Electrochemical Behavior of Carbon Electrodes for In Situ Redox Studies in a Transmission Electron Microscope

Electrochemical liquid cell transmission electron microscopy (TEM) is a unique technique for probing nanocatalyst behavior during operation for a range of different electrocatalytic processes, including hydrogen evolution reaction (HER), oxygen evolution reaction (OER), oxygen reduction reaction (ORR), or electrochemical CO2 reduction (eCO2R). A major challenge to the technique's applicability to these systems has to do with the choice of substrate, which requires a wide inert potential range for quantitative electrochemistry, and is also responsible for minimizing background gas generation in the confined microscale environment. Here, we report on the feasibility of electrochemical experiments using the standard redox couple Fe(CN)63-/4- and microchips featuring carbon-coated electrodes. We electrochemically assess the in situ performance with respect to flow rate, liquid volume, and scan rate. Equally important with the choice of working substrate is the choice of the reference electrode. We demonstrate that the use of a modified electrode setup allows for potential measurements relatable to bulk studies. Furthermore, we use this setup to demonstrate the inert potential range for carbon-coated electrodes in aqueous electrolytes for HER, OER, ORR, and eCO2R. This work provides a basis for understanding electrochemical measurements in similar microscale systems and for studying gas-generating reactions with liquid electrochemical TEM.