Kinetics and mechanism of electrochemical oxygen reduction using Platinum/clay/Nafion catalyst layer for polymer electrolyte membrane fuel cells

This work demonstrates the use of amino functionalized Mg-phyllosilicate clay/Nafion nanocomposite film embedded with Pt nanoparticles (Pt/AC/N) for catalyzing oxygen reduction reaction (ORR) in sulphuric acid medium. Pt/AC/N nanocomposite films were surface characterized using transmission electron microscope. Cyclic and linear scan voltammetry studies were carried out under hydrodynamic conditions taking rotating-ring disc electrode (RRDE) as the working electrode. The effects of clay content, Pt mass loading, electrode rotation rate, and temperature on the ORR kinetics were studied. The Tafel slopes were found to vary between 118 and 126 mV dec⁻¹ indicating a good ORR kinetics. The exchange current density values calculated after mass transfer correction ranged from 5.8 × 10⁻⁷ to 2.4 × 10⁻⁶ A cm⁻². From the RRDE disc currents, Koutecky-Levich plots were constructed and the ORR mechanism was found to follow a four electron path with minimum H₂O₂ formation of ∼1.6%. The effect of temperature on ORR kinetics was found at 25, 40, and 50 °C. The energy of activation calculated to be 7.68 kJ mol⁻¹ and comparable to the standard Pt/C catalyzed ORR systems.