Two of the most daunting problems facing humankind in the twenty-first century are energy security and climate change. This report summarizes work accomplished towards addressing these problems through the execution of a Grand Challenge LDRD project (FY09-11). The vision of Sunshine to Petrol is captured in one deceptively simple chemical equation: Solar Energy + xCO{sub 2} + (x+1)H{sub 2}O {yields} C{sub x}H{sub 2x+2}(liquid fuel) + (1.5x+.5)O{sub 2} Practical implementation of this equation may seem far-fetched, since it effectively describes the use of solar energy to reverse combustion. However, it is also representative of the photosynthetic processes responsible for much of life on earth and, as such, summarizes the biomass approach to fuels production. It is our contention that an alternative approach, one that is not limited by efficiency of photosynthesis and more directly leads to a liquid fuel, is desirable. The development of a process that efficiently, cost effectively, and sustainably reenergizes thermodynamically spent feedstocks to create reactive fuel intermediates would be an unparalleled achievement and is the key challenge that must be surmounted to solve the intertwined problems of accelerating energy demand and climate change. We proposed that the direct thermochemical conversion of CO{sub 2} and H{sub 2}O to CO and H{sub 2}, which are the universal building blocks for synthetic fuels, serve as the basis for this revolutionary process. To realize this concept, we addressed complex chemical, materials science, and engineering problems associated with thermochemical heat engines and the crucial metal-oxide working-materials deployed therein. By project's end, we had demonstrated solar-driven conversion of CO{sub 2} to CO, a key energetic synthetic fuel intermediate, at 1.7% efficiency.
The Sunshine to Petrol effort at Sandia National Laboratories aims to convert CO 2 and water to liquid hydrocarbon fuel precursors using concentrated solar energy with redox-active metal oxide systems, such as ferrites: Fe 3O 4→3FeO+ 0.5O 2 (>1350°C) 3FeO + CO 2→Fe 3O 4 + CO (<1200°C). However, the ferrite materials are not repeatedly reactive on their own and require a support, such as yttria-stabilized zirconia (YSZ). The ferrite-support interaction is not well defined, as there has been little fundamental characterization of these oxides at the high temperatures and conditions present in these cycles. We have investigated the microstructure, structure-property relationships, and the role of the support on redox behavior of the ferrite composites. In-situ capabilities to elucidate chemical reactions under operating conditions have been developed. The synthesis, structural characterization (room and high- temperature x-ray diffraction, secondary ion mass spectroscopy, scanning electron microscopy), and thermogravimetric analysis of YSZ-supported ferrites will be discussed.
In this project, we developed a confined cooperative self-assembly process to synthesize one-dimensional (1D) j-aggregates including nanowires and nanorods with controlled diameters and aspect ratios. The facile and versatile aqueous solution process assimilates photo-active macrocyclic building blocks inside surfactant micelles, forming stable single-crystalline high surface area nanoporous frameworks with well-defined external morphology defined by the building block packing. Characterizations using TEM, SEM, XRD, N{sub 2} and NO sorption isotherms, TGA, UV-vis spectroscopy, and fluorescence imaging and spectroscopy indicate that the j-aggregate nanostructures are monodisperse and may further assemble into hierarchical arrays with multi-modal functional pores. The nanostructures exhibit enhanced and collective optical properties over the individual chromophores. This project was a small footprint research effort which, nonetheless, produced significant progress towards both the stated goal as well as unanticipated research directions.
This report summarizes the findings of a five-month LDRD project funded through Sandia's NTM Investment Area. The project was aimed at providing the foundation for the development of advanced functional materials through the application of ultrathin coatings of microporous or mesoporous materials onto the surface of substrates such as silicon wafers. Prior art teaches that layers of microporous materials such as zeolites may be applied as, e.g., sensor platforms or gas separation membranes. These layers, however, are typically several microns to several hundred microns thick. For many potential applications, vast improvements in the response of a device could be realized if the thickness of the porous layer were reduced to tens of nanometers. However, a basic understanding of how to synthesize or fabricate such ultra-thin layers is lacking. This report describes traditional and novel approaches to the growth of layers of microporous materials on silicon wafers. The novel approaches include reduction of the quantity of nutrients available to grow the zeolite layer through minimization of solution volume, and reaction of organic base (template) with thermally-oxidized silicon wafers under a steam atmosphere to generate ultra-thin layers of zeolite MFI.
Our ability to field useful, nano-enabled microsystems that capitalize on recent advances in sensor technology is severely limited by the energy density of available power sources. The catalytic nanodiode (reported by Somorjai's group at Berkeley in 2005) was potentially an alternative revolutionary source of micropower. Their first reports claimed that a sizable fraction of the chemical energy may be harvested via hot electrons (a 'chemicurrent') that are created by the catalytic chemical reaction. We fabricated and tested Pt/GaN nanodiodes, which eventually produced currents up to several microamps. Our best reaction yields (electrons/CO{sub 2}) were on the order of 10{sup -3}; well below the 75% values first reported by Somorjai (we note they have also been unable to reproduce their early results). Over the course of this Project we have determined that the whole concept of 'chemicurrent', in fact, may be an illusion. Our results conclusively demonstrate that the current measured from our nanodiodes is derived from a thermoelectric voltage; we have found no credible evidence for true chemicurrent. Unfortunately this means that the catalytic nanodiode has no future as a micropower source.
The Sunshine to Petrol effort at Sandia aims to convert carbon dioxide and water to precursors for liquid hydrocarbon fuels using concentrated solar power. Significant advances have been made in the field of solar thermochemical CO{sub 2}-splitting technologies utilizing yttria-stabilized zirconia (YSZ)-supported ferrite composites. Conceptually, such materials work via the basic redox reactions: Fe{sub 3}O{sub 4} {yields} 3FeO + 0.5O{sub 2} (Thermal reduction, >1350 C) and 3FeO + CO{sub 2} {yields} Fe{sub 3}O{sub 4} + CO (CO{sub 2}-splitting oxidation, <1200 C). There has been limited fundamental characterization of the ferrite-based materials at the high temperatures and conditions present in these cycles. A systematic study of these composites is underway in an effort to begin to elucidate microstructure, structure-property relationships, and the role of the support on redox behavior under high-temperature reducing and oxidizing environments. In this paper the synthesis, structural characterization (including scanning electron microscopy and room temperature and in-situ x-ray diffraction), and thermogravimetric analysis of YSZ-supported ferrites will be reported.
The Sunshine to Petrol effort at Sandia aims to convert carbon dioxide and water to precursors for liquid hydrocarbon fuels using concentrated solar power. Significant advances have been made in the field of solar thermochemical CO{sub 2}-splitting technologies utilizing yttria-stabilized zirconia (YSZ)-supported ferrite composites. Conceptually, such materials work via the basic redox reactions: Fe{sub 3}O{sub 4} {yields} 3FeO + 0.5O{sub 2} (Thermal reduction, >1350 C) and 3FeO + CO{sub 2} {yields} Fe{sub 3}O{sub 4} + CO (CO{sub 2}-splitting oxidation, <1200 C). There has been limited fundamental characterization of the ferrite-based materials at the high temperatures and conditions present in these cycles. A systematic study of these composites is underway in an effort to begin to elucidate microstructure, structure-property relationships, and the role of the support on redox behavior under high-temperature reducing and oxidizing environments. In this paper the synthesis, structural characterization (including scanning electron microscopy and room temperature and in-situ x-ray diffraction), and thermogravimetric analysis of YSZ-supported ferrites will be reported.