Development of Cryogenic Atom Probe Tomography for Analysis of Aqueous Electrochemical Interfaces

Abstract
Electrochemical interfaces in corrosion and catalysis have the potential to shape our future manufacturing and sustainability practices [1], [2]. Visualising and resolving the complex interfacial properties that govern these systems is vital for further understanding of electrochemical reactions occurring over these regions [3], [4]. However, direct characterisation of multiphase (liquid–solid) systems at near-atomic resolution, with simultaneous light-element sensitivity, has remained limited.
In this study, we utilise cryogenic atom probe tomography to characterise frozen solid-liquid interfaces, building upon previous cryo-APT aqueous interface studies [5], [6], [7], and focusing our development on two main areas: enhancing detection of frozen anions (particularly halide ions due to their electronegativity) in cryo-APT and developing techniques that enable the systematic cryo-APT analyses of solid-liquid interfaces under electrochemical conditions.
First, we investigate the interactions between iodide and sodium ions and Au-rich, nano-confined surfaces within nanoporous gold (NPG). Across multiple scales of nanoconfinement, we observe strong iodide–gold interactions and metallic complexation, evidenced by significant detection of AuI⁺ and I⁺ ions located at and within gold nanoligaments. Second, we introduce an electrochemical cell capable of applying controlled potentials directly to cryo-APT specimens, eliminating the lengthy disassembly and freezing steps required in conventional electrochemical setups. This prevents relaxation of the interface prior to freezing and enables us to directly examine the dealloying mechanism of Ag₈₀Au₂₀ at.% alloys responsible for NPG formation.
Together, these developments demonstrate tangible progress toward routine, reproducible cryo-APT analysis of aqueous electrochemical interfaces and open new opportunities for resolving interfacial processes inaccessible through conventional techniques.

References
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