Paper SS3-TuA9
Search for Chemicurrent during CO Oxidation on Pt/GaN and Pt/TiO2 Nanodiodes
Tuesday, November 10, 2009, 4:40 pm, Room N
| Session: |
Catalysis: Mechanisms & Morphology |
| Presenter: |
J.R. Creighton, Sandia National Laboratories |
| Authors: |
J.R. Creighton, Sandia National Laboratories
E.J. Heller, Sandia National Laboratories
K.H.A Bogart, Sandia National Laboratories
M.E. Coltrin, Sandia National Laboratories
E.N. Coker, Sandia National Laboratories
K.C. Cross, Sandia National Laboratories
|
| Correspondent: |
Click to Email |
In 2005, Gabor Somorjai’s group demonstrated the capture of chemical energy liberated during carbon monoxide oxidation on Pt and Pd surfaces by using a structure they described as a “catalytic nanodiode” [1-2]. This device is a Schottky diode where the metal contact is made of an ultrathin (~5 nm) catalytic metal, deposited on a wide bandgap semiconductor such as GaN or TiO2. During the exothermic oxidation of CO, some fraction of the chemical energy may be dissipated by creation of hot electrons in the catalytic metal, and some of these electrons are potentially collected on the semiconductor side of the Schottky barrier. In principle, this “chemicurrent” formed by hot electron generation, transport, and collection represents the conversion of chemical energy directly into electrical energy. For some conditions using a Pt/TiO2 nanodiode, a remarkable conversion efficiency of 3 electrons per 4 CO2 produced was measured [1]. We have fabricated several versions of catalytic nanodiodes using GaN and TiO2 films deposited and characterized in-house. During CO oxidation on Pt/GaN and Pt/TiO2 nanodiodes we also detect a current that is unambiguously a result of the chemical reaction. We measure current densities up to 100 nA/mm2 and reaction conversion efficiencies in the range of 10-5-10-3 electrons per CO2, which are quantitatively similar to reports in more recent publications [3-4]. However, the behavior of this chemical signal as a function of diode impedance indicates that it is derived from a voltage source, and not from a current source. In fact, the chemical signal is primarily, if not entirely, due to the thermoelectric voltage generated and/or modified by the exothermicity of the reaction. We have yet to find any conclusive evidence supporting true “chemicurrent” formation during CO oxidation on Pt/GaN or Pt/TiO2 nanodiodes.
References:
[1] Z.J. Xiao and G.A. Somorjai, J. Phys. Chem. B 109 (2005) 22530.
[2] J. Xiaozhong, A. Zuppero, J.M. Gidwani, and G.A. Somorjai, J. Amer. Chem. Soc. 127 (2005) 5792.
[3] J.Y. Park, J. R. Renzas, B.B. Hsu, and G.A. Somorjai, J. Phys. Chem. C, 111 (2007) 15331
[4] J.Y. Park, J. R. Renzas, A.M. Contreras, and G.A. Somorjai, Topics in Catalysis, 46 (2007) 217
(Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy under Contract DE-AC04-94AL85000.)