Christen Courter, James Stewart,听and Tanja Cuk*
Journal of Physical Chemistry C, 2023, DOI:听
Water dissociation on transition metal oxide (TMO) surfaces regulates their catalytic activity in aqueous media. Ambient pressure X-ray photoelectron spectroscopy (AP-XPS) has differentiated TMO surfaces by the population of their first hydration layer on a scale between water molecularly absorbed and water fully dissociated into hydroxyl groups. Here, we show that electron-doping a single TMO (SrTiO3: STO) can also span this range, with the data on lightly (0.1 wt % Nb) and moderately (0.7 wt % Nb) doped STO suggestive of partial and full water dissociation, respectively. The hydroxyl coverage is a factor of 9 greater in 0.7% Nb STO than in 0.1% Nb STO at low relative humidity (鈭�10鈥�3听% RH) and a factor of 2 greater at 1% RH, for which multilayers have already formed. Given the lack of a clear differentiation in surface morphology and termination, stoichiometry, or chemical environment of the two doped surfaces, the suggestion is made that the factor of 鈭�10 increase in electron density is the most likely origin of the marked increase in water dissociation across RH. Nonetheless, since the electron density delocalizes across many titanium oxygen bonds while surface characterizations are site-based, defining similar enough surfaces for which such a collective effect dominates remains a topic of future work. This work provides a benchmark for the effect of delocalized electron density, which can now be further tested by theoretical calculations and a broader material scope of low-to-moderately doped TMOs.
