ABSTRACT
The adsorption properties of CO2 on the SrTiO3(001) surface were investigated using ambient pressure X-ray photoelectron spectroscopy under elevated pressure and temperature conditions. On the Nb-doped TiO2-enriched (1 × 1) SrTiO3 surface, CO2 adsorption, i.e., the formation of CO3 surface species, occurs first at the oxygen lattice site under 10-6 mbar CO2 at room temperature. The interaction of CO2 molecules with oxygen vacancies begins when the CO2 pressure increases to 0.25 mbar. The adsorbed CO3 species on the Nb-doped SrTiO3 surface increases continuously as the pressure increases but starts to leave the surface as the surface temperature increases, which occurs at approximately 373 K on the defect-free surface. On the undoped TiO2-enriched (1 × 1) SrTiO3 surface, CO2 adsorption also occurs first at the lattice oxygen sites. Both the doped and undoped SrTiO3 surfaces exhibit an enhancement of the CO3 species with the presence of oxygen vacancies, thus indicating the important role of oxygen vacancies in CO2 dissociation. When OH species are removed from the undoped SrTiO3 surface, the CO3 species begin to form under 10-6 mbar at 573 K, thus indicating the critical role of OH in preventing CO2 adsorption. The observed CO2 adsorption properties of the various SrTiO3 surfaces provide valuable information for designing SrTiO3-based CO2 catalysts.
ABSTRACT
Depth profiling is an essential method to investigate the physical and chemical properties of a solid electrolyte and electrolyte/electrode interface. In conventional depth profiling, various spectroscopic tools such as X-ray photoelectron spectroscopy (XPS) and secondary ion mass spectroscopy (SIMS) are utilized to monitor the chemical states along with ion bombardment to etch a sample. Nevertheless, the ion bombardment during depth profiling results in an inevitable systematic error, i.e., the accumulation of mobile ions at the electrolyte/electrode interface, known as the ion pile-up phenomenon. Here, we propose a novel method using bias potential, the substrate-bias method, to prevent the ion pile-up phenomena during depth profiling of a solid electrolyte. When the positive bias potential is applied on the substrate (electrode), the number of accumulating ions at the electrolyte/electrode interface is significantly reduced. The in-depth XPS analysis with the biased electrode reveals not only the suppression of the ion pile-up phenomena but also the altered chemical states at the interfacial region between the electrolyte and electrode depending on the bias. The proposed substrate-bias method can be a good alternative scheme for an efficient yet precise depth profiling technique for a solid electrolyte.
