Mediated Reduction of Dioxygen in Aqueous Electrolytes

Macrocyclic-Mediated Reduction of Dioxygen in Aqueous Electrolytes 

Solutions to the governing differential equations that account for the large disparity between the diffusion coefficients of the macrocycles and dioxygen can be obtained using numerical methods, as illustrated by Bowers et al. for the RDE [46]. 

The macrocycles Co (111) (cyclam) and Fe( 111)TM PyP display high activity for dioxygen reduction and negligible affinity for carbonaceous surfaces providing close to ideal conditions to warrant analyses of electrochemical data within the strict homogeneous electrocatalysis framework. Their most salient features are summarized in the two sub-sections to follow. 

RRDE assembly for 2.2 mM Co(lll)(cyclam) in air-saturated (curves 2 and 4), that is,/Co(cydam)/0j large, and the flux of cyclam to the surface is 3.4-times larger than that of 02, and deaerated (curves 1 and 3) in 0.5 M HCIO4 aqueous solutions for Ering = 0.6V. Curve 5 in this panel was obtained for Ering= 1.2V. (C) Current versus potential curves for the Pt ring upon polarizingthe carbon disk at 0.1 V (curve 1) and —0.4 V (curve 2). 

Also displayed in these subpanels, are curves recorded in solutions of Co(III) (cyclam) devoid of 02 (see curves 1). As is evident from these data, the onset potential for reduction on the disk in the presence of 02 is about 0.1 V positive than that observed in the absence of 02, regardless of the value of/ cydam) /0 . This behavior is 

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