Dr. Sabolsky's research focuses on the development of piezoelectric/dielectric materials, chemical sensors, reforming catalyst, battery materials, solid-oxide and direct-carbon fuel cells, and ceramic separation membranes. This research includes the synthesis and electrochemical testing of complex oxide powders, ceramic nanomaterials, and novel ceramic monolithic structures to improve performance. Dr. Sabolsky has authored more than twenty papers in technical literature, and has received two patents.

In light of global warming concerns and the ever present need for domestic energy sources, never before has there been a call for the development of new energy systems that operate efficiently and cleanly on renewable fuels (like biofuels and potentially hydrogen) and abundant domestic fossil fuels. One such energy system is the solid-oxide fuel cell (SOFC) technology. SOFC's offer many advantages over other fuel energy conversion devices due to its high efficiency, high heat-recovery capabilities and fuel flexibility. The operation of SOFCs depends upon the reduction and incorporation of O_2- ions into an electrolyte material, and the transport of these ions across the electrolyte to the anode where the fuel is oxidized. SOFCs operate at higher temperatures (500-1000°C) where the electrolyte diffusivity of O_2- ions is high, while the electrolyte membrane remains an electronic insulator. The electrodes on each side of the electrolyte membrane provide both an electrical connection and electrocatalytic sites for oxygen reduction (cathode electrode) and fuel oxidation (anode electrode).

Electrolytes:

SOFCs have many challenges that limit the direct commercialization of these systems. The main issues are related to the high production costs, high operation temperature, and low durability of the ceramic cells themselves. Several parallel approaches are being pursued to reduce the cost of these systems by increasing cell power density and lowering the overall operating temperature. One approach to achieve both of these goals focuses on the development of new electrolytes that operate at lower temperatures within various contaminant fuel streams. Doped-zirconia (ZrO₂) has been the state-of-the-art electrolyte for decades due to its versatility. Doped- ZrO₂ possess high thermal, mechanical, and chemical stability over a broad range of temperatures/pressures. Unfortunately, their ionic conductivity is low within the desired temperature regime (400-800°C) needed for greater efficiency and durability.

The lower operating temperature would decrease SOFC cost, and therefore, increase application. There is a critical need for new high-performance electrolyte materials and the corresponding electrodes required for their electrochemical functionality. Research is required to develop the next generation of solid ionic electrolytes for these applications that display ionic conductivities exceeding 10^-2 S/cm at temperatures <600˚C. The typical approach to achieve this goal is through doping of various fluorite, perovskite, and pyrochlore structured materials to alter ionic vacancy concentration and order. Relatively few researchers have explored methods of manipulating the microstructure of bulk ceramic oxides to control diffusional kinetics. Research on controlling sintering, grain growth, and grain orientation of Bi₂Cu_xV_1-xO_5.5-z  and silicate oxyapatites (RE_10-x(SiO₄)₆O_3-1.5x where RE=La, Pr) ceramics are currently being completed within our research group.

Anodes:

One major issue limiting the application of SOFCs to Clean Coal technologies is the degradation of the anode upon exposure to trace amounts of impurities that exist within coal-derived syngas. Specifically, H₂S and PH₃ have been shown to have an immediate effect on cell performance for cells with Ni-based anodes. The nickel reacts to form various nickel-phosphide and -sulfide phases that inhibit catalytic activity. Thus, our work focuses on developing mixed-conducting oxides as alternate anodes that show stable long-term performance. Our studies not only exam the effect of the impurities in the new anodes and traditional cermet anodes, but the role that fuel delivery configuration has on cell performance and degradation.

Cathodes:

The widely used fabrication route to form cathode structures with graded porosity is through the sequential printing of multiple layers that are compositionally and microstructurally different. The porosity level is typically controlled by the particle size of the constituents and the partial sintering of thick-film powder compacts. The relatively low annealing temperature leads to incomplete densification of the thick film, and thus, formation of a porous microstructure. Various researchers have investigated incorporation of nano-catalysts materials into cathode microstructures produced by this simple, but labor intensive method with mixed results.

A more versatile, single-step technique that permits the direct engineering of porosity, pore morphology and size distribution is required in order to enhance cathode performance and allow for similar nano-catalyst impregnation. The goal of our work is to develop methods to form continuously gradient pore structures throughout the cathode material. In addition, the process may be distinctly controlled in order to incorporate nanomaterials and nanoporosity into the legs or interconnected cathode materials. The idea is to build a cathode architecture that possesses an exceptionally high TBP concentration near the electrolyte, while transitioning to an exceptionally open porous structure towards the cell surface.

Increasing environmental pressures to regulate emission gases has created an explicit requirement for the development of chemical sensors and sensor arrays to detect gases such as CO/CO₂, NO_x, H₂S, and SO_x, within high-temperature environments (>500°C). These sensors will enable an inexpensive implementation of sensor nets for in situ gas testing for three-dimensional fuel and emission maps within various industrial energy applications, such as current coal-fired power plants. The micro-sensors may also be applied within future Integrated Combined Cycle Gasification (IGCC) systems and direct-coal fuel cell generator systems, providing instantaneous feedback on fuel utilization and emission control systems.

Current chemical sensors based on chromatography, electrochemistry, and spectroscopy are not available to suit the desired application, cost, and performance within the proposed high temperature and harsh chemical environmental targets. Our research investigates chemi-resistive sensors that are based on stable high-temperature, semiconducting oxides which demonstrate a change in resistance due to surface interaction with select chemical species. In order to achieve the above mentioned performance and application targets, our work concurrently addresses issues relating to sensor stability, selectivity, and miniaturization of the chemi-resistive sensors. 

The objective of our research is to design a suitable battery that can maintain its structural integrity while enduring extreme stresses and environments, such as a large temperature gradients and large forces. In order to achieve these goals, our work focuses on the incorporation of active battery components within structural composite architectures. This process has the ultimate goal of merging the power supply directly into the structure of unmanned air vehicles (UAVs). By doing this, UAVs will be more functional and versatile due to massive volume, and potentially weight, reductions.

One route is to develop a solid-state Li-ion battery based on a glass-ceramic composite structure that can be reversibly operated above 4 V with >200 mAhg^-1 discharge capacity at ~25°C. Our research focuses on the synthesis and characterization of solid-state Li-ion electrolytes and compatible solid-state electrode systems, and the incorporation of these solid-state batteries within the vehicle support structure.

Another route is to develop a composite multifunctional Li-ion battery with tunable mechanical properties depending on the composition and microstructure of the battery components. Combining the mechanical structure and the battery function into a single architecture permits improvements in performance not possible through the individual components. The design of composite multifunctional batteries for optimal performance involves precise selection of materials, architectures, and the interconnection between the battery components.

Recently, greater attention towards various power harvesting strategies has increased due to the need for alternative and clean power sources.  Power harvesting is a process of collecting ambient or waste energy from the environment and transforming this mechanical, thermal, or electromagnetic energy into electrical power. The two most well-known power harvesting devices are solar cells and windmills. Another means of harvesting energy is through mechanical devices that directly transform mechanical movement or vibration into electrical power.

Piezoelectric energy-harvesting systems offer one of the most direct and intergraded structures for converting mechanical energy into electrical energy. Piezoelectric materials display the inherent nature of producing a dielectric polarization or voltage with the application of a stress. In simplistic terms, when a stress is applied to the ceramic element parallel to the direction of ionic polarization within the material, the element will reversibly deform in the direction of the polarization and an electric field (or increased polarization) will be created. This phenomenon can be mathematically represented as:

E= -(g₃₃X)      or        Q= -(g₃₃e^XX)

where E is electrical field, g is piezoelectric voltage constant (in 33-direction), X is stress, e^X is permittivity at constant stress, and Q is the total generated charge. The voltage or charge can be utilized in these systems in static or dynamic manner. A common application of an open circuit piezoelectric generator used in a dynamic manner is a spark generator for gas ignition in stoves and heaters. In contrast, piezoelectric generators used in lower frequency applications can be used to charge capacitors or batteries through properly designed electrical circuits. A simplistic electrical circuit containing piezoelectric generators includes diodes to prevent charge back-flow to the generators during oscillating loading and parallel capacitors to reduce voltage and temporarily store electrical energy. The goal of our work is to develop an electromechanical structure that directly converts wind and vibrational energy to electrical power through the use of piezoelectric materials. 

Research is on-going to identify micro-patterning methods for incorporating nanomaterials into single and array sensors.  Our work focuses on novel methods and in-depth investigation of processing issues in the deposition and micro-patterning of nanomaterial suspensions into complex 3-D architectures. 

Current work concentrates on the deposition of refractory nanomaterials through lithographic and direct-write techniques. This work investigates the effects of colloidal stabilization, suspension characteristics, photoresist composition, photoresist-suspension interactions, micro-mold geometry, and thermal processing.  The impact of this work will foster the inexpensive implementation of sensor arrays to a host of industrial and military applications where efficient electrochemical, electromechanical, or electromagnetic sensing is required.