Strain-Induced Microstructure Damage in SrCoO3-δThin Films during the Oxygen Evolution Reaction

The use of multivalent transition-metal oxides for oxygen evolution reaction (OER) electrodes has been facing a lot of stability issues such as amorphization, dissolution, phase transformations, etc. However, the microstructure damage of the catalyst during the OER has rarely been reported and has yet to be explored. In this work, we use SrCoO3-δ (SCO) films as an example to demonstrate the structure evolution and the resulting catalytic degradation by varying the thickness. It was found that the insertion of oxygen into the sample led to a lattice shrink and caused a strain between the transformed perovskite SCO and the raw brownmillerite SCO. For films thinner than 20 nm, the P-SCO layer was pinned by the substrate. However, it was peeled off in thicker films due to the strain relaxation and resulted in laminate cracking and tilting along the out-of-plane direction. This microstructure damage suppressed the catalytic current flowing through the electrode and thus hampered the OER performance significantly. These findings indicate the importance of eliminating intrinsic strains for antidegradation in electrochemical electrodes.