UC Irvine

Electrochemical interfaces govern the performance of technologies ranging from energy conversion devices to chemical sensors, yet two fundamental knowledge gaps persist in our understanding of these critical boundaries. The first concerns ion-exchange membranes (IEMs), where the relationship between non-equilibrium ion transport and thermodynamically quasi-equilibrated interfaces remains poorly understood. The second involves electrochemical catalysis, where the heterogeneity of most electrode surfaces obscures the molecular-level details of interfacial ion-transfer reactions. This dissertation addresses both challenges through complementary investigations of ionic transport across membrane-electrolyte interfaces and molecularly defined active sites for electrochemical catalysis.Chapter 2 demonstrates that leaky IEMs, which are inherently non-equilibrium systems at nonzero temperature, generate additional free energy in the form of intra-membrane liquid-junction potentials that can amplify cell potentials beyond traditional Nernstian predictions. Through development of a steady-state diffusion model based on discretized Fick's laws and the Nernst-Planck treatment of electrodiffusion, transient open-circuit potential measurements are used to extract intra-membrane ion diffusion coefficients. Analysis reveals that steady-state interfacial Donnan potentials are often far smaller than equilibrium theory predicts due to concentration polarization in boundary layers and coupled ion crossover. For a singly charged salt, the total cell potential can, in principle, approach four times the Nernstian value—a factor of two from combined Donnan and Nernst potentials and another factor of two from intra-membrane liquid-junction potentials. Additionally, net power generation from devices utilizing IEMs can be achieved when electron flux in the external circuit exceeds ionic leakage flux across the membrane, allowing for the conversion of chemical potential to electricity. Chapter 3 describes synthetic strategies for accessing 4,5-disubstituted o-phenylenediamines as precursors to molecularly defined graphite-conjugated electrodes. Three modular approaches are explored: a double electrophilic aromatic substitution strategy that provides symmetric diamines but suffers from poor functional-group tolerance, an electrophilic aromatic substitution/nucleophilic aromatic substitution hybrid that enables access to asymmetric scaffolds, and a double nucleophilic aromatic substitution strategy beginning from 1,2-dinitro-4,5-difluorobenzene that allows stepwise installation of diverse functional groups in as few as two steps from commercial starting materials. Electrochemical characterization via cyclic voltammetry reveals the expected quasi-reversible redox waves associated with interfacial proton-coupled electron transfer, with apparent rate constants and charge-transfer coefficients determined using the Laviron formalism. These synthetic routes dramatically expand the scope of molecularly defined active sites available for studying structure-function relationships in interfacial ion-transfer reactions, enabling systematic interrogation of how local environment, electric fields, and pendant functionality influence electrocatalytic kinetics.