Completed Exploratory Projects 2009
Development of an Immobilized Enzyme System for Lignocellulosic Biomass Saccharification
Richard Zare, Department of Chemistry, Stanford University
This exploratory project is aimed at solving the problems associated with a critical, rate-limiting step in the conversion of lignocellulosic biomass to the sugar feedstock for biofuels synthesis. Microfibrillar cellulose, the major source of these sugars, requires a suite of specialized enzymes acting in a concerted fashion, to break it down to its individual sugars. This research sets out to immobilize these enzymes in such a way that their active sites are brought into close proximity to the substrate and to one another leading to enhancement of enzymatic activity. Using a sol-gel polymer to immobilize the enzymes by entrapment and covalent attachment, the researchers will test enzyme stability for optimal conditions for cellulase bioconversion and kinetics compared to free cellulase.
Electrocatalytic Water Oxidation to Dioxygen in Molecular PdII/IV Coordination Environment
Dmitry Yandulov, Department of Chemistry, Stanford University
The goal of this exploratory project is to find electrocatalysts for the oxidation of water to oxygen at close to the thermodynamic potential. A new mechanistic approach will be explored using well-defined coordination complexes of PdII-IV. The proposed studies will test the feasibility of the key elementary steps of the proposed reaction mechanism and provide the foundation necessary for systematic improvement of water oxidation catalysis efficiency by design. The studies will begin with ligand and PdII complex synthesis, evaluation of aqueous pH stability limits of representative PdII(N-heterocyclic carbene) complexes, and screening of catalytic activity in water oxidation with Ce4+.
Nanostructured MoS2 and WS2 for the Solar Production of Hydrogen
Thomas Jaramillo, Chemical Engineering, Stanford University
Hydrogen production from photoelectrochemical (PEC) water splitting has been extensively investigated in the last few decades following the first experimental demonstrations using TiO2-based photoanodes. The realization of efficient and cost-effective PEC systems requires the identification of material candidates with the following properties: optimal bandgap for improved solar absorption; band edges aligned with the energy levels required for the redox water splitting reaction; sufficient carrier mobility for the photogenerated charges to reach the electrode/water interface before recombination; stability against corrosion; optimal catalytic properties for H2 and O2 evolution; and low cost. This exploratory program aims at investigating the potential of nanostructured earth-abundant, non-toxic dichalcogenide semiconductors (molybdenum and tungsten disulfides) where bulk and surface properties could be tailored independently to satisfy the above criteria by controlling their nanostructure.
Spectroscopic Characterization of Multi-Exciton Generation Efficiency in Nano-Structured Materials
Kelly Gaffney, SLAC; Yi Cui and Mike McGehee, Materials Science & Engineering, Stanford University
This exploratory project aims at implementing a novel time-resolved spectroscopic diagnostic technique to validate recent experimental estimates of the efficiency of multiple exciton generation (MEG) in semiconductor nanoparticles following the absorption of a single high-energy photon. As opposed to traditional transient absorption measurements performed at the band gap energy, the proposed experiment uses the excited-state absorption as a signature of multiple exciton generation. This approach avoids using questionable assumptions, such as the weak interaction between multiple excitons within a quantum dot, in interpreting the results.