Multicomponent charge transport in electrolyte solutions
Psaltis, Steven Timothy Peter (2012) Multicomponent charge transport in electrolyte solutions. PhD thesis, Queensland University of Technology.

Steven Psaltis Thesis
(PDF 3MB)

Abstract
The work presented in this thesis investigates the mathematical modelling of charge transport in electrolyte solutions, within the nanoporous structures of electrochemical devices. We compare two approaches found in the literature, by developing onedimensional transport models based on the NernstPlanck and MaxwellStefan equations.
The development of the NernstPlanck equations relies on the assumption that the solution is infinitely dilute. However, this is typically not the case for the electrolyte solutions found within electrochemical devices. Furthermore, ionic concentrations much higher than those of the bulk concentrations can be obtained near the electrode/electrolyte interfaces due to the development of an electric double layer. Hence, multicomponent interactions which are neglected by the NernstPlanck equations may become important.
The MaxwellStefan equations account for these multicomponent interactions, and thus they should provide a more accurate representation of transport in electrolyte solutions. To allow for the effects of the electric double layer in both the NernstPlanck and MaxwellStefan equations, we do not assume local electroneutrality in the solution.
Instead, we model the electrostatic potential as a continuously varying function, by way of Poisson’s equation. Importantly, we show that for a ternary electrolyte solution at high interfacial concentrations, the MaxwellStefan equations predict behaviour that is not recovered from the NernstPlanck equations.
The main difficulty in the application of the MaxwellStefan equations to charge transport in electrolyte solutions is knowledge of the transport parameters. In this work, we apply molecular dynamics simulations to obtain the required diffusivities, and thus we are able to incorporate microscopic behaviour into a continuum scale model. This is important due to the small size scales we are concerned with, as we are still able to retain the computational efficiency of continuum modelling. This approach provides an avenue by which the microscopic behaviour may ultimately be incorporated into a full devicescale model.
The onedimensional MaxwellStefan model is extended to two dimensions, representing an important first step for developing a fullycoupled interfacial charge transport model for electrochemical devices. It allows us to begin investigation into ambipolar diffusion effects, where the motion of the ions in the electrolyte is affected by the transport of electrons in the electrode. As we do not consider modelling in the solid phase in this work, this is simulated by applying a timevarying potential to one interface of our twodimensional computational domain, thus allowing a flow field to develop in the electrolyte. Our model facilitates the observation of the transport of ions near the electrode/electrolyte interface. For the simulations considered in this work, we show that while there is some motion in the direction parallel to the interface, the interfacial coupling is not sufficient for the ions in solution to be "dragged" along the interface for long distances.
Impact and interest:
Citation counts are sourced monthly from Scopus and Web of Science® citation databases.
These databases contain citations from different subsets of available publications and different time periods and thus the citation count from each is usually different. Some works are not in either database and no count is displayed. Scopus includes citations from articles published in 1996 onwards, and Web of Science® generally from 1980 onwards.
Citations counts from the Google Scholar™ indexing service can be viewed at the linked Google Scholar™ search.
Fulltext downloads:
Fulltext downloads displays the total number of times this work’s files (e.g., a PDF) have been downloaded from QUT ePrints as well as the number of downloads in the previous 365 days. The count includes downloads for all files if a work has more than one.
ID Code:  60964 

Item Type:  QUT Thesis (PhD) 
Supervisor:  Farrell, Troy & Will, Geoffrey 
Keywords:  ambipolar, charge transport, diffusion, diffusivities, double layer, electrochemistry, electrolyte, iodide, lithium, mathematical modelling, migration, MaxwellStefan, molecular dynamics, multicomponent, nanoporous, NernstPlanck, thin film, triiodide, two dimensions 
Divisions:  Current > QUT Faculties and Divisions > Science & Engineering Faculty Past > Schools > Mathematical Sciences 
Institution:  Queensland University of Technology 
Deposited On:  27 Jun 2013 02:30 
Last Modified:  10 Sep 2015 02:37 
Export: EndNote  Dublin Core  BibTeX
Repository Staff Only: item control page