Probing the Nano-electrocatalyst using Multimodal Operando Techniques

Title: Revealing catalyst restructuring and composition during nitrate electroreduction through correlated operando microscopy and spectroscopy
Authors: Yoon, et al.,
Journal: Nature Materials Link

Direct visualization of dynamic electrochemical processes inside a transmission electron microscope (TEM) is crucial for understanding nanoscale energy systems. This approach becomes even more powerful when complemented by well-established spectroscopic techniques. Electrochemical liquid cell transmission electron microscopy (EC-TEM) has proven to be a valuable tool for observing the electrically driven shape evolution of nanostructures in liquid. However, its limited spectroscopic capability—due to the thickness of the chip window and liquid—has restricted its widespread adoption in the research community.

In this study, the authors developed a method to comprehensively track the evolution of Cu₂O nanocubes during nitrate reduction, a key electrocatalytic reaction. By integrating EC-TEM with transmission X-ray microscopy (TXM), they successfully achieved both imaging and spectroscopic analysis without compromising the reaction environment. This was possible because X-rays experience less attenuation from the electrolyte and window membranes than electrons, better in preserving data quality.

To validate their findings, the authors further employed operando hard X-ray absorption spectroscopy (XAS), which provided bulk-level oxidation state analysis of nanoparticles extracted at the same potential in an electrolyte of identical composition to that used in TEM/TXM. Their results demonstrated how the evolution of Cu₂O nanocubes depends on nitrate reduction conditions, such as applied potential and chemical atmosphere. Additionally, they revealed that chemical heterogeneities arising from phase formation at different reductive potentials significantly impact ammonia selectivity, likely through electrocatalytic conversion reaction activation.