Associate Professor of Chemical Engineering
- Electrochemical Engineering
- Advanced Measurement and Modeling of Solid State Electrochemical Systems
- Kinetic, Transport, and Thermodynamic Properties of Solids
Solid-State Electrochemical Engineering, Electrocatalysis, Ionic Transport, Ceramics, Fuel Cells
The research of my group seeks to better understand the thermodynamic, kinetic, and transport properties of solids, and how these properties relate to electrochemical devices and processes. Electrochemical solids are used in a wide spectrum of applications, from sensors, batteries, and fuel cells to large-scale separations and processing of liquid fuels.
In many cases, electrochemical applications are developed or optimized using empirical data, or rules of thumb derived from well-studied systems. The purpose of our work is to provide improved measurement methods and analysis techniques that link device or process performance more directly to the properties and geometry of constituent materials. This approach allows us to better design electrochemical systems, choose or screen candidate materials, diagnose device degradation, and develop appropriate fabrication methods.
To fully understand the electrochemical properties and behavior of solids, we must bring together two well-established ways of viewing physical phenomena. The continuum view (e.g. concentration, potential, flux) is well established for understanding aqueous electrochemical systems, but lacks direct applicability to solids, whose properties differ from liquids in fundamental ways. The atomistic view (e.g. crystal and electronic structure, atomic motion, microstructure) provides a basis for understanding solid properties, but lacks direct linkages to electrochemical modeling and measurement. In order to bridge atomistic and continuum understanding, we must address a spectrum of length scales, both experimentally and theoretically. General questions include:
- What is the best and most meaningful way to measure electrochemical performance?
- How do we distinguish thermodynamic, kinetic, and transport effects in complex electrochemical systems?
- Once we understand the properties of a material, how do we link those properties quantitatively to device or system performance?
- In what way are the electrochemical properties of solids related to atomic and electronic structure?
- What role does secondary structure (microstructure or nanostructure) influence or determine properties?
- How do we best define continuum species and driving forces in a macroscopic model of transport and reaction?
- How does materials processing influence the electrochemical properties of solids?
As with many fields, progress in solid-state electrochemical engineering requires a two-pronged approach involving both experiment and modeling. On the experimental side, we employ transient measurements of system electrochemical behavior (a.c. impedance and current-interruption) in order to separate complex overlapping physical phenomena by timescale. We also develop novel methods of isolating and measuring the electrochemical properties of solids independently of the electrochemical system; this approach allows us to develop (and explore the validity of) electrochemical models without relying on adjustable parameters. These measurements include thermodynamic, kinetic, and transport measurements under unusual temperature and atmospheric conditions (using TGA, coulometry, magnetometry, and dilatometry), and materials characterization (using scanning electron microscopy, elemental spectroscopies, X-ray diffraction, and secondary ion mass spectrometry). Finally, some of our more recent work involves measuring the electrochemical behavior of micro-fabricated model systems, where we have control over length scales governing transport, reaction, and catalysis. This work has been done in collaboration with our Micro-Electronics Design Center.
On the theoretical side, our approach has been to break-down electrode reactions or device operation into individual physical processes, which can be modeled based on independent measurement. Some of our work involves analytical models of porous electrode behavior using perturbation methods. We have also begun to tackle nonlinear systems using a hybrid approach, treating the steady-state or step-transient equations with numerical finite-element methods, but preserving the analytical approach for small-amplitude perturbations (such as a.c. impedance). This approach allows us to best relate electrochemical behavior to independently-measurable parameters governing reaction, transport, and thermodynamics. On the atomic level, we have also been working on new theoretical treatments of defect and electronic structure that help us better explain the thermodynamic properties (oxygen exchange and chemical expansion) of mixed conducting oxides. In the future, we hope to use atomic modeling methods in conjunction with atomic and electronic-structure measurements (magnetometry and/or Solid-State NMR) to better rationalize or extrapolate properties of materials
- Lu, Y.X., Kreller, C., Adler, S.B. Measurement and Modeling of the Impedance Characteristics of Porous La1-xSrxCoO3-δ Electrodes. Journal of the Electrochemical Society 2009, 156(4), pp. B513-B525.
- Green, R.D., Liu, C.C., Adler, S.B. Carbon dioxide reduction on gadolinia-doped ceria cathodes. Solid State Ionics 2008, 179(17-18), pp. 647-660.
- Baskar, D., Adler, S. B. High Temperature Magnetic Properties of Sr-doped Lanthanum Cobalt Oxide (La1-xSrxCoO3-δ). Chem. Materials 2008, 20(8), pp. 2624.
- Wilson, J.R., Sase, M., Kawada, T., Adler, S. B. Measurement of Oxygen Exchange Kinetics on Thin-Film La0.6Sr0.4CoO3-δ Using Nonlinear Electrochemical Impedance Spectroscopy (NLEIS). Electrochemical and Solid-State Letters 2007, 10(5), pp. B81-B86.
- Adler, S.B., Chen, X.Y., Wilson, J.R. Mechanisms and rate laws for oxygen exchange on mixed-conducting oxide surfaces. Journal of Catalysis 2007, 245, pp. 91–109.
- Wilson, J.R., Kobsiriphat, W., Mendoza, R., Chen, H.Y., Hiller, J.M., Miller, D.J., Thornton, K., Voorhees, P.W., Adler, S.B., Barnett, S.A. Three-dimensional reconstruction of a solid-oxide fuel-cell anode. Nature Materials 2006, 5(7), pp. 541-544.
- Chen, X., Yu, J., Adler, S.B. Thermal and Chemical Expansion of Sr-Doped Lanthanum Cobalt Oxide (La1-xSrxCoO3-δ). Chem. Materials 2005, 17, pp. 4537.
- Adler, S. B. Factors Governing Oxygen Reduction in Solid Oxide Fuel Cell Cathodes. Chemical Reviews 2004, 104(10), pp. 4791-4843.
- Adler, S. B. Reference Electrode Placement in Thin Solid Electrolytes. J. Electrochem Soc. 2002, 149(5), pp. E166-E172.
- Adler, S. B. Mechanism and kinetics of oxygen reduction on porous La1-xSrxCoO3-δ electrodes. Solid State Ionics. 1998, 111(1-2), pp. 125-134.
- Adler, S. B., Lane, J. A.; Steele, B. C. H., “Electrode Kinetics of Porous Mixed-conducting Oxygen Electrodes,” J. Electrochem Soc. 1996, 143(11), pp. 3554.
- Adler, S. B., Reimer, J. A., Baltisberger, J., Werner, U. Chemical Structure and Oxygen Dynamics in Ba2In2O5. J. Amer. Chem. Soc. 1994, 116, pp. 675.