Biogenic Transition Metal Oxides as Water-Oxidation Electrocatalysts

University Of California-Davis, Davis CA

Investigators

Abstract

Biogenic Transition Metal Oxides as Water-Oxidation Electrocatalysts. With this award from the Chemical Catalysis Program of the Chemistry Division, Professor R. David Britt of the University of California at Davis is studying a novel type of biological catalyst which will contribute to clean and renewable energy technology. Certain bacteria use an enzyme to generate a manganese oxide material which Britt and coworkers have shown can split water, a key step in making inexpensive solar fuels, using energy from sunlight. The Britt lab is producing this material under different conditions, and exploring the activity of mutants of this enzyme, to optimize the water splitting activity of the manganese oxide material. The goal is to make an inexpensive bio-material using earth abundant manganese to replace existing catalysts based on expensive rare metals. Outreach activities coupled to this research program include summer research opportunities at both the high school and college level, motivating students by introducing them to this interesting interface of chemistry and biology that is relevant to renewable energy and environmental issues. A discrete manganese oxide (MnOx) unit was selected by Nature as the catalyst for O2 evolution - the Mn4O5Ca oxygen-evolving-complex (OEC) found in all oxygenic photosynthetic organisms. Inspired by the OEC, many manganese complexes and nanoparticles have been synthesized and investigated as catalysts for water-oxidation reaction. In this project in the laboratory of Professor R. David Britt of the University of California at Davis, a multicopper oxidase (MCO) enzyme, Mnx, which oxidizes aqueous Mn(II) driven by the oxidation potential of atmospheric O2, is offering a convenient means to generate a MnOx material in a fully biological fashion. The biological reactivity of the Mnx enzyme is allowing the Britt lab to systematically vary the structure and composition of the resulting MnOx and test what factors give rise to the highest activities. Specifically, this project is focusing on the following three aspects. 1) To explore the molecular mechanism of Mnx-catalyzed Mn(II) oxidation. 2) To characterize the resultant biogenic MnOx forms by multiple techniques (high-field EPR, XAS, SEM, etc) and employ the varied forms as water-oxidation electrocatalysts, in order to establish a structure-activity relationship. 3) Biogenic metal/mixed-metal oxides as catalysts: the reduction potential of type 1 Cu in Mnx enzyme can be tuned through site-directed mutagenesis of the axial ligand. Therefore, the type of substrates may be broadened (e.g. Fe(II), Co(II) or Ni(II)) and metal/mixed-metal oxides may be generated and tested as water-oxidation electrocatalysts. The project has broad impacts in training graduate and undergraduate and even visiting high school students in transition metal coordination chemistry, biochemistry, electrochemistry, and spectroscopy, and is being integrated into energy focused chemistry lectures that Professor Britt teaches each year.