Electrochemical catalytic reactions for the energy transition (hydrogen evolution reaction (HER), carbon dioxide (CO2RR), oxygen reduction reaction (ORR), oxygen evolution reaction (OER)) attract considerable interest from the scientific community. In order to accelerate rational design of efficient catalysts with high activity, selectivity and stability, it is important to understand the fundamental mechanisms involved in the electrochemical processes. To this aim, advanced in situ / operando characterization techniques provide insight into the correlation between physical-chemical properties and the electrochemical performance. Specifically, electrochemical liquid phase transmission electron microscopy (EC-LPTEM) provides real-time morphological, structural and chemical information regarding catalytic materials under electrochemical stimulation [1]. EC-LPTEM experiments are typically performed in miniaturized liquid cell TEM holders with controlled liquid flow, where the three electrode configuration (working electrode WE, counter electrode CE, reference electrode RE) is implemented through MEMS-based technology. The stringent requirements for operation in the TEM column (electron-transparency, compatibility with high vacuum conditions) have a strong influence on the liquid cell geometry. As a result, EC-LPTEM experiments inevitably differ from the commonly used macroscopic benchmarking reactors. It is of considerable scientific interest to understand how to improve the experimental design in order to reach relevant operando conditions.

In this work, we show different approaches to the modification of the EC-LPTEM setup, with the goal of improving the experimental control of mass transport and electrochemical conditions during in situ / operando experiments.

At first, the implications of a rationally-optimized cell geometry, enhancing diffusion as main mass transport mechanism, are investigated in electrochemical experiments in aqueous electrolyte. It Is shown that with the diffusion cell geometry it is possible to perform electrochemical experiments in conditions which were previously not accessible with the standard planar EC-LPTEM cell geometry [2]. Experimental examples include the electrodeposition of Zn nanostructures for energy storage applications and the dynamical evolution of a copper-based catalyst for CO2RR applications. In the second part of this work, we focus on improving the control and stability of the electrochemical conditions during EC-LPTEM experiments. Nanostructuration of the on-chip CE and RE by electrodeposition of metallic nanostructures is presented as innovative approach for decreasing the polarization of the CE during operation while simultaneously enhancing the stability over time of the RE. The presented work aims to inspire the development of a comprehensive optimization approach of all the experimental parameters (mass trasnport, electrochemistry, radiolysis), with the aim of enhancing the capabilities of future in situ/ operando experiments.