Identification and Analysis of Electrochemical Instrumentation Limitations through the Study of Platinum Surface Oxide Formation and Reduction.

Anodic polarization of Pt electrodes in aqueous H2SO4 leads to the formation of a surface oxide (PtO). Herein, the surface oxide growth is accomplished using three different approaches: (i) chronoamperometry (CA); (ii) chronocoulometry (CC); and (iii) a combination of cyclic voltammetry (CV) and CA. The PtO reduction is accomplished potentiodynamically using voltammetry. The oxide growth takes place at defined polarization potentials (E(p)), polarization times (t(p)), and temperatures (T). The oxide charge density (q(ox)) is determined for both the formation (q(ox,form)) and reduction (q(ox,red)) processes. The oxide reduction CV profiles are integrated to determine the charge density values for oxide reduction (q(ox,red,CV)) which are compared with the q(ox,form,CA) and q(ox,form,CC) values. The values of q(ox,form,CC) are greater than those of q(ox,form,CA), but both potentiotatic methods (CA and CC) produce q(ox,form) values that are consistently lower than those of q(ox,red,CV). In the case of oxide formation with combined CV and CA, the values of q(ox,form,CV+CA) are found to be lower than the values of q(ox,red,CV), although the difference is small. Electrochemical quartz crystal nanobalance (EQCN) is used to monitor the mass variation at the electrode surface during the oxide formation and reduction process at E(p) = 1.20 V with various t(p) values. Equal mass changes during oxide formation and reduction are detected by the EQCN. The nature of the differences in q(ox,form) and q(ox,red) encountered with the different experimental methods are discussed in terms of instrumental limitations.