Catalysis of hydrogen evolution on Pt(111) by absorbed hydrogen.

The activity of Pt(111) electrodes for the hydrogen evolution reaction (HER) in 0.5M H₂SO₄ solution is found to increase with continuous potential cycling in the HER potential region. In addition, the basic cyclic voltammograms obtained in 0.5M H₂SO₄ saturated with N₂ after HER show several characteristic changes: the current waves for hydrogen adsorption in the region of0.2 < E < 0.35 V and for sulfate adsorption at 0.35 < E < 0.5 V decrease and the current spike at 0.44 V for the phase transition of the sulfate adlayer gradually disappears. We suggest that these changes are caused by the absorption of a small amount of hydrogen in the subsurface layer and propose a mechanism by which this enhances hydrogen evolution. [ABSTRACT FROM AUTHOR]