Effect of Cations on the TiO₂/Acetonitrile Interface Structure: A Molecular Dynamics Study

Abstract

The TiO2/electrolyte interface was investigated as a key element of dye-sensitized solar cells (DSSCs). The influence of cations such as lithium (Li+), 1,2-dimethyl-3-propylimidazolium (DMPIM+), and tetrabutylammonium (TBA+) on the double-layer structure in acetonitrile-based electrolyte at the anatase (101) surface was studied by molecular dynamics (MD) simulation. The calculations were performed for the uncharged surface as well as for the negatively charged one, which imitated TiO2 nanocrystals with excess electron density under light irradiation. It was shown that acetonitrile molecules form a self-assembled monolayer on the anatase (101) surface, inhibiting adsorption/desorption of both cations and anions. The effective dipole moments of acetonitrile molecules in the monolayer are directed away from the surface and produce a potential drop across the interface of ∼1.3 V. The characteristic time for the reversible adsorption/desorption process of Li+ cations occurs in the second time range. The MD simulations show that cationic species have a strong effect on the electrolyte structure both in bulk and at the interface. In particular, a significant influence of cations on the density distribution of I– at the interface was found. This result suggests that the mechanism, by which cations affect the dye regeneration kinetics, consists of the local change of I– density in the region where the −NCS groups of ruthenium dyes (involved in the regeneration process) are located.

Effects of carbon surface topography on the electrode/electrolyte interface structure and relevance to Li–air batteries

“…This observation reflects the typical behavior of liquid at a crystal surface. A similar layered structure has been previously predicted in our works on MD simulation of various surface/liquid interfaces [34][35][36][37][38][39]55 and has been confirmed experimentally. 44,[56][57][58] The layered structure is also observed near the edge of the single-layer graphene (Fig.…”

“…28 However, the electrode/ electrolyte interface structure leaves out of account. In our previous works, it was shown by molecular dynamics (MD) simulation that an electrolyte is ordered at the interface, [34][35][36][37][38][39] and this ordering influences the kinetics of heterogeneous processes. 36,37 On the other hand, computer simulation and experimental results show the dependence of the interface structure on the surface type.…”

“…In our previous works, it was shown by molecular dynamics (MD) simulation that an electrolyte is ordered at the interface, [34][35][36][37][38][39] and this ordering influences the kinetics of heterogeneous processes. 36,37 On the other hand, computer simulation and experimental results show the dependence of the interface structure on the surface type. [40][41][42][43][44] Thus, it can be supposed that the variation of the surface topography results in restructuring of the electrode/electrolyte interface and, in turn, affects the kinetics of the ORR.…”

Alignment of energy levels in dye/semiconductor interfaces byGWcalculations: Effects due to coadsorption of solvent molecules

“…Indeed, the I − density profiles within a TiO 2 /liquid acetonitrile interface were studied in Ref. [22]. Depending on the chosen cation, different I − density profiles were obtained, such profiles showing peaks in the region where the the dye groups involved in the regeneration process are typically located [22].…”

“…This dipole layer, if acting in the proper direction, can favorably shift the semiconductor bands [22][23][24]. In semisquarylium dye sensitized solar cells no significant band shifts are reported, although the solvent layer (in this case methoxypropionitrile) is important for blocking electron-hole recombination by damping TiO 2 surface states [25].…”