GDE vs RDE: Impact of operation conditions on intrinsic catalytic parameters of FeNC catalyst for the oxygen reduction reaction

We present a comprehensive comparison of the catalytic evaluation of a FeNC catalyst using two different approaches, i.e., employing the rotating ring disk electrode (RRDE) technique and a gas diffusion electrode (GDE) setup. With both techniques, the FeNC catalyst is evaluated in acidic as well as in alkaline environment. The oxygen reduction reaction (ORR) is studied and parameters such as ORR kinetic activity, Tafel slope, and the apparent activation energy are determined at different applied temperatures/overpotentials. The obtained results offer clear evidence that in alkaline medium, the GDE offers reaction conditions with improved reactant mass transport enabling an evaluation of the FeNC catalyst closer to membrane electrode assembly (MEA) testing. As compared to the RRDE evaluation, the ORR rate is higher in the GDE setup and the potential range for extracting kinetics and activation energies is substantially improved. However, in acidic environment only minor differences between the two reaction environments (RRDE and GDE) are observed. The difference between alkaline and acidic conditions is rationalized based on the different reaction pathway in the two environments.