In-operando GC-MS : A new tool for the understanding of degradation processes occurring in electrochemical capacitors

In this work, we present an innovative design of an electrochemical three-electrode cell for in-operando gas chromatography-mass spectrometry analysis, which allows performing electrochemical measurements while probing and analyzing the liquid electrolyte in real-time. The presented cell shows similar electrochemical performance to commonly used lab-scale cells and can be utilized for the investigation of any kind of electrochemical system. The three-electrode configuration enables the differentiation of processes occurring at the respective positive or negative electrode. Investigating the aging of electrochemical cells, it is possible to obtain a detailed time-resolved insight into occurring decomposition processes. As a model case, we investigated aging
processes occurring in an electric double-layer capacitor containing a one-molar solution of tetraethylammonium tetrafluoroborate in acetonitrile. Showing a time- and voltage-dependent evolution, decomposition products of the salt, solvent, and electrode were detected and assigned to aging processes occurring at the respective positive and/or negative electrode-electrolyte interphase. Used for the detection of soluble decomposition species within the electrolyte, in-operando gas chromatography-mass spectrometry is uniquely suited to be combined with techniques focused on the electrode and/or gas phase of electrochemical energy storage devices.