Theory of the electrostatic surface potential and charge transfer for SOFC electrodes
File(s)
Author(s)
Williams, Nicholas
Type
Thesis
Abstract
Nonequilibrium thermodynamics describe the current-voltage characteristics of electrochemical devices. For conventional electrode-electrolyte interfaces, the local activation overpotential is used to describe the electrostatic potential step between the two materials as a current is generated. However, the activation overpotential for the metal/mixed ionic-electronic conducting (MIEC) composite electrodes (Ni/CGO) studied in this work originates at the MIEC-gas interface. First, Gaussian process regression under inequality constraints, or finite Gaussian process, was used for calculating the DRT of Ni/CGO electrodes as part of a symmetrical cell and a full stack. By varying the current density it was possible to derive a Tafel plot for the isolated electrode process, something which is completely missing from literature for the Ni/CGO electrode.
The theory of the electrostatic potential at the MIEC–gas interface was then developed as an electrochemical driving force for charge transfer at the ceria–gas interface. Using density functional theory, the relationship between the electrostatic surface potential and the reservoir chemical potential at the CGO-($\mathrm{H_2/H_2O}$) interface replicated the experimental measurements with striking accuracy, where it was proven that the magnitude of the electrostatic surface potential is correlated with the intrinsic dipole potential of the adsorbate. Moreover, the theory was extended to analyse CGO-($\mathrm{CO/CO_2}$) and $\mathrm{LaFeO_3}$-$\mathrm{O_2}$ systems by simulating an electric field across the electrode-gas interface.
Finally, by treating both protons and electrons as quantum particles, the theory of proton-coupled electron transfer (PCET) was adapted to account for the both the electrostatic surface potential at both the two phase (2PB) and three phase boundary (3PB). This formulation was used to fit the current-voltage data, where the results illustrated that the 3PB pathway dominated the total current density.
The theory of the electrostatic potential at the MIEC–gas interface was then developed as an electrochemical driving force for charge transfer at the ceria–gas interface. Using density functional theory, the relationship between the electrostatic surface potential and the reservoir chemical potential at the CGO-($\mathrm{H_2/H_2O}$) interface replicated the experimental measurements with striking accuracy, where it was proven that the magnitude of the electrostatic surface potential is correlated with the intrinsic dipole potential of the adsorbate. Moreover, the theory was extended to analyse CGO-($\mathrm{CO/CO_2}$) and $\mathrm{LaFeO_3}$-$\mathrm{O_2}$ systems by simulating an electric field across the electrode-gas interface.
Finally, by treating both protons and electrons as quantum particles, the theory of proton-coupled electron transfer (PCET) was adapted to account for the both the electrostatic surface potential at both the two phase (2PB) and three phase boundary (3PB). This formulation was used to fit the current-voltage data, where the results illustrated that the 3PB pathway dominated the total current density.
Version
Open Access
Date Issued
2022-12-07
Date Awarded
01/03/2023
License URL
Advisor
Skinner, Stephen
Sponsor
Ceres Power (Firm)
Publisher Department
Materials
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)