Tip generation–substrate collection–tip collection mode scanning electrochemical microscopy of oxygen reduction electrocatalysts

Concentric microring-disk tips for scanning electrochemical microscopy (SECM) were fabricated and used in a new “tip generation–substrate collection–tip collection” (TG–SC–TC) mode to determine the activity of an Au electrocatalyst for the oxygen reduction reaction (ORR), while simultaneously monitoring hydrogen peroxide produced during the reaction. ORR electrocatalysis/hydrogen peroxide detection measurements were performed by evolving O2 at the Au microring of the SECM tip while it was positioned close to an Au substrate. The O2 diffused to the Au substrate where it was reduced generating a substrate current. At the same time, hydrogen peroxide generated during the ORR was detected by oxidation at the SECM tip microdisk. The effects of the microring current, the tip-substrate distance and the substrate potential during the TG–SC–TC experiment have been determined and are described. The ability to use these SECM tips to scan electrocatalyst surfaces while generating maps containing electrocatalytic and mechanistic data is then demonstrated and the prospects for the use of these SECM tips in screening arrays of ORR electrocatalysts discussed.