Single Pd atoms in activated carbon fibers and their contribution to hydrogen storage

Cristian I. Contescu; Klaus Van Benthem; Sa Li; Cecile S. Bonifacio; Stephen J. Pennycook; Puru Jena; Nidia C. Gallego

doi:10.1016/j.carbon.2011.05.021

Single Pd atoms in activated carbon fibers and their contribution to hydrogen storage

Cristian I. Contescu, Klaus Van Benthem, Sa Li, Cecile S. Bonifacio, Stephen J. Pennycook, Puru Jena, Nidia C. Gallego

Nanomaterials Chemistry Group

Research output: Contribution to journal › Article › peer-review

77 Scopus citations

Abstract

Palladium-modified activated carbon fibers (Pd-ACF) were synthesized by melt-spinning, carbonization and activation of an isotropic pitch carbon precursor premixed with an organometallic Pd compound. The hydrogen uptake at 25 °C and 20 bar on Pd-ACF exceeded the expected capacity based solely on Pd hydride formation and hydrogen physisorption on the microporous carbon support. Aberration-corrected scanning transmission electron microscopy (STEM) with sub-ngstrom spatial resolution provided unambiguous identification of isolated Pd atoms occurring in the carbon matrix that coexist with larger Pd particles. First principles calculations revealed that each single Pd atom can form Kubas-type complexes by binding up to three H₂ molecules in the pressure range of adsorption measurements. Based on Pd atom concentration determined from STEM images, the contribution of various mechanisms to the excess hydrogen uptake measured experimentally was evaluated. With consideration of Kubas binding as a viable mechanism (along with hydride formation and physisorption to carbon support) the role of hydrogen spillover in this system may be smaller than previously thought.

Original language	English
Pages (from-to)	4050-4058
Number of pages	9
Journal	Carbon
Volume	49
Issue number	12
DOIs	https://doi.org/10.1016/j.carbon.2011.05.021
State	Published - Oct 2011

Funding

Research supported by the US Department of Energy, Basic Energy Sciences, Materials Sciences and Engineering Division (C.I.C., K.v.B., S.J.P., N.C.G.) and in part by the Scientific User Facilities Division, DOE Office of Basic Energy Sciences (K.v.B). K.v.B. and C.S.B. acknowledge additional financial support through UC Davis start-up funds (analysis of electron microscopy results). S.L. and P.J. (computational studies) acknowledge support from National Energy Research Scientific Computing Center (NERSC), which is supported by the Office of Science of US Department of Energy under Contract No. DE-AC02-05CH11231. Fruitful discussions with D.D. Edie and H. Tekinalp (Clemson University) and Mr. Tekinalp’s contribution for synthesis of materials are gratefully acknowledged. Thanks are also due to Dr. Xianxian Wu for measurements of hydrogen adsorption data during a post-doctoral stage under ORNL Postdoctoral Associate Program administered jointly by ORISE and ORNL.

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10.1016/j.carbon.2011.05.021

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title = "Single Pd atoms in activated carbon fibers and their contribution to hydrogen storage",

abstract = "Palladium-modified activated carbon fibers (Pd-ACF) were synthesized by melt-spinning, carbonization and activation of an isotropic pitch carbon precursor premixed with an organometallic Pd compound. The hydrogen uptake at 25 °C and 20 bar on Pd-ACF exceeded the expected capacity based solely on Pd hydride formation and hydrogen physisorption on the microporous carbon support. Aberration-corrected scanning transmission electron microscopy (STEM) with sub-ngstrom spatial resolution provided unambiguous identification of isolated Pd atoms occurring in the carbon matrix that coexist with larger Pd particles. First principles calculations revealed that each single Pd atom can form Kubas-type complexes by binding up to three H2 molecules in the pressure range of adsorption measurements. Based on Pd atom concentration determined from STEM images, the contribution of various mechanisms to the excess hydrogen uptake measured experimentally was evaluated. With consideration of Kubas binding as a viable mechanism (along with hydride formation and physisorption to carbon support) the role of hydrogen spillover in this system may be smaller than previously thought.",

author = "Contescu, {Cristian I.} and {Van Benthem}, Klaus and Sa Li and Bonifacio, {Cecile S.} and Pennycook, {Stephen J.} and Puru Jena and Gallego, {Nidia C.}",

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AU - Contescu, Cristian I.

AU - Van Benthem, Klaus

AU - Li, Sa

AU - Bonifacio, Cecile S.

AU - Pennycook, Stephen J.

AU - Jena, Puru

AU - Gallego, Nidia C.

PY - 2011/10

Y1 - 2011/10

N2 - Palladium-modified activated carbon fibers (Pd-ACF) were synthesized by melt-spinning, carbonization and activation of an isotropic pitch carbon precursor premixed with an organometallic Pd compound. The hydrogen uptake at 25 °C and 20 bar on Pd-ACF exceeded the expected capacity based solely on Pd hydride formation and hydrogen physisorption on the microporous carbon support. Aberration-corrected scanning transmission electron microscopy (STEM) with sub-ngstrom spatial resolution provided unambiguous identification of isolated Pd atoms occurring in the carbon matrix that coexist with larger Pd particles. First principles calculations revealed that each single Pd atom can form Kubas-type complexes by binding up to three H2 molecules in the pressure range of adsorption measurements. Based on Pd atom concentration determined from STEM images, the contribution of various mechanisms to the excess hydrogen uptake measured experimentally was evaluated. With consideration of Kubas binding as a viable mechanism (along with hydride formation and physisorption to carbon support) the role of hydrogen spillover in this system may be smaller than previously thought.

AB - Palladium-modified activated carbon fibers (Pd-ACF) were synthesized by melt-spinning, carbonization and activation of an isotropic pitch carbon precursor premixed with an organometallic Pd compound. The hydrogen uptake at 25 °C and 20 bar on Pd-ACF exceeded the expected capacity based solely on Pd hydride formation and hydrogen physisorption on the microporous carbon support. Aberration-corrected scanning transmission electron microscopy (STEM) with sub-ngstrom spatial resolution provided unambiguous identification of isolated Pd atoms occurring in the carbon matrix that coexist with larger Pd particles. First principles calculations revealed that each single Pd atom can form Kubas-type complexes by binding up to three H2 molecules in the pressure range of adsorption measurements. Based on Pd atom concentration determined from STEM images, the contribution of various mechanisms to the excess hydrogen uptake measured experimentally was evaluated. With consideration of Kubas binding as a viable mechanism (along with hydride formation and physisorption to carbon support) the role of hydrogen spillover in this system may be smaller than previously thought.

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Single Pd atoms in activated carbon fibers and their contribution to hydrogen storage

Abstract

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