ELECTROCHEMICAL CHARACTERIZATION OF HIGH AREA PLATINUM DISPERSED ON THE SURFACE OF A GLASSY CARBON ROTATING DISK ELECTRODE IN THE ABSENCE OF BINDERS OR OTHER ADDITIVES

摘要

Electrode materials in high area form are of common use in electrochemical energy storage and energy generation applications as in batteries and fuel cells. Attempts to extract information regarding intrinsic properties of such highly divided materials in environments that resemble actual devices are often compromised by the presence of binders and/or additives, including complications derived from mass transport hindrances and potential distribution associated with often highly convoluted structures. Efforts toward eliminating some of these problems have been implemented in our laboratory using the embedded particle technique for both electrochemical and spectroelectrochemical measurements, and also by the elegant approach introduced by Uchida et al. who relied on micromanipulators to isolate the electrochemical response of single particles a few tens μm in diameter. Ingenious methods have also been described to examine far smaller Pt particles of the type used in fuel cells dispersed on smooth carbonaceous supports. For example, Schmidt et al. immobilized high area Pt dispersed on the surface of a glassy carbon rotating disk electrode (RDE) by placing a layer on Nafion on the surface allowing measurements of solution phase hydrogen oxidation to be performed at rotation rates of up to 3600 rpm. More recently, Weaver and Wieckowski used Pt dispersions on GC without a Nafion overlayer to monitor in situ, infrared spectra of adsorbed CO as a function of the applied potential. The results to be presented in this work indicate that carefully dispersed high area Pt on the surface of a GC RDE of a GC/Pt ring disk electrode assembly displays good adherence without the need of a Nafion overlayer even when rotated for minutes at rates of up to 2500 rpm as judged by quantitative coulometry of cyclic voltammetric curves recorded before and after rotation. Furthermore, dynamic polarization curves for 0_2 reduction in aqueous 0.5 M H_2SO_4 yielded results bearing close resemblance to on Pt dispersed on GC-RDE surface covered with a Nafion layer under otherwise identical conditions and also to those observed on a solid Pt electrode in 0.5 M H_2SO_4.