Andrea Ambrosini

Sr- and Mn-doped LaAlO3−δ for solar thermochemical H2 and CO production

The increasing global appetite for energy within the transportation sector will inevitably result in the combustion of more fossil fuel. A renewable-derived approach to carbon-neutral synthetic fuels is therefore needed to offset the negative impacts of this trend, which include climate change. In this communication we report the use of nonstoichiometric perovskite oxides in two-step, solar-thermochemical water or carbon dioxide splitting cycles. We find that LaAlO3 doped with Mn and Sr will efficiently split both gases. Moreover the H2 yields are 9× greater, and the CO yields 6× greater, than those produced by the current state-of-the-art material, ceria, when reduced at 1350 °C and re-oxidized at 1000 °C. The temperature at which O2 begins to evolve from the perovskite is fully 300 °C below that of ceria. The materials are also very robust, maintaining their redox activity over at least 80 CO2 splitting cycles. This discovery has profound implications for the development of concentrated solar fuel technologies.

Characterization of Pyromark 2500 Paint for High-Temperature Solar Receivers

Pyromark 2500 is a silicone-based high-temperature paint that has been used on central receivers to increase solar absorptance. The radiative properties, aging, and selective absorber efficiency of Pyromark 2500 are presented in this paper for use as a baseline for comparison to high-temperature solar selective absorber coatings currently being developed. The solar absorptance ranged from ∼0.97 at near-normal incidence angles to ∼0.8 at glancing (80°) incidence angles, and the thermal emittance ranged from ∼0.8 at 100 °C to ∼0.9 at 1000 °C. After thermal aging at temperatures of ∼750 °C or higher, the solar absorptance decreased by several percentage points within a few days. It was postulated that the substrate may have contributed to a change in the crystal structure of the original coating at elevated temperatures.

Ferrite-YSZ composites for solar thermochemical production of synthetic fuels: in operando characterization of CO2 reduction

Ferrites are promising materials for enabling solar-thermochemical cycles. Such cycles utilize solar-thermal energy for the production of hydrogen from water, or carbon monoxide from carbon dioxide. Mixing ferrites with zirconia or yttria-stabilized zirconia (YSZ) greatly improves the cyclability of the ferrites and enables a move away from powder to monolithic systems. This synergistic effect is only partially understood. In order to unravel the underlying mechanisms of the effect and to understand the evolution of thermochemically active phases, we have studied the behaviour of iron oxides co-sintered with 8YSZ (8 mol% Y2O3) using in operando X-ray diffraction and thermogravimetric analysis at temperatures up to 1500 °C and under environments representative of those present in a thermochemical cycle. The solubility of iron oxide in 8YSZ measured by XRD at room temperature, following calcination to 1500 °C in air, was 9.4 mol% Fe. The solubility increased to at least 10.4 mol% Fe when heated between 800 and 1000 °C under inert (He) atmosphere. Furthermore iron was found to migrate in and out of the 8YSZ phase as the temperature and oxidation state of the iron changed. In samples containing insoluble iron (i.e., containing >9.4 mol% Fe) stepwise heating to 1400 °C under helium caused reduction of Fe2O3 (hematite) to Fe3O4 (magnetite) to FeO (wustite). This gradual thermal reduction from hematite to wustite was accompanied by evolution of oxygen. The wustite remained stable upon cooling to room temperature in the helium environment, although after multiple consecutive cycles some of the wustite was observed to disproportionate to Fe metal and magnetite. Exposure of the wustite-containing material to CO2 at 1100 °C enabled re-oxidation of the wustite to magnetite with evolution of CO. Thermogravimetric analysis during thermochemical cycling of materials with iron oxide contents between 1.8 and 27.6 mol% Fe showed that samples with mostly dissolved iron utilized a greater proportion of the iron atoms present than did samples possessing a significant fraction of un-dissolved iron oxides.

Oxygen transport and isotopic exchange in iron oxide/YSZ thermochemically-active materials via splitting of C(18O)2 at high temperature studied by thermogravimetric analysis and secondary ion mass spectrometry

Ferrites are promising materials for enabling solar-thermochemical cycles for the production of synthetic fuels. Such cycles utilize solar-thermal energy for the production of hydrogen from water, or carbon monoxide from carbon dioxide. Recent work studying the thermochemical behaviour of iron oxides co-sintered with yttria-stabilised zirconia (YSZ) using thermogravimetric analysis revealed a striking difference in behaviour of iron that is in solid solution with the YSZ and that which exists as a second iron oxide phase. Materials in which the majority of iron was dissolved in the YSZ exhibited enhanced utilization of iron over those which possessed larger fractions of un-dissolved, bulk iron oxides. To illuminate this phenomena further, several samples of thermally-reduced iron oxide/8YSZ were re-oxidised using isotopically labelled C(18O)2. Post mortem characterization by Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS), with the application of multivariate analysis tools, enables the differentiation between 18O and 16O signals emanating from iron oxide particles. The distribution of 18O is uniform throughout the iron-doped 8YSZ, but concentrated at the surface of iron oxide particles embedded in this matrix. After identical thermal reduction and re-oxidation treatments, the gradient of 18O/16O across the iron oxide particles is found to depend on the size of the iron oxide particles, as well as the method of synthesis of the iron oxide/YSZ material. Comparative thermogravimetric analyses of the 18O-labelled materials and analogous un-labelled materials revealed that exposure to CO2 at 1100 °C results in rapid oxygen isotopic exchange.

Improved High Temperature Solar Absorbers for Use in Concentrating Solar Power Central Receiver Applications

Concentrating solar power (CSP) systems use solar absorbers to convert the heat from sunlight to electric power. Increased operating temperatures are necessary to lower the cost of solar-generated electricity by improving efficiencies and reducing thermal energy storage costs. Durable new materials are needed to cope with operating temperatures >600 C. The current coating technology (Pyromark High Temperature paint) has a solar absorptance in excess of 0.95 but a thermal emittance greater than 0.8, which results in large thermal losses at high temperatures. In addition, because solar receivers operate in air, these coatings have long term stability issues that add to the operating costs of CSP facilities. Ideal absorbers must have high solar absorptance (>0.95) and low thermal emittance (<0.05) in the IR region, be stable in air, and be low-cost and readily manufacturable. We propose to utilize solution-based synthesis techniques to prepare intrinsic absorbers for use in central receiver applications.

Characterization of Pyromark 2500 for High-Temperature Solar Receivers

Pyromark 2500 is a silicone-based high-temperature paint that has been used on central receivers to increase solar absorptance. The cost, application, curing methods, radiative properties, and absorber efficiency of Pyromark 2500 are presented in this paper for use as a baseline for comparison to high-temperature solar selective absorber coatings currently being developed. The directional solar absorptance was calculated from directional spectral absorptance data, and values for pristine samples of Pyromark 2500 were as high as 0.96–0.97 at near normal incidence angles. At higher irradiance angles (>40°–60°), the solar absorptance decreased. The total hemispherical emittance of Pyromark 2500 was calculated from spectral directional emittance data measured at room temperature and 600°C. The total hemispherical emittance values ranged from ∼0.80–0.89 at surface temperatures ranging from 100°C – 1,000°C. The aging and degradation of Pyromark 2500 with exposure at elevated temperatures were also examined. Previous tests showed that solar receiver panels had to be repainted after three years due to a decrease in solar absorptance to 0.88 at the Solar One central receiver pilot plant. Laboratory studies also showed that exposure of Pyromark 2500 at high temperatures (750°C and higher) resulted in significant decreases in solar absorptance within a few days. However, at 650°C and below, the solar absorptance did not decrease appreciably after several thousand hours of testing. Finally, the absorber efficiency of Pyromark 2500 was determined as a function of temperature and irradiance using the calculated solar absorptance and emittance values presented in this paper.© 2012 ASME

ABO3 (A = La, Ba, Sr, K; B = Co, Mn, Fe) perovskites for thermochemical energy storage

The use of perovskite oxides as a medium for thermochemical energy storage (TCES) in concentrating solar power systems is reported. The known reduction/oxidation (redox) active perovskites LaxSr1-xCoyMn1-yO3 (LSCM) and LaxSr1-xCoyFe1-yO3 (LSCF) were chosen as a starting point for such research. Materials of the LSCM and LSCF family were previously synthesized, their structure characterized, and thermodynamics reported for TCES operation. Building on this foundation, the reduction onset temperatures are examined for LSCM and LSCF compositions. The reduction extents and onset temperatures are tied to the crystallographic phase and reaction enthalpies. The effect of doping with Ba and K is discussed, and the potential shortcomings of this subset of materials families for TCES are described. The potential for long-term stability of the most promising material is examined through thermogravimetric cycling, scanning electron microscopy, and dilatometry. The stability over 100 cycles (450-1050 °C) of an LSCM com...

Reimagining liquid transportation fuels : sunshine to petrol.

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 projects end, we had demonstrated solar-driven conversion of CO{sub 2} to CO, a key energetic synthetic fuel intermediate, at 1.7% efficiency.

Solid Oxide Electrochemical Reactor Science

Solid-oxide electrochemical cells are an exciting new technology. Development of solid-oxide cells (SOCs) has advanced considerable in recent years and continues to progress rapidly. This thesis studies several aspects of SOCs and contributes useful information to their continued development. This LDRD involved a collaboration between Sandia and the Colorado School of Mines (CSM) ins solid-oxide electrochemical reactors targeted at solid oxide electrolyzer cells (SOEC), which are the reverse of solid-oxide fuel cells (SOFC). SOECs complement Sandias efforts in thermochemical production of alternative fuels. An SOEC technology would co-electrolyze carbon dioxide (CO{sub 2}) with steam at temperatures around 800 C to form synthesis gas (H{sub 2} and CO), which forms the building blocks for a petrochemical substitutes that can be used to power vehicles or in distributed energy platforms. The effort described here concentrates on research concerning catalytic chemistry, charge-transfer chemistry, and optimal cell-architecture. technical scope included computational modeling, materials development, and experimental evaluation. The project engaged the Colorado Fuel Cell Center at CSM through the support of a graduate student (Connor Moyer) at CSM and his advisors (Profs. Robert Kee and Neal Sullivan) in collaboration with Sandia.

Commercial PV Property Appraiser Survey: Summary of Results

Author(s): Hoen, B; Klise, G; Ambrosini, A; Garber, B; Thatcher, J | Abstract: Solar photovoltaic systems can be a valuable asset when attached to a property. Therefore, providing market participants with information and tools to credibly assess the value that PV adds to property is important. To that end, LBNL, SNL and AI conducted a survey of commercial appraisers to assess methods of valuing commercial properties with existing PV systems, current trends, and factors that help or hurt market adoption. The survey elicited 44 responses. Although an overwhelming majority of the respondents had conducted appraisals of properties with solar, how such systems are valued varied widely. Less than half of the respondents reported utilizing AI-endorsed tools such as PV Value ® or Ei Value ® for assignments, which may indicate a lack of awareness that such tools exist. A number of appraisers have taken the AI Residential a Commercial Valuation of Solar course and/or pursued a number of self-study avenues to increase their knowledge of PV systems. A majority indicated that they would be interested in taking an online course if it was offered. Overall, preliminary results point to a need for standardization of valuation metrics and a method of disseminating (e.g. classes) and utilizing (e.g. assessment tools) such metrics in order for appraisers to consistently evaluate and increase demand of properties with PV systems.