期刊
INTERNATIONAL JOURNAL OF HYDROGEN ENERGY
卷 35, 期 16, 页码 8609-8620出版社
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.ijhydene.2010.05.117
关键词
Pd nanoparticle; Pd hydride; In situ X-ray diffraction
资金
- NSF of China [20673136, 20706056]
- National 863 Programs of China [2007AA05Z141, 2008AA05Z102]
- CAS
- National Science Council [NSC 97-2113-M-008-004]
High resolution in situ XRD was used to study the hydriding behavior of palladium electrocatalysts, prepared from two precursors, (NH4)(2)PdCl6 (4.3 nm), and palladium acetylacetonate [Pd(acac)(2)] (6.2 nm), and supported on porous carbon XC-72R. X-ray line profile analysis revealed a defective fcc lattice with internal strains and a high stacking fault probability of 12%. Importantly, no change, neither of the size, nor the state of defects was observed during the phase transition (alpha <-> beta). Based on this finding, a two-phase model adopted from bulk palladium hydride was proposed to describe the transition trough the miscibility gap (MG). Apparently, Pd nanoparticles can breathe hydrogen, without modifying their intrinsic crystal structure: A 3-parameter algorithm perfectly reproduces the anomalous line profiles observed inside the MG by a simple rescaling of the intensity profiles measured outside the MG. The algorithm delivers accurate values for the phase boundaries alpha-max, beta-min. They depend sensitively on the particles size and surface state, but also surprisingly on the branch of the hysteresis loop. Time dependent studies verify a hindered kinetics of hydride formation in the presence of surface oxide species. (C) 2010 Published by Elsevier Ltd on behalf of Professor T. Nejat Veziroglu.
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