Due to its role as the primary competing reaction to CO2 reduction, H2 evolution is one of the most important products to consider. Under basic conditions the H2 evolution reaction proceeds through direct water reduction and the Volmer-Tafel or Volmer-Heyrovsky steps (see EIS Fig. ). For commonly-used metals such as Cu, Au and Ag, the Volmer step is particularly sluggish in basic conditions due to both poor water dissociation properties and weak *H binding energies, which is pushed even further to the right and away from the peak of the classical volcano plot under higher pH conditions. Simultaneous CO2 reduction occurring on a catalyst's surface also tends to further suppress H2 activity by weakening hydrogen binding, occupying surface sites and consuming protons. For catalysts on the left side of the hydrogen binding energy volcano curve, however, hydrogen evolution under locally basic conditions may increase for the same fundamental reasons.