Trends in the Exchange Current for Hydrogen Evolution

Abstract

A density functional theory database of hydrogen chemisorption energies on close packed surfaces of a number of transition and noble metals is presented. The bond energies are used to understand the trends in the exchange current for hydrogen evolution. A volcano curve is obtained when measured exchange currents are plotted as a function of the calculated hydrogen adsorption energies and a simple kinetic model is developed to understand the origin of the volcano. The volcano curve is also consistent with Pt being the most efficient electrocatalyst for hydrogen evolution.

Calculated Phase Diagrams for the Electrochemical Oxidation and Reduction of Water over Pt(111)

“…25 According to the model, the formation of OH* is down hill in free energy for potentials above 0.79 V. This value is not trivially compared to voltammograms on Pt(111). The theoretical value denotes the potential at which reaction 5 is in equilibrium, this means that it should be compared with the reversible potential from the voltammogram.…”

Nanostructured hydrotreating catalysts for electrochemical hydrogen evolution

“…The simple kinetic model proposed by Norskov and co-workers to explain the origin of the volcano plot is shown as the solid lines. 15 The volcano plot reflects the Sabatier principle. Metals to the left of Pt bind hydrogen atoms too strongly, blocking the active site and failing to evolve hydrogen.…”

“…The Gibbs free energy for hydrogen adsorption (G H* ) on a metal has been proposed to be a good descriptor of the intrinsic activity of a metal for HER. [15][16][17][18] A plot of exchange current densities against G H* has a volcano shape. Pt group metals are at the summit of the volcano, having the highest activity and close to zero hydrogen absorption energy (Fig.…”

“…The adsorption free energy of hydrogen on the Ni 2 P (001) surface has also been calculated by DFT to be 0.31 eV 19 and recently a turn over frequency (TOF) of 0.015 s -1 was estimated at  = 100 mV for an active Ni 2 P HER electrocatalyst. 20 The measured TOF is equivalent to an exchange current density of j 0 = 7.2x10 -6 A cm -2 , assuming an active site density of 1.5x10 15 site cm -2 . The activity of an electrocatalyst is often expressed as a given current density at a given overpotential.…”

Nanohybrids of Two‐Dimensional Transition‐Metal Dichalcogenides and Titanium Dioxide for Photocatalytic Applications

“…[41,42] In addition, theoretical calculations have indicated that the Gibbs free energy of adsorbed atomic hydrogen for TMDCs is close to zero (+ 0.08 Vf or the MoS 2 edge), demonstrating their potentialf or H 2 evolution reaction. [43] TMDCsasp hotosensitizer for improving photocatalytic activity of TiO 2 nanostructures Considering that TiO 2 can only absorb the UV portion of solar spectrum,i ti sh ighly crucial to enhance the photocatalytic efficiencyo fT iO 2 -based photocatalysts by extending their lightharvesting window to the visible light range using TMDC nanosheets due to their relatively narrow band gap. The mechanism for photocatalytic hydrogen evolution in TMDC/TiO 2 nanocomposites can be described as follows:u pon light irradiation, the electrons are injected from the valence band of TMDC nanosheets to the conduction band, leaving behind holes in the valenceb and.…”