Josh A. Whaley

Note: Fixture for characterizing electrochemical devices in-operando in traditional vacuum systems

We describe a fixture that allows electrochemical devices to be studied under electrical bias in the type of vacuum systems commonly used in surface science. Three spring-loaded probes provide independent contacts for device operation and the characterization in vacuum or under in situ conditions with reactive gases. We document the robustness of the electrical contacts over large temperature changes and their reliability for conventional electrochemical measurements such as impedance spectroscopy. The optical access provided to the device enables the analysis by many techniques, as we demonstrate using x-ray photoelectron spectroscopy to measure local electrical potentials on a solid-oxide electrolyte device operating at high temperature in near-ambient pressure.

Angle-resolved low-energy ion scattering studies of quasicrystalline Al-Pd-Mn

Abstract We present angle-resolved low-energy ion scattering data that provide information about the composition of the topmost surface layers and atomic arrangement for a clean, 5-fold surface of a single-grain of icosahedral Al–Pd–Mn. The results show that the surface of this material has 5-fold periodicity and has a surface composition with a higher Al content than the bulk material (Al-86, Pd-13, Mn-1 versus Al-71, Pd-20, Mn-9 atom%). A predominant neighbor atom distance of 7.6±0.5 A is calculated from the results, consistent with scanning probe measurements and bulk models of Al–Pd–Mn quasicrystals. We calculate a nearest neighbor distance of 3.0±0.2 A. We also find that a Pd-rich layer exists just below an Al-rich outer layer, in agreement with dynamical low-energy electron diffraction calculations.

Sheath physics study using the divertor materials evaluation system (DIMES) on DIII‐D

A set of 19 dome‐shaped divertor Langmuir probes similar in design to probes used in JET and JT‐60 has been used successfully in DIII‐D to measure the divertor electron temperature, particle flux, and floating potential. A comparison of the power flux using IR cameras with the particle flux and electron temperature from the probes using collisionless sheath theory has indicated that the particle flux to the divertor surface may be strongly modified by collisions within the magnetic sheath. In order to study this effect, a set of probes have been designed that can be inserted into the divertor plasma using DIMES. Two dome‐shaped probes compare fluxes intercepted both above and within the magnetic sheath of the divertor surface. In addition, a third probe oriented normal to the magnetic field is used to verify the projected area of the probe surface. The probe design accommodates parallel power fluxes up to 50 MW/m2 for 30 ms, allowing for the study of beam‐heated plasmas in DIII‐D.

Characterization of a compact ECR plasma source and its applications to studies of helium ion damage to tungsten

Exposure of tungsten to low energy (<100 eV) helium plasmas at temperatures between 900–1900 K in both laboratory experiments and tokamaks has been shown to cause severe nanoscale modification of the near surface resulting in the growth of tungsten tendrils. Tendril formation can lead to non-sputtered erosion and dust formation. Here we report on characterization of a compact electron cyclotron resonance (ECR) He plasma source with an ion flux of ~2.5 × 1019 ions m−2 s−1, average fluence of 3 × 1024 ions m−2, and the surface morphology changes seen on the exposed tungsten surfaces. Exposures of polished tungsten disks at temperatures up to 1270 K have been performed and characterized using scanning electron microscopy and atomic force microscopy (AFM) scans. Bubbles and craters have been seen on the exposed tungsten surface growing to up to 150 nm in diameter. The ECR source has been tested for eventual use on a scanning tunneling microscopy experiment intended to study the early stages of surface morphology change due to He ion exposure.

Design and Construction of a Cascading Pressure Reactor Prototype for Solar Thermochemical Hydrogen Production

Recent work regarding the efficiency maximization for solar thermochemical fuel production in two step cycles has led to the design of a new type of reactor—the cascading pressure reactor—in which the thermal reduction step of the cycle is completed in multiple stages, at successively lower pressures. This approach enables lower thermal reduction pressures than in single-staged reactors, and decreases required pump work, leading to increased solar to fuel efficiencies. Here we report on the design and construction of a prototype cascading pressure reactor and testing of some of the key components. We especially focus on the technical challenges particular to the design, and their solutions.

Low-Energy Ion Scattering Measurements from an Al-Pd-Mn Quasicrystal

Energy-angle distributions of low-energy inert-gas ions scattered from surfaces provide information about surface composition and structure. We have measured energy spectra of He + scattered from an Al 71 Pd 20 Mn 9 quasicrystal, which was oriented perpendicular to the 5-fold axis, along various azimuthal directions. Strong scattering signals are seen from Al and Pd, but only a weak Mn signal is observed. From measurements made of He + at an oblique angle of incidence scattered in the forward direction, we observe a 72° periodicity in the azimuthal dependence of the scattering signal intensity from Al surface atoms. The effect arises from shadowing effects involving neighboring surface atoms and provides direct evidence that Al surface atoms exist in a local environment with 5-fold symmetry. In addition, measuring the variation of the signal intensity with incidence angle provides information about neighboring atom distances, which compare favorably with a model of the quasicrystal surface derived from the bulk structure.

Hydrogen interactions with quasicrystalline Al-Pd-Mn surfaces

In this work we examine the interaction of molecular and atomic deuterium with the fivefold surface of an icosahedral (i-) Al–Pd–Mn alloy using angle-resolved low-energy ion scattering under ultrahigh vacuum conditions. i-Al–Pd–Mn has been studied extensively and is known to form a laterally-bulk-terminated surface that is Al-rich. The density of Al atoms on the clean surface of fivefold i-Al–Pd–Mn is about that of Al(111) and hence we compare our results to studies of molecular and atomic hydrogen adsorbed on Al(111). We find that molecular deuterium does not adsorb or dissociate on i-Al–Pd–Mn, as on Al(111). Atomic D, however, readily adsorbs on both surfaces and on i-Al–Pd–Mn attenuates the scattering signals from Al, Pd and Mn substrate atoms. It thus appears that D chemisorbs on the outer layer of i-Al–Pd–Mn and bonds with Al atoms.

Permeation of "Hydromer" Film: An Elastomeric Hydrogen-Capturing Biopolymer.

This report analyzes the permeation resistance of a novel and proprietary polymer coating for hydrogen isotope resistance that was developed by New Mexico State University. Thermal gravimetric analysis and thermal desoprtion spectroscopy show the polymer is stable thermally to approximately 250 deg C. Deuterium gas-driven permeation experiments were conducted at Sandia to explore early evidence (obtained using Brunauer - Emmett - Teller) of the polymers strong resistance to hydrogen. With a relatively small amount of the polymer in solution (0.15%), a decrease in diffusion by a factor of 2 is observed at 100 and 150 deg C. While there was very little reduction in permeability, the preliminary findings reported here are meant to demonstrate the sensitivity of Sandias permeation measurements and are intended to motivate the future exploration of thicker barriers with greater polymer coverage.

Mechanisms for charge-transfer processes at electrode/solid-electrolyte interfaces.

This report summarizes the accomplishments of a Laboratory-Directed Research and Development (LDRD) project focused on developing and applying new x-ray spectroscopies to understand and improve electric charge transfer in electrochemical devices. Our approach studies the device materials as they function at elevated temperature and in the presence of sufficient gas to generate meaningful currents through the device. We developed hardware and methods to allow x-ray photoelectron spectroscopy to be applied under these conditions. We then showed that the approach can measure the local electric potentials of the materials, identify the chemical nature of the electrochemical intermediate reaction species and determine the chemical state of the active materials. When performed simultaneous to traditional impedance-based analysis, the approach provides an unprecedented characterization of an operating electrochemical system.