Probing the Surface Chemistry of Nanoporous Gold via Electrochemical Characterization and Atom Probe Tomography.

Amirhossein Foroozan-Ebrahimy,Brian Langelier,Roger Charles Newman

doi:10.3390/nano11041002

Amirhossein Foroozan-Ebrahimy, Brian Langelier + Show 1 more

Open Access

https://doi.org/10.3390/nano11041002

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Journal: Nanomaterials	Publication Date: Apr 14, 2021
Citations: 1	License type: CC BY 4.0

Affiliation: University of Toronto, McMaster University

Abstract

Surface chemistry information is crucial in understanding catalytic and sensing mechanisms. However, resolving the outermost monolayer composition of metallic nanoporous materials is challenging due to the high tortuosity of their morphology. In this study, we first elaborate on the capabilities and limitations of atom probe tomography (APT) in resolving interfaces. Subsequently, an electrochemical approach is designed to characterize the surface composition of nanoporous gold (NPG), developed from dealloying an inexpensive precursor (95 at. % Ag, 5 at. % Au), by the means of aqueous electrochemical measurements of the selective electrosorption of sulfide ions, which react strongly with Ag, but to a significantly lesser extent with Au. Accordingly, cyclic voltammetry was performed at various scan rates on NPG in alkaline aqueous solutions (0.2 M NaOH; pH 13) in the presence and absence of 1 mM Na2S. Calibrations via similar voltammetric measurements on pure polycrystalline Ag and Au surfaces allowed for a quantitative estimation for the Ag surface coverage of NPG. The sensitivity threshold for the detection of the adsorbate–Ag interaction was assessed to be approximately 2% Ag surface coverage. As curves measured on NPG only showed featureless capacitive currents, no faradaic charge density associated with sulfide electrosorption could be detected. This study opens a new avenue to gain further insight into the monolayer surface coverage of metallic nanoporous materials and assists in enhancement of the interpretation of APT reconstructions.

Highlights

Nanoporous gold (NPG) derived from selective electrolytic dissolution of Ag fromAg–Au(-Pt) alloys [1,2] has shown promising results in terms of catalysis, sensing, bioanalytical and biomedical applications [3,4,5,6,7]
Obtaining insight into the entire surface composition of such tortuous nanostructures has proved to be challenging despite the use of various advanced atomic-scale characterization techniques such as atom probe tomography (APT) [8,9]
This study is an attempt at shedding further light on the surface composition of NPG by augmenting APT data with aqueous electrochemical techniques

Summary

Introduction

Nanoporous gold (NPG) derived from selective electrolytic dissolution of Ag fromAg–Au(-Pt) alloys [1,2] has shown promising results in terms of catalysis, sensing, bioanalytical and biomedical applications [3,4,5,6,7]. Gaining insight into the surface composition of metallic nanoporous materials could enhance the understanding of the underlying mechanisms of nanoporosity evolution and catalysis, but would be crucial in biosensing applications, in particular, in vivo sensors. Obtaining insight into the entire surface composition of such tortuous nanostructures has proved to be challenging despite the use of various advanced atomic-scale characterization techniques such as atom probe tomography (APT) [8,9]. APT is a destructive and highly localized method of investigation, there is a need for a non-local and non-destructive surface analysis method to investigate the surface composition of such nanoporous materials. This study is an attempt at shedding further light on the surface composition of NPG by augmenting APT data with aqueous electrochemical techniques.

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