Direct Observation of Oxygen Evolution and Surface Restructuring on Mn₂O₃ Nanocatalysts Using In Situ and Ex Situ Transmission Electron Microscopy

Abstract

Direct observation of oxygen evolution reaction (OER) on catalyst surface may significantly advance the mechanistic understanding of OER catalysis. Here, we report the first real-time nanoscale observation of chemical OER on Mn 2 O 3 nanocatalyst surface using an in situ liquid holder in a transmission electron microscope (TEM). The oxygen evolution process can be directly visualized from the development of oxygen nanobubbles around nanocatalysts. The high spatial and temporal resolution further enables us to unravel the real-time formation of a surface layer on Mn 2 O 3 , whose thickness oscillation reflects a partially reversible surface restructuring relevant to OER catalysis. Ex situ atomicresolution TEM on the residual surface layer after OER reveals its amorphous nature with reduced Mn valence and oxygen coordination. Besides shedding light on the dynamic OER catalysis, our results also demonstrate a powerful strategy combining in situ and ex situ TEM for investigating various chemical reaction mechanisms in liquid.

Progress in In Situ Research on Dynamic Surface Reconstruction of Electrocatalysts for Oxygen Evolution Reaction

“…In recent years, various in situ imaging technologies have developed rapidly, among which the most typical is in situ TEM. [116][117][118][119] In situ TEM can directly observe the catalytic process and catalyst evolution. As a dynamic process, catalysis mainly includes molecular adsorption, activation, and desorption.…”

Insights into Heterogeneous Catalysts under Reaction Conditions by In Situ/Operando Electron Microscopy

“…The improved activity Reproduced with permission. [230] Copyright 2021, American Chemical Society. and stability of the perovskite electrocatalysts are tunable by changing the transition metal-oxygen covalence bonds.…”

“…An intriguing oxide thickness oscillation is recently revealed in an in situ liquid cell TEM study of Mn 2 O 3 catalyst under OER conditions. [ 230 ] The surface layer on Mn 2 O 3 is linked to the oxygen‐nanobubble formation. The reactivity produces an oscillation in thickness as a result of the dynamic surface restructuring in terms of the oxygen deficiency's formation and filling on the surface of Mn 2 O 3 .…”

“…b) Evolution profiles of the surface layer thickness (red) as marked by red arrows, and the nanobubble volume (blue) as indicated by the blue arrows. (Scale bar: 20 nm).Reproduced with permission [230]. Copyright 2021, American Chemical Society.…”

In Situ TEM Technique Revealing the Deactivation Mechanism of Bimetallic Pd–Ag Nanoparticles in Hydrogen Sensors

“…One of the ideal strategies is to introduce a second metal into Pd catalysts to form bimetallic Pd-based alloy catalysts. Numerous experiments verified that bimetallic Pd-based alloy catalysts exhibit a synergistic effect that can dramatically improve the H 2 -sensing properties of bare Pd catalysts. − However, SMO-based gas sensors are always operated at high temperatures of up to hundreds of degrees Celsius in air, which causes Pd-based catalyst deactivation or deterioration. − To reveal the deactivation mechanism, the morphological/structural evolution of bimetallic catalysts under the operating conditions of H 2 sensors must be characterized in situ . − However, carrying out in situ characterization of bimetallic catalysts with conventional analysis methods such as scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD) is still challenging. − …”