Oxygen Evolution Reaction in Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3-δ Aided by Intrinsic Co/Fe Spinel-Like Surface

Area of Science:

• Materials Science
• Electrochemistry
• Catalysis

Background:

• Perovskites are promising catalysts for the oxygen evolution reaction (OER).
• Ba$_{0.5}$Sr$_{0.5}$Co$_{0.8}$Fe$_{0.2}$O$_{3-δ}$ (BSCF) shows high OER activity, attributed to surface reconstruction and oxygen vacancies.
• Understanding surface transformations is crucial for designing efficient oxide catalysts.

Purpose of the Study:

• To investigate the local structure and chemistry of BSCF surfaces during OER.
• To elucidate the role of surface reconstruction in BSCF's electrocatalytic activity.
• To provide insights into the fundamental transformations of oxide catalysts.

Main Methods:

• Transmission electron microscopy (TEM) techniques, including post-mortem and identical location TEM.
• Analysis of local structure and chemistry of BSCF surfaces.
• Electrochemical processing and characterization.

Main Results:

• As-synthesized BSCF surfaces are rich in Cobalt (Co) and Iron (Fe) and exhibit a spinel-like structure with reduced Co valence.
• The Co/Fe spinel-like surface maintains chemical stability of Co/Fe ions, despite structural weakening after electrochemical treatment.
• The Co/Fe spinel-like surface facilitates the formation of the highly active Cobalt/Iron oxyhydroxide (Co(Fe)OOH) phase before OER onset.

Conclusions:

• The study reveals dynamic surface reconstruction in BSCF, leading to a stable spinel-like layer.
• This surface layer is key to promoting the formation of the active Co(Fe)OOH phase, enhancing OER performance.
• The findings offer fundamental understanding for developing advanced oxide catalysts for electrochemical applications.