Stability of the Au/electrolyte interface during hydrogen evolution: A Cyclic Plasmo-Voltammetry study

Metal-electrolyte interfaces are dynamic entities, the potential and electrolyte dependent mobility of the metal atoms leading to surface restructuring with possible dissolution and degradation. In this work, we investigate the stability of the Au/aqueous electrolyte interface with in situ differential Cyclic Plasmo-Voltammetry (dCPV), augmented by ex situ atomic force microscopy and finite differential time domain simulations. We demonstrate that even the onset of hydrogen evolution is accompanied by pronounced morphological changes of the interface which are by far more prominent than those occurring during Au oxidation and reduction. Furthermore, the stability of the interface heavily depends on pH, the degradation of the electrode being considerably stronger in acidic than in neutral electrolyte. In addition, a clear hydrogen adsorption peak was observed in neutral electrolytes during the cathodic scan, which was more pronounced on a freshly prepared Au electrode than on an aged one. The measured dCPVs in acidic and neutral electrolytes can be explained consistently assuming that (1) adsorbed hydrogen is absorbed into the subsurface region of the Au electrode once HER starts; its subsequent removal as molecular hydrogen causes morphological changes; (2) in the presence of metal cations, adsorbed hydrogen is stabilized through the formation of ternary metal hydrides on the gold surface that stabilize the surface Au-H bonds and hinder further absorption of H into the subsurface region as well as the release of hydrogen into the electrolyte.