title: Electrochemical water oxidation with cobalt-based electrocatalysts from pH 0-14: the thermodynamic basis for catalyst structure, stability, and activity.
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.
authors.affiliation: Department of Chemistry, University of Wisconsin-Madison, 1101 University Avenue, Madison, Wisconsin 53706-1322, USA.
authors.forename: James B
authors.initials: JB
authors.lastname: Gerken
authors.forename: J Gregory
authors.initials: JG
authors.lastname: McAlpin
authors.forename: Jamie Y C
authors.initials: JY
authors.lastname: Chen
authors.forename: Matthew L
authors.initials: ML
authors.lastname: Rigsby
authors.forename: William H
authors.initials: WH
authors.lastname: Casey
authors.forename: R David
authors.initials: RD
authors.lastname: Britt
authors.forename: Shannon S
authors.initials: SS
authors.lastname: Stahl
mesh_terms: D002384:Catalysis; D003035:Cobalt / Q000737:chemistry*; D055664:Electrochemical Techniques; D019277:Entropy; D006861:Hydrogen Peroxide / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D010084:Oxidation-Reduction; D010087:Oxides / Q000737:chemistry*; D014867:Water / Q000737:chemistry*
chemical_list: D010087:Oxides; D014867:Water; D003035:Cobalt; D006861:Hydrogen Peroxide; C060728:cobalt oxide