Exploratory Efforts 2008
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.
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+.
Geological Sequestration of CO2 – An Exploratory Study of the Mechanisms and Kinetics of CO2 Reaction with Mg-Silicates
Gordon Brown, Dennis K. Bird, Kate Maher and Wendy Mao, Geo & Environmental Science, Stanford University
A possible strategy for geological sequestration of CO2 is in the reaction of CO2 and Mg silicates. Mg silicates are present in the form of picrites and serpentinites which are abundant and thermodynamically convenient rocks to form Mg-carbonates. This exploratory project focuses on the mechanism and kinetics of CO2 (and H2O) interactions with both serpentinites and picrites, as well as in individual serpentine minerals and individual minerals found in picritic basalts. This investigation will focus on 1) changes in the surface chemistry of these minerals following carbonation reactions, 2) molecular-level characterization of the reaction products, and 3) kinetic studies of these surface carbonation reactions using stable isotopes as tracers. Results from the project may open pathways to enhance reaction kinetics of CO2 with these minerals such that costs can be reduced at scale.
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.
Multijunction Nanowire Solar Cells for Inexpensive and Highly Efficient Photoelectricity: Enabling Methods
Paul McIntyre, Materials Science & Engineering, Stanford University
This exploratory program aims at investigating a novel multijunction solar cell design to address the high fabrication costs of traditional multijunction devices, which use expensive-to-grow, high-quality semiconductor single crystals. The proposed design uses vertical semiconductor nanowire arrays grown on inexpensive polycrystalline germanium substrates, and takes advantage of the elastic dilatation property of nanowires that can relax misfit trains and allows the growth of high-quality nanowire heterojunctions with no dislocations. The program focuses on three enabling methods required for nanowire multijunction solar cells: 1) catalysis of Ge nanowire growth using inexpensive metal catalysts which, unlike the standard Au catalyst, do not produce deep carrier traps in the Ge bandgap; 2) nucleation and growth of dense, vertical Ge nanowire arrays on (111)-oriented polycrystalline Ge thin films on inexpensive glass substrates; and 3) formation of heterostructure GaAs/Ge nanowires by continuous, locally catalyzed deposition on Ge wires using Ga and As precursors.
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.