Insights into the effect of aluminum oxyhydrates properties on their electrochemical behavior

Alumina oxyhydrates have different structural and textural properties, as well as different density of surface functional groups. Three alumina oxyhydrates with different water content, 3mol H2O/ mol Al2O3 (gibbsite), 1mol H2O/ mol Al2O3 (boehmite) and 0.6 mol H2O/ mol Al2O3 (α,γ-alumina phase), were used in this study. The samples were used as modifiers of carbon paste electrode. Their electrochemical behavior toward ferricyanide/ferrocyanide redox probe was evaluated by electrochemical impedance spectroscopy and cyclic voltammetry. Ferricyanide/ferrocyanide redox system has a well-known electrochemical behavior and is sensitive to the changes occurring at the electrode surface. The lowest charge transfer resistance was obtained for α,γ-alumina phase. The redox process of ferri/ferro redox probe on investigated electrodes exhibited a quasi-reversible behavior, since the obtained values of peak-to-peak separation are greater than 59 mV value expected for a reversible process. The response toward quinone/hydroquinone redox probe was evaluated by cyclic voltammetry in buffered solutions at various pH. Gibbsite and boehmite showed expected response, while the surface groups of α,γ-alumina phase enabled quinone oxidation to proceed through two pathways simultaneously. The surface chemistry of investigated samples influenced their electrochemical properties.