Electrochemical force microscopy and potentiostatic measurements of the solid-liquid interface

Future development of energy devices and materials such as batteries and supercapacitors widely depend on understanding the relationship between elemental structure, electrostatic and electrochemical functionality at below micron level. Individual structural elements (i.e. step edges, defects, grain boundaries) that are below or at micron level must be correlated with electrochemical or electrostatic inhomogeneities acting as nucleation centres of failure sites. Thus, the relationship between macroscopic device behaviour and local nanoscopic electrochemical/electrostatic processes should be understood well through local electrochemical/electrostatic functionality in order to improve the next generation of long-lifetime and high-power energy devices and materials. Kelvin probe force microscopy (KPFM) is widely used to combine local structural and electrostatic characterization of materials at the solid-gas interface, however, KPFM cannot be implemented in ionic liquids due to the presence of mobile ions. This hurdle is overcome by Electrochemical force microscopy (EcFM) which is an advanced version of KPFM that allows the application of DC bias in a controlled manner and collecting the corresponding deflection response at each location upon a force curve. EcFM enables us to unravel the underlying mechanisms behind local electrostatic processes and ion dynamics at the solid-liquid interface through its bias- and time-resolved response in order to better understand and improve energy devices through local information. In this work, we identify the limitations of EcFM and then overcome these limitations to make EcFM a suitable technique for energy devices/materials, such that we integrate a potentiostat to EcFM in order to collect electrochemical information along with electrostatic response. We also develop a new open loop (OL) KPFM method implemented in our EcFM setup, which is shown to provide the same response with a reduction in the required voltage, crucial for a controlled electrochemical environment, in air and liquid as compared to other OL-KPFM modes. Moreover, we pay a detailed attention to the instrumental limitations and settings of our EcFM setup leading to foresee the maximum measurable molarity from simulations and followed by the verification with experimental data, extending the previous reports from MilliQ to 1 mM. By combination of all of these improvements, we demonstrate that EcFM is capable of investigating charge screening mechanisms up to 1 mM and electrochemical reactions in the probe-sample junction and further establish EcFM as a force-based imaging mode to visualize local electrochemical/electrostatic properties across a sample with contrast. EcFM is expected to improve our understanding of performance and lifetime of energy devices and materials by providing bias- and time-resolved both electrostatic and electrochemical information at the nanoscale level.