Mechanisms of Co, Ni, and Mn based water splitting catalysts probed by advanced EPR spectroscopy

University Of California-Davis, Davis CA

Investigators

Abstract

With this award from the Chemical Catalysis Program of the Division of Chemistry, Professor R. David Britt from the University of California at Davis will study an efficient solar water splitting catalysis that would serve as the basis of a clean renewable energy technology, producing hydrogen gas, which could be stored and then reoxidized to generate electricity in a fuel cell, or used as a reductive intermediate in forming a liquid fuel. The studies are based on the discovery by Kanan and Nocera that cobalt(II) in neutral phosphate buffer spontaneously forms a water splitting catalyst on a polarized electrode surface. The Britt laboratory will use multifrequency EPR spectroscopy to investigate details of the structure of this cobalt catalyst and the mechanism by which it splits water. Continous wave (CW) and pulsed EPR instruments of the CalEPR laboratory will be used, over a frequency range from 8 to 130 GHz, as well as higher frequency instruments at the NHMFL in Florida. Multifrequency EPR will be used to examine the geometric and electronic structure of the cobalt catalyst. Pulsed double resonance experiments (ENDOR, ESEEM, and HYSCORE) will be probing the interaction of unpaired electrons on the cobalt ions with magnetic nuclei such as cobalt(59), oxygen(17), and phosphorus(31), and the results will be compared with model cobalt complexes of known structure. New studies on nickel borate analogues will be complementing the cobalt film studies, and additional work on a manganese catalyst formed in a Nafion membrane will help in bridging between these self assembled inorganic catalysts and the important Photosystem II Mn oxygen evolving complex. Understanding the details of the production of hydrogen gas is essential for energy generation and it is important to motivate students on renewable energy and environmental issues. Every year the PI teaches an honors general chemistry sequence, and the topics covered; electrochemistry, transition metal coordination chemistry, chemical kinetics, and spectroscopy, are ideally suited to tie lectures directly to current research in inorganic approaches to water splitting and solar fuels, in both synthetic and biological systems. The PI will integrate aspects of this research project into the lectures. The PI plans to recruit several first year students to work in the laboratory on these topics over the summer. In addition, he is teaching an upper division instrumental analysis class, which will provide a further opportunity to introduce undergraduates to electron paramagnetic resonance (EPR) techniques and energy research. His research group is also participating in the department's new NSF-REU program, which has an energy emphasis.