Density functional theory calculations for the hydrogen evolution reaction in an electrochemical double layer on the Pt(111) electrode

We present results of density functional theory calculations on a Pt(111) slab with a bilayer of water, solvated protons in the water layer, and excess electrons in the metal surface. In this way we model the electrochemical double layer at a platinum electrode. By varying the number of protons/electrons in the double layer we investigate the system as a function of the electrode potential. We study the elementary processes involved in the hydrogen evolution reaction, 2(H⁺ + e^-) → H₂, and determine the activation energy and predominant reaction mechanism as a function of electrode potential. We confirm by explicit calculations the notion that the variation of the activation barrier with potential can be viewed as a manifestation of the Brønsted-Evans-Polanyi-type relationship between activation energy and reaction energy found throughout surface chemistry.