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Title: Final Report: Characterization of Hydrogen Adsorption in Carbon-Based Materials by NMR

Abstract

In support of DOE/EERE's Fuel Cell Technologies Program Hydrogen Sorption Center of Excellence (HSCoE), UNC conducted Nuclear Magnetic Resonance (NMR) measurements that contributed spectroscopic information as well as quantitative analysis of adsorption processes. While NMR based Langmuir isotherms produce reliable H2 capacity measurements, the most astute contribution to the center is provided by information on dihydrogen adsorption on the scale of nanometers, including the molecular dynamics of hydrogen in micropores, and the diffusion of dihydrogen between macro and micro pores. A new method to assess the pore width using H2 as probe of the pore geometry was developed and is based on the variation of the observed chemical shift of adsorbed dihydrogen as function of H2 pressure. Adsorbents designed and synthesized by the Center were assessed for their H2 capacity, the binding energy of the adsorption site, their pore structure and their ability to release H2. Feedback to the materials groups was provided to improve the materials’ properties. To enable in situ NMR measurements as a function of H2 pressure and temperature, a unique, specialized NMR system was designed and built. Pressure can be varied between 10-4 and 107 Pa while the temperature can be controlled between 77K and roommore » temperature. In addition to the 1H investigation of the H2 adsorption process, NMR was implemented to measure the atomic content of substituted elements, e.g. boron in boron substituted graphitic material as well as to determine the local environment and symmetry of these substituted nuclei. The primary findings by UNC are the following: • Boron substituted for carbon in graphitic material in the planar BC3 configuration enhances the binding energy for adsorbed hydrogen. • Arrested kinetics of H2 was observed below 130K in the same boron substituted carbon samples that combine enhanced binding energy with micropore structure. • Hydrogen storage material made from activated PEEK is well suited for hydrogen storage due to its controlled microporous structure and large surface area. • A new porosimetry method for evaluating the pore landscape using H2 as a probe was developed. 1H NMR can probe the nanoscale pore structure of synthesized material and can assess the pore dimension over a range covering 1.2 nm to 2.5 nm, the size that is desired for H2 adsorption. • Analysis of 1H NMR spectra in conjunction with the characterization of the bonding structure of the adsorbent by 13C NMR distinguishes between a heterogeneous and homogeneous pore structure as evidenced by the work on AX21 and activated PEEK. • Most of the sorbents studied are suited to hydrogen storage at low temperature (T < 100K). Of the materials investigated, only boron substituted graphite has the potential to work at higher temperatures if the boron content in the favorable planar BC3 configuration that actively contributes to adsorption can be increased.« less

Authors:
;
Publication Date:
Research Org.:
Universty of North Carolina
Sponsoring Org.:
DOE/EERE: The Fuel Cell Technologies Program Hydrogen Sorption Center of Excellence (HSCoE)
OSTI Identifier:
1018531
Report Number(s):
Final Report: Characterization of Hydrogen Adsorption in Carbon-Based Materials by NMR
GO15081; TRN: US1103550
DOE Contract Number:  
FC36-05GO15081
Resource Type:
Technical Report
Country of Publication:
United States
Language:
English
Subject:
08 HYDROGEN; 36 MATERIALS SCIENCE; ADSORBENTS; ADSORPTION; BINDING ENERGY; BORON; CARBON; CHEMICAL SHIFT; DIFFUSION; FUEL CELLS; GEOMETRY; GRAPHITE; HYDROGEN; HYDROGEN STORAGE; ISOTHERMS; KINETICS; NMR SPECTRA; NUCLEAR MAGNETIC RESONANCE; NUCLEI; PORE STRUCTURE; SORPTION; SURFACE AREA; SYMMETRY; Hydrogen adsorption; Sorbent Materials; Nuclear Magnetic Resonance; Adsorption; Langmuir

Citation Formats

Wu, Yue, and Kleinhammes, Alfred. Final Report: Characterization of Hydrogen Adsorption in Carbon-Based Materials by NMR. United States: N. p., 2011. Web. doi:10.2172/1018531.
Wu, Yue, & Kleinhammes, Alfred. Final Report: Characterization of Hydrogen Adsorption in Carbon-Based Materials by NMR. United States. doi:10.2172/1018531.
Wu, Yue, and Kleinhammes, Alfred. Mon . "Final Report: Characterization of Hydrogen Adsorption in Carbon-Based Materials by NMR". United States. doi:10.2172/1018531. https://www.osti.gov/servlets/purl/1018531.
@article{osti_1018531,
title = {Final Report: Characterization of Hydrogen Adsorption in Carbon-Based Materials by NMR},
author = {Wu, Yue and Kleinhammes, Alfred},
abstractNote = {In support of DOE/EERE's Fuel Cell Technologies Program Hydrogen Sorption Center of Excellence (HSCoE), UNC conducted Nuclear Magnetic Resonance (NMR) measurements that contributed spectroscopic information as well as quantitative analysis of adsorption processes. While NMR based Langmuir isotherms produce reliable H2 capacity measurements, the most astute contribution to the center is provided by information on dihydrogen adsorption on the scale of nanometers, including the molecular dynamics of hydrogen in micropores, and the diffusion of dihydrogen between macro and micro pores. A new method to assess the pore width using H2 as probe of the pore geometry was developed and is based on the variation of the observed chemical shift of adsorbed dihydrogen as function of H2 pressure. Adsorbents designed and synthesized by the Center were assessed for their H2 capacity, the binding energy of the adsorption site, their pore structure and their ability to release H2. Feedback to the materials groups was provided to improve the materials’ properties. To enable in situ NMR measurements as a function of H2 pressure and temperature, a unique, specialized NMR system was designed and built. Pressure can be varied between 10-4 and 107 Pa while the temperature can be controlled between 77K and room temperature. In addition to the 1H investigation of the H2 adsorption process, NMR was implemented to measure the atomic content of substituted elements, e.g. boron in boron substituted graphitic material as well as to determine the local environment and symmetry of these substituted nuclei. The primary findings by UNC are the following: • Boron substituted for carbon in graphitic material in the planar BC3 configuration enhances the binding energy for adsorbed hydrogen. • Arrested kinetics of H2 was observed below 130K in the same boron substituted carbon samples that combine enhanced binding energy with micropore structure. • Hydrogen storage material made from activated PEEK is well suited for hydrogen storage due to its controlled microporous structure and large surface area. • A new porosimetry method for evaluating the pore landscape using H2 as a probe was developed. 1H NMR can probe the nanoscale pore structure of synthesized material and can assess the pore dimension over a range covering 1.2 nm to 2.5 nm, the size that is desired for H2 adsorption. • Analysis of 1H NMR spectra in conjunction with the characterization of the bonding structure of the adsorbent by 13C NMR distinguishes between a heterogeneous and homogeneous pore structure as evidenced by the work on AX21 and activated PEEK. • Most of the sorbents studied are suited to hydrogen storage at low temperature (T < 100K). Of the materials investigated, only boron substituted graphite has the potential to work at higher temperatures if the boron content in the favorable planar BC3 configuration that actively contributes to adsorption can be increased.},
doi = {10.2172/1018531},
journal = {},
number = ,
volume = ,
place = {United States},
year = {2011},
month = {7}
}