Origin of the Volume Contraction during Nanoporous Gold Formation by Dealloying for High-Performance Electrochemical Applications

Nanoporous metals used in various electrochemical applications including electrochemical actuators, electrocatalysts, supercapacitors, and batteries exhibit an irreversible volume shrinkage during their formation by dealloying, the origin of which remains obscure. Here we use dilatometry techniques to measure the irreversible shrinkage in nanoporous Au in situ during electrochemical dealloying. A linear contraction up to ∼9% was recorded. To identify the origin of this dimensional change, we borrow the time-dependent isothermal shrinkage model from sintering theory, which we use to fit the dimensional changes measured in our nanoporous Au during dealloying. This shrinkage model suggests that bulk transport through plastic flow is the primary mass transport mechanism responsible for the material contraction in dealloying. Based on the current understanding of the mechanism of porosity formation in dealloying, mass transport through surface diffusion of undissolved materials is critical in the process. The present work sheds new light in the sense that bulk transport through plastic flow seems also to play an important role in dealloying.