The stability of perovskite oxide catalysts for the oxygen evolution reaction (OER) plays a critical role for their applicability in water splitting concepts. Decomposition of perovskite oxides under applied potential is typically linked to cation leaching and amorphization of the material. However, structural changes and phase transformations at the catalyst surface were also shown to govern the activity of several perovskite electro-catalysts under applied potential. Hence, it is crucial for the rational design of durable perovskite catalysts to understand the interplay between the formation of active surface phases and stability limitations under OER conditions. In the present study, we reveal a surface-dominated activation and deactivation mechanism of the prominent electrocatalyst La0.6Sr0.4CoO3-ẟ under steady-state OER conditions. Using a multi-scale micros-copy and spectroscopy approach, we identify evolving Co-oxyhydroxide as catalytically active surface species and La-hydroxide as inactive species involved in the transient degradation behavior of the catalyst. While the leaching of Sr results in the formation of mixed surface phases, that can be considered as a part of the active surface, the gradual depletion of Co from a self-assembled active CoO(OH) phase and the relative enrichment of passivating La(OH)3 at the electrode surface results in the failure of the perovskite catalyst under applied potential.
Supporting Information: Activation and degradation of La0.6Sr0.4CoO3 ẟ electrocatalysts
Recrystallization procedure of the FIB lamella, ETEM in-vestigation in O2 environment, Investigation of the LSCO surface dynamics in 0.5 Pa of H2O, EELS analysis of the La-M-edge, On-line ICP-MS analysis including contact peak, Angle-dependent XPS analysis of as-prepared LSCO, XPS analysis of the surface chemistry of LSCO after the end of the catalyst lifetime.
Environmental transmission electron microscopy: complementary movies
Investigation of the surface dynamics of LSCO in O2 (M1: 2.7 Pa) and in H2O environment (M2: 0.5 Pa, M3: 7 Pa, M4: 11 Pa) by environmental transmission electron microscopy.