| AVS 57th International Symposium & Exhibition | |
| Surface Science | Wednesday Sessions |
| Session SS-WeA |
| Session: | Chemisorption and Surface Reactions |
| Presenter: | J.R. Creighton, Sandia National Laboratories |
| Authors: | J.R. Creighton, Sandia National Laboratories M.E. Coltrin, Sandia National Laboratories R.P. Pawlowski, Sandia National Laboratories K.C. Baucom, Sandia National Laboratories |
| Correspondent: | Click to Email |
Previous results from Gabor Somorjai’s group demonstrated the production of chemicurrent during catalytic reactions on Pt and Pd surfaces using a Schottky diode structure described as a “catalytic nanodiode” [1-2]. During the exothermic oxidation of CO, some fraction of the chemical energy may be dissipated by formation of hot electrons in the catalytic metal via electronic excitation. If the catalytic metal film is thin enough (nanometer scale) some of these hot electrons may be collected on the semiconductor side of the Schottky barrier in the form of a “chemicurrent”. We have fabricated several versions of catalytic nanodiodes, and during CO oxidation we also detect a current that is unambiguously a result of the chemical reaction. We typically measure current densities up to 100 nA/mm2 and reaction conversion efficiencies in the range of 10-5-10-3 electrons per CO2 produced; results which are quantitatively similar to reports in more recent publications [3-4].
However, details of the electronic nature this chemical signal indicates that it is derived from a voltage source; not from a current source. In fact, the chemical signal is primarily, if not entirely, due to the thermoelectric voltage generated by changes in the lateral temperature gradient between the two electrical contacts in the nanodiode. We have used a 3D heat transfer model to simulate the time dependent temperature profile in the nanodiode during CO oxidation on Pt/GaN devices. This information, along with independent experimental measurements of the Seebeck coefficient allows us to quantitatively simulate the thermoelectric voltage signal generated during a typical experiment involving time-dependent CO oxidation. Our results indicate that the nanodiode is simply operating as a thermal detector via a thermoelectric voltage. Unfortunately we have not yet found evidence supporting true “chemicurrent” formation during CO oxidation on Pt/GaN 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