New Insights into Corrosion of Ruthenium and Ruthenium Oxide Nanoparticles in Acidic Media

The dissolution behaviors of Ru and ruthenium oxide nanoparticles in acidic media were studied for the first time using highly sensitive in situ measurements of concentration by inductively coupled plasma mass spectrometry (ICP-MS). Online time- and potential-resolved electrochemical dissolution profiles revealed novel corrosion features (signals) in the potential window from 0 to ∼1.4 V, where known severe dissolution due to the oxygen evolution reaction (OER) takes place. Most of the features follow the thermodynamic changes of the Ru oxidation/reduction state, which consequently trigger so-called transient dissolution. An as-synthesized Ru sample was found to exhibit an order-of-magnitude higher dissolution rate than an electrochemically oxidized amorphous Ru sample. The latter, in turn, dissolved about 10 times faster than rutile RuO₂. The observed OER activity was in an inverse relationship with the measured dissolution. Disagreement was found with the general assumption that the onset of the OER should coincide with the onset of Ru dissolution. Interestingly, in all samples, Ru dissolution was observed at about 0.17 V lower potentials than the OER. The present results are relevant for various energy-conversion and -storage devices such as proton-exchange membrane electrolyzers, low-temperature fuel cells, reverse fuel cells, supercapacitors, batteries, and photocatalysts that can contain Ru as an active component

Electrochemical Dissolution of Iridium and Iridium Oxide Particles in Acidic Media: Transmission Electron Microscopy, Electrochemical Flow Cell Coupled to Inductively Coupled Plasma Mass Spectrometry, and X‑ray Absorption Spectroscopy Study

Iridium-based particles, regarded as the most promising proton exchange membrane electrolyzer electrocatalysts, were investigated by transmission electron microscopy and by coupling of an electrochemical flow cell (EFC) with online inductively coupled plasma mass spectrometry. Additionally, studies using a thin-film rotating disc electrode, identical location transmission and scanning electron microscopy, as well as X-ray absorption spectroscopy have been performed. Extremely sensitive online time-and potential-resolved electrochemical dissolution profiles revealed that Ir particles dissolve well below oxygen evolution reaction (OER) potentials, presumably induced by Ir surface oxidation and reduction processes, also referred to as transient dissolution. Overall, thermally prepared rutile-type IrO₂ particles are substantially more stable and less active in comparison to as-prepared metallic and electrochemically pretreated (E-Ir) analogues. Interestingly, under OER-relevant conditions, E-Ir particles exhibit superior stability and activity owing to the altered corrosion mechanism, where the formation of unstable Ir­(>IV) species is hindered. Due to the enhanced and lasting OER performance, electrochemically pre-oxidized E-Ir particles may be considered as the electrocatalyst of choice for an improved low-temperature electrochemical hydrogen production device, namely a proton exchange membrane electrolyzer