Degree
Doctor of Philosophy (PhD)
Department
Chemical Engineering
Document Type
Dissertation
Abstract
The activity and selectivity of an electrocatalyst are governed by the kinetic barriers of its elementary steps, but these barriers are difficult to compute because electrochemical transition states form at charged, solvated, constant-potential interfaces and often involve charged species moving through the double layer. Consequently, many DFT studies use reaction thermodynamics as a proxy for kinetics, leaving transition-state-controlled selectivity partly understood.
This dissertation develops and applies a thermodynamically consistent DFT framework for computing potential-dependent activation barriers directly. The approach combines VASPsol++ implicit electrolyte model, which captures electrostatics and compact double-layer effects, with an explicit solvation scheme in which explicit water molecules accurately represent strong H-bonds that stabilize charged species. An empirical hydrogen-bonding correction calibrated to water self-solvation enables the model to reproduce aqueous reference quantities, including water auto-ionization free energy and the electron chemical potential of the standard hydrogen electrode. Validation on HER on Pt(111) shows that electrolyte representation is a controlling variable: solvent-cavity choice and acidic versus alkaline proton-transfer mechanisms shift barriers by about 0.15 eV, producing orders-of-magnitude rate differences.
The framework is applied to CO and CO₂ reduction on Cu(100), with each activation barrier obtained from explicit transition-state searches. The networks reveal a simple organizing principle: elementary steps are either surface-mediated, such as hydrogenation, C–O cleavage, and C–C coupling, or electrolyte-mediated, such as proton transfer and hydroxide elimination. Selectivity is determined at electrolyte-mediated branch points by the binding strength of the product formed. At the C₂ branch point *HCCOH, hydroxide elimination forms the strongly bound ethylene precursor *CCH, whereas protonation forms the weaker-bound oxygenate precursor *H₂CCOH. Because lateral repulsion from co-adsorbed *CO destabilizes strongly bound intermediates more strongly, steady-state *CO coverage becomes a control parameter that shifts selectivity from ethylene toward ethanol and acetate. The same motif explains methane-versus-methanol branching at *CHOH.
Finally, HER on Cu(100) is examined across five proton donors and twelve potentials. Donor charge controls kinetics, with Volmer barriers at USHE = −1.0 V ranging from 0.30 eV for H₃O⁺ to 1.92 eV for HPO₄²⁻. This work provides design principles for tuning C₂ selectivity through *CO coverage and suppressing HER through pH and proton-donor control.
Date
7-16-2026
Recommended Citation
Kingsley, Nkechi, "Calculating Kinetic Barriers for Electrocatalytic Reactions Using a Hybrid Implicit/Explicit Electrolyte Model" (2026). LSU Doctoral Dissertations. 7165.
https://repository.lsu.edu/gradschool_dissertations/7165
Committee Chair
Plaisance, Craig
LSU Acknowledgement
1
LSU Accessibility Acknowledgment
1