Influence of specific surface area and microporosity-mesoporosity of pristine and Pt-nanoclusters modified carbide derived carbon electrodes on the oxygen electroreduction

• Oxygen electroreduction (ORR) strongly depends on the porosity and specific surface area of carbon catalysts.
• There is an optimal ratio between the microporosity-mesoporosity and crystallographic ordering of the carbon structure.
• Very high values of ORR current density were calculated for Pt-C(Mo2C)800 °C, and the half-wave potential is nearly 30-60 mV more positive compared with Pt-Vulcan®XC72 based catalyst.

Oxygen electroreduction reaction (ORR) on pristine porous carbide derived carbons (CDCs) and on CDC supports modified with Pt-nanoclusters has been studied in 0.5 M H2SO4 solution using cyclic voltammetry, rotating disk electrode and electrochemical impedance spectroscopy methods. The CDCs were prepared from Mo2C (noted as C(Mo2C)) at different fixed chlorination temperatures from 600 °C to 1000 °C. The CDCs have tuneable specific surface area, micro- and mesoporosity, good electrical conductivity and corrosion stability at positive electrode potentials. Pt-nanoclusters were deposited onto/into C(Mo2C) powders using sodium borohydride reduction method. The X-ray diffraction and high-resolution transmission electron microscopy were applied for the structural and chemical characterization, and the nitrogen sorption method was used for the porosity analysis of the electrode materials studied. The cathodic current densities depend strongly on the synthesis temperature of C(Mo2C), indicating that, in addition to the specific surface area and porosity, the crystallinity (density of defects in amorphous areas) has noticeable influence on the ORR rate. Impedance data demonstrated nearly capacitive behaviour in the low AC frequency region, explained by quick cathodic ORR followed by slow adsorption step of the intermediates and reaction products at/inside microporous-mesoporous C(Mo2C) and Pt-C(Mo2C) electrodes.