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Electrocatalytic Dioxygen Reduction by Carbon Electrodes Noncovalently Modified with Iron Porphyrin Complexes: Enhancements from a Single Proton Relay
Author(s) -
Sinha Soumalya,
Aaron Michael S.,
Blagojevic Jovan,
Warren Jeffrey J.
Publication year - 2015
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201502618
Subject(s) - porphyrin , chemistry , photochemistry , electrode , relay , reduction (mathematics) , electrocatalyst , oxygen reduction reaction , carbon fibers , materials science , electrochemistry , physics , power (physics) , geometry , mathematics , quantum mechanics , composite material , composite number
Oxygen reduction in acidic aqueous solution mediated by a series of asymmetric iron (III)‐tetra(aryl)porphyrins adsorbed to basal‐ and edge‐ plane graphite electrodes is investigated. The asymmetric iron porphyrin systems bear phenyl groups at three meso positions and either a 2‐pyridyl, a 2‐benzoic acid, or a 2‐hydroxyphenyl group at the remaining meso position. The presence of the three unmodified phenyl groups makes the compounds insoluble in water, enabling catalyst retention during electrochemical experiments. Resonance Raman data demonstrate that catalyst layers are maintained, but can undergo modification after prolonged catalysis in the presence of O 2 . The introduction of a single proton relay group at the fourth meso position makes the asymmetric iron porphyrins markedly more robust catalysts; these molecules support higher sustained current densities than the parent iron tetraphenylporphyrin. Iron porphyrins bearing a 2‐pyridyl group are the most active catalysts and operate at stable current densities ≥1 mA cm −2 for over 5 h. Comparative analysis of the catalysts with different proton relays also is reported.