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.