Interfacial electron transfer at hydroxylated zinc oxide-carbon electrodes: a DFT-assisted cyclic voltammetric study...

Interfacial physicochemical characteristics, electronic structure modulation, and charge transfer dynamics govern the efficiency of metal oxides and carbon systems for electrochemical reactivity and catalytic performance. In this study, density functional theory (DFT) calculations were used as a simplified local interfacial model to examine possible adsorption, charge redistribution, and noncovalent interactions at ZnO/ZnOH-carbon contact motifs. The molecular models are not intended to reproduce the full crystallographic, defect, or size-dependent electronic structure of the experimentally synthesised ZnO nanoparticles; rather, they provide qualitative insight into local ZnO-carbon and hydroxylated ZnO-carbon interactions. Charge analysis suggests that hydroxylated ZnO-carbon motifs can promote a donor-to-surface charge-transfer tendency compatible with caffeic acid oxidation. QTAIM analysis indicates that caffeic acid adsorption is stabilised mainly by noncovalent π-stacking and hydrogen-bonding interactions. These theoretical trends are discussed alongside cyclic voltammetric measurements using ZnO-modified and NaOH-pretreated ZnO-modified carbon paste electrodes. The surface morphology of ZnO nanoparticles was investigated by SEM, EDX, XRD and BET analysis. The modified electrode yields a low detection limit (0.0023 µM), high sensitivity (1.17 µA µM^-1 cm^-2), and diffusion-controlled kinetics. It exhibits good repeatability (RSD 0.65%), excellent reproducibility and stability (98.8% retention after 30 days).