The importance of carefully choosing vertex potentials in hydrogen underpotential deposition

Accurate determination of electrochemical surface area (ECSA) is not always possible even for simple monometallic catalysts with well-known techniques. An example is Pt and the determination of its ECSA by hydrogen underpotential deposition (HUPD) used to determine the specific activity. Here, we show an important problem in determining the ECSA of Pt (both wire and foil electrodes) using HUPD which is the changing ECSA with the changing anodic and cathodic vertex potentials (E_vertex) set in HUPD analysis. The results confirm that just by varying the E_vertex one could get a wide range of values for ECSA and the ECSA normalized specific activity for the same Pt electrode. This calls for instant remedial action as Pt is not just any catalyst but state-of-the-art in many energy conversion reactions and our study suggests that the E_vertex should be chosen based on whether or not to have the effect of Pt oxidation on ECSA.