YU Research Group – Nano Energy Lab

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● Self-assembled Three-dimensional Carbon Nanotubes and Functionalization for Electrochemical Cells

As-synthesized carbon nanotubes are powdery, which requires assembly processes to make the material functional. This project studies the self-assembly process of carbon nanotubes during the synthesis process as well as seeks methods for controlling the porosity. Furthermore, the surface of the carbon nanotubes are functionalized for catalytic activities so that the three-dimensional porous carbon nanotubes sponges can be used for various electrochemical cells such as batteries, fuel cells, etc. for high capacity, oxygen reduction reactions, CO2 conversion, etc.

- G. Yang, W. Choi, X. Pu, C. Yu, “Scalable synthesis of bi-functional high-performance carbon nanotube sponge catalysts and electrodes with optimum C-N-Fe coordination for oxygen reduction reaction,” Energy Environ. Sci., 8, 1799-1807 (2015). - W. Choi, G. Yang, S. L. Kim, P. Liu, H.-J. Sue, C. Yu, “One-step synthesis of nitrogen-iron coordinated carbon nanotube catalysts for oxygen reduction reaction,” J. Power Sources, 313, 128-133 (2016). - W. Choi, K. Choi, C. Yu, “Ultrafast nanoscale polymer coating on porous 3D structures using microwave irradiation,” Adv. Funct. Mater., 28, 1704877 (2018).

● Next Generation Lithium-Sulfur Batteries with High Energy Density and Low Cost

This project is to overcome the key hurdle in deploying electric vehicles and renewable energy conversion systems such as solar panels by lowering the cost of rechargeable batteries as well as increasing their energy density. Our battery technology can potentially achieve an energy density five times higher than that of the current Li-ion batteries as well as a manufacturing cost as low as 1/300 of the cost of Li-ion batteries, based on the testing results with lab-scale batteries. High energy density Li-S batteries have been enabled by carbon nanotube sponges, serving as cathode. Porous and self-standing carbon nanotube sponges were used as catholyte (dissolved active material in electrolyte) reservoirs. The carbon nanotube sponges are composed of highly conductive carbon nanotubes enabling a 3D conductive framework. Li-S pouch cells fabricated in lab with size similar to small commercial Li-ion pouch cells also shows higher energy densities (cell level).

- G. Yang, J. Tan, H. Jin, Y. H. Kim, X. Yang, D. H. Son, S. Ahn, H. Zhou, C. Yu, “Creating effective nanoreactors on carbon nanotubes with mechanochemical treatments for high‐areal‐capacity sulfur cathodes and lithium anodes,” Adv. Funct. Mater., 28, 1800595 (2018). - X. Pu, G. Yang, C. Yu, “Trapping polysulfides in free-standing carbon nanofiber sponges for improving the performances of sulfur batteries,” J. Electrochem. Soc., 162, A1396-A1400 (2015). - X. Pu, G. Yang, C. Yu, “Liquid-type cathode enabled by 3D sponge-like carbon nanotubes for high energy density and long cycling life of Li-S batteries,” Adv. Mater., 26, 7456-7461 (2014). - X. Pu, G. Yang, C. Yu, “Safe and reliable operation of sulfur batteries with lithiated silicon,” Nano Energy, 9, 318-324 (2014).

● Thermally Chargeable Solid-State Supercapacitor for Wearable Electronics & Internet of Things (IoT)

Energy conversion and storage are becoming the two most important technologies for the rapid development of portable and wearable electronic devices. Typically, energy harvesting and storage devices are two different physical units, which should be connected together by a power management circuit to enable a sustainable power supply. For wearable applications, it is highly desirable to improve the integration level so that we can simplify the structure and minimize the energy loss between each unit. The goal of this research is to develop new self-charging flexible energy devices by integrating a thermal energy harvester into an electrochemical supercapacitor, which can simultaneously convert thermal energy into electricity and store electrical energy into chemical energy. Solid-state polymeric ion conductors have been utilized as thermal energy harvesters, which can produce high voltage by using thermally-driven ion diffusions (Soret effect) at a temperature gradient. Such an integrated device can be simply charged up by any temperature gradients (e.g., human body heat for wearable electronics).

- S. L. Kim, J.-H. Hsu, C. Yu, “Intercalated graphene oxide for flexible and practically large thermoelectric voltage generation and simultaneous energy storage,” Nano Energy, 48, 582-589 (2018). - S. L. Kim, H. T. Lin, C. Yu, “Thermally chargeable solid-state supercapacitor,” Adv. Energy Mater., 6, 1600546 (2016). - S. L. Kim, J.-H. Hsu, C. Yu, “Thermoelectric effects in solid-state polyelectrolytes,” Org. Electron., 54, 231–236 (2018).

● Flexible Thermoelectric Polymer Nanocomposites for Energy Harvesting and Cooling

Typical organic materials have low thermal conductivities that are best suited to thermoelectrics, but their poor electrical properties with strong adverse correlations have prevented them from being feasible candidates. Our composites, containing partially percolated single-wall carbon nanotubes and poly(3,4 ethylenedioxythiophene) (PEDOT) with tetrakis(dimethylamino) ethylene treatment show rarely reported n-type behavior and a high thermoelectric figure-of-merit up to ~0.5 at 300 K. A high power factor up to ~1050 µW/m-K^2 was achieved owing to relatively low carrier concentrations (resulting in high thermopower) and high mobility from carbon nanotubes (resulting in high electricl conductivity).

- H. Wang, J.-H. Hsu, S.-I. Yi, S. L. Kim, K. Choi, G. Yang, C. Yu, “Thermally driven large n-type voltage responses from hybrids of carbon nanotubes and poly(3,4-ethylenedioxythiophene) with tetrakis(dimethylamino)ethylene,” Adv. Mater., 27, 6855-6861 (2015). - J.-H. Hsu, W. Choi, G. Yang, C. Yu, “Origin of unusual thermoelectric transport behaviors in carbon nanotube filled polymer composites after solvent/acid treatments,” Org. Electron., 45, 182–189 (2017). - K. Choi, S. L. Kim, S.-I. Yi, J.-H. Hsu, C. Yu, “Promoting dual electronic and ionic transport in PEDOT by embedding carbon nanotubes for large thermoelectric responses,” ACS Appl. Mater. Interfaces, 10, 23891-23899 (2018). - S. L. Kim, K. Choi, A. Tazebay, C. Yu, “Flexible power fabrics made of carbon nanotubes for harvesting thermoelectricity,” ACS Nano, 8, 2377-2386 (2014). - D. Kim, Y. S. Kim, K. Choi, J. C. Grunlan, C. Yu, “Improved thermoelectric behavior of nanotube-filled polymer composites with poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate),” ACS Nano, 4, 513-523 (2010).

● Power Generation and Wastewater Treatment with Microbial Fuel Cells

Carbon nanotube (CNT) sponges are used as key materials for both cathode and anode of microbial fuel cells in order to replace precious metal based catalysts used in typical microbial fuel cells. For the cathode, the CNT sponge incorporated with nitrogen on the surface shows higher voltage output and power density. For the anode, CNT sponge showed excellent charge transfer (13 times lower charge transfer resistance compared to that of carbon felt) between its surface and microbes. Both cathode and anode demonstrate excellent long-term stability and substantially reduced cost compared to commercial Pt-based catalysts.

- G. Yang, C. Erbay, S.-I. Yi, P. de Figueiredo, R. Sadr, A. Han, C. Yu, “Bifunctional nano-sponges serving as non-precious metal catalysts and self-standing cathodes for high performance fuel cell applications,” Nano Energy, 22, 609-614 (2016). - C. Erbay, G. Yang, P. de Figueiredo, R. Sadr, C. Yu, A. Han, “Three-dimensional porous carbon nanotube sponges for high-performance anodes of microbial fuel cells,” J. Power Sources, 298, 177-183 (2015). - C. Erbay, X. Pu, W. Choi, M.-J. Choi, Y. Ryu, H. Hou, F. Lin, P. de Figueiredo, C. Yu, A. Han, “Control of geometrical properties of carbon nanotube electrodes towards high-performance microbial fuel cells,” J. Power Sources, 280, 347-354 (2015).

● Lithium-Air Batteries with Extremely High Energy Density and Improved Cycling Performance

Large capacity and long cycling performance nonaqueous Li-O2 batteries have been made with carbon nanotube (CNT) arrays containing in-situ decorated 𝛼-Fe2O3 nanoparticles as both a binder-free catalyst and a cathode. Fe2O3-decorated CNTs greatly helped to form Li2O involving the four-electron reduction pathway in addition to Li2O2 commonly formed via the one/two-electron reduction pathway, and thereby delivered a very large capacity of 26.5 Ah/g at the 1st discharge and a relatively long cycling performance (48 cycles with a capacity limit of 1.5 Ah/g).

- S. Jee, W. Choi, C. H. Ahn, G. Yang, H. K. Cho, J.-H. Lee, C. Yu, “Enhanced oxygen reduction and evolution by in-situ decoration of hematite nanoparticles on carbon nanotube cathode for high-capacity nonaqueous lithium-oxygen batteries,” J. Mater. Chem. A, 3, 13767-13775 (2015).

● Soft Robots Capable of Freeform Motions

This collaborative study presents systematic design of soft robots from material developments, sensing and control, motion planning to implementation in real applications. The fundamental research accomplishments of the proposed study will include: (1) exploring the use of IPMCs in reconfiguring structural patterns in auxetic metamaterials; (2) understanding the effects of various structural patterns and sizes on the free-from shapes and motions of auxetic metamaterials; (3) engineering new ionic polymer membrane composites (IPMCs) with improved actuation characteristics (faster response and minimum back relaxation); (4) designing computationally scalable methods for the control of continuum robot via primitive behaviors and employing models of these behaviors for motion planning.

Last updated: June-2019