| AVS 61st International Symposium & Exhibition | |
| Energy Frontiers Focus Topic | Tuesday Sessions |
| Session EN+EM+NS-TuA |
| Session: | Charge Storage Materials and Devices |
| Presenter: | Markus Gnerlich, University of Maryland, College Park |
| Authors: | M. Gnerlich, University of Maryland, College Park E.I. Tolstaya, University of Maryland, College Park J. Culver, University of Maryland, College Park D. Ketchum, University of Maryland, College Park R. Ghodssi, University of Maryland, College Park |
| Correspondent: | Click to Email |
The 3D micro-supercapacitor reported here utilizes a novel bottom-up assembly method that combines genetically modified Tobacco mosaic virus (TMV-1Cys) with deposition of RuO2 on multi-metallic microelectrodes. The nanostructured RuO2 coating is selectively deposited on the electrodes due their unique composition, which is a significant advantage for microfabrication process integration. Test results show electrode capacitance as high as 18 mF/cm2 in 1.0M H2SO4 electrolyte and 7.2 mF/cm2 in solid Nafion electrolyte.
The device fabrication involves the photolithographic patterning of titanium nitride (TiN) microelectrodes with Au cap on top of polyimide micropillars supported by a silicon wafer. A schematic cross section of the device is shown in Figure 1 and a photograph of the fabricated chip in Figure 2. The complexity of the self-assembly process in multiple chemically reactive solutions required the development of a special kind of micro-electrode. The TiN functions as a chemically resistant current collector, the Au cap as an adhesion layer for the TMV-1cys, and the Ni pad as a sacrificial material during the RuO2 deposition process. After microfabrication, each chip is submerged in TMV-1Cys solution for 24 hours and then transferred to a 0.5% solution of RuO4. A nanostructured coating of RuO2 forms on all exposed electrode areas as the Ni is sacrificed in a galvanic displacement reaction. EDX spectral imaging of the constituent elements on the electrode demonstrates selective RuO2 coating (Figure 3), and SEM images of the electrodes before and after TMV/RuO2 coating shows the TMV-1Cys/RuO2 nanostructures (Figure 4).
Cyclic voltammetry (CV) was performed from 0-800mV versus Ag/AgCl at 10 mV/s in 1.0M H2SO4 electrolyte. Figure 5 shows the CV curves, and Figure 6 shows the associated capacity fading, which was insignificant after 100 cycles for electrodes annealed at 150°C. Separately prepared chips were coated with Nafion dispersion and tested in a controlled humidity environment. The measured capacitance drops from 18 to 7.2 mF/cm2 per electrode due to ionic conductivity limitations, but 80% capacity is retained after 12,000 cycles (Figure 7). Associated rate capability (Figures 8-9) shows 60% capacity is retained when comparing 3 uA/cm2 to 3000 uA/cm2, and the low leakage current of only 5 nA (Figure 10) enables use in a wide variety of energy storage applications.
The primary challenge of nanomaterials is often integration into microfabrication processes. The RuO2 electrode developed here is optimized for compatibility with standard microfabrication steps by using a novel bottom-up assembly approach for manufacturing micro-supercapacitors.