Publications Details

Origin and Tunability of Unusually Large Surface Capacitance in Doped Cerium Oxide Studied by Ambient-Pressure X-Ray Photoelectron Spectroscopy

Gopal, Chirranjeevi B.; El Gabaly Marquez, Farid E.; McDaniel, Anthony H.; Chueh, William C.

The surface chemical capacitance of ceria and SDC was investigated using in situ ambient pressure X-ray photoelectron spectroscopy (APXPS) in H2 H 2O environments at elevated temperatures. The spectra were collected in situ after equilibrating the samples under oxygen chemical potentials spanning -2.95 and -3.44 eV versus 1 atm O2. Consequently, the volumetric chemical capacitance of the surface, in the range of 103-104Fcm-3, is nearly two orders of magnitude larger than that of the bulk. Addition of Sm leads to a slight decrease of surface Ce3+ concentration, but a 10-fold enhancement in the surface capacitance under H2 H 2O atmospheres. Our hypothesis for this observation is that Sm lowers defect interactions. The areal surface capacitance calculated for SDC is in good agreement with literature values extrapolated from electrochemical measurements.