Cole Petersburg

A Phenomenological Study of the Metal-Oxide Interface : The Role of Catalysis in Hydrogen Production from Renewable Resources

The truth about Cats: The metal-oxide interface of a Pd-Rh/CeO{sub 2} catalyst was studied in the context of developing active, selective and durable solid catalytic materials for the production of hydrogen from renewables. The presence of a stable contact between finely dispersed transition-metal clusters (Pd and Rh) on the nanoparticles of the CeO{sub 2} support leads to a highly active and stable catalyst for the steam reforming of ethanol.

Comparative Study of the Capacity and Rate Capability of LiNi y Mn y Co1–2y O2 (y = 0.5, 0.45, 0.4, 0.33)

An unresolved question for the layered oxides is: what is the optimum value of y in the formula LiNi{sub y}Mn{sub y}Co{sub 1-2y}O{sub 2} for energy storage at moderate reaction rates? Here we report a systematic study of the specific capacity, rate capability and cycle life of Li{sub x}Ni{sub y}Mn{sub y}Co{sub 1-2y}O{sub 2}(y = 0.5, 0.45, 0.4, and 0.333). The voltage of the Li/y = 0.333 couple crosses over those of lower cobalt content for x 0.333 when charging above 4 V. Overall the y = 0.4 material has the optimum properties, having the highest theoretical capacity, less of the expensive cobalt and yet rate capabilities and capacity retention comparable to the y = 0.333 material.

Oxygen and transition metal involvement in the charge compensation mechanism of LiNi1/3Mn1/3Co1/3O2 cathodes

X-ray absorption spectroscopy at the Ni, Mn, and Co K-edges is used to investigate the charge compensation mechanism and its relationship to the magnetic moments in Li1−xNi1/3Mn1/3Co1/3O2. Multiple analytical methods are compared to separate element-specific redox trends from collective effects. EXAFS is used not only for structural, but also for chemical information while XANES is used not only for chemical, but also for structural information. While Ni is found to be the only transition metal involved in the charge compensation reaction until half the Li is removed, the second half of the deintercalation reaction is not accompanied by transition-metal oxidation. It is deduced that over the second half of Li deintercalation, the oxidation of oxygen ions bonded to cobalt is responsible for charge compensation and for an increase in the magnetic moment.

In-situ oxygen x-ray absorption spectroscopy investigation of the resistance modulation mechanism in LiNbO2 memristors

In situ near edge x-ray absorption fine structure spectroscopy (NEXAFS) is performed on LiNbO2 analog memristors to identify the underlying analog resistance modulation mechanism. Empty electronic state gradients in the NEXAFS difference spectra are observed in biased devices indicating a gradual movement of lithium. This movement of lithium supports the assertion that simple ion dopant drift and diffusion dominate the analog memristor’s resistance response. By identifying the physical memristance mechanism in analog LiNbO2 memristors, suggestions are made for additions to the memristor to modify device performance for both neuromorphic computing and memory applications.

Soft X-ray Characterization Technique for Li Batteries Under Operating Conditions

O K-edge and Co L-edge near-edge X-ray absorption fine structure has been used to examine the cathode of an intact solid-state lithium ion battery. The novel technique allowed for the simultaneous acquisition of partial electron yield and fluorescence yield data during the first charge cycle of a LiCoO(2)-based battery below the intercalation voltage. The chemical environments of oxygen and cobalt at the surface are shown to differ chemically from those in the bulk. The present design enables a wide variety of in situ spectroscopies, microscopies and scattering techniques.

Interactions of Oxygen and Ethylene with Submonolayer Ag Films Supported on Ni(111)

We investigate the oxidation of, and the reaction of ethylene with, Ni(111) with and without sub-monolayer Ag adlayers as a function of temperature. The addition of Ag to Ni(111) is shown to enhance the activity towards the ethylene epoxidation reaction, and increase the temperature at which ethylene oxide is stable on the surface. We present a systematic study of the formation of chemisorbed oxygen on the Ag-Ni(111) surfaces and correlate the presence and absence of O(1-) and O(2-) surface species with the reactivity towards ethylene. By characterizing the samples with low-energy electron microscopy (LEEM) in combination with X-ray photoelectron spectroscopy (XPS), we have identified specific growth of silver on step-edge sites and successfully increased the temperature at which the produced ethylene oxide remains stable, a trait which is desirable for catalysis.

In situ investigation of the channel conductance of a Li1−xCoO2 (0<x<0.5) ionic-electronic transistor

An ion gated transistor is shown to have an analog electronic channel resistance that is dependent on the ion concentration in a solid state device. The ionic transistor made from a common battery cathode material, LiCoO2, is investigated for use in devices that exploit the interaction between ions and electrons with applications in low-power neuromorphic computing and non-volatile memory. The majority of the resistance change in LiCoO2 occurs close to the stoichiometric point, and thus, nanoscale LiCoO2-based ionic electronic devices are expected to consume minimal power and avoid structural phase changes leading to improved reliability.