An accurate evaluation for the activity of nano-sized electrocatalysts by a thin-film rotating disk electrode: Oxygen reduction on Pt/C

Up to now, it remains to be a challenge to accurately and reproducibly evaluate the oxygen reduction reaction (ORR) activity by a thin-film rotating disk electrode (TF-RDE) and results in literatures often disagree. In this work, we developed an intermittently microcontact-coating fine-droplets method of preparing homogeneous thin-film to guarantee the accuracy of electro-catalytic activity evaluation by a TF-RDE, in which the measured electrode current is controlled by both the diffusion of the reactant from the electrolyte bulk to the surface of the electro-catalyst and the kinetic process on the surface of the electro-catalyst. By precisely controlling the distribution and varying the loading of nano-sized Pt/C particles on a smooth glassy carbon substrate with an in-house-developed automated electrode-preparation device, we investigated the effect of the distribution of the particles on the accuracy of compensating for diffusion limitations of ORR in an aqueous acid solution. As a reference, a smooth Pt bulk disk electrode was evaluated under the same environment to clarify the effect of the within-thin-film diffusion, which may occur in the TF-RDE. The results show that, the accuracy of correction for diffusion limitations cannot be guaranteed by only a linear relation of 1/I versus (rotation rate)(-1/2) in Koutecky-Levich plot and significantly depends on the distribution of the particles on the substrate. Some criteria for judging the accuracy of the compensation and optimization of the thin-film structure have been systematically discussed. (C) 2012 Elsevier Ltd. All rights reserved.