| Abstract
| - A facile method for the direct preparation of carbon nanofiber (CNF) electrodes by pyrolysis of iron(II)phthalocyanine on nickel substrates is reported. Uniform, large area coverage is observed with aligned bundlesof CNFs exhibiting bamboo-like, hollow fibril morphology possessing diameters of 40−60 nm and lengthsof ∼10 μm. The electrochemical behavior and stability of CNF electrodes as oxygen reduction catalysts wereinvestigated by electrochemical methods. Without necessitation for extensive electrode pretreatment or surfaceactivation, these electrodes demonstrate significant electrocatalytic activity in aqueous KNO3 solutions atneutral to basic pH for the reduction of dioxygen to hydrogen peroxide, O2 + H2O + 2e- ⇌ H+ OH-.As determined from chronocoulometry, slopes of Anson plots indicate that the overall electrochemical reactionproceeds by the peroxide pathway via two successive two-electron reductions. pH-dependent cyclic voltammetrystudies indicate that the CNF electrodes are very active toward adsorption. At pH < 10 the one-electronreduction of O2 to superoxide is rate limiting, whereas at more alkaline pH the reduction process is limitedby the protonation of adsorbed superoxide. This is reflected by a change in measured apparent charge-transfercoefficient (αobs) from αobs = 0.5 to αobs = 1 at neutral and high pH values, respectively. XPS, Raman, andTEM measurements suggest that the disorder in the graphite fibers and the presence of exposed edge planedefects and nitrogen functionalities are important factors for influencing adsorption of reactive intermediatesand enhancing electrocatalysis for O2 reduction.
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