The term ‘electrionics’ is synthesis of the words ‘electronic’and ‘ionic’ and materials that exhibit coupled interactions are termed as electrionic materials.
Electrionic materials include a diverse selection – from soft biological self-assemblies to organic polymers and hard inorganic ceramics. The fundamental property of electrionic materials have been leveraged to create devices – sensors, actuators, energy conversion and storage devices.
Ionic Redox Transistor
Energy Environ. Sci., 2016, 9, 2555-25621
The ionic redox transistor is a conducting polymer membrane in which ion transport is regulated by its redox state. In the case of our implementation, the magnitude of ionic current through the membrane is dependent on the reduced/oxidized state and allows for the membrane to be switched between ON/OFF state. Our results indicate that ionic current across the polymer in its reduced state is facilitated by the affinity of cations to immobile anionic dopant (DBS) and increases with concentration and applied transmembrane potential. The first generation of ionic redox transistor has a maximum conductance of 30μS/cm and a current gain of 60X as the polymer switches between oxidized (Vm>-200mV) and reduced state (Vm<-600mV), as shown in the figure below.
The demand for rechargeable electrochemical energy storage with high specific energy (SE) and specific power (SP) is driven by drivetrain power and energy requirements in ground transportation, unmanned aerial vehicles (UAVs), electrification of avionics, and miniaturization of consumer-electronic gadgets. Electric vehicles powered by Li-ion batteries are limited by short driving range, long recharge time and capacity fade to compete with fossil fuel-powered vehicles. Alternatives to Li-ion batteries such as supercapacitors and redox flow batteries with comparably high specific power and rapid recharge/refill have poor energy density due to self-discharge.
The scientific challenges in designing rechargeable batteries with high SE, SP and high MPMs can be understood from the mechanics of charge storage in electrode materials. It should be noted that the projected technology roadmap for rechargeable lithium-ion batteries lacks a practical solution to design batteries with high GED, SP and 100s of MPM (as shown in MPM plot). A true mass-market adoption of electric vehicles for transportation and aerial vehicles will require technologies that do not compromise on MPM.
Ongoing research in the lab address these issues by designing novel architectures for Lithium ion batteries, fundamental characterization experiments to study electrodes and looking at alternative battery chemistries.
Mechanoelectrochemistry is the study of charge and mass transport, volumetric expansion and dynamic evolution of localized stress/strain. My group has pioneered recent advances in scanning electrochemical microscopy and shear force imaging (SECM+SF imaging) through structural models of nanoelectrodes and surface-tracking techniques. These developments now enable our group to be the first to study the evolution and dynamics of ion transport into and out of cathodes and anodes for batteries. This knowledge will be essential for building high performance Li-ion batteries for aerospace and automotive applications. The SECM+SF Imaging hardware and correlated fluorescent imaging platform (SECM+SF+FL) in my group as shown in the figure below is unique to our lab. This simultaneous electrochemical, topography and optical imaging is applicable for electroactive surfaces, cells and tissues and will allow my group to collaborate with other researchers in mechanical engineering, material science, chemistry, cellular and molecular biology and play a supportive role in new materials development.
Ionic smart materials that are fabricated with biological macromolecules are referred to as ‘Biomolecular materials’ (or) ‘Bioderived materials’. Starting from Prof. Sundaresan’s doctoral thesis on ‘Biological Ion Transporters as Gating Devices for Chemomechanical and Chemoelectrical Energy Conversion’, research on bimolecular materials has been one of our major thrusts and we continue to make significant contributions in this area. This research group’s work in this area has led to Dr. Hao Zhang’s doctoral thesis and Robert Northcutt’s master’s thesis at Virginia Commonwealth University.
Bioinspiration has ‘seeded’ innovative and simple solutions to complex engineering problems. Our group looks to biology at the nanoscale towards the development of engineering solutions and this page presents a glimpse of some of our projects that have this flavor.
Bioderived Ionic Transistors
A novel active material system is formed from integrating the ionic properties of a bio-derived membrane and a conjugated polymer into a thin-film hybrid membrane. This hybrid membrane is a laminate arrangement of bioderived membrane and a conjugated polymer and referred to as a Bioderived Ionic Transistor (BIT). We are investigating changes to the physical properties of a conjugated polymer membrane using proteins (channels, ions and pumps) in bio-derived membranes and developing techniques to fabricate this assembly into a thin-film device for sensing, controlled actuation and energy storage. The research objective of this program is the development of a hybrid membrane that can respond to low power electrical signal (nanowatt) or low concentration chemical trigger and perform electrochemical work using ambient chemical gradients.
R. Northcutt, and V.B. Sundaresan, Fabrication and characterization of an integrated ionic device from suspended polypyrrole and alamethicin-reconstituted lipid bilayer membranes. Smart Materials and Structures, 2012. 21(9): p. 094022.
H. Zhang, S. Salinas, and V.B. Sundaresan, Conducting polymer supported bilayer lipid membrane reconstituted with alamethicin. Smart Materials and Structures, 2011. 20(9): p. 094020.
Biotemplated Polypyrrole Membranes
Sundaresan and Salinas discovered the formation of nanostructured polypyrrole membranes during the electropolymerization of pyrrole with phospholipid vesicles. This novel, biologically inspired one-step electropolymerization process (or, biotemplating) produces a nanostructured polypyrrole (PPy) membrane using unilamellar phospholipid vesicles. Biotemplated electropolymerization of PPy doped with dodecylbenzenesulfonate (DBS) (above critical micellar concentration (cmc)) consists of 100mM pyrrole and 2.5 mg.ml-1 1,2-diphytanoyl-sn-glycero-3-phosphocholine (DPhPC) vesicles over gold-evaporated silicon-silicon nitride wafers. From SEM imaging, columnar structures measuring 4-5µm due to DBS- micelles along with ϕ1-1.5 µm sponge-like nodules due to DPhPC templating span the thickness of the biotemplated PPy(DBS) and increase the interfacial surface area between the PPy(DBS) membrane and electrolytic solution. Charge capacity of the PPy(DBS) membranes are quantified by cyclic voltammetry at various concentrations of NaCl and LiCl and normalized to the mass of the membrane. From cyclic voltammetry, biotemplated membranes have a 45% increased anodic current vs planar and the capacitance for a monovalent cation is 666.7 F.g-1 for a 2.5 mm2 projected area. Biotemplated membranes are more robust than the planar counterparts (100s of cycles vs 10s in high salt concentrations) and can be used for fabricating flexible electrodes and packed into tight geometries for designing novel power sources. Ongong research addresses the following research questions: role of the phospholipids in the final structure of the PPy(DBS) membranes, charge storage in PPy(DBS)-DPhPC matrix using scanning electrochemical microscopy, structure-function (charge storage) relation and design rules for battery and supercapacitor electrodes.
R. Northcutt and V.B. Sundaresan, Phospholipid Vesicles as Soft Templates for Electropolymerization of Nanostructured Polypyrrole Membranes with Long Range Order. Journal of Materials Chemistry A, 2014 (DOI: 10.1039/C4TA02352H)
R. Northcutt and V.B. Sundaresan, “Characterization of Electrochemical Capacity of Biotemplated Conducting Polymer Membrane”, Proceedings of 2013 ASME Conference on Smart Materials, Adaptive Structures and Intelligent Systems, Bioinspired Smart Materials and Structures Symposium, Sep 16-18, 2013, Snowbird, UT.
S. Salinas and V.B. Sundaresan, “Integrated Bioderived-Conducting Polymer Membrane Nanostructures for Energy Conversion and Storage”, Proceedings of 2012 ASME Conference on Smart Materials, Adaptive Structures and Intelligent Systems, Bioinspired Smart Materials and Structures Symposium, Sep 19-21, 2012, Stone Mountain, GA.
Other papers published by Sundaresan and colleagues on Bioderived Materials
V. B. Sundaresan, S. Sarles, and D. Leo, “Bioderived Smart Materials,” in Encyclopedia of Nanotechnology, B. Bhushan, Ed., ed: Springer Netherlands, 2012, pp. 201-213.
V. B. Sundaresan and D. J. Leo, “Chemoelectrical Energy Conversion of Adenosine Triphosphate Using ATPases,” Journal of Intelligent Material Systems and Structures, vol. 21, pp. 201-212, 2010.
V.B. Sundaresan, S. Sarles, D. Leo, Characterization of porous substrates for biochemical energy conversion devices, Proceedings of SPIE Vol. 6928, 69280K (2008).
V. B. Sundaresan and D. J. Leo, “Modeling and Characterization of a Chemomechanical Actuator Using Protein Transporters,” Sensors and Actuators B: Chemical, vol. 131, pp. 384-393, 2008.
V. B. Sundaresan and D. J. Leo, “Controlled Fluid Transport Using ATP-Powered Protein Pumps,” Smart Mater. Struct., vol. 16, pp. S207-S213, 2007.
V. B. Sundaresan and D. J. Leo, “Chemomechanical Model for Actuation Based on Biological Membranes,” Journal of Intelligent Material Systems and Structures, vol. 17, pp. 863-870, 2006.
V. B. Sundaresan, C. Homison, L. M. Weiland, and D. J. Leo, “Biological Transport Processes for Microhydraulic Actuation,” Sensors and Actuators B:Chemical, vol. 123, pp. 685-695, 2007.