Visualization of the local catalytic activity of electrodeposited Pt-Ag catalysts for oxygen reduction by means of SECM.

Pt-Ag nanoparticle co-deposits with different Pt-Ag ratios were prepared on a glassy carbon (GC) surface by pulsed electrodeposition and investigated for their catalytic activity in electrocatalytic oxygen reduction by using cyclic voltammetry (CV), rotating disc electrode (RDE) and scanning electrochemical microscopy (SECM) in 0.1 M phosphate buffer (pH 7.0). The atomic composition of the Pt-Ag co-deposits was studied by means of energy-dispersive X-ray analysis (EDAX). In combination with X-ray diffraction (XRD), the presence of partly alloyed Pt and Ag on the GC surface was confirmed. Scanning electron microscopy (SEM) images indicate that the prepared Pt-Ag catalyst particles are homogenously dispersed over the GC surface. Their size and morphology depend on their composition. The electrocatalytic activity of Pt-Ag deposits with high Pt content was the highest, exceeding even that of electrodeposited Pt as evaluated by quantitative RDE analysis. The redox competition mode of scanning electrochemical microscopy (RC-SECM) was successfully used to visualize the local catalytic activity of the deposited Pt-Ag particles. Semi-quantitative assessment of the SECM results confirmed the same order of activity of the different catalysts as the RDE investigations.