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28. Bismuth Oxychloride Nanoflakes Enabled High Sensitivity Colorimetric UV Dosimetry.

Author

Troche, Kyle, Ramaiyan, Kannan, Boyle, Timothy J., and Garzon, Fernando H.

Abstract

Excessive exposure to sunlight's ultraviolet (UV) radiation causes adverse effects such as premature aging, sunburn, and skin cancers. Monitoring daily exposure to sunlight is essential to avoid developing health risks. Colorimetric UV sensors change color as a function of UV exposure, provide onsite information about the level of exposure, and can act as a personal wearable device to assist in making informed decisions on sunlight exposure. These sensors utilize radiation-induced reactions on a dye to produce a color change. Here, BiOCl based UV sensor is reported for monitoring UV exposure where a white-to-black color transformation is induced due to the creation of oxygen vacancies in BiOCl. This color transformation is not quantifiable in bulk BiOCl; hence BiOCl was purposely dispersed on filter paper to form petal-like nanostructures that help quantify the color change. Four different dye molecules, 6-carboxyfluorescein, 5-carboxyfluorescein, rhodamine-B, and Prussian blue were evaluated, where 6-carboxyfluorescein gave the best color contrast. The sensor responds to UVA, UVB, and UVC and with proper UV filters can be made selective for specific UV radiations. This unique colorimetric UV sensor can help manage personal UV exposure and reduce the risk of sun exposure ailments. [ABSTRACT FROM AUTHOR]

Published
2023
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29. Landscape disturbances in the Sumapaz páramo area during and after the Colombian armed conflict

Author

Mendez Garzon, Fernando Arturo and Valanszki, Istvan

Abstract

The Sumapaz páramo has been widely studied for its high supply of goods and ecosystem services provided to Bogotá, the central Colombian region and for its role as an ecological network linking the foothills rainforest of the Orinoquia and Amazonas with the montane forest of the Andean highlands. Sumapaz is the largest páramo in the world, with 333.420 ha; it is in Colombia's eastern Andean mountain range between 3,250 to 4,230 m.a.s.l. The landscape comprises a wide range of ecosystems, from the páramo and sub-páramo with montane forests, shrubs forests, and peatlands until the super-páramo of alpine tundra landscape with open vegetation of small bushes, frailejones (Espeletia sp) and grasslands. During the Colombian internal armed conflict and due to the strategic location of Sumapaz, the guerrillas found refuge in páramos and high mountains, generating a series of problems that strongly affected the landscape. They developed activities such as the construction of camps, collection and burning of firewood, deforestation and earthworks to build trenches, roads, guard posts, canalization and damming of water. Currently, the landscape disturbances are primarily due to fires, crops or pastures for livestock. This study presents a qualitative and quantitative assessment linking how disturbance rates are related directly to the conflict intensity data and the geographic location. We identified landscape disturbances, such as degradation and deforestation generated by direct causes such as military confrontations, antipersonnel mines, and trenches, or indirect causes such as crops, mining, livestock, or forced migration. We used Google Engine to perform the Hansen and Coded algorithm to identify these disturbances from 2001 to 2020 using Landsat TM 4-5, Landsat ETM+ 7, and Landsat 8 OLI satellite imagery. We found a noticeable pattern of higher landscape disturbance during the high-intensity conflict period (2001-2012) compared with a decrease in deforestation rates since the peace talks (2012-2016) and post-agreement period (2016-2020). Studies like the ones presented here can become a tool to understand the reasons behind the conflict and its consequences in highly vulnerable landscape networks and ecosystems, such as the páramo.

Published
2022
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45. Selective electrochemical oxidative coupling of methane mediated by Sr2Fe1.5Mo0.5O6-δ and its chemical stability.

Author

Ramaiyan, Kannan P., Denoyer, Luke H., Benavidez, Angelica, and Garzon, Fernando H.

Subjects
OXIDATIVE coupling, CHEMICAL stability, METHANE, CARBON dioxide in water, STEAM reforming, PARTIAL oxidation, NATURAL gas reserves
Abstract

Efficient conversion of methane to value-added products such as olefins and aromatics has been in pursuit for the past few decades. The demand has increased further due to the recent discoveries of shale gas reserves. Oxidative and non-oxidative coupling of methane (OCM and NOCM) have been actively researched, although catalysts with commercially viable conversion rates are not yet available. Recently, Sr 2 F e 1.5 + 0.075 M o 0.5 O 6 − δ (SFMO-075Fe) has been reported to activate methane in an electrochemical OCM (EC-OCM) set up with a C2 selectivity of 82.2%1. However, alkaline earth metal-based materials are known to suffer chemical instability in carbon-rich environments. Hence, here we evaluated the chemical stability of SFMO in carbon-rich conditions with varying oxygen concentrations at temperatures relevant for EC-OCM. SFMO-075Fe showed good methane activation properties especially at low overpotentials but suffered poor chemical stability as observed via thermogravimetric, powder XRD, and XPS measurements where SrCO3 was observed to be a major decomposition product along with SrMoO3 and MoC. Nevertheless, our study demonstrates that electrochemical methods could be used to selectively activate methane towards partial oxidation products such as ethylene at low overpotentials while higher applied biases result in the complete oxidation of methane to carbon dioxide and water. Catalytic conversion of methane to ethene is limited by poor conversion, selectivity, and catalyst stability. Here a solid oxide electrolysis process is reported as a promising method for selective, partial oxidation of methane with low overpotentials. [ABSTRACT FROM AUTHOR]

Published
2021
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46. Intragranular Phase Proton Conduction in Crystalline Sn1–xInxP2O7(x= 0 and 0.1)

Author

Kreller, Cortney R., Pham, Hieu H., Wilson, Mahlon S., Mukundan, Rangachary, Henson, Neil, Sykora, Milan, Hartl, Monika, Daemen, Luke, and Garzon, Fernando H.

Abstract

Materials that exhibit fast ionic conduction in the intermediate temperature range are highly sought after for applications in fuel cells, electrolyzers, and sensors. Initial reports on tin pyrophosphate indicted that this material exhibited excellent protonic conductivity at 100–300 °C and that transport occurred via proton hopping through the bulk crystalline lattice. In this work, we conclusively show that the high conductivity reported by other research groups is not attributable to the bulk crystalline phase. The proton conduction mechanism of well-characterized Sn1–xInxP2O7(x= 0 and 0.1) was investigated using ac impedance spectroscopy and inelastic neutron scattering. The crystalline MP2O7phase possesses negligible bulk conductivity below 600 °C. Above 600 °C, the total conductivity exhibits Arrhenius behavior with an activation energy of ∼1 eV, with an increase in conductivity observed for the In-doped sample. Inelastic neutron scattering data indicates that no appreciable changes in proton concentration occur between hydrated and dehydrated samples of SnP2O7while changes in proton vibrational mode amplitudes occur with indium doping. The vibrational modes identified for the two materials are consistent with atomistic models of the bulk crystalline conductivity mechanism, where our calculations show that doping of In does not increase the mobility; instead, it helps to incorporate protons. This is also consistent with the Arrhenius behavior of the conductivity in which the activation energy is very similar between the undoped and doped material but with the doped material showing a larger pre-exponential constant. Our modeling results indicate that the interoctahedra hop between two M–O–P bridges is the most dominant transport pathway irrespective of doping. This work helps resolve the ongoing discrepancies in the literature regarding the mechanism of proton conduction in this material system. There exist two distinct conduction mechanisms between stoichiometric Sn1–xInxP2O7and excess polyphosphate containing Sn0.9In0.1P2+xO7±z. Intragranular proton transport through the bulk crystalline Sn1–xInxP2O7material occurs only at elevated temperatures. An amorphous polyphosphate phase residing at the crystalline grain boundaries (not the intercrystalline grain boundaries of the metal pyrophosphate itself) is required to obtain the high conductivity at reduced temperatures reported in the literature.

Published
2024
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48. Chemical Stability of BaMg0.33Nb0.67-XFexO3-δin High Temperature Methane Conversion Environments

Author

Denoyer, Luke H, Benavidez, Angelica, Brearley, Adrian, Ramaiyan, Kannan, and Garzon, Fernando H.

Abstract

Doped perovskite metal oxide catalysts of the form A(BxM1-x)O3-δhave been instrumental in the development of solid oxide electrolyzers/fuel cells. In addition, this material class has also been demonstrated to be effective as a heterogeneous catalyst. Co-doped barium niobate perovskites have shown remarkable stability in highly acidic CO2sensing measurements/environments (1). However, the reason for their chemical stability is not well understood. Doping with transition metal cations for B site cations often leads to exsolution under reducing conditions. Many perovskites used for the oxidative coupling of methane (OCM) or the electrochemical oxidative coupling of methane (E-OCM) either lack long term stability, or catalytic activity within these highly reducing methane environments. The Mg and Fe co-doped barium niobate BaMg0.33Nb0.67-xFexO3-δshown activity in E-OCM reactors over long periods (2) (>100 hrs) with no iron metal exsolution observed by diffraction or STEM EDX measurements. In contrast, iron decorated BaMg0.33Nb0.67O3 showed little C2 conversion activity.

Published
2023
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49. Role of Dopants in Fine-Tuning the Electrical and Catalytic Properties of Barium Niobate Perovskites Towards High-Temperature Electrolyzer Application

Author

Ramaiyan, Kannan, Denoyer, Luke H, Benavidez, Angelica, and Garzon, Fernando H.

Abstract

Perovskite materials are used for high temperature electrochemical applications such as solid oxide fuel cells (SOFC) and electrolyzers due to their tunable conductivity and catalytic activity. However, high temperature operation poses significant challenges in both fabrication and durable operation that is further complicated by the operating environment. We studied barium niobates with various A and B site dopants. These doped niobates showed enhanced thermochemical stability in SOFC relevant conditions and catalytic activity towards methane activation. The redox behavior of the Nb4+/5+couple seem to be at a key reason behind this redox stability while the size and electronegativity of the dopants affect the electrical properties. The chemical stability was analyzed by TGA measurements followed by analysis of the perovskite powders using PXRD measurements. Impedance measurements were utilized to analyze their electrical conductivity. Our results demonstrate doped barium niobates as a promising candidate for stable operation in high temperature electrochemical applications.

Published
2023
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50. Bipropellant Enabled Solid Oxide Fuel Cell Stack Power Supply: Energy Agility for Space Vehicles

Author

Plumley, John Bryan, Benavidez, Angelica, Jemison, Noah, Spears, Andre, Elangovan, S, Pike, Jenna, Hollist, Michele, Larsen, Dennis, Garzon, Fernando H., and Peng, Thomas

Abstract

A Solid Oxide Fuel Cell (SOFC) system capable of running on the same fuel and oxidizer as an onboard bipropellant thruster can create enhanced operational flexibility. If a spacecraft needs thrust, the bipropellant can be ignited to provide thrust. If a spacecraft needs electric power, the spacecraft can consume bipropellant to generate auxiliary power. In this work, the proven bipropellant pair ammonia (NH3) and nitrous oxide (N2O) are shown to be a viable fuel and oxidant for SOFCs, as in situ thermal NH3cracking will generate H2and N2O decomposition will generate O2. A 5 cell SOFC stack produced 89 W when fueled with NH3and N2O. The results of this study demonstrate the potential for a bifunctional spacecraft system that can satisfy both operational power and on-orbit maneuverability requirements.

Published
2023
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