| AVS 62nd International Symposium & Exhibition | |
| Thin Film | Tuesday Sessions |
| Session TF-TuA |
| Session: | ALD for Emerging Applications |
| Presenter: | Jasmine Wallas, University of Colorado, Boulder |
| Authors: | J.M. Wallas, University of Colorado, Boulder M.J. Young, University of Colorado, Boulder C.B. Musgrave, University of Colorado, Boulder S.M. George, University of Colorado, Boulder |
| Correspondent: | Click to Email |
Capacitive deionization (CDI) is a promising water desalination technique based on the reversible electrosorption of anions (Cl-) and cations (Na+). Traditional CDI relies on ion storage in the electric double layer (EDL) on the surface of carbon electrodes. Additional ion storage can be achieved through charge storage in thin films of various materials, such as manganese oxide, that are deposited on the electrodes. In this work, we have demonstrated a dramatic improvement in reversible Na+ ion storage using MnO2 films on electrodes prepared using atomic layer deposition (ALD).
The MnO2 films were prepared by first growing MnO ALD films using bis(ethylcyclopentadienyl) manganese and H2O on flat Ti electrodes. These MnO films were then electrochemically oxidized to MnO2. Conversion of MnO to MnO2 was monitored during electrochemical oxidation with cyclic voltammetry. A large increase in capacitance occurred concurrently with the conversion to MnO2. The reversible adsorption of Na+ under applied potential in NaCl solutions was then confirmed with electrochemical quartz crystal microbalance (E-QCM) analysis. Adsorption of Na+ and an elemental composition of Na0.25MnO2 after Na+ adsorption was further verified with x-ray photoelectron spectroscopy (XPS) studies.
MnO2 films on flat Ti electrodes dramatically increased the ion storage from NaCl solutions. A maximum areal capacitance of 5.6 mF/cm2 was observed from MnO2 films prepared from MnO ALD films with an initial thickness of 447 Å. This areal capacitance is >170 times larger than the areal capacitance of an uncoated Ti electrode. MnO2 films were also prepared on electrodes composed of high surface area carbon nanotubes (CNTs) using 200 cycles of MnO ALD and electrochemical oxidation. These MnO2-coated CNT electrodes also displayed a significant increase in areal capacitance compared with uncoated CNT electrodes. These results indicate that MnO2 coatings on electrodes could substantially enhance the charge storage for CDI and water desalination.