On the role of Grain Boundary Character in the Stress Corrosion Cracking of Nanoporous Gold Thin Films

TL;DR

This study investigates how grain boundary characteristics influence stress corrosion cracking in nanoporous gold thin films, revealing that certain boundary types enhance stability and longevity during dealloying.

Contribution

It provides a systematic analysis linking grain boundary structure and chemistry to cracking resistance in nanoporous gold films, highlighting the role of coherent sigma 3 boundaries.

Findings

Higher density of coherent sigma 3 boundaries reduces cracking.

Temperature during synthesis affects grain boundary types and stability.

Grain boundary chemistry influences dealloying behavior and durability.

Abstract

For its potential as a catalyst, nanoporous gold (NPG) prepared through dealloying of bulk Ag-Au alloys has been extensively investigated. NPG thin films can offer ease of handling, better tunability of the chemistry and microstructure of the nanoporous structure, and represent a more sustainable usage of scarce resources. These films are however prone to intergranular cracking during dealloying, limiting their stability and potential applications. Here, we set out to systematically investigate the grain boundaries in Au28Ag72 thin films. We observe that a sample synthesized at 400 {\deg}C is at least 2.5 times less prone to cracking compared to a sample synthesized at room temperature. This correlates with a higher density of coincident site lattice grain boundaries, especially the density of coherent sigma 3, increased, which appear resistant against cracking. Nanoscale compositional analysis of random high-angle grain boundaries reveals prominent Ag enrichment up to 77 at.%, whereas sigma 3 coherent twin boundaries show Au enrichment of up to 30 at.%. The misorientation and the chemistry of grain boundaries hence affect their dealloying behavior, which in turn controls the cracking, and the possible longevity of NPG thin films for application in electrocatalysis.