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P. Lackner, J. Hulva, E. Köck, W. Mayr-Schmölzer, J. Choi, S. Penner, U. Diebold, F. Mittendorfer, J. Redinger, B. Klötzer, G. Parkinson, M. Schmid:
"Water adsorption at zirconia: from the ZrO₂(111)/Pt₃Zr(0001) model system to powder samples";
Journal of Materials Chemistry A, 6 (2018), 17587 - 17601.

We present a comprehensive study of water adsorption and desorption on an ultrathin trilayer zirconia
fi
lm
using temperature programmed desorption (TPD), X-ray photoelectron spectroscopy (XPS), as well as
scanning tunneling microscopy (STM) at di
ff
erent temperatures. The saturation coverage is one H
2
O per
surface Zr atom, with about 12% dissociation. The monolayer TPD peak (180 K, desorption barrier 0.57

0.04 eV) has a tail towards higher temperatures, caused by recombinative desorption from defect sites
with dissociated water. STM shows that the defects with the strongest H
2
O adsorption are found above
subsurface dislocations. Additional defect sites are created by multiple water adsorption/desorption
cycles; these water-induced changes were also probed by CO
2
TPD. Nevertheless, the defect density is
much smaller than in previous studies of H
2
O/ZrO
2
. To validate our model system, transmission Fourier-
transform infrared absorption spectroscopy (FTIR) studies at near-ambient pressures were carried out on
monoclinic zirconia powder, showing comparable adsorption energies as TPD on the ultrathin
fi
lm. The
results are also compared with density functional theory (DFT) calculations, which suggest that sites with
strong H
2
O adsorption contain twofold-coordinated oxygen.