Date on Master's Thesis/Doctoral Dissertation
12-2025
Document Type
Doctoral Dissertation
Degree Name
Ph. D.
Department
Chemistry
Degree Program
Chemistry, PhD
Committee Chair
Wilson, Andrew J.
Committee Member
Zamborini, Francis
Committee Member
Thompson, Lee
Committee Member
Sathitsuksanoh, Noppadon
Author's Keywords
Plasmon; electrochemistry
Abstract
Plasmon-assisted electrochemistry has received attention due to its effects of hot charge carriers, photothermal heating, and enhanced electromagnetic field impact on electrochemical transformation. These effects have contributed to lowering the onset potential and increasing the reaction kinetics. Numerous studies have been employed to differentiate the effect of photothermal heating from hot charge carriers on the electrochemical reaction. Most of these studies have been employed to measure and quantify the photothermal heating effects at equilibrium temperature; however, localized heating from the incident light does not result in homogeneous heating across the electrochemical cell. Many studies investigating the photothermal heating effect in electrochemical reactions have been conducted in diverse experimental setups. Hence, it is evident that isolating and quantifying photothermal heating is a highly controversial and potentially ambiguous process. To address these challenges, this dissertation presents a novel electrochemical approach that can precisely isolate and quantify the photothermal effects in electrochemical reactions, along with other non-thermal effects in plasmon-assisted electrochemistry. To make an accurate quantification of photothermal heating and its impact on activity and selectivity in electrochemical reactions, we have incorporated a specifically heated electrode system that creates a temperature gradient between the electrode surface and the bulk electrolytic solution, which resolves the issue with conventional heating bath electrolytes that exclude the temperature gradient effect. It has been observed that temperature gradient increases mass transfer limiting current, which comes from convection by the temperature gradient, inducing fluid velocity. It is surprising that a small temperature change between the electrode and electrolytes can make a significant enhancement of mass transfer limiting at lower scan rates, which was absent in the conventional control experiment for photothermal heating. It also confirmed that interband transition of Au under visible light excitation contributed to photothermal heating induced mass transfer limiting current by over 100%. Plasmonic excitation of Au under visible light has enhanced mass transfer limiting current ca. 70% to photothermal heating and ca. 30% to non-thermal contributions, such as optical field-driven processes. Finite-element analysis has shown a similar pattern, which supports the photothermal heating as well as optical field-driven processes leading to enhanced mass transfer limiting current. To see the impact of temperature gradient on the product selectivity, we have employed the heated electrode system in the electrochemical conversion of CO2 in an aqueous system at pH =7.0. We observed that the activity and selectivity of CO2 reduction over H2O reduction were enhanced at non-isothermal conditions, but it was almost similar at isothermal conditions. Finite element analysis has corroborated that a temperature gradient at the electrode-electrolytes interface enhances the fluid velocity, leading to improved mass transport. Simulation was also extended to evaluate the fluid velocity distribution with variation of electrode orientation, size, and position of the electrode surface inside the H-cell and other electrolysers, such as flow cell. We found that the selectivity of CO2 reduction over H2O reduction at pH = 7.0 was dependent on these factors. These outcomes not only revealed the impact of non-isothermal conditions on electrochemical CO2 reduction but also highlighted the importance of designing and interpreting electrochemical experiments for any other reaction.
Recommended Citation
Al Amin, Md, "Thermal and non-thermal mass transport effects in plasmon-assisted electrochemistry." (2025). Electronic Theses and Dissertations. Paper 4648.
Retrieved from https://ir.library.louisville.edu/etd/4648
