Alina Kozinda

Uniformly Embedded Metal Oxide Nanoparticles in Vertically Aligned Carbon Nanotube Forests as Pseudocapacitor Electrodes for Enhanced Energy Storage

Carbon nanotube (CNT) forests were grown directly on a silicon substrate using a Fe/Al/Mo stacking layer which functioned as both the catalyst material and subsequently a conductive current collecting layer in pseudocapacitor applications. A vacuum-assisted, in situ electrodeposition process has been used to achieve the three-dimensional functionalization of CNT forests with inserted nickel nanoparticles as pseudocapacitor electrodes. Experimental results have shown the measured specific capacitance of 1.26 F/cm(3), which is 5.7 times higher than pure CNT forest samples, and the oxidized nickel nanoparticle/CNT supercapacitor retained 94.2% of its initial capacitance after 10,000 cyclic voltammetry tests.

Flexible energy storage devices based on lift-off of CNT films

We report a transfer process for CNT films with intrinsic bottom metal contacts to construct mechanically bendable, densely aligned carbon nanotube (CNT) forests for energy storage devices. The flexible electrode created and investigated as a supercapacitor has the following salient features: (1) excellent transfer of charge from the aligned CNTs to the substrate, (2) simple fabrication, and (3) easy integration with a variety of surfaces and topographies. Preliminary testing results with a CNT forest of 5 × 10 mm2 in area on Au/Kapton® film show a specific capacitance of 7.0 mF/cm2.

ALD ruthenium oxide-carbon nanotube electrodes for supercapacitor applications

This work presents the first demonstration of atomic layer deposition (ALD) ruthenium oxide (RuO2) and its conformal coating onto vertically aligned carbon nanotube (CNT) forests as supercapacitor electrodes. Specific accomplishments include: (1) successful demonstration of ALD RuO2 deposition, (2) uniform coating of RuO2 on a vertically aligned CNT forest, and (3) an ultra-high specific capacitance of 100 mF/cm2 from prototype electrodes with a scan rate of 100 mV/s. Advantages of the ALD method include precise control of the RuO2 layer thickness and composition without the use of CNT-binder molecules. In addition to high capacitance, preliminary results indicate that the ALD RuO2-CNTs have good stability over repeated cycling. Besides its use in supercapacitors, ALD-RuO2 has potential NEMS applications: in biosensors and pH sensing [1], as a strong oxidative material in multiple chemical processes [2], and in catalytic reactions for photocatalytic systems [3].

A hybrid supercapacitor using vertically aligned CNT-polypyrrole nanocomposite

We have successfully demonstrated, for the first time, the fabrication of vertically aligned carbon nanotube (VACNT)-polypyrrole (PPY) nanocomposites as a “hybrid supercapacitor” material directly integrated on silicon-based electrodes. In contrast to previous works, three distinctive achievements have been accomplished: (1) a “hybrid supercapacitor” using VACNT forest with electroplated PPY and dodecylbenzenesulfonate (DBS) as a dopant in acetonitrile, (2) realizing 500% higher capacitance as compared to the capacitance of electrodes made of VACNT or DBS-doped PPY alone, and (3) highly reversible cycling between -1 V and +1 V with improved knee frequency at 797 Hz. As such this hybrid nanocomposite could become a new class of material for future supercapacitors.

Stackable cow dung based microfabricated microbial fuel cells

μL-scale microbial fuel cell (μMFC) technology has the potential to serve as an efficient renewable energy harvester for a variety of applications ranging from, on chip devices to autonomous sensors in remote locations. However, low voltage and power outputs have restricted such microbial fuel cells (MFCs) from most practical applications. To bypass this limitation, we present a stackable microfabricated high-voltage cow dung-based μL-scale microbial fuel cell (CDFC) that utilizes a complex natural substrate (cow dung) and microstructures to attain higher voltages and power densities. Specifically utilizing micropillars which increased the electrode surface area 155 % compared to planar electrodes and a rich microbial consortium in the cow dung. Experimental results for the CDFC revealed open circuit potentials (OCPs) of 0.85±0.05 V, which represent the highest reported for a μMFC thus far. The CDFC was also found to produce power densities of 95±10 W/m3. By using two CDFCs stacked in series OCPs were increased by approximately 100%. These results suggest that the CDFC methodology represents a big step towards making μMFCs viable energy harvesters for both electronic and biological applications.

Amorphous silicon-coated CNT forest for energy storage applications

This work is based on developing an amorphous silicon-coated, vertically aligned carbon nanotube (CNT) forest for energy storage applications. The architecture of the electrode has three valuable features: (1) enhanced charge transfer via aligned CNTs to the substrate, (2) excellent charge storage capability via amorphous silicon, and (3) the preservation of high surface area and porosity with enhanced energy storage capacity. As such, this work could offer a new type of nanomaterial for energy storage applications. A supercapacitor electrode is used in this work for the energy storage demonstration.

ALD titanium nitride coated carbon nanotube electrodes for electrochemical supercapacitors

We present titanium nitride (TiN) coated carbon nanotube (CNT) forest electrodes by means of atomic layer deposition (ALD) to store charges in the electrochemical supercapacitors for the first time. The specific achievements as compared with the state-of-art supercapacitor electrodes include: (1) 400 times higher capacitance than a flat-shape electrode; (2) conformal and uniform coating of TiN; and (3) greater than 500% enhancement of electrochemical capacitance at 81mF/cm2 than CNT electrodes without TiN at 14mF/cm2 due to increased oxygen vacancies on the TiN surfaces. As such, this work presents a new path to increase energy density of supercapacitors using TiN-based porous materials.

Solid-state flexible micro supercapacitors by direct-write porous nanofibers

Solid-state flexible micro supercapacitors based on porous and conducting polymer nanofibers via the direct-write, near-field electrospinning process have been constructed. Testing results have shown a capacitance of 0.3mF/cm2, 30X larger as compared with those of flat electrodes. Key innovations of this work include: (1) densely-packed, porous 3D nanostructures with conductive nanofibers via the near-field electrospinning process; (2) flexible solid-state micro electrodes with high energy density using the pseudocapacitive effect; and (3) simple yet versatile manufacturing process compatible with various substrates and surfaces. As such, this technology is readily available to make practical MEMS energy storage devices.