Mechanistic Studies of the Oxygen Evolution Reaction by a Cobalt-Phosphate Catalyst at Neutral pH
ABSTRACT The mechanism of the oxygen evolution reaction (OER) by catalysts prepared by electrodepositions from Co(2+) solutions in phosphate electrolytes (Co-Pi) was studied at neutral pH by electrokinetic and (18)O isotope experiments. Low-potential electrodepositions enabled the controlled preparation of ultrathin Co-Pi catalyst films (<100 nm) that could be studied kinetically in the absence of mass transport and charge transport limitations to the OER. The Co-Pi catalysts exhibit a Tafel slope approximately equal to 2.3 × RT/F for the production of oxygen from water in neutral solutions. The electrochemical rate law exhibits an inverse first order dependence on proton activity and a zeroth order dependence on phosphate for [Pi] ≥ 0.03 M. In the absence of phosphate buffer, the Tafel slope is increased ∼3-fold and the overall activity is greatly diminished. Together, these electrokinetic studies suggest a mechanism involving a rapid, one electron, one proton equilibrium between Co(III)-OH and Co(IV)-O in which a phosphate species is the proton acceptor, followed by a chemical turnover-limiting process involving oxygen-oxygen bond coupling.
- SourceAvailable from: Alfonso Pozio
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- "Deposition of IrO í µí±¥ , CoO í µí±¥ , and RuO í µí±¥ cocatalysts on n-semiconductors seems all to enhance the activity for O 2 evolution and CoO í µí±¥ was found to be the best one. As example, Surendranath et al. described the self-assembly of a highly active cobalt-based oxygen evolving catalyst that forms as a thin film on inert electrodes when aqueous solutions of Co 2+ salts are electrolyzed in presence of phosphate or borate . These authors evidenced that this catalyst can be interfaced with light absorbing and charge separating materials to affect photoelectrochemical water-splitting. "
ABSTRACT: This work is intended to define a new possible methodology for the TiO2 doping through the use of an electrochemical deposition of cobalt directly on the titanium nanotubes obtained by a previous galvanostatic anodization treatment in an ethylene glycol solution. This method does not seem to cause any influence on the nanotube structure, showing final products with news and interesting features with respect to the unmodified sample. Together with an unmodified photoconversion efficiency under UV light, the cobalt doped specimen reports an increase of the electrocatalytic efficiency for the oxygen evolution reaction (OER).
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- "O-O bond formation reactions mediated by cobalt phosphate and nickel borate films on inert electrodes (Dinca et al., 2010; Surendranath et al., 2010; Bediako et al., 2012). "
ABSTRACT: O-O bond formation is one of the key reactions that ensure life on earth. Dioxygen is produced in photo-system II, as well as in chlorite dismutase. The reaction mechanisms occurring in the enzyme active sites are con-troversially discussed – although their structures have been resolved with less unambiguity. Artificial molecular catalysts have been developed in the last years to obtain vital insights into the O-O bond formation step. This review put together the scarce literature on the topic that helped in understanding the key steps in the O-O bond formation reactions mediated by high-valent oxo complexes of the first-row transition metals.Inorganic Reaction Mechanisms 06/2012; 8(1):41-57. DOI:10.1515/irm-2012-0004 · 0.14 Impact Factor
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ABSTRACT: Co-M (M= Co, Ni, Fe, Mn) layered double hydroxides (LDHs) were successfully fabricated by a hexamethylenetetramine (HMT) pyrolysis method. Composite electrodes were made using a self-assembly fashion at inorganic/organic surface binder-free and were used to catalyze oxygen evolution reaction. Water oxidation can take place in neutral electrolyte operating with modest overpotential. The doping of other transitional metal cations affords mix valences and thus more intimate electronic interactions for reversible chemisorption of dioxygen molecules. The application of employing LDH materials in water oxidation process bodes well to facilitate future hydrogen utilization.06/2012; 6(2). DOI:10.1007/s11706-012-0162-8