Effect of Alkali Metal Cations and Trace Metal Impurities on Cathodic Corrosion of Gold Electrode Surfaces

Cathodic corrosion, a phenomenon critical for understanding the stability and performance of metal electrodes during several energy conversion reactions, is known to be influenced by various factors including the nature and concentration of alkali metal cations. However, a clear understanding of this behavior has not yet been developed. Through a comprehensive investigation of cathodic corrosion of Au electrodes as a function of the identity of alkali metal hydroxides (LiOH, NaOH, KOH, and CsOH) at different concentrations and various negative potentials, we reveal that the interfacial water adlayer's structure and the ratio of free water as well as water bound in hydration shells control the overall cathodic corrosion behavior, alongside with the specific adsorption of alkali metal cations. Moreover, we highlight the crucial role of electrolyte cleanliness, particularly regarding the presence of trace metal impurities, in accurately assessing the proper effects of alkali metal cations on cathodic corrosion. Interestingly, the presence of trace amounts of nickel and iron in as-received CsOH suppresses cathodic corrosion by their deposition onto Au surfaces. In contrast, after purification, the polarization of Au surfaces in 10 M CsOH leads to the formation of nanoporous surfaces with high electrochemically active surface area, in which the degree of porosity can be tuned by varying the polarization time at –1.6 V vs. RHE. This work contributes to the understanding of how alkali metal cations and metal impurities affect the cathodic corrosion of Au surfaces and offers practical guidelines for nanostructuring and facetting Au electrodes.