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Anodic molecular hydrogen formation on Ru and Cu electrodes

Wednesday 21 Oct 20
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hemical hydrogen adsorption and desorption, and the state of adsorbed hydrogen (*H) on metal surfaces are of fundamental interest as well as practical importance for the hydrogen evolution reaction (HER) and electrochemical hydrogenation reactions including CO2 and CO electroreduction. Here, we report a previously undiscovered phenomenon whereby *H desorbs as H2 during an anodic potential sweep at potentials anodic of (more positive than) the equilibrium potential of U0(H2/H+), hence at potentials where hydrogen desorption would be expected as H+. 

Using electrochemistry – online mass spectrometry, we observe, quantify, and characterize the phenomenon on two different materials in two different environments – Ru(0001) in acid and polycrystalline Cu in alkaline. For both Ru and Cu, the anodic H2 formation seems to coincide with *OH adsorption, which would be consistent with a displacement mechanism. We propose that a high barrier for the Volmer step causes some of the displaced *H to desorb as H2 (Tafel step) rather than the thermodynamically more favorable desorption as H+ (Volmer step).

Soren B. Scott, Albert K. Engstfeld, Zenonas Jusys, Degenhart Hochfilzer, Nikolaj Knøsgaard, Daniel B. Trimarco, Peter C. K. Vesborg, R. Jürgen Behm and Ib Chorkendorff 

CATALYSIS SCIENCE & TECHNOLOGY, Volume: 10 Issue: 20 Pages: 6870-6878

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