First insights of the electrocatalytical properties of stepped silver electrodes for the hydrogen evolution reaction

Silver Leakage from Ag/AgCl Reference Electrodes as a Potential Cause of Interference in the Electrocatalytic Hydrogen Evolution Reaction

The electrocatalytic hydrogen evolution reaction (HER) is of considerable interest for the production of H₂ from sustainable sources. Herein, we show that under conditions commonly employed in identifying new electrocatalysts for this reaction (using Ag/AgCl reference electrodes in 1 M H₂SO₄), silver ions can leak from the reference electrode into solution and then deposit on the working electrode as Ag(0), giving current densities for the HER of over 5 mA cm^-2 at ∼500 mV overpotential. This is well within the activity range reported for many electrocatalysts of the HER and calls into question the validity of any reports using Ag/AgCl reference electrodes which either fail to explicitly exclude silver as a cause of the electrocatalytic activity or else cannot demonstrate significantly superior activity to this baseline.

Volcano plots in hydrogen electrocatalysis - uses and abuses

Sabatier's principle suggests, that for hydrogen evolution a plot of the rate constant versus the hydrogen adsorption energy should result in a volcano, and several such plots have been presented in the literature. A thorough examination of the data shows, that there is no volcano once the oxide-covered metals are left out. We examine the factors that govern the reaction rate in the light of our own theory and conclude, that Sabatier's principle is only one of several factors that determine the rate. With the exception of nickel and cobalt, the reaction rate does not decrease for highly exothermic hydrogen adsorption as predicted, because the reaction passes through more suitable intermediate states. The case of nickel is given special attention; since it is a 3d metal, its orbitals are compact and the overlap with hydrogen is too low to make it a good catalyst.