1. Electrochemical water oxidation with cobalt-based electrocatalysts from pH 0-14: the thermodynamic basis for catalyst structure, stability, and activity
- Author
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William H. Casey, R. David Britt, Matthew L. Rigsby, Shannon S. Stahl, James B. Gerken, J. Gregory McAlpin, and Jamie Y. C. Chen
- Subjects
Aqueous solution ,Chemistry ,Entropy ,Inorganic chemistry ,Water ,Homogeneous catalysis ,Oxides ,General Chemistry ,Electrolyte ,Pourbaix diagram ,Cobalt ,Electrochemical Techniques ,Hydrogen Peroxide ,Hydrogen-Ion Concentration ,Electrochemistry ,Heterogeneous catalysis ,Biochemistry ,Redox ,Catalysis ,Colloid and Surface Chemistry ,Oxidation-Reduction - Abstract
Building upon recent study of cobalt-oxide electrocatalysts in fluoride-buffered electrolyte at pH 3.4, we have undertaken a mechanistic investigation of cobalt-catalyzed water oxidation in aqueous buffering electrolytes from pH 0-14. This work includes electrokinetic studies, cyclic voltammetric analysis, and electron paramagnetic resonance (EPR) spectroscopic studies. The results illuminate a set of interrelated mechanisms for electrochemical water oxidation in alkaline, neutral, and acidic media with electrodeposited Co-oxide catalyst films (CoO(x)(cf)s) as well as for a homogeneous Co-catalyzed electrochemical water oxidation reaction. Analysis of the pH dependence of quasi-reversible features in cyclic voltammograms of the CoO(x)(cf)s provides the basis for a Pourbaix diagram that closely resembles a Pourbaix diagram derived from thermodynamic free energies of formation for a family of Co-based layered materials. Below pH 3, a shift from heterogeneous catalysis producing O(2) to homogeneous catalysis yielding H(2)O(2) is observed. Collectively, the results reported here provide a foundation for understanding the structure, stability, and catalytic activity of aqueous cobalt electrocatalysts for water oxidation.
- Published
- 2011