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Name (Title):
Yoshitaka Tateyama (Dr.)
Affiliation:
International Centre for Materials Nanoarchitectonics, National Institute for
Materials Science
Address:
1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan
Email: TATEYAMA.Yoshitaka@nims.go.jp
Home Page: http://www.nims.go.jp/mana/members/team/cpc/
Presentation Title:
Ab initio MD study on redox reactions in electrolyte solutions of DSSC
Abstract:
Chemical reactions coupled to electron transfer (ET), so called 'redox reactions', play crucial
roles in diverse topics such as battery, fuel cell, catalysis. Fundamental quantities of redox
reactions are characterized by free energies, which are mainly governed by structural fluctuations
of the target species (solute) and the environment (solvent) as well as the electronic states of
frontier orbitals involved in the ET process. Quantitative calculation methods for such processes
thus need to take into account the free energies as well as the electronic states.
For this purpose, we have recently established ab initio molecular dynamics (MD) methods for
redox reactions. The first idea is combining the essence of the Marcus theory for ET [3,4] with
ab initio MD technique [1]. The formulation is found quite compatible with density functional
theory (DFT). Incorporating constrained MD scheme of Blue-Moon Ensemble, we have extended
the method to reactions with bond breaking/formation coupled to ET on the basis of the
thermodynamic integration scheme [2].
We have applied these methods to redox reactions associated with triiodide
-
(I3 ) and iodide (I-)
ions in typical electrolyte solutions of dye-sensitised solar cell (DSSC). In spite of many
applications as electrolyte, the atomistic mechanisms of these iodide redox reactions have not
been fully understood due to the complex nature involving multiple electron transfers and bond
changes. There are other issues such as the symmetry breaking of
-
I3 depending on the solvents.
We have calculated free energies and reaction pathways of the elementary redox processes
between
-
I3 and I
-
, and obtained possible scenario why acetonitrile solution gives better
performance than water in DSSC. In the talk we also discuss the application to solid/solution
interfaces.
References:
[1] Y. Tateyama et al. J. Chem. Phys. 122, 234505 (2005).
[2] Y. Tateyama et al. J. Chem. Phys. 126, 204506 (2007).
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