 2, and their electrochemical properties were fully investigated in different electrolyte environments. Because of different mechanisms, the hydrothermal method gave an ultrathin layer of MnO 2 nanosheets with a large accessible electrochemical surface area, while the electrodeposition method resulted in the formation of MnO 2 nanorods with a rather limited opening area. The electrochemical performance of hydrothermally prepared MnO 2 was much better in specific capacitance and overall resistance, except the cycling durability, as a result of its unique structure.

Capacity Fade of NaTi2(PO4)3 in Aqueous Electrolyte Solutions: Relating pH Increases to Long Term Stability

The inherent chemical stability of NaTi2(PO4)3 in aqueous solutions with higher pH values, and resulting implications for using this material as an anode are explored. Scanning electron microscopy, x-ray powder diffraction, and Fourier transform infrared spectroscopy were used to investigate morphological, structural, and chemical changes for samples exposed to varying basic pHs at 25°C and 70°C. Significant structural degradation and precipitation of a secondary phase were observed in all samples prepared at 70°C along with 25°C samples exposed to more extreme pH solutions. Infrared spectroscopy results indicated a loss of phosphate from the precipitated material, while x-ray diffraction shows that the secondary phases were from the layered sodium titanate family. Cyclic voltammetry of the samples indicated some degree of capacity loss for all of the samples, while some showing features related to the observed secondary phase that has some electrochemical functionality. The implications of these results on the stability of NaTi2(PO4)3 in various electrolyte environments is discussed.

Impact of Local Electric Fields on Charge-Transfer Processes at the TiO2/Dye/Electrolyte Interface

Photoinduced electron-transfer processes at the TiO2/dye/electrolyte interface are vital for various emerging technologies. Here, the impact of the local electric field at this interface on the charge-transfer processes was investigated in two aspects: (a) charge recombination between the electrons accumulated within TiO2 and the photoxidized dye and (b) regeneration of the dyes by the cobalt bipyridyl redox mediators. The amplitude of the local electric field was changed by use of different cations in the electrolytic environment, in the order ECa2+ > EMg2+ > ENa+ > ELi+ characterized by the transient absorption spectroscopy. For the charge recombination process, the kinetic time constant showed a remarkable linear correlation with the relative electric field strength, while for the regeneration process, no evident dependence was observed. These results collectively suggest the spatial confinement of the effects of the local electric field on the interfacial electron-transfer processes.

Multi-scale, multi-physics modeling of electrochemical actuation of Ni nanohoneycomb in water

Recent experiments have shown that a composite cantilever structure comprising a Ni nanohoneycomb active layer, backed by a solid constraining layer of Ni, can exhibit bending in an electrolyte environment when a voltage is applied across the cantilever and electrolyte. In this work, a multi-scale, multi-field simulation approach is used to model such an electrochemical actuation behavior. Specifically, molecular dynamics simulations with reactive force-field potentials and a modified charge-equilibrium (QEq) method are used to calculate the surface stress built up in Ni(100) surface in contact with water electrolyte due to a voltage applied across the interface, as a result of capacitive charging of the double layer in the contacting electrolyte as well as redox reaction of the Ni surface. The calculated surface stress is then used as input in a meso-scale finite-element (FE) model to compute the actuating stress set up in a single hexagonal unit cell of the Ni nanohoneycomb structure. The single-unit actuating stress is eventually used in a continuum FE model at a larger scale, to calculate the bending of an entire bilayered cantilever which replicates experimental conditions. The actuation deflection of the bilayered nanohoneycomb nickel is predicted to be 41.4μm at 0.43V vs the point of zero charge (PZC), which corresponds to ∼0.48V vs saturated calomel electrode (SCE), and this is in excellent agreement with the experimental value of 45–62μm at a similar voltage vs SCE. This is the first successful attempt to simulate the electrochemical actuation of a real-sized, nano-porous metallic structure in an electrolytic environment.

Site-specific catalytic activity of model platinum surfaces in different electrolytic environments as monitored by the CO oxidation reaction

Stepped Pt surfaces having different width (111) terraces interrupted by (110) or (100) monoatomic steps were employed to evaluate the catalytic activity toward CO oxidation at Pt specific sites in HClO4, H2SO4, and H3PO4 solutions, as well as in phosphate buffer and alkaline solution. The catalytic activity at the (111) terraces was sensitive to the nature of the anions derived from the electrolyte dissociation, while no effect on activity was detected at the monoatomic steps. A change in solution pH, passing from acid to alkaline solutions, had contrasting effects on catalytic activity at the (111) terraces and the step sites, with the catalytic activity of the (111) terraces improving, while activity at the step sites deteriorated. During the CO adlayer oxidation, the release of surface sites occurred preferentially from the (111) terraces of the Pt(s)−[(n−1)(111)×(110)] surfaces, while from Pt(s)−[(n)(111)×(100)] surfaces, (111) terrace and (100) step sites were released simultaneously.

Atomic force microscopy study of the biofouling and mechanical properties of virgin and industrially fouled reverse osmosis membranes

The mechanical properties of virgin and industrially fouled reverse osmosis membranes (composite polyamide) used for the purification and desalination of seawater in desalination processes were characterised using novel atomic force microscopy (AFM) methods. Polymeric surface elasticity has previously been demonstrated to strongly affect the adhesion of bacteria; hence the study examined membrane surface elasticity to demonstrate how AFM can be used to assess the bio-fouling potential of membranes. An AFM colloid probe technique was used to determine the mechanical properties of the membrane, the adhesion forces and the work of adhesion at the membrane surfaces. The mean values of Young's modulus for the virgin membrane decreased in magnitude with increasing pH values, where these values were significantly different (p<0.017) between both pH3 (1450kPa), pH7 (1327kPa) and pH9 (788kPa). These differences were attributed to differences in membrane swelling and indicate possible control parameters that could be exploited to improve membrane cleaning regimes. A membrane with a higher modulus will be stronger and potentially more resistant to chemical and physical processes during operation and cleaning. Significant differences (p<0.017) in force measurements were also found between different electrolytic conditions for each of the membranes, where for the virgin membrane the adhesion force values were 6.00nN at pH3, 1.77nN at pH7 and 0.98N at pH9, and also the work of adhesion were 153.6nJ at pH3, 22.8nJ at pH7 and 9.9nJ at pH9 in 0.6M NaCl. These observations further confirm the importance of the electrolytic environment on the nanoscale interactions of the membrane which should be considered to control fouling during operation and cleaning cycles. AFM images and streaming potential measurements of virgin and fouled membranes were also obtained to aid analysis of the industrial membrane system. The novel application of AFM to membranes to measure Young's moduli and work of adhesion is a new addition to the AFM tools that can be used to unravel separation processes at the membrane surface. In addition, this study further demonstrates that AFM force spectroscopy can be used as part of a sophisticated membrane autopsy procedure for the elucidation of the mechanisms involved in membrane fouling.

Single Molecule Nanoelectrochemistry in Electrical Junctions.

It is now possible to reliably measure single molecule conductance in a wide variety of environments including organic liquids, ultrahigh vacuum, water, ionic liquids, and electrolytes. The most commonly used methods deploy scanning probe microscopes, mechanically formed break junctions, or lithographically formed nanogap contacts. Molecules are generally captured between a pair of facing electrodes, and the junction current response is measured as a function of bias voltage. Gating electrodes can also be added so that the electrostatic potential at the molecular bridge can be independently controlled by this third noncontacting electrode. This can also be achieved in an electrolytic environment using a four-electrode bipotentiostatic configuration, which allows independent electrode potential control of the two contacting electrodes. This is commonly realized using an electrochemical STM and enables single molecule electrical characterization as a function of electrode potential and redox state of the molecular bridge. This has emerged as a powerful tool in modern interfacial electrochemistry and nanoelectrochemistry for studying charge transport across single molecules as a function of electrode potential and the electrolytic environments. Such measurements are possible in electrolytes ranging from aqueous buffers to nonaqueous ionic liquids. In this Account, we illustrate a number of examples of single molecule electrical measurements under electrode potential control use a scanning tunneling microscope (STM) and demonstrate how these can help in the understanding of charge transport in single molecule junctions. Examples showing charge transport following phase coherent tunneling to incoherent charge hopping across redox active molecular bridges are shown. In the case of bipyridinium (or viologen) molecular wires, it is shown how electrochemical reduction leads to an increase of the single molecule conductance, which is controlled by the liquid electrochemical gating. This has been referred to as to a "single molecule transistor configuration" with the gate voltage being provided by the controllable potential achieved through the electrochemical double layer. It is shown how the electrolyte medium can control such gating, with ionic liquids providing more efficient gate coupling than aqueous electrolytes. Control of the conductance of viologen molecular wires can also be achieved by encapsulating the viologen redox moiety within a molecular cage, thereby controlling its immediate environment. Molecular conductance can also be gated through multiple redox states. This has been shown for the redox moiety pyrrolo-tetrathiafulvalene, which undergoes single molecule electrochemical transistor gating through three redox states in molecular junctions. Charge transport through this junction follows a two-step hopping mechanism, demonstrating the role of the redox center in electron transfer across the molecular bridge. Recent electrolyte gating studies of rigid, conjugated redox-active metal complexes with tailored terpyridine coordinating ligands and anchors are also presented. These aforementioned studies have all been performed with gold electrode contacts. The Account concludes with recent data showing that it is now possible to study single molecule electrochemical gating with nickel electrodes. This opens up new perspectives for studying interfacial charge transfer with a wide variety of other electrode materials including semiconductor electrodes and also points toward future opportunities for coupling molecular spintronics and nanoelectrochemistry.

Measurement of high carrier mobility in graphene in an aqueous electrolyte environment

Graphene is a promising material for applications in aqueous electrolyte environments. To explore the impact of such environments on graphene's electrical properties, we performed Hall bar measurements on electrolyte-gated graphene. Assuming a Drude model, we find that the room temperature carrier mobility in water-gated, SiO2-supported graphene reaches 7000 cm2/Vs, comparable to the best dry SiO2-supported graphene devices. Our results show that the electrical performance of graphene is robust, even in the presence of dissolved ions that introduce an additional mechanism for Coulomb scattering.

Anodic Bubble Behavior and Voltage Drop in a Laboratory Transparent Aluminum Electrolytic Cell

The anodic bubbles generated in aluminum electrolytic cells play a complex role to bath flow, alumina mixing, cell voltage, heat transfer, etc., and eventually affect cell performance. In this paper, the bubble dynamics beneath the anode were observed for the first time from bottom view directly in a similar industrial electrolytic environment, using a laboratory-scale transparent aluminum electrolytic cell. The corresponding cell voltage was measured simultaneously for quantitatively investigating its relevance to bubble dynamics. It was found that the bubbles generated in many spots that increased in number with the increase of current density; the bubbles grew through gas diffusion and various types of coalescences; when bubbles grew to a certain size with their surface reaching to the anode edge, they escaped from the anode bottom suddenly; with the increase of current density, the release frequency increases, and the size of these bubbles decreases. The cell voltage was very consistent with bubble coverage, with a high bubble coverage corresponding to a higher cell voltage. At low current density, the curves of voltage and coverage fluctuated in a regularly periodical pattern, while the curves became more irregular at high current density. The magnitude of voltage fluctuation increased with current density first and reached a maximum value at current density of 0.9 A/cm2, and decreased when the current density was further increased. The extra resistance induced by bubbles was found to increase with the bubble coverage, showing a similar trend with published equations.