Assessing the Correct Electrochemical Surface Area of Gold Electrocatalysts by Copper Underpotential Deposition

Abstract

Abstract Knowing the electrochemical surface area (ECSA) is crucial to fully understand an electrocatalytic system and correctly contextualize the behavior of a catalyst. We show that the surface oxidation method poses several problems for the ECSA determination, while the copper underpotential deposition method (Cu-UPD) allows reproducible and non-destructive determination of the ECSA of gold-based catalysts. To quantify the copper underpotential deposition charge, we combine single-crystalline Au(111) and Au(110) gold samples with surface-sensitive scanning tunneling microscopy and X-ray photoelectron spectroscopy characterization, providing a precise and independent calibration procedure to link the oxidation of one deposited Cu atom in Cl–-containing electrolyte to a passed charge of 1.01 ± 0.04 electrons per Cu atom for Au(111) and 0.98 ± 0.15 e–/Cu for Au(110). Relating to the gold surface area, the copper oxidation charges amount to 137 ± 6 μC/cmAu(111)2 and 134 ± 20 μC/cmAu(110)2. Reliable results are obtained by using an electrochemical cell that allows for air-free transfer to and from the vacuum-based preparation and characterization methods. Due to the low applied potentials, the Cu-UPD method does not alter the structure of the original gold surface itself.