Electrochemical and physical characterisation of Pt-nanocluster activated molybdenum carbide derived carbon electrodes

Abstract

Oxygen electroreduction (ORR) on Pt-nanoclusters activated electrodes, based on different microporous–mesoporous carbon supports, were studied in 0.5M H2SO4 solution using cyclic voltammetry, rotating disc electrode (RDE), and impedance methods. The C(Mo2C) carbon supports with variable specific surface area, microporosity–mesoporosity, good electrical conductivity and corrosion stability at positive potentials were prepared from Mo2C at 600°C and 800°C using chlorination synthesis method. Pt-nanoclusters were deposited onto/into carbons using sodium borohydride reduction method. XRD, XRF, XPS, SEM-EDX, and HRTEM data confirm that catalysts under study are free from chlorine, chloride ions, and other residuals of raw materials, and have highly porous hierarchical structure with homogenously dispersed Pt-nanoclusters. RDE data show that the kinetic current densities are higher and half-wave potentials are more positive for Pt–C(Mo2C)800°C than for Pt–C(Mo2C)600°C in 0.5M H2SO4 solution. The limiting diffusion currents are independent of the catalyst composition used due to the proceeding of ORR process in the outer-diffusion mode. Analysis of impedance data demonstrated nearly capacitive behaviour in low ac frequency region, explained by quick cathodic electroreduction of oxygen followed by slow electrical double-layer formation step limited by adsorption of ions and intermediates at/inside microporous–mesoporous C(Mo2C) and Pt-nanocluster modified electrodes. High series and parallel capacitance values (100–250Fg−1) have been established, attractive also for hybrid supercapacitor applications. High frequency series resistance values are higher for more amorphous C(Mo2C)600°C than for C(Mo2C)800°C supported electrode.