Showing papers by "Philip A. Parilla published in 2012"

Designing Higher Surface Area Metal-Organic Frameworks: Are Triple Bonds Better than Phenyls?

Abstract: We have synthesized, characterized, and computationally validated the high Brunauer–Emmett–Teller surface area and hydrogen uptake of a new, noncatenating metal–organic framework (MOF) material, NU-111. Our results imply that replacing the phenyl spacers of organic linkers with triple-bond spacers is an effective strategy for boosting molecule-accessible gravimetric surface areas of MOFs and related high-porosity materials.

Spectroscopic Identification of Hydrogen Spillover Species in Ruthenium-Modified High Surface Area Carbons by Diffuse Reflectance Infrared Fourier Transform Spectroscopy

Abstract: In recent years, carbon-based sorbents have been recognized for their potential application within vehicular hydrogen storage applications. One method by which sorbents have been reported to store appreciable hydrogen at room temperature is via a spillover process: where molecular hydrogen is first dissociated by metal nanoparticle catalysts and atomic hydrogen subsequently migrates onto the carbon substrate. Many reports have invoked the spillover mechanism to explain enhancements in reversible room temperature hydrogen uptake for metal-decorated sorbents. However, there is a lack of experimental evidence for the proposed chemical species formed as well as several differing theoretical explanations describing the process. In this report, we utilize diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) to identify the various chemical species formed upon room temperature H2 charging of ruthenium-decorated high surface area carbons. Room temperature H2 loading of a control sample with no rut...

Manipulation of Hydrogen Binding Energy and Desorption Kinetics by Boron Doping of High Surface Area Carbon

Abstract: Boron-doped high surface area carbon is shown to have unique chemical and structural properties that are advantageous for hydrogen storage. High surface area boron-doped carbon sorbents were produced by chemical vapor deposition of a boron-doped carbon (BCX) layer onto CM-Tec activated carbon. Photoelectron spectroscopy indicates the incorporation of boron at levels up to 14.3 at. % into sites with varying bonding environments. High-resolution microscopy characterization demonstrates that the turbostratic boron–carbon layer has a c-plane spacing of 4.02 ± 0.24 A, large enough to allow the diffusion of hydrogen intercalated between BCX layers. Slower adsorption and desorption kinetics that depend sensitively on H2 charging duration and temperature suggest the presence of hidden surface area of the turbostratic BCX and enhanced binding energy sites. Our study suggests that the increased c-plane spacing, together with a significant concentration of electron-deficient sp2 boron sites, combine to create a stro...

Reactions and reversible hydrogenation of single-walled carbon nanotube anions

Abstract: Single-walled carbon nanotube (SWNT) radical anions will react with tetrahydrofuran and generate ethylene, enolates, and a partially hydrogenated nanotube backbone. The experimental evidence suggests that there are sp3 C-H binding interactions. The total gravimetric content of hydrogen on a sample averages from 3.5% to 3.9% w/w, about four times the total amount observed for nanotubes hydrogenated via traditional Birch reduction reactions. Furthermore, the hydrogen desorbs at temperatures up to 400 °C less than those observed for the hydrogenated SWNTs formed after the Birch reduction. Finally, the first room temperature electron spin resonance spectrum of a nanotube radical ion is also reported.