Completed Exploratory Projects 2010
Carbon-ion Conducting Thin Film Membranes Towards Efficient CO2 Separation
Fritz Prinz, Mechanical Engineering; Turgut Gur, Materials Science and Engineering, Stanford University
Thin-film membrane materials that selectively transport carbon ions through electrochemical means may create a method of capturing and separating CO2 in a single process step. This project will identify, design, dope, fabricate, and screen ion-conducting carbide materials and demonstrate selective transport of carbon ions through a dense nonporous membrane. When a direct current bias is applied across the carbide-membrane material, it provides extremely steep gradients of virtual pressure. This gradient combined with an ultra-thin membrane can yield high fluxes practical for CO2 capture and separation at a large scale, such as in flue gas streams of coal-fired power plants.
Efficient Cell-Free Hydrogen Production from Glucose
James Swartz, Chemical Engineering and of Bioengineering, Stanford University
The major goal of this exploratory project is to achieve efficient hydrogen production from glucose derived from cellulosic hydrolysates using a cell-free technology based on enzymes made in E. coli. The expression of hydrogen producing enzymes will be induced in densely grown and specially engineered E.coli cells. The unique features that will be engineered into the E.coli will increase hydrogen production yields and rates compared to reported methods. The concentrations of cofactors such as nicotinamide adenine dinucleotide phosphate (NADP) and enzymes of the electron transport chain will be adjusted to direct reactions towards the production of hydrogen. The flow of glucose into the glycolysis breakdown pathway will be blocked using an inhibitor making more of it available for hydrogen production. With these adjustments, this cell-free technology will allow precise control over metabolic fluxes having the potential of reaching a production level of 8 mmoles hydrogen per mole of glucose at a rate of 3 mmoles hydrogen/gram of cells/hour, higher than any system has reportedly achieved to date.
Fundamental Studies of Plasma Air Separation
Mark Cappelli, Mechanical Engineering, Stanford University
This research explores the use of an atmospheric-pressure dielectric plasma discharge to enrich an air flow with oxygen, with the ultimate goal of providing a novel low-cost technology for air separation. This work will lead to better understanding of the fundamental challenges that need to be addressed to generate negatively charged oxygen ions in such a plasma configuration and to effectively separate oxygen by having the plasma impart momentum to the neutral air molecules. Results from this project will provide the scientific basis necessary to assess the feasibility of this air separation technology.
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.
High Capacity Molecular Hydrogen Storage in Novel Crystalline Solids
Wendy Mao, Geological and Environmental Sciences, Stanford University
A major barrier to the use of hydrogen as an energy carrier is finding a practical hydrogen storage material for mobile applications. Extreme environments provide a broader space to search for phases with desirable properties. For example, one promising compound discovered at high pressure is tetrahydrogen-methane (CH4(H2)4), which contains 33.4 wt% molecular hydrogen, not including the hydrogen in the methane itself. This exploratory activity uses a closely coupled experimental and theoretical approach to identify several promising hydrogen-rich, crystalline solids, determine their structures, and then attempt to stabilize these phases near ambient conditions (e.g. by the addition of chemical promoters). The goal of this effort is to ultimately provide guidance in developing improved hydrogen storage materials.
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.
Next Generation High-Efficiency Low-Cost Thin Film Photovoltaics
May 2009 - April 2011
Bruce Clemens and Alberto Salleo, Materials Science and Engineering, Stanford University
This research investigates ion-beam assisted deposition (IBAD) of textured templates that can be used to make efficient crystalline-Si thin-film solar cells. The idea behind this approach is that ion beams can be used to selectively determine the crystal orientation of the deposited crystalline films. By means of this technique, one could grow a polycrystalline film with well-aligned grains and therefore “smoother” grain-to-grain interfaces. As a result, the charges generated within the light-absorbing thin-film would undergo much fewer recombination processes at the grain boundaries and the overall conversion efficiency of the photovoltaic cell would be substantially improved.