Abstract
Edge plane pyrolytic graphite (EPG) electrodes coated with the Co(II)/Pt(II)2 analog of 5,15-bis-(4-pyridyl)-10,20-bis-(3-methoxy-4-hydroxyphenyl)porphyrin undergo an electrochemical-chemical-electrochemical (ECE) reaction when anodically scanned in 1.0 M sulfuric acid. The new redox couple formed from this anodic conditioning of the coated electrode is dependent on the pH of the solution. Roughened EPG electrodes coated with the Co(II)/Pt(II)2 trimetallic porphyrin show a catalytic shift of 400 mV for the reduction of O2 when compared to the reduction of O2 at a bare EPG electrode. An additional catalytic shift of ca. 150 mV is observed for O2 reduction at an EPG electrode coated with the Co(II)/Pt(II)2 porphyrin which has been oxidized in 1.0 M sulfuric acid. In addition to the added electrocatalysis, a significant percentage of O2 reduced at the oxidized Co(II)/Pt(II)2 EPG electrode is converted to H2O as determined by rotating disk electrode measurements.
Highlights
Fuel cell technology has gained considerable attention over the past couple of decades in part due to its high efficiency and low pollutant output
This laboratory has recently shown that by anodically conditioning edge plane pyrolytic graphite (EPG), electrodes coated with cobalt(II) 5,10,15,20-tetra-(3-methoxy-4-hydroxyphenyl) porphyrin in acidic media create a stable electrocatalyst for oxygen reduction [19]
To further this study we present the synthesis of a new cobalt(II) porphyrin containing two peripheral platinum moieties, complex I (Scheme 1), to determine if further backbonding will facilitate the complete reduction of oxygen to water
Summary
Fuel cell technology has gained considerable attention over the past couple of decades in part due to its high efficiency and low pollutant output. Reduction of oxygen to water in buffered pH 7.0 solutions has been accomplished by platinum electrodes modified with Iron(III) 5,10,15,20-tetra-(3-methoxy-4-hydroxyphenyl)porphyrin formed by cycling the electrode in basic solutions of the iron porphyrin [18]. This laboratory has recently shown that by anodically conditioning edge plane pyrolytic graphite (EPG), electrodes coated with cobalt(II) 5,10,15,20-tetra-(3-methoxy-4-hydroxyphenyl) porphyrin in acidic media create a stable electrocatalyst for oxygen reduction [19]. When EPG electrodes coated with this complex, cobalt(II) 5-(4-pyridyl)-10,15,20-tris-(3-methoxy-4-hydroxyphenyl) porphyrin with PtCl2 (dmso) coordinated to the peripheral nitrogen of the pyridyl group was anodically conditioned in acidic media, and a catalytic shift in the reduction of oxygen was observed. To further this study we present the synthesis of a new cobalt(II) porphyrin containing two peripheral platinum moieties, complex I (Scheme 1), to determine if further backbonding will facilitate the complete reduction of oxygen to water
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