Electrochemical capacitors (ECs) are a vital component of today’s electrochemical energy storage, having energy and power densities ideally approaching that of batteries and electrolytic capacitors. Typical ECs utilize porous carbon electrodes and store charge in the electrochemical double layer (EDL) formed at the electrode/electrolyte interface. In order to understand and improve current capacitor technology, fundamental electrochemical processes at the solid/liquid interface need to be understood. This includes the EDL and the transport of ions across the solid/liquid interface into the electrode material. Due to the characteristic sizes of EDL’s, this requires characterization techniques capable of resolving nm length scales. Here, we show how to use scanning probe microscopy based techniques to understand electrochemical processes at the solid/liquid interface. The first example is the imaging of the EDL in a room temperature ionic liquid (RTIL) on charged surfaces. RTIL exhibit unique properties such as broad electrochemical stability and as such have found a wide variety of applications over the past number of years, particularly in the field of electrochemistry. However, the EDL in those liquids is poorly understood. The structure of the EDL will be measured as function of position and applied voltage and compared with molecular dynamics (MD) predictions. In a second example, we demonstrate how the ionic transport across the solid/liquid interface can be tracked using changes in mechanical properties when cations are inserted from an aqueous solution into 2D layered transition metal carbides (MXenes). Due to the compositional versatility, MXene materials, which are etched from their parent layered MAX phase, significantly broadened the spectrum of 2D materials and therefore opened exciting opportunities for various electrochemical applications. For Ti3C2, the insertion of ions results in a change of interaction strength of MXene layers which results in a measurable change of electrode stiffness. The tracking of spatially resolved changes in material stiffness allows identifying fast ionic pathways into MXene particles.

In-situ study of electric double layers and ionic transport across the solid/liquid interface using scanning probe microscopy

251st National Meeting (2016)

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