Metal deposition and electrocatalysis for elucidating structural changes of gold electrodes during cathodic corrosion

Abstract

Several electrochemical conversion reactions occur under high cathodic currents, where electrocatalysts can experience substantial alterations in their surface structure through cathodic corrosion, influencing their electrocatalytic performance. Thus, understanding the structural changes of metal surfaces upon cathodic polarization is crucial for the rational design of active and stable electrocatalysts in the context of a transition towards green technologies. In this work, we probe the structural changes of Au surfaces after cathodic corrosion in 10 M NaOH and 10 M KOH at different potentials, using metal deposition and electrocatalytic surface-sensitive reactions. Cathodic polarization increases the electrochemically active surface area and alters the distribution of crystal facets, as evidenced by underpotential deposition of Pb and the electrochemical behaviour in 0.1 M H₂SO₄. The Au electrode surfaces obtained in NaOH and KOH exhibit different distributions and sizes of (111)-facets. The electrocatalytic activity of the restructured Au electrodes towards the formic acid oxidation reaction (FAOR) and the hydrogen evolution reaction (HER) is evaluated. The nanostructured Au electrodes obtained after polarization in NaOH show superior HER activity compared to those obtained in KOH, which is related to the formed nanostructures and the influence of low-coordination sites. Furthermore, the FAOR activity of the Au electrodes with higher (111)-contribution, achieved through polarization in 10 M KOH, is comparable to well-ordered Au(111) single crystals, emphasizing the key role of terraces in FAOR rather than surface steps as active sites responsible for the extraordinary HER activity. To further explore the electrocatalytic performance, we demonstrate the electrochemical fabrication of Pd–Au bimetallic nanostructures with varying contributions of (111)-facets, obtained through a combination of cathodic corrosion and electrodeposition. Remarkably, the electrocatalytic activity of Pd films on nanostructured Au electrodes towards FAOR in HClO₄ and H₂SO₄ solutions is significantly enhanced compared to as-polished Au electrodes and is dependent on the contribution of (111)-facets. The present findings are relevant to the stability and long-term performance of cathodes in a variety of applications including electrosynthesis.