LaMattina Lecture Series

Heinz Frei, Ph.D.

Senior Scientist
Lawrence Berkeley National Laboratory

"Hierarchical Inorganic Assemblies for the Photocatalytic Reduction of CO2 by H2O"



February 9, 2016
11:10 a.m.
Parsons N104, Iddles Auditorium

The multi-electron processes of CO2 reduction and H2O oxidation, which constitute the essential reactions of sunlight to fuel conversion (artificial photosynthesis) require efficient coupling of light absorber and catalyst. Using all-inorganic heterobinuclear units such as ZrOCo anchored on high surface area silica, we have developed photodeposition methods for the directional assembly of nanometer sized catalyst clusters for H2O oxidation or CO2 reduction with proper coupling to the binuclear light absorber. Copper oxide nanoclusters were assembled adjacent to the Zr acceptor sites of the heterobinuclear unit, and light driven reduction of CO2 upon excitation of the ZrOCo unit demonstrated. Illumination of the ZrOCo chromophore coupled to an Ir oxide nanocatalyst for H2O oxidation affords closing the photocatalytic cycle in the absence of sacrificial agents. Time resolved FT-IR spectroscopy provides detailed mechanistic insight into the multi-electron reactions on the metal oxide catalyst surface under reaction conditions, while transient optical studies reveal the origin of the favorable electron transfer behavior of the light absorbers.

To achieve CO2 photoreduction by H2O under product separation on the nanoscale, Co3O4-SiO2 core-shell nanotubes were developed in which the inner surface acts as efficient water oxidation catalyst while the nanoscale silica layer with embedded molecular wires serves as a proton conducting, gas impermeable separation membrane with tight control of electron transport. Completing the photocatalytic cycle on the nanoscale seeks to minimize side reactions and efficiency degrading transport processes. Characterization of the assembly by transient spectroscopy and photoelectrochemical measurements will be discussed. Using nanofabrication based on sacrificial Si nanowire array methods, macroscale arrays of Co oxide-silica nanotubes are being developed for accomplishing the complete photocatalytic cycle in a macroscale assembly.  

Heinz Frei studied chemistry at the Swiss Federal Institute of Technology (ETH) Zurich (PhD in physical chemistry 1977).  After a postdoctoral stay at the Chemistry Department of the University of California at Berkeley, he started a research group in solar photochemistry at LBNL with focus on chemistry with near infrared light, work for which he received the Werner Prize of the Swiss Chemical Society in 1990. Over the past two decades, Frei has established new methods for utilizing visible and near infrared light for the environmentally friendly synthesis of useful chemicals, and for the chemical storage of solar photons. He has developed time-resolved FT-infrared spectroscopic methods for unraveling mechanisms of heterogeneous catalysis under reaction conditions. Currently, his research effort focuses on the scientific challenges of the direct conversion of carbon dioxide and water to a liquid fuel by artificial photosynthesis. He served as a Deputy Director of LBNL’s Physical Biosciences Division (1998-2007) and the Helios Solar Energy Research Center (2008-2011). Frei was one of the founding scientists of the Joint Center for Artificial Photosynthesis (JCAP, the U.S. Dept. of Energy Innovation Hub for Fuels from Sunlight), Leader of its Interface Project 2010-2015, and Acting Dept. Head of JCAP at LBNL in 2012. A frequent plenary lecturer at international conferences and member of U.S. Department of Energy workshop panels and advisory groups for foreign science foundations, he has co-organized several symposia on solar photochemistry in the past few years and is Joint-Chair of the 2016 Gordon Research Conference on Solar Fuels. He was elected Fellow of the American Association for the Advancement of Science in 2014.