Visualization of local electrocatalytic activity of metalloporphyrins towards oxygen reduction by means of redox competition scanning electrochemical microscopy (RC-SECM)

The redox competition mode of scanning electrochemical microscopy (RC-SECM) has been utilized to visualize the local electrocatalytic activity of metalloporphyrin spots towards oxygen reduction in 0.1 M phosphate buffer as electrolyte solution. The metalloporphyrin spots were obtained by electrochemically induced deposition using a droplet cell. Tetratolyl porphyrins (TTPs) of Mn, Fe and Co have been investigated, with that containing Mn as central metal atom showing highest catalytic activity. The multiple stable oxidation states of Mn were seen as a key factor in the influence of the metal ion on the catalytic activity. From the RC-SECM results, it is shown that oxygen reduction at a manganese TTP (MnTTP) modified electrode surface yielded the least amount of H₂O₂ when compared to iron TTP (FeTTP) and cobalt TTP (CoTTP). As further confirmed by means of rotating disc electrode (RDE) measurements this was attributed to the high activity of MnTTP for H₂O₂ reduction.