Atomic‐Level Observation of Potential‐Dependent Variations at the Surface of an Oxide Catalyst during Oxygen Evolution Reaction

Understanding the intricate details of the surface atomic structure and composition of catalysts during the oxygen evolution reaction (OER) is crucial for developing catalysts with high stability in water electrolyzers. While many notable studies highlight surface amorphization and reconstruction, systematic analytical tracing of the catalyst surface as a function of overpotential remains elusive. Heteroepitaxial (001) films of chemically stable and lattice‐oxygen‐inactive LaCoO3 are thus utilized as a model catalyst to demonstrate a series of atomic‐resolution observations of the film surface at different anodic potentials. The first key finding is that atoms at the surface are fairly dynamic even at lower overpotentials. Angstrom‐scale atomic displacements within the perovskite framework are identified below a certain potential level. Another noteworthy feature is that amorphization (or paracrystallization) with no long‐range order is finally induced at higher overpotentials. In particular, surface analyses consistently support that the oxidation of lattice oxygen is coupled with amorphous phase formation at the high potentials. Theoretical calculations also reveal an upward shift of oxygen 2p states toward the Fermi level, indicating enhanced lattice oxygen activation when atom displacement occurs more extensively. This study emphasizes that the degradation behavior of OER catalysts can distinctively vary depending on the overpotential level. Identifying catalyst surface structure during the OER is vital for sustainable water electrolysis. A series of dynamic displacements, paracrystallization, and further amorphization are observed at the (001) surface in LaCoO3 under different overpotentials. Theoretical calculations also suggest lattice oxygen activation with extensive atom displacement induced at higher anodic potentials. This highlights significant variations in the degradation behavior of OER catalysts, strongly depending on overpotential levels.