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Control of both particle and pore size in nanoporous palladium alloy powders

Powder Technology

Jones, Christopher G.; Cappillino, Patrick C.; Stavila, Vitalie; Robinson, David

Energy storage materials often involve chemical reactions with bulk solids. Porosity within the solids can enhance reaction rates. The porosity can be either within or between individual particles of the material. Greater control of the size and uniformity of both types of pore should lead to enhancements of charging and discharging rates in energy storage systems. To control both particle and pore size in nanoporous palladium (Pd)-based hydrogen storage materials, we have first created uniformly sized copper particles of about 1. μm diameter by the reduction of copper sulfate with ascorbic acid. In turn, these were used as reducing agents for tetrachloropalladate in the presence of a block copolymer surfactant. The copper reductant particles are geometrically self-limiting, so the resulting Pd particles are of similar size. The surfactant induces formation of 10. nm-scale pores within the particles. Some residual copper is alloyed with the Pd, reducing hydrogen storage capacity; use of a more reactive Pd salt can mitigate this. The reaction is conveniently performed in gram-scale batches. © 2014 Elsevier B.V.

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TYPE Journal Article YEAR 2014
DOIOSTIScopus

Kinetics and mechanism of metal-organic framework thin film growth: Systematic investigation of HKUST-1 deposition on QCM electrodes

Chemical Science

Stavila, Vitalie; Volponi, Joanne V.; Katzenmeyer, Aaron M.; Dixon, Matthew C.; Allendorf, Mark D.

We describe a systematic investigation of the factors controlling step-by-step growth of the metal-organic framework (MOF) [Cu 3(btc) 2(H 2O) 3]·xH 2O (also known as HKUST-1), using quartz crystal microbalance (QCM) electrodes as an in situ probe of the reaction kinetics and mechanism. Electrodes coated with silica, alumina and gold functionalized with OH- and COOH-terminated self-assembled monolayers (SAMs) were employed to determine the effects of surface properties on nucleation. Deposition rates were measured using the high sensitivity available from QCM-D (D = dissipation) techniques to determine rate constants in the early stage of the process. Films were characterized using grazing incidence XRD, SEM, AFM, profilometry and reflection-absorption IR spectroscopy. The effects of reaction time, concentration, temperature and substrate on the deposition rates, film crystallinity and surface morphology were evaluated. The initial growth step, in which the surface is exposed to copper ions (in the form of an ethanolic solution of copper(ii) acetate) is fast and independent of temperature, after which all subsequent steps are thermally activated over the temperature range 22-62 °C. Using these data, we propose a kinetic model for the Cu 3(btc) 2 growth on surfaces that includes rate constants for the individual steps. The magnitude of the activation energies, in particular the large entropy decrease, suggests an associative reaction with a tight transition state. The measured activation energies for the step-by-step MOF growth are an order of magnitude lower than the value previously reported for bulk Cu 3(btc) 2 crystals. Finally, the results of this investigation demonstrate that the QCM method is a powerful tool for quantitative, in situ monitoring of MOF growth in real time. © 2012 The Royal Society of Chemistry.

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TYPE Journal Article YEAR 2012
ScopusOSTI
Results 176–200 of 226
Results 176–200 of 226
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