Time and potential resolved dissolution analysis of rhodium using a microelectrochemical flow cell coupled to an ICP-MS

The dissolution of polycrystalline rhodium in 0.1 M H2SO4 is quantitatively investigated during potential cycling and potential step experiments using a novel setup which consists of a microelectrochemical scanning flow cell (SFC) linked to an inductively coupled plasma-mass spectrometer (ICP-MS). The time-resolved dissolution profile during electrochemical treatment is presented for the first time and used for quantitative determination of area-normalized dissolution rates. A high time resolution and very low detection limits allow distinguishing between anodic and cathodic dissolution at a sufficiently low scan rate. It has been found that the reduction of surface oxides triggers a significantly higher mass loss than the oxide formation (about 4–10 fold), and that this ratio and the overall extent of dissolution are dependent on the upper potential limit. Furthermore, a strong scan rate dependence was observed for both the anodic and cathodic dissolution peaks, with a decrease of the amount of rhodium dissolved per cycle with increasing scan rate and a minimum at potentiostatic step experiments between the respective potential limits. Clear evidence for steady state dissolution of the oxidized surface is presented as well, even though this value ranges around a few femtograms per second and square centimeter at potentials up to 1.4 VSHE. The differences in dissolution cover more than two orders of magnitude, potentially providing valuable information for electrode operating conditions and degradation mechanisms of noble metal materials.