Odd Random Phase Electrochemical Impedance Spectroscopy and interfacial analysis of PEDOT:PSS aluminium electrolytic capacitors

Poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) is been proven as a versatile and
resistant conductive polymer with a wide range of applications [1]. Among others, its use as electrolyte in
electrolytic capacitors is one of the most predominant. PEDOT:PSS – aluminium electrolytic capacitors show
low internal equivalent series resistances (ESR) and can resist temperatures up to 280 ºC. The most common
method of applying PEDOT:PSS is coating it from a water dispersion. PEDOT:PSS dispersions admit
additional components (secondary dopants) that enhance properties such as conductivity, rheology or
electrochemical behavior of the final layer. There has been fundamental research about how the structure of
PEDOT:PSS changes upon the interactions with the substrate is coated on [2]. However, it has never been
studied experimentally how PEDOT:PSS behaves on top of the layer of aluminium oxide that works as the
dielectric in polymer electrolytic capacitors.
This work aims to study the properties of model systems involving different PEDOT:PSS dispersions on top
of aluminium substrates that works as the anode in polymer electrolytic capacitors. In this study, two
approaches will be used to analyze such systems: an electrochemical analysis and an analysis of the interface.
Electrochemically, the systems will be studied thanks to odd random phase electrochemical impedance
spectroscopy (ORP-EIS). ORP-EIS is a technique that derives from impedance spectroscopy with the added
value of exciting at once several odd frequencies with a multisine signal. Thanks to a throughout analysis of
the data not only the electrochemical behavior of the system is obtained, but also information about its linearity
and stationarity upon the application of the multisine signal. Parallel to the electrochemical analysis, crosssections
will be obtained to access the interface between the polymer and the electrode thanks to an ion milling
polisher. These complex systems (Al substrate, Al2O3 and PEDOT:PSS) are then studied via secondary
electron spectroscopy (SEM), which provides morphological information, and energy-dispersive X-rays
(EDX) and X-ray photoelectron spectroscopy (XPS) that provides elementary information of the systems and
the interaction between layers.