Publications by authors named "Alexander Wollbrink"

2 Publications

  • Page 1 of 1

Linking the Electrical Conductivity and Non-Stoichiometry of Thin Film CeZrO by a Resonant Nanobalance Approach.

Materials (Basel) 2021 Feb 5;14(4). Epub 2021 Feb 5.

Institute of Energy Research and Physical Technologies, Clausthal University of Technology, 38640 Goslar, Germany.

Bulk ceria-zirconia solid solutions (CeZrO, CZO) are highly suited for application as oxygen storage materials in automotive three-way catalytic converters (TWC) due to the high levels of achievable oxygen non-stoichiometry δ. In thin film CZO, the oxygen storage properties are expected to be further enhanced. The present study addresses this aspect. CZO thin films with 0 ≤ x ≤ 1 were investigated. A unique nano-thermogravimetric method for thin films that is based on the resonant nanobalance approach for high-temperature characterization of oxygen non-stoichiometry in CZO was implemented. The high-temperature electrical conductivity and the non-stoichiometry δ of CZO were measured under oxygen partial pressures O in the range of 10-0.2 bar. Markedly enhanced reducibility and electronic conductivity of CeO-ZrO as compared to CeO and ZrO were observed. A comparison of temperature- and O-dependences of the non-stoichiometry of thin films with literature data for bulk CeZrO shows enhanced reducibility in the former. The maximum conductivity was found for CeZrO, whereas CeZrO showed the highest non-stoichiometry, yielding δ = 0.16 at 900 °C and O of 10 bar. The defect interactions in CeZrO are analyzed in the framework of defect models for ceria and zirconia.
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http://dx.doi.org/10.3390/ma14040748DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7915746PMC
February 2021

High-Flux Carbon Molecular Sieve Membranes for Gas Separation.

Angew Chem Int Ed Engl 2017 06 1;56(27):7760-7763. Epub 2017 Jun 1.

Fraunhofer Institute for Ceramic Technologies and Systems, IKTS-Hermsdorf branch, Michael-Faraday-Strasse 1, 07629, Hermsdorf, Germany.

Carbon membranes have great potential for highly selective and cost-efficient gas separation. Carbon is chemically stable and it is relative cheap. The controlled carbonization of a polymer coating on a porous ceramic support provides a 3D carbon material with molecular sieving permeation performance. The carbonization of the polymer blend gives turbostratic carbon domains of randomly stacked together sp hybridized carbon sheets as well as sp hybridized amorphous carbon. In the evaluation of the carbon molecular sieve membrane, hydrogen could be separated from propane with a selectivity of 10 000 with a hydrogen permeance of 5 m (STP)/(m hbar). Furthermore, by a post-synthesis oxidative treatment, the permeation fluxes are increased by widening the pores, and the molecular sieve carbon membrane is transformed from a molecular sieve carbon into a selective surface flow carbon membrane with adsorption controlled performance and becomes selective for carbon dioxide.
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http://dx.doi.org/10.1002/anie.201701851DOI Listing
June 2017