RuO2 electrode surface effects in electrocatalytic oxidation of glucose

We have studied the electrocatalytic activity of RuO2-PVC film electrodes, fabricated using RuO2 powders prepared at five different temperatures, viz., 300, 400, 500, 600 and 700 degrees C, for the oxidation of glucose in high alkaline media, 1 to 3 M NaOH. The RuO2-PVC film electrodes have been first characterized in 1 to 3 M NaOH solution by cyclic voltammetry (CV) and rotating disc electrode (RDE) techniques in a wide potential range -1,100 to 450 mV (SCE), and three redox pairs representing Ru(IV)/Ru(III), Ru(VI)/Ru(IV) and Ru(VII)/Ru(VI) transitions have been identified. The voltammetric peaks at low sweep rates have been analyzed using surface activity theory formulated for interacting electroactive adsorption sites, and interaction terms have been evaluated. The total voltammetric surface charges have been analyzed as per Trassatti's formalism with respect to their dependence on potential sweep rate, and charges associated with less accessible and more accessible surface sites have been calculated. For glucose oxidation, the results have indicated that RuO2 (700 degrees C)-PVC electrode shows two oxidation peaks in contrast to RuO2 (300 degrees C)-PVC electrode. Also, RuO2 (700 degrees C)-PVC electrode exhibits higher intrinsic electrocatalytic activity than the 300 degrees C electrode, although the former possesses lower electrochemically active surface area. Additionally, kinetic analyses made from RDE results with reference to Michealis-Menten (MM) enzyme catalysis has shown that RuO2 (700 degrees C) electrode possesses extended glucose-sensing range in terms of MM kinetic constant, K (M) , compared to other electrodes. Possible reasons for such differences in the behavior of the electrodes of different temperatures towards glucose oxidation are identified from studies on oxidation of glucose in solutions of different pH, oxidation of different glucose derivatives, and also from physicochemical results from BET, XRD, SEM, DTGA, XPS analysis of RuO2 powder samples.