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2008 Distinguished Lecturers printer friendly format
Chris Chidsey



Christopher Chidsey
Chemistry, Stanford University

Presentation Title: Toward Atomistic Control of Electrocatalysis for Energy-Intensive Applications

Abstract: Dramatic improvement in the interconversion of chemical and electrical energy would revolutionize energy systems, particularly in the areas of mobile power, energy storage, and chemical processing. However, the slow rates and poor energy efficiency of most electrochemical transformations currently limit these options. In the field of homogeneous catalysis, discrete metal complexes, precisely tailored at the atomic level, are used to catalyze difficult reactions. Coupling discrete metal complexes to electrodes can create energetically efficient and chemically specific electrocatalysts for a wide range of interconversions. We have developed modular methods to immobilize a range of discrete metal complexes onto oxidatively robust, high surface-area electrodes. We have studied dioxygen reduction, alcohol oxidation, and other reactions that will be needed for energy-efficient technologies in a resource-constrained world.

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Biography: Professor Chidsey holds a bachelor’s degree in Chemistry from Dartmouth College and a Ph.D. in Physical Chemistry from Stanford University. After postdoctoral work in electrochemistry with Royce Murray at the University of North Carolina, he joined the technical staff at AT&T Bell Laboratories where he probed long-distance electron transfer across interfaces and contributed to developments in scanning tunneling microscopy, nonlinear optical materials, and optical materials processing. He has been a member of the Stanford Department of Chemistry since 1992 where he has studied the role of chemical bonding in promoting long-distance electron tunneling across interfaces and has contributed to the development of silicon and germanium surface chemistry.

At the current time, the Chidsey lab uses surface chemistry and electrochemistry to control and investigate a number of important interfacial phenomena. A major effort in the lab is the covalent attachment of electrocatalysts to carbon electrodes and other oxidation-resistant conductive substrates for use in ambient-temperature fuel cells and related energy- and chemical-conversion systems. A new covalent chemistry on graphitic carbon surfaces, based on the ‘click’ reaction of azides and alkynes, has been developed. Another effort in the Chidsey lab involves the formation of electroactive self-assembled thiol monolayers on gold surfaces—an area Chidsey pioneered beginning 15 years ago. This effort is currently focused on using ‘click’ chemistry on self-assembled monolayers to build models for multi-electron redox reactions of fundamental mechanistic interest. A related area is the use of ‘click’ chemistry to immobilize biomolecules to siloxane monolayers on glass to enable various biochemical analyses.

A separate effort in the lab involves the deterministic growth and characterization of Ge nanowires from patterned, electrodeposited metal catalysts for use in nanoelectronic and molecular electronic applications. Finally, the Chidsey lab has made on-going efforts to build the chemical base for molecular electronics. These include the synthesis the molecular and nanoscopic systems, and the development of the analytical tools and the theoretical understanding with which to study electron transfer between electrodes and redox species through insulating molecular bridges. Members of the group have synthesized several series of saturated and conjugated oligomers with which to study the fundamental aspects of electron tunneling through well-defined molecular bridges.


Tony Kovscek



Tony Kovscek
Energy Resources Engineering, Stanford University

Presentation Title: CO2 Sequestration: What Have We Found? What Should Future Priorities Be? (PDF, 12.9Mb)

Abstract: Geological sequestration remains one of the most promising and easiest to achieve measures to reduce atmospheric emissions of CO2 in the short term. The analogy between enhanced oil and gas recovery and CO2 sequestration is incomplete, however, especially for candidate coalbed sequestration sites. While it is true that wells can be drilled and completed and that subsurface flows can be managed in oil and gas settings, we cannot yet conduct compelling simulations of multicomponent, multiphase flow with adsorption in coalbeds. Moreover, the displacement of water or oil by CO2 is unstable and similarly is subject to poor predictive capability. Such simulations are a step toward the engineering and public acceptance of the sequestration option. To address such questions, our work integrates experiments and theory. In the area of coalbed sequestration we have compiled a data base of adsorption isotherms of CH4, N2 and CO2 on Powder River Basin, WY samples, conducted corresponding CH4 displacements by mixtures of CO2/N2 in the laboratory, and developed a high-resolution numerical model for gas transport with adsorption through coal. We have found that coal swelling and changes in injectivity are mitigated through selection of an appropriate CO2/N2 mixture and that gas flow in coal exhibits chromatographic type separation of gas species. The state-of-the-art extended Langmuir model for multicomponent adsorption was unable to describe the behavior of ternary CH4/CO2/N2 displacements whereas a more sophisticated ideal adsorbate solution model yielded more accurate results. In short, sequestration processes display rich dynamical behavior that remains to be fully described in a conceptual and numerical simulation framework. Future priorities should include studies of the fundamentals of mass transport and coupled geomechanical behavior of coal, aquifers, and hydrocarbon reservoirs so that effective methods to assess and access these important geological storage sites are developed.

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Biography: Professor Tony Kovscek is an Associate Professor of Energy Resources Engineering at Stanford University. His academic interests center around the physics of heat and fluid transport in porous media as well as the efficient use of energy.

Kovscek and his research group examine the physics of transport in porous media at length scales that vary from the pore-scale, core-scale and up to the reservoir scale. They use flow imaging and image analysis to delineate the mechanisms of multiphase flow (oil, water, and gas) in porous media and the synthesis of models from experimental, theoretical, and field data. In all work, physical observations, obtained mainly from laboratory and field measurements, are interwoven with theory.

Kovscek holds BS and PhD degrees from the University of Washington and the University of California at Berkeley, respectively. In 2006, he was awarded the Distinguished Achievement Award for Faculty from the Society of Petroleum Engineers.


Chris Field
Chris Field
Department of Global Ecology, Carnegie Institution
Biological Sciences, Stanford University

Presentation Title: Biomass Energy: The Climate Protective Domain (PDF, 1.6Mb)

Abstract: Biomass offers the potential of providing abundant renewable energy, but it can also have environmental and societal downsides. Converting forest lands into bioenergy agriculture can accelerate climate change by releasing carbon stored in forests, while converting food agriculture lands into bioenergy agriculture can raise food prices and threaten food security. Both problems are potentially avoided by developing abandoned agriculture lands for bioenergy agriculture. This sustainable option has the potential to provide less than 8% of current primary energy demand. The energy content of potential biomass grown on abandoned agriculture lands is less than 10% of primary energy demand for most nations in North America, Europe, and Asia, but it represents many times the energy demand in some African nations where grasslands are relatively productive and current energy demand is low. Defining and working within the sustainable domain will likely be critical for the long-term success and acceptance of biomass energy.

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Biography: Professor Chris Field is the founding director of the Carnegie Institution's Department of Global Ecology, a Professor of Biological Sciences at Stanford University, and the Faculty Director of Stanford's Jasper Ridge Biological Preserve.

For most of the last two decades, Field has worked to establish the science of global ecology. His research emphasizes mechanisms that control the carbon cycle and its interactions with climate, from the molecular to the global scale.

In more than 200 scientific publications, Field and his colleagues have used diverse approaches, integrating information from plant physiological approaches, satellites, atmospheric observations, historical data, and models. They have explored local- and global-scale patterns of climate-change impacts, vegetation-climate feedbacks, carbon cycle dynamics, primary production, forest management, and fire. At the ecosystem-scale, Field has, for more than a decade, led major experiments on responses of California grassland to multi-factor global change, experiments that integrate approaches from molecular biology to remote sensing.

Field has served on many national and international committees related to global ecology, including committees of the National Research Council, the International Geosphere-Biosphere Programme, and the Earth System Science Partnership.

He was a coordinating lead author for the fourth assessment report of the Intergovernmental Panel on Climate Change, with responsibility for the chapter on North America. Field is a fellow of the ESA Aldo Leopold Leadership Program and a member of the US National Academy of Sciences. He has served on the editorial boards of Ecology, Ecological Applications, Ecosystems, Global Change Biology, and PNAS.

Field received his PhD from Stanford in 1981 and has been at the Carnegie Institution since 1984.


Gavin Conibeer
Gavin Conibeer
University of New South Wales
Deputy Director, Photovoltaics Centre of Excellence

Presentation Title: Third Generation Photovoltaics (PDF, 1.6Mb)

Abstract: To achieve the International Panel on Climate Change recommended 60% reduction in emissions by 2050—the minimum needed to offset the worst effects of climate change—a large scale implementation of sustainable and renewable energy technologies is required. Amongst these renewable energies, photovoltaics is the fastest growing technology with more than 30% growth per year over the last 10 years and more than 60% growth in 2007; although worldwide installation is still small. This growth in manufacture is currently driven by subsidies, primarily in Europe, but the increase itself leads to a learning effect as the technology matures, which brings down the cost per unit. In order to maintain the leverage this steep learning curve applies to unit price, a transition of technology from the first generation approaches based on single crystal wafer based solar cells to second generation thin film, with their much lower energy intensity and material usage, is required. However to project this downward pressure on price onto ever larger production volumes, a further generation change is required to push up efficiencies whilst still maintaining the low cost approaches of thin film cells.

The reason that such third generation technologies can achieve such a “best of both worlds” result is that the vast majority of current production cells consist of only one absorbing semiconductor material. But such single semiconductor band gap devices have to compromise in their absorption of the very polychromatic solar spectrum, with a wide range of photon energies. This leads to significant energy losses through two main routes. At first, solar photons at less than the band gap energy are not absorbed at all and are wasted. Secondly, for photons well above the band gap energy, a large fraction of their energy is lost as heat in the device. Third generation devices use multiple energy levels, often in the form of several different semiconductor materials, to extract energy efficiently from a greater fraction of these photons. Examples of such approaches will be discussed, with specific mention of tandem solar cells that use quantum dot nanostructures based on silicon; devices which can up-convert low energy photons such that they are absorbed; and hot carrier cells which seek to extract the energy gained from high energy photons before it can be lost to the lattice. The status of and prospects for these approaches will be assessed.

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Biography: Dr. Gavin Conibeer received his PhD from Southampton University, UK, in Semiconductor Physics for tandem solar cells in 1995. He also has a BSc in Materials Science and MSc in Polymer Science from London University. Conibeer has held research positions at Oxford, Cranfield, Southampton, and Monash Universities where he has worked on most of the materials systems used in photovoltaics.

Conibeer joined the University of New South Wales, Sydney, Australia in 2002 and was appointed a Deputy Director in the Photovoltaics Centre of Excellence in 2003, in charge of Third Generation Photovoltaics. This group of 22 researchers is investigating the fabrication of silicon, germanium and tin nanostructures in oxide, nitride or carbide matrices; up or down conversion of the incident solar spectrum; and hot carrier solar cells.

Conibeer’s personal research interests encompass a wide range of third generation and advanced photovoltaic concepts, including silicon quantum dot based tandem solar cells, hot carrier solar cells, up-conversion and photoelectrochemical cells.

He is author of over 100 publications including 35 journal articles.

 
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