Tellurium adatoms as an in-situ surface probe of (111) two-dimensional domains at platinum surfaces

Irreversibly adsorbed tellurium has been studied as a probe to quantify ordered domains in platinum electrodes. The surface redox process of adsorbed tellurium on the Pt(111) electrode and Pt(111) stepped surfaces takes place around 0.85 V in a well-defined peak. The behavior of this redox process on the Pt(111) vicinal surfaces indicates that the tellurium atoms involved in the redox process are only those deposited on the (111) terrace sites. Moreover, the corresponding charge density is proportional to the number of sites on (111) ordered domains (terraces) that are, at least, three atoms wide. Hence, this charge density can be used to measure the number of (111) terrace sites on any given platinum sample. Structural information about tellurium adsorption is obtained from atomic-resolution STM images for the Pt(111) and Pt(10, 10, 9) electrodes. A rectangular structure (2 x root 3) and a compact hexagonal structure (11 x 8) were identified. However, the redox peak for adsorbed tellurium on (100) domains at 1.03 V overlaps with peaks arising from steps and (110) sites. Therefore, it cannot be used without problems for the determination of (100) sites on a platinum sample. On the (100) terraces, the surface structure of the adsorbed tellurium is c(2 x 2), as revealed by STM. Finally, tellurium irreversible adsorption has been used to estimate the number of (111) ordered domains terrace sites on different polycrystalline platinum samples, and the results are compared to those obtained with bismuth irreversible adsorption.