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Fellowships awarded annually since 1984.
Program Manager, Lee Lynd, Thayer School of Engineering, Dartmouth College
www.linkenergy.org
Rebecca GhanadanEnergy and Resources Group, University of California, Berkeley
Advisor: Dr. Daniel Kammen
Email Address: Rebeccag@socrates.berkeley.edu
Title: Putting Energy Technologies to Use in Africa: Improving Community-Level Access to Energy
Running fast just to stay put is how future energy needs in Africa have been characterized. My Ph.D. dissertation research is motivated by the conviction that developing, improving, and disseminating integrated community energy systems are some of the most effective ways to increase energy access in Africa. Existing research on energy access in Africa falls primarily into two categories: extension of “modern” energy supply chains into rural areas and studies of individual distributed energy technologies, including renewables. While these efforts focus on technology and supply gaps at the level of individual households, it is now increasingly recognized that better models for local involvement are needed for a larger number of households and communities to benefit from these opportunities. My dissertation takes the next critical step in energy research and examines energy use and energy systems at the community level - where energy generation technologies and energy end-use technologies may be employed to increase access and put technology opportunities to use serving community and productive energy needs. The three primary goals of my research on rural and urban community energy system in Tanzania are 1) to examine the technological and organizational requirements and the existing barriers to successful community energy systems 2) to develop a set of viability criteria for extending models of access to other contexts, and 3) to disseminate results of this research in forms that are accessible both to researchers and local groups interested in energy alternatives. Combining academic research with grassroots involvement and information sharing, my research will address a critical energy need in Africa and will have lasting impacts beyond the period of this fellowship.
David Michalak
Department of Chemistry and Chemical Engineering, California Institute of
Technology
Research Advisor: Nathan Lewis
Email Address: Michalak@its.caltech.edu
Title: Solar Paint
In order for solar energy devices to become economically competitive with fossil fuels, the high cost of producing efficient solar cells from high-purity single-crystal semiconductor wafers must be lowered. Use of non single-crystal semiconductors requires that surfaces and interior grain boundaries of polycrystalline wafers must be passivated. Solar devices made from semiconductor particles may offer other advantages, but still require surface passivation as well as a method for linking them together. The goal for this project is to create "solar paint": an efficient solar energy device and composite structure involving several "painted" layers of modified silicon particles that are inexpensive to fabricate, without demanding high-purity silicon or compromising efficiency.
We have already shown that chemical passivation of single-crystal silicon surfaces can be accomplished by alkylation techniques. In this project, we plan to apply these passivation techniques to small silicon particles. But instead of passivating the entire particle surface with one alkyl group, we plan to introduce a second functional group that has strong electronic coupling with either electrons or holes. The next step is to crosslink the silicon particles with these tailored electron- or hole-transporting organic groups into a network of either electron- or hole-transporting particles.
Viologens are a natural choice for coupling to electrons since the redox potentials for viologens are close to the vacuum energy of the conduction band. Proposed mechanisms include direct reaction of 4,4'-dipyridyl with a halogenated silicon surface or synthesis of a viologen Grignard reagent and subsequent chlorination/alkylation of the silicon surface. A related argument yields that ferrocenes or tetrathiafulvalenes could provide good coupling to holes. Hall measurements on a network of crosslinked particles would verify that carrier-specific transport properties have been accomplished.
In order to create a device resembling a photodiode, a network of electron-transporting silicon particles must be placed in electrical contact with a network of hole-transporting particles. This requires an interfacial region of silicon particles that are bifunctional, having both electron- and hole-conductive linkers on opposite ends. Using rods created from a porous silicon template and with proper masking techniques, functionalizing two opposite sides of a rod or particle with two different linker groups would be possible.
The benefits for using small particles are twofold: first, small particles are inexpensive and readily available and, second, the small particle size allows carriers to leave the particle before recombining. Once the carrier is on the linker, or in subsequent particles, recombination is suppressed by the highly reduced mobility of the other carrier in that half of the network. In this manner, greater effective diffusion lengths can be obtained than for the same material on a bulk size, thus tricking the lower-quality silicon into behaving like a high-quality silicon device.
Obviously, the desired form of a solar paint requires the use of conductive polymers as interparticle linkers rather than short organic functional groups. This will be investigated using the silicon particles as above in a matrix of conductive polymer tuned for the transport of either electrons or holes.
Jesse Rowsell
Department of Chemistry, University of Michigan
Research Advisor: Omar Yaghi
Email Address: Jrowsell@umich.edu
Title: Metal-Organic Frameworks as a New Alternative for Hydrogen Storage
The scientific community has touted hydrogen as the “fuel of tomorrow” for some time now, yet the movement away from carbon-based energy generation remains sluggish despite our recognition of the environmental consequences. While the automotive industry has acted progressively in the development of hydrogen-powered vehicles, the three storage techniques used in present-day prototypes —compression, liquefaction, and formation of solid metal hydrides—are each encumbered by concerns about safety and efficiency. Our laboratory has developed a new class of porous materials synthesized from inexpensive, non-toxic zinc salts and organic acids, which we have shown to be ideal hosts for the sorption of gas molecules. Preliminary studies have shown that several of these compounds uptake hydrogen to a respectable level. Moreover, the subtle host-guest interaction allows cycling of hydrogen uptake and release at practical rates with negligible loss. Through chemical modification of both the organic and inorganic components of these hybrid compounds, I plan to optimize a material with a hydrogen storage capacity at the level targeted by the Department of Energy for mobile applicability. Fortunately, the highly crystalline nature of these products allows the use of very sophisticated methods of characterization, including x-ray diffraction and inelastic neutron scattering, with which we hope to gain a full understanding of the sorptive process.