Fluorescence imaging of the heterogeneous reduction of oxygen.

The reduction of oxygen at a variety of solid electrodes was spatially imaged using fluorescence microscopy. Hydroxide produced during electrolysis of oxygen converted the acid-base indicator, fluorescein, into its fluorescent form. Fluorescence intensity was collected as a function of potential at platinum, silver, and glassy carbon disk electrodes and tracked the faradaic current due to oxygen reduction at platinum electrodes. The ability to observe spatial variations in electron-transfer kinetics was demonstrated at a bimetallic electrode prepared from silver and platinum. Fluorescence imaging of oxygen reduction on silver electrodeposited on glassy carbon revealed the location and size of the silver deposits. Imaging of oxygen reduction at a ruthenium-graphite composite electrode demonstrated the ability to identify electrochemically active sites on a spatially complex surface.