Electrolyte Environment Research Articles

Thermal batteries with ceramic felt separators – Part 1: Wetting, loading behavior and chemical stability

The use of a thermally and chemically stable ceramic felt separator for thermal batteries is believed to enhance the reliability by minimizing the sudden failure of an electrolyte upon shock compared to the conventional pellet-pressed one. To achieve desirable electrochemical properties for applications in thermal batteries, the separator should hold a sufficient amount of molten electrolyte with a minimal leakage to prevent physical contact between the cathode and anode. In addition, the chemical stability of the separator materials should be maintained under a very reactive molten Li-salt electrolyte environment to confer high ionic conductivity and reliability. To assess the feasibility of 3 types of ceramic felt as a separator for thermal batteries, 2 types of Al2O3 felt with different porosity and one ZrO2 felt are examined using binary LiCl-KCl and ternary LiF-LiCl-LiBr as the electrolytes. This Part 1 explains the wetting, loading and leakage behaviors of the ceramic felts for molten electrolytes along with the chemical stability. The ionic conductivity of the electrolytes and electrochemical properties of the resulting thermal batteries will be presented in Part 2.

Interdye Hole Transport Accelerates Recombination in Dye Sensitized Mesoporous Films.

Charge recombination between oxidized dyes attached to mesoporous TiO2 and electrons in the TiO2 was studied in inert electrolytes using transient absorption spectroscopy. Simultaneously, hole transport within the dye monolayers was monitored by transient absorption anisotropy. The rate of recombination decreased when hole transport was inhibited selectively, either by decreasing the dye surface coverage or by changing the electrolyte environment. From Monte Carlo simulations of electron and hole diffusion in a particle, modeled as a cubic structure, we identify the conditions under which hole lifetime depends on the hole diffusion coefficient for the case of normal (disorder free) diffusion. From simulations of transient absorption and transient absorption anisotropy, we find that the rate and the dispersive character of hole transport in the dye monolayer observed spectroscopically can be explained by incomplete coverage and disorder in the monolayer. We show that dispersive transport in the dye monolayer combined with inhomogeneity in the TiO2 surface reactivity can contribute to the observed stretched electron-hole recombination dynamics and electron density dependence of hole lifetimes. Our experimental and computational analysis of lateral processes at interfaces can be applied to investigate and optimize charge transport and recombination in solar energy conversion devices using electrodes functionalized with molecular light absorbers and catalysts.

Analysis of cantilever NEMS in centrifugal-fluidic systems

Electromechanical nanocantilevers are promising for using as sensors/detectors in centrifugal-fluidic systems. For this application, the presence of angular speed and electrolyte environment should be considered in the theoretical analysis. Herein, the pull-in instability of the nanocantilever incorporating the effects of angular velocity and liquid media is investigated using a size-dependent continuum theory. Using d’Alembert principle, the angular speed is transformed into an equivalent centrifugal force. The electrochemical and dispersion forces are incorporated considering the corrections due to the presence of electrolyte media. Two different approaches, i.e., the Rayleigh–Ritz method (RRM) and proposing a lumped parameter model (LPM), were applied to analyze the system. The models are validated with the results presented in literature. Impacts of the angular velocity, electrolyte media, dispersion forces, and size effect on the instability characteristics of the nanocantilever are discussed.

Block Copolymer Sdapp Membranes for Vanadium Redox Flow Batteries-Strategy to Address Transport and Durability

The electrolyte separator (membrane) is a key component in vanadium redox flow batteries (VRFB) for large scale electrical energy storage. In the VRFB cell, the separator serves to physically separate positive and negative electrolyte solutions while establishing ionic conduction to pass current between two half cells. High ionic conductivity, low vanadium permeability, chemical stability and low cost are desired properties of RFB separators. To serve as a separator, the membrane should deter unwanted redox species transport while maintaining excellent ionic transport properties to minimize ohmic resistance. In the harsh electrolyte environment, the membrane must be stable enough to withstand chemical attacks in the electrolyte environment for a long lifespan. Moreover, the cost of the separator must be kept low enough to be integrated into large-scale battery system. Generally, ion exchange membranes are used as electrolyte separator in VRFBs. Sulfonated Diels Alder poly(phenylene) (SDAPP) cation exchange membranes have emerged as a good membrane candidate for both proton exchange membrane fuel cell and VRFB. The first generation SDAPP is a partially sulfonated poly(phenylene) random polymer. The random SDAPP membrane has shown comparable performance to Nafion in transport study and battery testing.1 From the perspective transport properties, SDAPP is satisfactory as anelectrolyte separator in VRFBs. However, random SDAPP is not chemically stable enough in the electrolyte environment to serve for a targeted lifespan because the unfunctionalized benzene ring in SDAPP is vulnerable to attack from V5+ (VO2 +) ion, a strong oxidant. Sulfonated polyphenylene/polysulfone block copolymer SDAPP membranes show significantly improved resistance to V5+ attack and excellent cell performance.2 The SDAPP block copolymer consists of a hydrophilic segment of fully sulfonated polyphenylene and hydrophobic segment of polysulfone. The block-SDAPP membrane provides an extended lifespan within VRFB environment in comparison to random SDAPP. Chemical stability of block-SDAPP is enhanced by full sulfonation of poly(phenylene) in the hydrophilic segment. Ionic conductivity is not sacrificed by block copolymerization. In the battery, the performance of block-SDAPP can be better than state of art Nafion 212. As is shown in the figure, at 500 mA/cm2cycling current density, cells equipped with three different block-SDAPP membranes can reach 76% energy efficiency, compared to 70% with Nafion 212, with the same electrode and electrolyte conditions. About 80% voltage efficiency was achieved with block-SDAPP membranes, because of the lowered internal resistance. Moreover, the coulombic efficiency reached by the three block SDAPPs is respectively 97%, 95% and 93%, compared to 95% of Nafion. Vanadium crossover across block SDAPP membranes is similar to that in Nafion 212. Considering that block-SDAPPs have lower ASR in the battery, the ionic selectivity of block SDAPP is essentially better than Nafion. To further optimize the structure of block-SDAPP for VRFB application, we are investigating the correlation between structure and performance of block-SDAPP. Under battery electrolyte conditions, ionic equilibrium, ionic transport and membrane morphology will be studied via the protocol established in previous studies.3Sulfuric acid, water uptake and vanadium ion partitioning in membrane will be determined after being equilibrated in electrolyte of various acid and vanadium composition to simulate battery environment. Conductivity and vanadium permeability of block SDAPP will also be measured after the same equilibration. Since water is a critical mediator for proton and cation transport in aqueous media, pulsed field gradient nuclear magnetic resonance (PFG-NMR) will be performed to investigate proton and vanadium transport mechanisms in equilibrated membranes. Membrane morphology will be studied by transmission electron microscopy and small angle X-ray scattering will be used to establish the geometry of ionic cluster channel. Acknowledgement This work is supported by Dr. Imre Gyuk, Office of Electricity Delivery and Energy Reliability, US Department of Energy.

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.

Interactions Between Positive and Negative Electrodes in Li-Ion Cells Operated at High Temperature and High Voltage

Introduction When NMC/graphite Li-ion cells are operated at high temperature and a cut-off potential higher than 4.2 V, generated gaseous products and oxidized species which could passivate the positive electrode and/or dissolve in the bulk electrolyte could reach the negative electrode and be reduced there.1,2 In order to study electrode/electrode interactions, pouch bags were used to separate the two electrodes, so that interactions between two electrodes would be impossible. Pouch bags containing only the charged negative or positive electrode can be used as a simple tool to obtain valuable information concerning the consequences of the absence of an interaction with the other charged electrode. Experimental Before electrolyte filling, dry (no electrolyte) NMC442/graphite (240 mAh) pouch cells were cut below the seal and vacuum dried at 80°C for 14 h. The pouch cells were filled with 0.9 g of 1M LiPF6 in EC:EMC (3:7 by weight) (control electrolyte) plus 2 % vinylene carbonate (VC), 2% prop-1-ene-1,3-sultone (PES) or 2% pyridine-boron trifluoride (PBF) in an argon-filled glove box and vacuum sealed in the same glove box. All the additives were added by weight percentage. After electrolyte filling, cells were placed in a temperature box at 40. ± 0.1°C and held at 1.5 V for 24 h. They were then charged to 3.8 V at C/20, and transferred to a glove box for degassing (cut open below the seal and re-sealed under vacuum). After degassing, they were charged to either 4.4 V, then discharged to 2.8 V and charged back to the same charge cutoff voltage until the holding period for the NMC442/graphite cells reached 30 hours. Four cells either at 4.2 or 4.4 V were moved to a 60°C temperature box for storage. The other cells were transferred to the glovebox and dissembled there. The delithiated NMC442 electrodes collected from the pouch cell were inserted into pouch bags with 0.3 g EMC. The addition of 0.3 g EMC to the pouch bags created a similar electrolyte environment as in the original pouch cells, because EC and LiPF6 were still left in the electrode and only about 0.3 g of EMC evaporated from the positive electrodes. Figure 1 shows photographs to illustrate the process used to make and test pouch cells and pouch bags. Results and discussion Figure 2 shows gas evolution for pouch bags containing lithiated graphite electrodes which were taken from pouch cells with control electrolyte, electrolyte with 2% PES, 2% VC and 2% PBF. No volume changes were detected for these pouch bags during approximately 500 h storage at 60°C. This suggests that parasitic reactions between the lithiated graphite and electrolyte do not contribute to gas generation at 60 °C. Figure 3 shows the volume change versus time for pouch cells with control electrolyte, or electrolyte with 2% PES, 2% VC or 2% PBF and pouch bags containing charged positive electrodes taken from brother pouch cells during a 500 h storage period at 60°C. Figure 3 shows that the volume of the pouch cells and pouch bags containing the charged positive electrodes increased with time. Figure 3 also shows that the pouch bags containing the delithiated NMC442 electrodes produced almost two times more gas than the corresponding pouch cells during the storage period. This suggests that some gaseous products generated at the positive electrode are consumed at the negative electrode in a full cell. Pouch bags with the delithiated NMC442 electrode taken from pouch cells at 4.4 V produced more gas than those taken from pouch cells at 4.2 V. This means, unsurprisingly, that delithiated NMC442 electrodes at a higher potential oxidize electrolyte at a higher rate. Pouch bags containing the washed charged NMC442 electrode (DMC washing) + EC/EMC produced gas at a higher rate than those containing a charged NMC442 electrode without washing. This suggests that the presence of LiPF6 can affect the parasitic reactions at the positive electrode that cause gaseous products. The above results suggest that oxidized species such as gaseous products generated at the positive electrode can be consumed at the negative electrode leading to a smaller volume expansion in pouch cells than pouch bags. The “clean-up” of other oxidized species by the lithiated graphite electrode resulting in a lower rate of impedance increase at the positive electrode will be discussed.

Electrochemical Tuning of Amorphous Carbon Amount and Surface Oxidation Degree of Graphitic Quantum Dots

Graphitic quantum dots (GQDs) have attracted much interesting of researchers because of its amazing optical properties and its ability to be used for many applications. Now, there are various methods have been reported for preparation of GQDs. Among them electrochemical method is simple technology, while it can afford various conditions to realize controllable prepared of GQDs. In this study, we tuned the PH values of electrolyte to probe the relationship of electrolyte environment and GQDs' optical properties as well as to seek the effective controllable condition for GQDs' preparation. It is found that the density of oxygen-related functional groups and the amount of amorphous carbon of GQDs were related to the PH values of electrolyte. The amount of amorphous carbon decreased as the PH values increased in the region of 6.6 to 7.1. Although, the positions of photoluminescence (PL) peak almost no changed of GQDs with different density of oxygen-related functional groups, GQDs with the lowest amount of amorphous carbon achieved the maximum PL intensity. Therefore, controlling amorphous carbon's amount by electrochemical method may afford a new direction to improve the fluorescence (FL) emission of GQDs.

Alternating electric field actuated oscillating behavior of liquid metal and its application

As a class of newly emerging functional material, Gallium based liquid metals have attracted increasing attentions in many fields, such as chip cooling, printed electronics and microfluidics, etc. Particularly, the motion control of liquid metal droplet has been recently tried for its importance in microelectromechanical system (MEMS), microfluidics and potential use in micro-machine or reconfigurable soft robot. This paper is dedicated to explore the motion behavior of liquid metal droplet under AC electric field. The quickly induced oscillation phenomena of liquid metal droplet and surrounding electrolyte solution were observed and the major factors to influence such behaviors are theoretically interpreted and experimentally investigated, including the size of the liquid metal droplet, electrode voltage, electrolyte solution concentration and AC signal frequency etc. Moreover, some typical features to distinguish AC filed actuation with DC field are observed, such as intensive fluid waving induced by the resonance stimulation, and the efficient inhibition of solution electrolysis. Finally, two important applications of adopting AC induced surface oscillation of liquid metal droplet to develop solution mixer as well as fluidic pump were demonstrated which successfully avoid gas generation inside electrolyte environment. The bulk oscillation effects of liquid metal as clarified here could be very useful in a variety of areas such as solution disturbance and mixing, and fluid oscillator or pump etc.

Implant materials modified by colloids

AbstractRecent advances in general medicine led to the development of biomaterials. Implant material should be characterized by a high biocompatibility to the tissue and appropriate functionality, i.e. to have high mechanical and electrical strength and be stable in an electrolyte environment – these are the most important properties of bioceramic materials. Considerations of biomaterials design embrace also electrical properties occurring on the implant-body fluid interface and consequently the electrokinetic potential, which can be altered by modifying the surface of the implant. In this work, the surface of the implants was modified to decrease the risk of infection by using metal colloids. Nanocolloids were obtained using different chemical and electrical methods. It was found that the colloids obtained by physical and electrical methods are more stable than colloids obtained by chemical route. In this work the surface of modified corundum implants was investigated. The implant modified by nanosilver, obtained by electrical method was selected. The in vivo research on animals was carried out. Clinical observations showed that the implants with modified surface could be applied to wounds caused by atherosclerotic skeleton, for curing the chronic and bacterial inflammations as well as for skeletal reconstruction surgery.

A Comparative Study of Nickel Electrodeposition Using Deep Eutectic Solvents and Aqueous Solutions

Metal electrodeposition using ionic liquid electrolytes and deep eutectic solvents is now well known but to our knowledge for electrolytic deposition of metals such as nickel no direct comparison has thus far been drawn between deposition using aqueous solutions and DES under otherwise identical conditions. In the current study it is shown that nickel deposition can be carried out with similar deposition rates in aqueous and ionic media despite the significant differences in viscosity and conductivity. It is, however, shown that in ionic media the morphology of the deposits is markedly different from that achieved using a Watts nickel bath and that one aspect of these differences manifests itself in significant increase in the coating hardness. It is proposed that the observed morphology differences occur due to the variations of nickel speciation in each electrolyte environment.

Low-Temperature Electrochemical Ammonia Synthesis with Nanoscale Fe-Ni Bimetallic Catalysts

The ammonia production market in the U.S. is $20 billion in size, with ammonia being the primary chemical input to agricultural fertilizer. Currently, ammonia synthesis occurs through the Haber-Bosch process, which uses a bulk iron catalyst to reduce nitrogen and hydrogen gas at high temperature and pressure. The source of hydrogen primarily comes from steam reforming of natural gas, where methane combines with water to produce hydrogen, as well as carbon monoxide and carbon dioxide. As a result, the ammonia production industry is responsible for approximately 320 million tons of greenhouse gas emissions per year, putting the ammonia fertilizer industry as the second-largest contributor of greenhouse gas emissions in the U.S. While the invention of the Haber-Bosch process has been the primary reason for agricultural expansion and prosperity over the past 100 years, particularly in developed and industrialized nations, there remains an enormous opportunity to improve upon the Haber-Bosch process both in terms of the energy used and the greenhouse gases produced. Our work has focused on the development of a non-precious bimetallic FeNi nanoparticle material for the alkaline electrochemical reduction of nitrogen to ammonia. FeNi nanoparticles are synthesized using an aqueous-based solution synthesis technique, where first iron core nanoparticles are reduced from an argon-bubbled solution of ferrous sulfate heptahydrate and phosphonate ligand stabilizer. The nickel shell is then added through electroless deposition when a solution of nickel chloride hexahydrate and polyvinylpyrrolidone is added. Through the difference in the standard reduction potentials of Fe2+ and Ni2+ (E for Fe2+ = -0.44 V and E for Ni2+= -0.25 V), electrons are transferred from Fe in the core nanoparticle to nickel in solution at the surface of the nanoparticles, and nickel plates down onto the iron nanoparticle surface. The size and morphology of the FeNi nanoparticles are varied by changing the molar ratio of phosphonate stabilizer to iron and the molar ratio of nickel to iron. Alloy versions of the nanoparticles, made through a one-pot synthesis technique are used as comparisons to the core-shell morphology. Ammonia synthesis is evaluated through a series of potentiostatic experiments, where the effect of the applied potential on ammonia production rate is investigated. A gas-tight electrochemical cell is used for all experiments and an in-line acidic acid trap is used to capture offgased ammonia. Due to the alkaline electrolyte and high pH environment, all ammonia is expected to be in the NH3 form of the NH3/NH4 + pair, and constant nitrogen bubbling during electrochemistry experiments causes the ammonia to flow out of the electrochemical cell and become dissolved as NH4 +in the aqueous acid trap. Ammonia concentrations are quantified using a commercially-available assay, and mass concentrations are correlated to the current measured over time to determine ammonia production and efficiency as a function of applied potential. In this talk, nanoparticle synthesis and characterization will be discussed, as well as electrochemical and ammonia production results for specific FeNi nanoparticle catalysts.

Atomic Force Microscopy Applications for Energy Storage: Detecting the Structure and Dynamics of Fluid/Electrode Interfaces

The structure of ions at the electrode-electrolyte interface and their transport properties within electrode materials control the properties of energy storage devices, such as the energy density and rate capability. Tremendous efforts have been undergone to achieve fundamental understanding of interfacial structures, dynamics and reactivity in order to improve the energy efficiency of electric devices. However characterization tools able to probe interaction lengths as small as few nanometers are needed. Atomic Force Microscopy (AFM) techniques are well suited to investigate the nanoscale properties of energy storage materials and to characterize the electrode-electrolyte interface due to the high lateral and vertical resolution and sensitivity to weak forces. In this presentation we will discuss several AFM techniques used to investigate ionic transport across and near solid-liquid interfaces. The sensitivity of the AFM probe to very weak forces allows determining the structure of an ionic liquid within the electrical double layer with molecular-level resolution [1]. The influence of applied potential on the ions structure can be detected, and the excellent agreement with molecular dynamics simulations provides insight into the ion layering reactivity. Moreover, the unmatched lateral resolution of scanning probe techniques also opens the pathway to mapping the structure of the electrical double layer in a 3D manner. We will also show that AFM is capable of characterizing the changes induced during the electrochemical storage at the nanoscale for Li-ion electrode materials, where local phenomena at the tip-sample junction can be measured, analyzed and interpreted in terms of local ionic transport [2]. Furthermore, Electrochemical Strain Microscopy (ESM) technique has been used to study the ionic transport from the electrolyte into a variety of materials in-operando. For example, an ESM study of activated carbons of different pore sizes revealed faster cation adsorption kinetics vs. anion in an ionic liquid electrolyte [ 3]. More recently, AFM was used to evidence the anomalously large volume contraction of a 2D titanium carbide (MXene) electrode upon cation intercalation [4]. As the development of AFM techniques in electrolyte environment improve, achieving time-resolved tracking of ion storage in energy materials becomes more accessible and can lead to tuning surface interactions to improve the energy density of supercapacitors. This work was supported as part of the Fluid Interface Reactions, Structures and Transport (FIRST) Center, and Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences. Measurements were performed at the Center for Nanophase Materials Sciences, which is sponsored at Oak Ridge National Laboratory by the Scientific User Facilities Division, Office of Basic Energy Sciences. [1] J. M. Black, D. Walters, A. Labuda, G. Feng, P. C. Hillesheim, S. Dai, P. T. Cummings, S. V. Kalinin, R. Proksch, N. Balke, Nano Lett. 13 (2013) 5954-5960. [2] N. Balke, S. Jesse, A. N. Morozovska, E. Eliseev, D. W. Chung, Y. Kim, L. Adamczyk, R. E. García, N. Dudney, S.V. Kalinin, Nat. Nanotechnol. 5 (2010) 749-754. [3] J. M. Black, G. Feng, P. F. Fulvio, P. C. Hillesheim, S. Dai, Y. Gogotsi, P. T. Cummings, S. V. Kalinin, N. Balke, Adv. Energy Mater. 4 (2014). [4] J. Come, J. M. Black, M. Naguib, M. R. Lukatskaya, M. Beidaghi, A. J. Rondinone, D. J. Wesolowski, S. V. Kalinin, Y. Gogotsi, N. Balke, Nano Energy, accepted.

Pt Catalyst Degradation in Aqueous and Fuel Cell Environments studied via In-Operando Anomalous Small-Angle X-ray Scattering

The evolution of Pt nanoparticle cathode electrocatalyst size distribution in a polymer electrolyte membrane fuel cell (PEMFC) was followed during accelerated stress tests using in-operando anomalous small-angle X-ray scattering (ASAXS). This evolution was compared to that observed in an aqueous electrolyte environment using stagnant electrolyte, flowing electrolyte, and flowing electrolyte at elevated temperature to reveal the different degradation trends in the PEMFC and aqueous environments and to determine the relevance of aqueous measurements to the stability of Pt nanoparticle catalyst in the fuel cell environment. The observed changes in the particle size distributions (PSDs) were analyzed to elucidate the extent and mechanisms of particle growth and corresponding mass and active surface area losses in the different environments. These losses indicate a Pt nanoparticle surface area loss mechanism controlled by Pt dissolution, the particle size dependence of Pt dissolution, the loss of dissolved Pt into the membrane and electrolyte, and, to a lesser extent, the re-deposition of dissolved Pt onto larger particles. Based on the geometric surface area loss, mass loss, and mean particle size increase trends, the aqueous environment best reflecting the fuel cell environment was found to be one in which the electrolyte is flowing rather than stagnant. Pt nanoparticle surface area loss resulting from potential cycling can be inhibited by reducing the number of particles smaller than a critical particle diameter (CPD), which was found to be ∼3.5 to ∼4nm, with the CPD dependent on both the cycling protocol (square wave vs triangle wave) and the catalyst environment (fuel cell, aqueous stagnant, aqueous flowing electrolyte, or elevated temperature flowing electrolyte)

(Invited) Silicon Nanowire and Graphene Field-Effect Transistors for Sensing Applications

Ion-sensitive field-effect transistors (ISFETs)[1] offer a promising set of features for integrating sensor and readout electronics on the same chip, providing a portable and cost-effective sensing solution. Such sensors are label-free and convert chemical reactions into electrical signals via electrostatic gating of the FET by adsorbed chemical or biological species. During the past decade, the ISFET concept has been applied to nanoscale devices such as carbon nanotubes, graphene[2] or Si nanowires.[3, 4] Even though many exciting biosensing experiments have been reported, several key challenges are still limiting their wide-spread application. In particular, the miniaturization of the reference electrode[5] and resolving the stability and drift issues proved to be difficult tasks. Also, competing reactions at the sensor surface have to be taken into account as they limit the sensing performance and might lead to misreading.[6] Here, we discuss these and other issues related to sensing in an electrolyte environment based on our results using silicon nanowires[4-11] and graphene FETs[2, 12] as transducers. Several examples of specific detection of pH,[5, 6] sodium,[9] potassium,[12] and biomolecules in a reliable differential setup will be presented along with a new quantitative model for describing the competing reactions in an electrolyte environment.[6, 13] The application of these devices in the animal health sector for the diagnosis of bovine respiratory disease (BRD), which is a major cause of calf death, will also be addressed. 1. Bergveld, P., Thirty years of ISFETOLOGY: What happened in the past 30 years and what may happen in the next 30 years. Sens. Actuators B, 2003. 88(1): p. 1-20. 2. Fu, W., et al., Graphene transistors are insensitive to pH changes in solution. Nano Lett., 2011. 11(9): p. 3597-3600. 3. Cui, Y., et al., Nanowire Nanosensors for Highly Sensitive and Selective Detection of Biological and Chemical Species. Science, 2001. 293(5533): p. 1289-1292. 4. Knopfmacher, O., et al., Nernst Limit in Dual-Gated Si-Nanowire FET Sensors. Nano Lett., 2010. 10: p. 2268-2274. 5. Tarasov, A., et al., True reference nanosensor realized with silicon nanowires. Langmuir, 2012. 28(25): p. 9899-9905. 6. Tarasov, A., et al., Understanding the electrolyte background for biochemical sensing with ion-sensitive field-effect transistors. ACS Nano, 2012. 6(10): p. 9291-9298. 7. Tarasov, A., et al., Signal-to-Noise Ratio in Dual-Gated Silicon Nanoribbon Field-Effect Sensors. Appl. Phys. Lett., 2011. 98(1): p. 012114. 8. Knopfmacher, O., et al., Silicon‐Based Ion‐Sensitive Field‐Effect Transistor Shows Negligible Dependence on Salt Concentration at Constant pH. ChemPhysChem, 2012. 13(5): p. 1157-1160. 9. Wipf, M., et al., Selective sodium sensing with gold-coated silicon nanowire field-effect transistors in a differential setup. ACS Nano, 2013. 7(7): p. 5978-5983. 10. Bedner, K., et al., pH response of silicon nanowire sensors: impact of nanowire width and gate oxide. Sensors and Materials, 2013. 25(8): p. 567-576. 11. Bedner, K., et al., Investigation of the dominant 1/f noise source in silicon nanowire sensors. Sens. Actuators B, 2014. 191: p. 270-275. 12. Fu, W., et al., High mobility graphene ion-sensitive field-effect transistors by noncovalent functionalization. Nanoscale, 2013. 5(24): p. 12104-12110. 13. Stoop, R.L., et al., Competing Surface Reactions Limiting the Performance of Ion-Sensitive Field-Effect Transistors. ACS Appl. Mater. Interfaces, 2014. submitted.

(Invited) Integrated Semiconductor/Catalyst Assemblies for Sustained Photoanodic Water Oxidation

Photoelectrochemical conversion of solar energy to chemical fuel relies on the availability of semiconductors that are stable under aqueous conditions, possess bandgaps suitable for harvesting light from the sun, and can be integrated with active catalysts. Regardless of the desired reduced product, water oxidation is necessary to provide an abundant source of protons and electrons for fuel formation. However, semiconductor (photo)corrosion under oxidizing conditions is a central challenge. Here, we provide an overview of different approaches to achieving durable semiconductor photoanodes and highlight two specific examples of how catalyst integration can be used to improve chemical stability. In the first example, we show that plasma-assisted atomic layer deposition (PE-ALD) of cobalt oxide onto silicon enables efficient photoelectrochemical water splitting. These integrated assemblies are stable under aqueous conditions, including at pH 14. Structure and composition, which play crucial roles in performance, are investigated via a combination of X-ray absorption spectroscopy, X-ray photoelectron spectroscopy, grazing incidence wide angle X-ray scattering, and transmission electron microscopy. Together, these methods reveal that amorphous catalyst coatings are beneficial for enhancing stability and improving catalytic activity. In the second example, semiconductors that possess at least a modicum of native stability are investigated. These semiconductors are often polycrystalline thin film metal oxides possessing lateral inhomogeneities, poorly understood interactions with electrolyte environment, and relatively unknown optoelectronic properties. One such material is bismuth vanadate (BiVO4), a 2.4-2.5 eV bandgap n-type semiconductor. We have utilized a suite of spectroscopic and microscopic methods to probe local compositional non-uniformities, understand the role of catalyst integration on chemical stability, and determine electronic structure and photocarrier dynamics that govern charge extraction efficiency. These measurements provide valuable insight into basic properties – often defined by local nonuniformities – that affect ultimate performance of functional photoanodes. The examples presented here highlight that, although few materials are inherently stable under conditions required for artificial photosynthesis, conformal catalyst deposition provides a viable approach to sustained operation in harsh environments.

Accelerated degradation of Pt3Co/C and Pt/C electrocatalysts studied by identical-location transmission electron microscopy in polymer electrolyte environment

Identical-location transmission electron microscopy (ILTEM) coupled with X-ray energy dispersive spectroscopy (X-EDS) analyses were used to characterize the changes in the morphology and composition of Pt and Pt3Co nanoparticles deposited on high surface area carbon (Vulcan XC72) before and after electrochemical ageing tests performed in polymer electrolyte environment, using a “dry cell”. The Pt/C and Pt3Co/C electrocatalysts are modified upon electrochemical ageing, following changes in particle size, geometry, and composition; these changes are however milder to what happens upon aging in H2SO4 electrolyte, because of the lack of liquid water, a reactant in both carbon corrosion and Pt (Pt3Co) corrosion/dissolution reactions. The negative vertex potential of the ageing procedure also matters: Pt redeposition occurs at 0.1V vs. RHE and not at 0.6V vs. RHE, while carbon corrosion is emphasized after incursions at the lower vertex potential, in agreement to what demonstrated in liquid electrolyte. Besides, the presence of Co in Pt3Co alloys enables to somewhat slow-down the Pt corrosion from Pt3Co/C electrocatalysts, since cobalt acts as a sacrificial anode, which also lowers carbon corrosion.These morphology and composition changes were further used to explain the changes in ORR intrinsic activity of the electrocatalysts upon electrochemical aging; the ORR activity and the accelerated stress tests (AST) were measured/performed in a similar setup (at the interface with a polymer electrolyte) using an ultramicroelectrode with cavity. The ORR activity only improved for Pt/C nanoparticles when the AST contained the lower vertex potential (0.1V vs. RHE), thanks to the favorable increase of the particle sizes, favored because the Ptz+ ions released by the corrosion of the Pt/C nanoparticles at 0.9V vs. RHE remains trapped in the Nafion®, thereby easing its redeposition in the subsequent step at 0.1V vs. RHE. In all the other cases, the ORR activity decreased upon the AST. On Pt3Co/C the positive effect of Pt redeposition in the 0.1–0.9V vs. RHE ageing procedure is counterbalanced by a detrimental (and large) effect of Co dissolution, which adversely affects the nanoparticles composition for the ORR and pollutes the polymer electrolyte membrane (the Coy+ cations hinder O2 and H+ transport in the electrolyte membrane). After the 0.6–0.9V vs. RHE ageing procedure, the ORR activity always decreases, because the redeposition of Pt is not likely, therefore suppressing the positive effect of particle size increase monitored in the 0.1–0.9V vs. RHE ageing procedure, and because Co dissolution and adverse effect is maintained.

Compatibility of platinum with alkaline sulfide fuel: Effectiveness and stability of platinum as an anode catalyst in direct alkaline sulfide fuel cell

Exposure of Pt/C catalyst to sulfur-containing compounds has been avoided due to sulfur-induced deactivation of the catalyst. In this study, an aqueous alkaline sulfide medium, which was expected to provide an electrolyte environment that prevents Pt/C surface from poisoning, was selected as a fuel for direct alkaline sulfide fuel cell (DASFC) and its compatibility with Pt/C was evaluated. Pt/C was indeed shown to be an effective anodic catalyst for oxidizing sulfide, and the maximum power density of 39.20 mW cm−2 was recorded at 1 M Na2S, 3 M NaOH, and at 70 °C with Pt/C loading of 5 mg cm−2. 30h life test under highly sulfidic condition neither resulted in any appreciable drop in cell performance, nor caused irreversible formation of PtS or PtS2, ensuring not only performance stability and but also chemical stability of Pt/C in alkaline sulfide fuel. This study supports the possibility that like common fuel cell systems DASFC can benefit from the use of the powerful catalyst Pt.

New trends in biomedical engineering and bioinformatics applied to biomedicine - special issue of IWBBIO 2014.

New trends in biomedical engineering and bioinformatics applied to biomedicine - special issue of IWBBIO 2014.

Dynamic Control of Nanopore Wetting in Water and Saline Solutions under an Electric Field.

Field-induced nanopore wetting by aqueous solutions, including electrolytes, provides opportunities for a variety of applications. Conflicting porosity requirements have so far precluded direct implementations of a two-way control: the pores have to be sufficiently wide to allow water infiltration at experimentally relevant voltages but should not exceed the kinetic threshold for spontaneous expulsion in the absence of the field. Applicable widths are restricted below a few nanometers. Only a narrow window of fields and pore geometries can simultaneously satisfy both of the above requirements. Accurate accounts of wetting equilibria and dynamics at nanoscale porosity require molecular level descriptions. Here we use molecular dynamics simulations to study dynamic, field-controlled transitions between nanoconfined liquid and vapor phases in contact with an unperturbed aqueous or electrolyte environment. In nanopores wetted by electrolyte solutions, we observe depletion of salt compared to the bulk phase. The application of a local electric field enhances the uptake of water and ions in the confinement. In systems prone to capillary evaporation, the process can be reversed at sufficient strength of the electric field. For alternating displacement field, we identify the conditions where O (ns) responses of the reversible infiltration/expulsion cycle can be secured for experimentally realizable field strengths, porosity, and salinity of the solution.

Charging the quantum capacitance of graphene with a single biological ion channel.

The interaction of cell and organelle membranes (lipid bilayers) with nanoelectronics can enable new technologies to sense and measure electrophysiology in qualitatively new ways. To date, a variety of sensing devices have been demonstrated to measure membrane currents through macroscopic numbers of ion channels. However, nanoelectronic based sensing of single ion channel currents has been a challenge. Here, we report graphene-based field-effect transistors combined with supported lipid bilayers as a platform for measuring, for the first time, individual ion channel activity. We show that the supported lipid bilayers uniformly coat the single layer graphene surface, acting as a biomimetic barrier that insulates (both electrically and chemically) the graphene from the electrolyte environment. Upon introduction of pore-forming membrane proteins such as alamethicin and gramicidin A, current pulses are observed through the lipid bilayers from the graphene to the electrolyte, which charge the quantum capacitance of the graphene. This approach combines nanotechnology with electrophysiology to demonstrate qualitatively new ways of measuring ion channel currents.