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Structure-reactivity effects in electrocatalytic dioxygen reduction in aqueous solutions at electrodes coated by electrochemically synthesized molecularly imprinted polymers of a cobalt porphyrin diphenylamine derivative

Ievgen Obraztsov 1Krzysztof R. Noworyta 1Wlodzimierz Kutner 1Channa A. Wijesinghe 2Francis D'Souza 2

1. Polish Academy of Science, Institute of Physical Chemisty (PAN-ICHF), Kasprzaka 44/52, Warsaw 01-224, Poland
2. Wichita State University, Department of Chemistry, 1845, Fairmount, Wichita, KS 67260-0051, United States


Three different structural modifications of the tetrakis-[4-(N,N-diphenylamino)-phenyl]porphyrinatocobalt(II), (Ph2N)4CoP, polymer were prepared with the aim of developing an efficient electrocatalytic material for dioxygen electroreduction in aqueous solutions. The polymers were deposited on electrodes as thin films under cyclic voltammetry (CV) conditions by electrochemical polymerization of the (Ph2N)4CoP monomer or its complex either with a monodentate or bidentate cyclic amine ligand. A blank polymer film, prepared from genuine (Ph2N)4CoP under anaerobic conditions, served as the control. The bidentate ligand, vis. piperazine, was used as a template to form in solution a sandwich type stacked (Ph2N)4CoP complex while the monodentate ligand, vis. 3-bromopyridine, to form a non-stacked reference complex. Subsequently, the complexes were oxidatively electropolymerized to form a structured and non-structured, respectively, molecularly imprinted polymer (MIP) films. Then, the ligands were extracted from these films with acidic aqueous solutions. The presence of the axially coordinating ligand in the MIP film before and its absence after the extraction was confirmed by measurements of UV-vis absorption spectroscopy and XPS. Next, dioxygen was electrocatalytically reduced at the polymer film-coated electrodes. Integrity of the polymers was examined by SAXS and UV-vis reflection spectroscopy. Differences in the Soret band positions indicated structural differences between the structured and non-structured MIP films. The AFM imaging showed higher relative roughness of the structured than both the non-structured and pristine monomer containing polymer films. The electrocatalysis was examined for different pH aqueous buffer solutions under conditions of both CV at a stationary glassy carbon (GC) disk electrode and voltammetry at a rotating GC disk and a Pt-GC ring-disk, electrode. The structured MIP film appeared to be the most efficient catalyst for dioxygen electroreduction both in acidic and neutral solutions of promising ultimate application as a durable cathode material for fuel cells.


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Presentation: Poster at SMCBS'2009 International Workshop, by Ievgen Obraztsov
See On-line Journal of SMCBS'2009 International Workshop

Submitted: 2009-09-11 12:30
Revised:   2009-09-22 13:16