Hydrogen Nanobubbles at Roughness-Regulated Surfaces: Why Does the Standard Hydrogen Electrode Need a Platinized Platinum Electrode?

Hydrogen nanobubbles at the surfaces of platinum electrodes are investigated by atomic force microscopy and electrochemical methods. The existence of the bubbles at the Pt(111) electrode is revealed by observing the images indicating the repetition of the bubble formation and dissolution, which is synchronized with the electrode potential cycling. The degree of roughness at the surface of the single-crystalline electrode is systematically modified by the oxidation reduction cycles (ORCs), and the electroplating of platinum atoms provides the ultimately roughened surface. The nanobubble formation is favored at the polycrystalline electrode with a medium roughened surface (3 × 10³ times ORC). Not only at the atomically flat Pt(111) but also at the platinized platinum electrodes, however, the formation of the bubbles is much suppressed. The electrochemical hydrogen reaction is important for the energy standard in thermodynamics, as ΔG⁰ is defined to be zero for 2H⁺ + 2e^– ⇔ H₂ at a standard hydrogen electrode. Although the preparation of platinized platinum electrodes is much simpler than that of the Pt(111) electrode, both of them are concluded to be well designed for minimizing the possible potential fluctuation caused by the surface nanobubbles. These observations are harmonized with the conjecture by molecular dynamics predicting that the nanobubble formation is favorable at the surface with moderate roughness rather than at the surface with low and high roughness.