Understanding Reaction Mechanisms in Electrochemistry and Corrosion: Liquid-Cell S/TEM

Abstract

Electrochemical and corrosion studies have greatly benefited from using liquid-cell S/TEM techniques for providing real-time information on the nanoscale mechanisms occurring at solid-liquid interfaces [1]. Within a liquid environment, nanoscale electrodes and metals undergo reactions with the solution creating surface layers and films at the interface. In batteries, these interface layers are known as solidelectrolyte interfaces (SEI). In corrosion experiments, the surface layers are known as scale materials. These systems have related domination of the surface film composition and structure impacting the overall behavior of the electrode and the rate of reaction during corrosion. Therefore, to better understand these material systems and determinant mechanisms, we are investigating using real-time imaging and spectroscopy to characterize these interfaces for initial structural identification, in-situ monitoring of interfacial processes, and post-mortem analysis of electrode/material surfaces.Electrochemical control within a TEM was pioneered by F. Ross in 2003 using MEMS technology [2] to study electrochemical processes at nanoscale resolution [3][4]. The Center for Integrated Nanotechnologies has successfully designed a microfabricated liquid-cell that can operate with picoampere current control over 10 ultramicroelectrodes while imaging within a TEM, FIG1 [5]. The electrodes are patterned onto a 50 nm SiNx membrane window, with an even fluid gap around 150 nm. This design allows for multiple experiments to be performed within the same closed cell, where we studied varied current densities and beam conditions under identical environmental conditions. The electrochemical platform is custom patterned using e-beam lithography to deposit working, counter and reference electrodes of customized material composition and volume. In addition, customization of the platform allows for localized heating of the liquid cell in the window region to study elevated temperature influence on electrochemical and corrosion processes [6]. These capabilities are beyond what is currently achievable using a commercial liquid-cell system. This presentation will cover recent results regarding upgrading our electrochemical TEM discovery platform. We will present on the development of heating and sensing capabilities and their impact on cycling of nanostructured Sn electrodes within carbonate electrolytes for Li-ion batteries. Development of Li metal counter and reference electrodes for cycling nanostructured electrodes within the confined liquid-cell. This capability is important in order to obtain realistic electrochemcial potentials for Li-ion battery systems that accompany high-resolution imaging, FIG2. Low-dose imaging of Li plating/stripping in carbonate electrolytes using the Gatan K2-IS direct electron detection camera for TEM imaging. In addition, experimental results will be provided that highlight the ability to gain insights into corrosion mechanism for steel and shale mineral samples. The breadth of experimental capabilities...