Adrian Hightower, PhD, PE, ENV-SP

Working toward fluoride batteries
Owing to the low atomic weight of fluorine, rechargeable fluoride-based batteries could offer very high energy density. However, current batteries need to operate at high temperatures that are required for the molten salt electrolytes. Davis et al. push toward batteries that can operate at room temperature, through two advances. One is the development of a room-temperature liquid electrolyte based on a stable tetraalkylammonium salt–fluorinated ether… Show more

Working toward fluoride batteries
Owing to the low atomic weight of fluorine, rechargeable fluoride-based batteries could offer very high energy density. However, current batteries need to operate at high temperatures that are required for the molten salt electrolytes. Davis et al. push toward batteries that can operate at room temperature, through two advances. One is the development of a room-temperature liquid electrolyte based on a stable tetraalkylammonium salt–fluorinated ether combination. The second is a copper–lanthanum trifluoride core-shell cathode material that demonstrates reversible partial fluorination and defluorination reactions. Show less

Barium titanate (BTO) nanoparticles (sizes 10–500 nm) exhibit a displacement of the Ti atom from the center of the perovskite unit cell as inferred from synchrotron x-ray diffraction patterns (XRD) analyzed using atomic pair distribution functions (PDFs). Fits to PDFs acquired at temperatures of 20 °C–220 °C indicate that these Ti displacements (∼0.1 Å) are comparable to or even greater than those in the bulk material. Moreover, these displacements persist at temperatures well above 120 °C… Show more

Barium titanate (BTO) nanoparticles (sizes 10–500 nm) exhibit a displacement of the Ti atom from the center of the perovskite unit cell as inferred from synchrotron x-ray diffraction patterns (XRD) analyzed using atomic pair distribution functions (PDFs). Fits to PDFs acquired at temperatures of 20 °C–220 °C indicate that these Ti displacements (∼0.1 Å) are comparable to or even greater than those in the bulk material. Moreover, these displacements persist at temperatures well above 120 °C, where the tetragonal-to-pseudocubic phase transition occurs in the bulk. Tetragonal Raman spectral lines were observed for all sizes of these BTO nanoparticles and confirm a distorted unit cell up to 120 °C. Above 120 °C, the small BTO nanoparticles (10, 50, 100 nm) continue to display tetragonal Raman lines, though with slowly decreasing amplitudes as the temperature rises. In contrast, the tetragonal Raman lines of large BTO nanoparticles (300, 400, 500 nm) disappear abruptly above 120 °C, suggestive of bulk material. Indeed, fits to large-particle x-ray PDFs over the range 20–60 Å reveal a sharp, long-range structural change toward a cubic lattice at 120 °C, again consistent with bulk material. This sharp, long-range structural change is absent in the small particles. In fact, laboratory XRD Bragg peak profiles for the small BTO particles appear to be singlets at 20 °C, indicating that significant long-range cubic order already exists at room temperature. By combining information from x-ray PDFs, Raman spectra, and Bragg peak profiles, we conclude that small BTO nanoparticles exhibit both short-range (unit-cell) distortion and long-range (mesoscale) cubic order from 20 °C to 220 °C, while the large nanoparticles behave as bulk material, differing from small particles only by exhibiting long-range tetragonal order below 120 °C and a mesoscale structural phase change at 120 °C. Show less

An activated carbon from Coconut (Cocos nucifera) shells was prepared by physical activation with carbon dioxide and water vapor. The activated carbon obtained has a surface area of 1058 m2 g−1 and such a high micropore volume of 0.49 cm3 g−1. This carbon was studied for the removal of lead from water. Sorption studies were performed at 30 °C, at different pH and adsorbent doses, in batch mode. Lead precipitation was observed on the surface of the activated carbon. Maximum adsorption occurred… Show more

An activated carbon from Coconut (Cocos nucifera) shells was prepared by physical activation with carbon dioxide and water vapor. The activated carbon obtained has a surface area of 1058 m2 g−1 and such a high micropore volume of 0.49 cm3 g−1. This carbon was studied for the removal of lead from water. Sorption studies were performed at 30 °C, at different pH and adsorbent doses, in batch mode. Lead precipitation was observed on the surface of the activated carbon. Maximum adsorption occurred at pH 9 for an adsorbent dose of 2 g L−1. Kinetic studies, at the initial concentration of 150 mg L−1 of lead, pH 5 and an adsorbent dose of 1 g L−1, yielded an equilibrium time of 50 h for this activated carbon. The kinetic data were modeled with the pseudo first order, the pseudo second order and the Bangham models. The pseudo second order model fitted the data well. The sorption rate constant (7 × 10−4 mol−1 Kg s−1) and the maximum amount of lead adsorbed (0.23 mol kg−1) are quite good compared to the data found in literature. Sorption equilibrium studies were conducted in a concentration range of lead from 0 to 150 mg L−1. In an aqueous lead solution with an initial concentration of 30 mg L−1, at pH 5, adsorbent dose 1 g L−1, activated Coconut shell carbon removed at equilibrium 100 % of the heavy metal. The equilibrium data were modeled with the Langmuir and Freundlich equations, of which the former gave the best fit. The Langmuir constants Qmax eq (0.23 mol kg−1) and KL (487667 L mol−1) are in good agreement with literature. XPS studies identified adsorbed species as lead carbonates and/or lead oxalates and precipitates as lead oxide and/or lead hydroxide on the activated carbon surface. The Coconut shell activated carbon is a very efficient carbon due to its high surface area, to surface micropores and to the presence surface groups like hydroxyls promoting adsorption in the porous system and lead crystal precipitation on the activated carbon surface. Show less

We quantitatively characterized oxygen reduction kinetics at the nanoscale Pt∣CsHSO4 interface at ∼150 °C in humidified air using conducting atomic force microscopy (AFM) in conjunction with AC impedance spectroscopy and cyclic voltammetry. From the impedance measurements, oxygen reduction at Pt∣CsHSO4 was found to comprise two processes, one displaying an exponential dependence on overpotential and the other only weakly dependent on overpotential. Both interfacial processes displayed… Show more

We quantitatively characterized oxygen reduction kinetics at the nanoscale Pt∣CsHSO4 interface at ∼150 °C in humidified air using conducting atomic force microscopy (AFM) in conjunction with AC impedance spectroscopy and cyclic voltammetry. From the impedance measurements, oxygen reduction at Pt∣CsHSO4 was found to comprise two processes, one displaying an exponential dependence on overpotential and the other only weakly dependent on overpotential. Both interfacial processes displayed near-ideal capacitive behavior, indicating a minimal distribution in the associated relaxation time. Such a feature is taken to be characteristic of a nanoscale interface in which spatial averaging effects are absent and, furthermore, allows for the rigorous separation of multiple processes that would otherwise be convoluted in measurements using conventional macroscale electrode geometries. The complete current−voltage characteristics of the Pt∣CsHSO4 interface were measured at various points across the electrolyte surface and reveal a variation of the oxygen reduction kinetics with position. The overpotential-activated process, which dominates at voltages below −1 V, was interpreted as a charge-transfer reaction. Analysis of six different sets of Pt∣CsHSO4 experiments, within the Butler−Volmer framework, yielded exchange coefficients (α) for charge transfer ranging from 0.1 to 0.6 and exchange currents (i0) spanning 5 orders of magnitude. The observed counter-correlation between the exchange current and exchange coefficient indicates that the extent to which the activation barrier decreases under bias (as reflected in the value of α) depends on the initial magnitude of that barrier under open circuit conditions (as reflected in the value of i0). The clear correlation across six independent sets of measurements further indicates the suitability of conducting AFM approaches for careful and comprehensive study of electrochemical reactions at electrolyte−metal−gas boundaries. Show less

Iodine adsorption on a polycrystalline gold electrode was studied by in situ electrochemical Rutherford backscattering (ECRBS) using an ultrahigh vacuum (UHV)-electrochemical cell comprising of a thin-film silicon nitride window. The depth resolution of RBS allowed for measurement of nuclide concentration of the diffuse double-layer, electrode surface and near-surface regions. ECRBS measurements on the gold electrode, initially exposed to −500 mV vs. a platinum pseudo-reference electrode, in a… Show more

Iodine adsorption on a polycrystalline gold electrode was studied by in situ electrochemical Rutherford backscattering (ECRBS) using an ultrahigh vacuum (UHV)-electrochemical cell comprising of a thin-film silicon nitride window. The depth resolution of RBS allowed for measurement of nuclide concentration of the diffuse double-layer, electrode surface and near-surface regions. ECRBS measurements on the gold electrode, initially exposed to −500 mV vs. a platinum pseudo-reference electrode, in a potassium iodide solution, showed an increase in the 2.07 MeV iodine peak indicative of iodine adsorption. The surface concentration of the iodine adlayer was directly measured by ECRBS to be 1.3 ± 0.3 nmol/cm2. ECRBS measurements on a gold electrode exposed to 1.5 V vs. a platinum pseudo-reference electrode, in a potassium iodide solution display a decrease in the 2.16 MeV gold peak and a shift to lower energies. Scanning electron microscopy images of electrodes studied by ECRBS displayed roughened surfaces consistent with gold dissolution. This work demonstrates the potential for in situ ECRBS using thin-film silicon nitride windows to become a powerful tool for the investigation of a wide range of electrochemical processes in areas such as corrosion, electrodeposition and electrocatalysis. Show less

The adsorption of CO on Pt(1 1 1), (2 × 2) and (√3 × √3)R30° Sn/Pt(1 1 1) surface alloys has been studied using temperature programmed desorption (TPD), low energy electron diffraction (LEED) and infrared reflection adsorption spectroscopy (IRAS). The presence of Sn in the surface layer of Pt(1 1 1) reduces the binding energy of CO by a few kcal/mol. IRAS data show two C–O stretching frequencies, ∼2100 and ∼1860 cm−1, corresponding to atop and bridge bonded species, respectively. Bridge bonded… Show more

The adsorption of CO on Pt(1 1 1), (2 × 2) and (√3 × √3)R30° Sn/Pt(1 1 1) surface alloys has been studied using temperature programmed desorption (TPD), low energy electron diffraction (LEED) and infrared reflection adsorption spectroscopy (IRAS). The presence of Sn in the surface layer of Pt(1 1 1) reduces the binding energy of CO by a few kcal/mol. IRAS data show two C–O stretching frequencies, ∼2100 and ∼1860 cm−1, corresponding to atop and bridge bonded species, respectively. Bridge bonded stretching frequencies are only observed for Pt(1 1 1) and (2 × 2) Sn/Pt(1 1 1) alloy surfaces. A slight coverage dependence of the vibrational frequencies is observed for the three surfaces. High pressure IRAS experiments over a broad temperature range show no indication of bridge bonded CO on any of the three surfaces. Direct CO adsorption on Sn sites is not observed over the measured temperature and pressure ranges. Show less

This paper presents a model that describes how liquid flow fills micro-fluidic components and networks. As an alternative to computational fluid dynamic (CFD) simulations, we use a constrained energy minimization approach. This approach is based on two assumptions that hold in many micro-fluidic devices: (i) The length scales are small, and we consider slow filling rates, hence fluid momentum and viscous terms are small compared to surface tension forces, consequently the liquid/gas interfaces… Show more

This paper presents a model that describes how liquid flow fills micro-fluidic components and networks. As an alternative to computational fluid dynamic (CFD) simulations, we use a constrained energy minimization approach. This approach is based on two assumptions that hold in many micro-fluidic devices: (i) The length scales are small, and we consider slow filling rates, hence fluid momentum and viscous terms are small compared to surface tension forces, consequently the liquid/gas interfaces can be viewed as a succession of quasi-steady equilibrium configurations. (ii) Any equilibrium configuration corresponds to a surface tension energy minima which is constrained by the device shape and the volume of liquid in the device. The model is developed for planar micro-fluidic devices, is based on a fundamental physical principle, and shows accurate agreement with experimental data. It takes us only a few minutes to evaluate the model for a planar component of any shape using the Surface Evolver software, and this is significantly less then the computer run time required for CFD simulations. Moreover, once a library of component models has been created (which takes less than an hour of computer time) it then takes only seconds to simulate different network architectures with thousands of components. This fast ‘reconfigure the network and simulate in seconds’ capability is essential for the design of truly complex networks that will enable the next generation of passive, micro-fluidic, lab-on-a-chip systems. Show less

This book provides a reference on electron energy loss spectrometry (EELS) with the transmission electron microscope, an established technique for chemical and structural analysis of thin specimens in a transmission electron microscope. Describing the issues of instrumentation, data acquisition, and data analysis, the authors apply this technique to several classes of materials, namely ceramics, metals, polymers, minerals, semiconductors, and magnetic materials.