Effect of porosity and active area on the assessment of catalytic activity of non-precious metal electrocatalyst for oxygen reduction

Abstract

We describe a method to study porous thin-films deposited onto rotating disc electrodes (RDE) applied to non-platinum group electrocatalyst obtained by pyrolysis of iron phthalocyanine and carbon, FePc/C. The electroactive area and porous properties of the thin film electrodes were obtained using electrochemical impedance spectroscopy under the framework of de Levie impedance model. The electrocatalytic activity of different electrodes was correlated to the total electroactive area (A_p) and the penetration ratio parameter through the film under ac current. The cylindrical pore model was extended to the RDE boundary conditions and derived in a Koutecky-Levich type expression that allowed to separate the effect of the electroactive area and structural properties. The resulting specific electrocatalytic activity of FePc/C heat treated at different temperatures was correlated to FePc surface concentration.

Keywords: diffusion penetration depth; electrocatalysis; oxygen reduction reaction; porosity; rotating disc electrode; x-ray photoelectron spectroscopy.