Dynamic observation of manganese adatom mobility at perovskite oxide catalyst interfaces with water

Abstract

Real time in-situ microscopy imaging of surface structure and atom dynamics of heterogeneous catalysts is an important step for understanding reaction mechanisms. Here, using in-situ environmental transmission electron microscopy (ETEM), we directly visualize surface atom dynamics at manganite perovskite catalyst surfaces for oxygen evolution reaction (OER), which are ≥20 times faster in water than in other ambients. Comparing (001) surfaces of La0.6Sr0.4MnO3 and Pr0.67Ca0.33MnO3 with similar initial manganese valence state and OER activity, but very different OER stability, allows us to distinguish between reversible surface adatom dynamics and irreversible surface defect chemical reactions. We observe enhanced reversible manganese adatom dynamics due to partial solvation in adsorbed water for the highly active and stable La0.6Sr0.4MnO3 system, suggesting that aspects of homogeneous catalysis must be included for understanding the OER mechanism in heterogeneous catalysis.

Direct evidence of cobalt oxyhydroxide formation on a La0.2Sr0.8CoO3 perovskite water splitting catalyst

“…3b), because spectra were acquired by dosing a 1 mbar water vapor background, without a stabilized electrolyte layer on top of the electrode and with no potential applied. According to the literature, 37 1 mbar water vapor pressure should lead to adsorption of approx. 3 monolayers of water.…”

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

“…The fact that the surface layer can become thinner indicates its instability during OER. With the negligible variation in the full size of nanocatalysts (SI Figure S5), the oscillation of surface layer thickness should not be caused by dissolution and redeposition 43 of the amorphous phase (through reacting with the CAN solution, which should change the nanocatalyst size). Considering only two parts observed in Mn 2 O 3 nanocatalysts, bulk Mn 2 O 3 and surface amorphous phase, the diminished surface layer must be transformed back to bulk Mn 2 O 3 and give rise to the reversible surface restructuring and oscillatory growth.…”

“…However, in situ liquid TEM suffers considerably degraded spatial resolution caused by additional electron scattering from liquid. To achieve the atomic level in situ observation, OER catalysis has been mostly studied using water vapor in environmental TEM, ,− which requires light or the electron beam − to trigger OER and is incapable of studying chemical or electrochemical OER. Despite the valuable insights obtained from this approach, it inevitably leads to the question whether the in situ observation in water vapor reflects faithfully the true OER mechanism of catalysts.…”

Atom Surface Dynamics of Manganese Oxide under Oxygen Evolution Reaction-Like Conditions Studied by In Situ Environmental Transmission Electron Microscopy

“…This allows for gaining insights into the surface dynamics of the MnO x material. However, high-resolution experiments in H 2 O vapor with a condensed H 2 O surface layer are presently restricted to pure H 2 O without addition of foreign ions, typical for real electrolytes …”