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

Abstract

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.

Real‐time Monitoring Reveals Dissolution/Redeposition Mechanism in Copper Nanocatalysts during the Initial Stages of the CO2 Reduction Reaction

“…In the corresponding FFT (Figure 1b)the d-spacing is assigned to Cu {111} planes, which confirms their metallic nature.F igure 1c then depicts the electrochemical chip design adopted specifically for the in situ CO 2 RR TEM experiments.T he ability to perform CO 2 RR inside the confined volume of the micro-cells used for in situ TEM demands the suppression of the hydrogen evolution reaction and the elimination of the intrinsic activity of the supporting electrode for CO 2 RR. [29,30] These requirements rule out the use of typical metals used for current collectors in micro-cells,s uch as platinum or gold. Glassy carbon or carbon felt is typically used as the supporting electrode for CO 2 RR nanoparticle catalysts due to its good conductivity,l ow chemical reactivity,l arge overpotential for HER and minimal activity for CO 2 RR.…”

“…Figure 1 c then depicts the electrochemical chip design adopted specifically for the in situ CO 2 RR TEM experiments. The ability to perform CO 2 RR inside the confined volume of the micro‐cells used for in situ TEM demands the suppression of the hydrogen evolution reaction and the elimination of the intrinsic activity of the supporting electrode for CO 2 RR [29, 30] . These requirements rule out the use of typical metals used for current collectors in micro‐cells, such as platinum or gold.…”

Insights into Electrocatalyst Transformations Studied in Real Time with Electrochemical Liquid-Phase Transmission Electron Microscopy

“…In this case, amorphous, glassy carbon (GC) electrodes have been shown to be excellent candidates. When we tested the electrochemically inert window for customized or commercial GC electrodes, we found them to be an adequate choice for many electrocatalysts studies, including the CO 2 ER at low potential, the ORR, and the OER, and under alkaline, neutral, or acidic conditions (Figure g). , We note that these electrodes show a typically increased resistivity (and hence a higher ohmic drop) and that owing to the difficulties of pretreating GC electrodes in the ec-LPTEM apparatus, there are often increased resistances that are attributed to slow charge-transfer rates at the electrolyte–electrode interface. , Additionally, we have found them to be highly fragile and they can withstand only limited reaction times in the highly negative potential ranges …”

Electrochemical Sensing at a Confined Space

“…The simulation results indicated that a uniform current distribution was observed when the ratio of the square of the coplanar electrode width to the cell height was greater than 5 . Recently, in order to acquire a wide inert potential window for quantitative electrochemical measurement in the catalytic process, Girod et al proposed a feasible electrochemical setup using carbon coated electrode . Through a series of cyclic voltammetry studies of the influence factors using the standard ferrocyanide/ferricyanide redox couple, the authors demonstrated the setup has the capability to detect several electrocatalytic systems, and the measured potential was related to the bulk system.…”