We define the potential of zero charge (U PZC ) in this work as the potential at which no excess charge exists on a metal electrode in contact with an electrolyte. This property of metal-water interfaces is an important parameter determining electrochemical behavior . For example, the U PZC determines the strength of the electric field at the interface at an applied potential, and hence the structure of the electric double layer (EDL). The structure of the EDL is in turn crucial in determining electrocatalytic activity and in rationalizing electrolyte effects (e.g. the electrolyte pH and cations) for several energy conversion processes occurring at the metal-water interface. Unfortunately, U PZC of a metal-solution interface can be very difficult to measure experimentally. Both the difficulty in handling and preparing pristine single crystal electrodes and the specific adsorption of ions in the potential regions near U PZC interfere with accurate measurements. Due to specific adsorption, U PZC is frequently distinguished as two distinct properties . The potential of zero total charge (U PZTC ) is the potential at which the total charge (q) that includes both charging related to adsorption/desorption events (for e.g. H* and OH*) and double layer charging, is equal to zero (q = 0). The potential of zero free charge, according to Trasatti's original definition, (U PZFC ), is the potential at which both q and the free surface charge density (σ) are zero (q = σ = 0), i.e. no specific adsorption at the PZFC. We note, that these definitions have not been consistently used throughout literature, e.g. in recent work the PZC of adsorbate-covered surfaces has been termed PZFC, even though σ includes contributions from excess free charge due to the adsorption .