Challenges to electrochemical evaluation of nanometric sandwiched thin specimens using liquid cells designed for application in liquid-phase TEM corrosion studies

A Kosari,H Zandbergen,F Tichelaar,P Visser,H Terryn,J.M.C Mol

doi:10.1016/j.corsci.2021.109864

Abstract

Liquid-phase transmission electron microscopy (LP-TEM) has provided corrosion scientists with a unique opportunity to directly correlate nanoscopic morphological and compositional evolutions to the corresponding electrochemical response of corroding thin TEM specimens. Electrochemical liquid cell designs are key components of a LP-TEM study towards an implementation which is representative for realistic exposure conditions of bulk samples. However, the application of commercially available liquid cells in corrosion studies brings along an important shortcoming of galvanic coupling effects due to the inevitable connection of the TEM specimens with Pt patterned electrodes. Here, we introduce an approach of fabricating electrochemical liquid cells to alleviate the current cell design challenge for corrosion studies. Besides, we present a protocol for preparing thin specimens to be electrochemically investigated with our home-made electrochemical liquid cell. We finally confirm the effectiveness of this methodology by electrochemically evaluating thin specimens of AA2024-T3 in an open-cell configuration through open circuit potential and potentiodynamic polarisation measurements.

Highlights

Electrochemical liquid phase-transmission electron microscopy (LPTEM) has recently emerged as an unparalleled opportunity to explore corrosion phenomena in situ and at the nanoscale [1,2]
It should be noted that covering the middle Pt electrodes with tetraethyl orthosilicate (TEOS) using the focused ion beam (FIB)/scanning electron microscopy (SEM) microscope is not possible because the scale of the Pt electrodes is too large for such a microscope to handle; local removal of an externally and earlier applied SixNy cover is more prac tical than later coverage within the microscope
This study shows the importance of real-time electrochemical measurements by liquid-phase TEM to be able to correlate microstructural evolution to the electrochemical response of individual phases, which are to be executed in a follow-up study

Summary

Introduction

Electrochemical liquid phase-transmission electron microscopy (LPTEM) has recently emerged as an unparalleled opportunity to explore corrosion phenomena in situ and at the nanoscale [1,2]. Thanks to the developed liquid cells, it is possible to polarise (bias) electrochemical reactions taking place at the specimen/electrolyte interface while the corresponding morphological and compositional changes are captured [3,4,5,6,7] This significant prospect in relation to the approach and its application in corrosion science studies comes with inherent experi mental challenges and concerns [8,9,10,11,12,13]. It should be mentioned that Pt WE electrodes on the electrochemical chips have a significantly higher surface area than the prepared thin specimens This phenomenon causes a considerably accelerated corrosion of the thin specimens, in particular when reactive materials such as common aluminium, zinc and magnesium engineering alloys are of interest. The specimens are evaluated morphologically before and after the tests using scanning electron microscopy (SEM)

Design of electrochemical liquid cell for corrosion studies

TEM specimen preparation procedure for corrosion studies

Results and discussion

Conclusions

Kosari