The goal of our work is to develop efficient, robust photocatalytic subsystems and complete systems for the synthesis of renewable fuels and chemicals using carbon dioxide and water as starting materials, and sunlight as energy source. All-inorganic oxo-bridged heterobinuclear light absorbers coupled to metal oxide nanoclusters are being developed for accomplishing visible light induced multi-electron catalysis for carbon dioxide reduction and water oxidation, using photodeposition methods for the proper coupling of chromophore and nanocluster catalyst. Structures, charge transfer processes and catalytic mechanisms are elucidated by FT-infrared, Raman and optical spectroscopy, X-ray spectroscopy, and atomic resolution imaging. The mechanistic understanding gained from the time-resolved FT-infrared studies combined with electron transfer investigations of the heterobinuclear charge transfer units by transient optical spectroscopy guide the design of units for improved photocatalytic efficiency under visible and near infrared light. Using low temperature atomic layer deposition and nanofabrication methods, metal oxide core-shell constructs are being developed for separating the water oxidation catalysis from light absorption and reduction chemistry by a nanoscale silica-based membrane. Synthetic methods have been established for embedding electron or hole conducting molecular wires into the insulating silica membrane, and proton transmission properties of the silica have been quantified. Emphasis is on tightly controlled electron transport from light absorber to catalyst through the molecular wires, on atomically defined contacts between the components, and on the elucidation of charge transport kinetics and efficiency across the assembly. The long term objective is to close the photocatalytic cycle of carbon dioxide reduction and water oxidation on the nanoscale while achieving product separation on the macroscale.
The ultrathin silica membranes with embedded molecular wires open up opportunities for exploring single integrated biohybrid assemblies to create function that combines the best of biology with the best of inorganic catalysis (BSP milestone). The membranes allow electronic coupling of life organisms with inorganic catalysis, with the incompatible reaction environments held in nanometer proximity. The approach drastically reduces efficiency losses due to transport of charges and chemical species over macroscale distances. Major effort will focus on spectroscopic and electrochemical studies to understand and control electron and proton transport pathways across both the silica and biological membrane, and to elucidate the catalytic mechanisms.