Template-free synthesis of Pt-MOx (M = Ni, Co & Ce) supported on cubic zeolite-A and their catalytic role in methanol oxidation and oxygen reduction reactions characterized by the hydrodynamic study

Abstract

Cubic zeolite-A (LTA) is synthesized and ion-exchanged with Pt, Ni, Co and Ce ions followed by reduction of Pt (IV) on the metal oxides (NiO, CoO and CeO2) formed in the zeolite matrix. Their catalytic performance in methanol oxidation (MOR) and oxygen reduction reactions (ORR) are evaluated. The structure, morphology and composition of these catalysts are investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectral analysis (EDS) and X-ray photoelectron spectroscopy. The activity of these electrocatalysts in methanol oxidation is analysed by cyclic voltammetry, linear sweep voltammetry, chronoamperometry and chronopotentiometry in acidic medium and compared with commercial Pt electrode. From the results of electrochemical characterization, it is observed that Pt-NiO on zeolite-A (Pt-NiO-A) exhibited high current density, lower onset potential, enhanced If/Ib values and better stability. The electrocatalytic activity of these catalysts are in the order, Pt-NiO-A > Pt-CoO-A > Pt-CeO2-A > Pt-A > Pt. The influence of rotation rate on MOR and ORR are investigated using rotating ring disc electrode (RRDE). With increasing rotation speed, the change observed in the disc (ID) and ring (IR) currents reveal the mechanism of the reactions. For oxygen reduction reaction (ORR), the number of electrons transferred (n) and % H2O2 produced is calculated. This is the first systematic study, reporting the hydrodynamic evaluation of these catalysts for MOR.