Hybrid materials based on platinum nanoparticles deposited on carbon nanotubes (Pt/MWCNTs) have been widely used in recent years as catalysts for oxygen reduction reaction (ORR). RRO is reaction most important for many environmental applications like electric energy generations by fuel cell or hydrogen peroxide production for degradation of pollutants in water. The electrochemical ORR proceeds via two routes, one direct transfer four electrons to produce water; and an indirect route transfer of two electrons producing hydrogen peroxide (H₂O₂). The electrocatalytic activity and kinetics of Pt/MWCNT catalysts in RRO depends of particle size, the surface atomic structure and the homogeneous distribution of the platinum particles on the carbon support, these three parameters are controlled by the synthesis method used.

Reverse microemulsions it’s a colloidal dispersion of water in oil stabilized by a surfactant film. The aqueous core of the reverse micelles plays a crucial role defining the size of formed particles. The water pool in the microemulsion solubilizes the reactants and provides the stage where the reaction occurs; because of this, the particle size can be controlled varying water concentration. The relation of water core with surfactant concentration is given by ω (ω=[H₂O]/[surfactant]). The amount of water within the micelle controls the amount of ions of the metal precursor and reducing agent as well as the lability of Interfas, which dictates the micellar exchange rate.

In this work is presented the effect of W in the activity of the Pt/MWCNT nanomaterial in the oxygen reduction reaction (ORR) and the reaction mechanism. Pt/MWCNT nanomaterials synthesized with a ω=22 and 91 show particles with mean diameters of 1.3 nm and 2.5 nm, respectively. Employing a ω=45 in the synthesis of nanomaterial Pt/MWCNT showed an average nanoparticle diameter of 3.2 nm, also the platinum loading was 2 times that nanomaterials synthesized with a W of 22 and 91. The nanomaterial synthesized with a ω=45 showed greater electrocatalytic activity than the other two nanomaterials, although a decrease in mass transfer was observed in this nanomaterial, besides the mechanism according to the Koutecky-Levich graphs was O₂ + 2H + + 2e^-→ H₂O₂.  Pt/MWCNT anomaterials synthesized with a ω=22 and 91 showed the following mechanism : O₂ + 4H⁺ + 4e^-→2H₂O. High values in the Tafel slopes of Pt/MWCNT nanomaterial synthesized with ω=45 confirm the presence of H₂O₂ on the surface.