19 research outputs found
Time-resolved single-particle x-ray scattering reveals electron-density as coherent plasmonic-nanoparticle-oscillation source
Dynamics of optically-excited plasmonic nanoparticles are presently
understood as a series of sequential scattering events, involving
thermalization processes after pulsed optical excitation. One important step is
the initiation of nanoparticle breathing oscillations. According to established
experiments and models, these are caused by the statistical heat transfer from
thermalized electrons to the lattice. An additional contribution by hot
electron pressure has to be included to account for phase mismatches that arise
from the lack of experimental data on the breathing onset. We used optical
transient-absorption spectroscopy and time-resolved single-particle
x-ray-diffractive imaging to access the excited electron system and lattice.
The time-resolved single-particle imaging data provided structural information
directly on the onset of the breathing oscillation and confirmed the need for
an additional excitation mechanism to thermal expansion, while the observed
phase-dependence of the combined structural and optical data contrasted
previous studies. Therefore, we developed a new model that reproduces all our
experimental observations without using fit parameters. We identified
optically-induced electron density gradients as the main driving source.Comment: 32 pages, 5 figures, 1 supporting information document include
Effect of Solution Composition on the Energy Production by Capacitive Mixing in Membrane-Electrode Assembly
The final edited version of the paper can be found at: http://pubs.acs.org/articlesonrequest/AOR-c9UMxSzGY3eiU5SENNgT The complete citation is: Ahualli, S.; et al. Effect of Solution Composition on the Energy Production by Capacitive Mixing in Membrane-Electrode Assembly. Journal of Physical Chemistry, 118(29): 15590-15599 (2014). DOI:10.1021/jp504461mOpen access in the Journal on May 26, 2015In this work we consider the extent to which the presence of multi-valent ions in solution modifies the equilibrium and dynamics of the energy production in a capacitive cell built with ion-exchange membranes in contact with high surface area electrodes. The cell potential in open circuit (OCV) is controlled by the difference between both membrane potentials, simulated as constant volume charge regions. A theoretical model is elaborated for steady state OCV, first in the case of monovalent solutions, as a reference. This is compared to the results in multi-ionic systems, containing divalent cations in concentrations similar to those in real sea water. It is found that the OCV is reduced by about 25 % (as compared to the results in pure NaCl solutions) due to the presence of the divalent ions, even in low concentrations. Interestingly, this can be related to the “uphill” transport of such ions against their concentration gradients. On the contrary, their effect on the dynamics of the cell potential is negligible in the case of highly charged membranes. The comparison between model predictions and experimental results shows a very satisfactory agreement, and gives clues for the practical application of these recently introduced energy production methods.The research leading to these results received funding from the European Union 7th
Framework Programme (FP7/2007-2013) under agreement No. 256868. Further financial
support from Junta de Andalucia, Spain (PE2012-FQM 694) is also acknowledged. One of us, M.M.F., received financial support throughan FPU grant from the Universityof Granada