DeCaluwe Group Techniques and Publications

CORES Research Group

Publications and Presentations
Electrochemistry · Surface Science · Reacting Flows

Publications

Citation numbers according to Google Scholar.

  1. DeCaluwe, S.C., Baker, A.M., Bhargava, P., Fischer, J.E., Dura, J.A., "Structure-property relationships at Nafion thin-film interfaces: Thickness effects on hydration and anisotropic ion transport." Nano Energy, 46, 2018, p. 91—100.

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    Lay Summary: The polymer Nafion is used in low-temperature fuel cells used in electric fuel cell vehicles (which run on hydrogen fuel and produce water as the only exhuast). In this paper, we study what hapens to the Nafion properties when the polymer films get very thin (< 100 nm thick).

    We show that the way Nafion interacts with nearby materials can affect how the polymer's molecules arrange themselves. When the polymer gets very thin, this impacts how much water the polymer can absorb and how it is able to move hydrogen ions to and from the fuel cell electrochemical reaction sites.

  2. Kogekar, G., Karakaya, C., Liskovich, G.J., Oehlschlaeger, M.A., DeCaluwe, S.C., Kee, R.J., "Impact of non-ideal behavior on ignition delay and chemical kinetics in high-pressure shock tube reactors." Combustion and Flame, 189, 2018, p. 1—11. Citations: 1.

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    Lay Summary: An equation of state is a mathematical formula (or set of formulae) that describe the behavior of chemical substances (solids liquids and gases). The ideal gas law is one commonly-known example. Here, we explore the impact of the equation of state (ideal gas law vs. a more accurate equation) on how the fuel n-dodecane combusts at high pressures.

    We find that the equation of state has a relatively small impact on the density during combustion of n-dodecane at up to 100 times atmospheric pressure. However, the equation of state has a significant impact on the reactivity of the species involved (i.e., the species activities), and this must be correctly incporporated for accurate combustion predicitons.


  3. Kee, B., Karakaya, C., Zhu, H. DeCaluwe, S.C., Kee, R.J., "The influence of hydrogen-permeable membranes and pressure on methane dehydroaromatization in packed-bed catalytic reactors." Ind. Eng. Chem. Res., 56(13), 2017, p. 3551—3559. Citations: 3.

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    Lay Summary: Methane Dehydroaromatization (MDA) is a way to turn cheap and plentiful methane into more valuable fuels, such as benzene. Here, we explore two possible methods to make MDA more efficient: use of a membrane to separate out reaction products (H2), and operation at high pressures.

    We find that hydrogen removal increases the rate at which methane is converted, but most of this increased conversion goes toward production of unwanted and harmful byproducts. Increasing the pressure decreases the methane conversion rate, but increases benzene prodution rates. This may be a viable path toward benzene production with more complicated reactor designs.

  4. DeCaluwe, S.C., Dhar, B.M., Huang, L., He, Y., Yang, K., Owejan, P., Zhao, Y., Talin, A.A., Dura, J.A., Wang, H., "Pore collapse and regrowth in silicon electrodes for rechargeable batteries." Phys. Chem. Chem. Phys., 17(17), 2015, p. 11301—11312. Citations: 11.

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    Lay Summary: Silicon is a promising material for rechargeable lithium batteries, as it can store significantly more energy per unit mass than current battery materials. However, it is not very durable, due to expansion and contraction during battery operation. Here, we use neutrons to study thin-film silicon anodes to better understand how it expands and contracts during battery cycling.

    We observe that small pores in the silicon film collapse and regrow during battery operation, acting as a sort of 'reservoir' to absorb some of the silicon volume expansion. This seems to help prevent the catastrophic breakup of the electrode, although minor degradation is still observed. These pores also help explain the volume expansion trends in this study and in several previous studies, which had not fully matched with predictions.

  5. DeCaluwe, S.C., Kienzle, P.A., Bhargava, P., Baker, A.M., Dura, J.A., "Phase segregation of sulfonate groups in Nafion interface lamellae, quantified via neutron reflectometry fitting techniques for multi-layered structures." Soft Matt., 10(31), 2014, p. 5763—5776. Citations: 29.

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    Lay Summary: The polymer Nafion is used in low-temperature (PEM) fuel cells used in electric fuel cell vehicles (which run on hydrogen fuel and produce water as the only exhuast). In this paper, we study very thin Nafion films (< 50 nm), similar to the thickness of the Nafion where many important fuel cell limitations occur.

    We confirm that the Nafion molecules spontaneously form sheet-like lamellae, and use the neutron measurements for a very accurate, quantitative description of this arrangement. This helps us understand movement of different chemical species (oxygen, hydrogen, water) and specifically how the Nafion binds to the solid surface, which can help future researchers make more durable or efficient fuel cells, in the future.

  6. Zhang, C.J., Grass, M.E., Yu, Y., Gaskell, K.J., DeCaluwe, S.C., Chang, R., Jackson, G.S., Hussain, Z., Bluhm, H., Eichhorn, B.W., Liu, Z., "Multielement activity mapping and potential mapping in solid oxide electrochemical cells through the use of operando XPS." ACS Catal., 2(11), 2012, p. 2297—2304. Citations: 37.

    Lay Summary: Solid Oxide Electrochemical Cells (SOECs) are high-temperature devices which convert energy between electrical and chemical (fuel + oxygen) forms. Here, we use a novel technique called Ambient Pressure XPS (AP-XPS) to understand the chemical reactions happening at the surfaces of some SOFC materials. XPS usually occurs at room temperature and under a vacuum, but AP-XPS can study material surfaces at higher temperatures and in relevant chemical environments.

    By tracking surface concentrations and electric potentials of active and inactive species, we are able to identify the electrochemically active region of the CeO2-x anode catalyst and directly evaluate the various surface overpotentials which contribute to performance losses in the SOECs.

  7. Eastman, S.A., Kim, S., Page, K.A., Rowe, B.W., Kang, S.H., DeCaluwe, S.C., Dura, J.A., Soles, C.L., Yager, K.G., "Effect of confinement on structure, water solubility, and water transport in Nafion thin films." Macromol., 45(19), 2012, p. 7920—7930. Citations: 104.

    Lay Summary: The polymer Nafion is used in low-temperature fuel cells used in electric fuel cell vehicles (which run on hydrogen fuel and produce water as the only exhuast). In this paper, we study what hapens to the Nafion properties (structure, ability to absorb water, and speed at which water can move inside the polymer [i.e. the water mobility]) when the polymer films get very thin (< 222 nm thick).

    We find that the polymer properties are mostly constant for films thicker than 60 nm, but ability to absorb water and the water mobility both decrease with decreasing thickness below 60 nm.

  8. Owejan, J.E., Owejan, J.P., DeCaluwe, S.C., Dura, J.A., "Solid electrolyte interphase in Li-ion batteries: Evolving structures measured in situ by neutron reflectometry." Chem. Mat., 24(11), 2012, p. 2133—2140. Citations: 71.

    Download Preprint Here.     Download Supplementary Information Here.

    Lay Summary: Advances in Li-ion batteries have enabled a range of energy storage applications for portable devices and intermittent renewable energy sources alike. One of the central remaining challenges in Li-ion batteries regards the solid electrolyte interphase (SEI), a protective layer in the battery that helps prevent breakdown of the battery materials. Improving this layer would lead to lighter and more durable batteries, but studying it is very difficult, because it is a very thin, chemically sensitive layer, buried inside the battery structure.

    Here, we use neutron scattering as a means to directly measure SEI thickness, porosity, and chemical composition during its growth. We find that the SEI is initially 4.0 nm thick, and grows thicker with addittional battery operation. We also find that the SEI evolves dynamically during the charging and discharging of the battery. Deposited materials are not permanently 'locked' in the SEI; rather, some components are deposited and re-dissolved continuously during battery operation.

  9. DeCaluwe, S.C., Grass, M.E., Zhang, C.J., El Gabaly, F., Bluhm, H., Liu, Z., Jackson, G.S., McDaniel, A.H., McCarty, K.F., Farrow, R.L., Linne, M.A., Hussain, Z., Eichhorn, B.W., "In situ characterization of ceria oxidation states in high-temperature electrochemical cells with ambient pressure XPS." J. Phys. Chem. C, 114(46), 2010, p. 19853—19861. Citations: 76.

    Download Preprint Here.     Download Supplementary Information Here.

    Lay Summary: Solid Oxide Electrochemical Cells (SOECs) are high-temperature devices which convert energy between electrical and chemical (fuel + oxygen) forms. Here, we use ambient pressure XPS (AP-XPS) to understand how the oxidation state of ceria (a catalyst that makes SOECs more tolerant to carbon and sulfur in fuels) changes as a function of operating conditions.

    The use of AP-XPS enables new insights into the properties of the ceria surface. First, we see that the surface has much less oxygen than the interior of ceria, likely due to surface strain energy. We also show that the amount of surface oxygen changes significantly during fuel cell operation, demonstrating that slow surface reaction rates limit ceria's performance in SOECs. Finally, we show the impact of mixed conductivity in ceria, as the reactions are able to occur much farther from the current collector (100s of microns) than in conventional SOEC materials.

  10. Zhang, C.J., Grass, M.E., McDaniel, A.H., DeCaluwe, S.C., El Gabaly, F., Liu, Z., McCarty, K.F., Farrow, R.L., Linne, M.A., Hussain, Z., Jackson, G.S., Bluhm, H., Eichhorn, B.W., "Measuring fundamental properties in operating solid oxide electrochemical cells by using in situ X-ray photoelectron spectroscopy." Nature Materials, 9(11), 2010, p. 944—949. Citations: 201.

    Download Preprint Here.     Download Supplementary Information Here.

    Lay Summary: Solid Oxide Electrochemical Cells (SOECs) are high-temperature devices which convert energy between electrical and chemical (fuel + oxygen) forms. Here, we demonstrate the first-ever use of ambient pressure XPS (AP-XPS) to study the active surface states in an operating SOEC.

    By evaluating the active catalyst and electrolyte surface chemical states and electric potentials, we directly resolve the surface voltahge losses in the SOEC, which directly match with conventional voltage measurements but give more specific information. We also use the change in surface concentrations and surface electric potentials to identify the active surface regions, which in the ceria electrode studied are much larger than in typical SOEC materials (e.g. nickel). Finally, by varying the ceria films thickness, we show that the ceria surface chemistry is a significant limiting factor in SOEC efficiency, with faster chemistry and higher efficiency found in thicker films.

  11. DeCaluwe, S.C., Zhu, H., Kee, R.J., Jackson, G.S., "Importance of anode microstructure in modeling solid oxide fuel cells." J. Electrochem. Soc., 155(6), 2008, p. B538—B546. Citations: 60.

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    Lay Summary: This paper looks at the importance of microstructure in modeling solid oxide fuel cell (SOFC) operation. SOFCs are high-temperature devices which convert chemical energy (fuel + air) to electrical energy. Here, we build a one-dimensional SOFC numerical model, and use it to understand the importance of various microstructural parameters in predicting SOFC performance.

    By comparing our simulations to previously published experimentals, we reach several key findings. First, we uncover a common error in porous media transport modeling, which persists back to the early 20th century. After correctly incorporating the tortuosity into transport calculations, we also find that the resistances due to gas transport, surface chemical reactions, and electrolyte-phase ion conduction are interrelated. For operating conditions where gas transport is limiting, these resistances cannot be calculated independent of one another.

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