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

Abstract

Among the perovskites used to catalyze the oxygen evolution reaction (OER), Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF) exhibits excellent activity which is thought to be related to dynamic reconstruction at the flexible perovskite surface due to accommodation of large amount of oxygen vacancies. By studying the local structure and chemistry of BSCF surfaces, in detail, via a range of transmission electron microscopy (TEM) methods, we show that the surfaces of the as-synthesized BSCF particles are Co/Fe rich, and remarkably, adopt a spinel-like structure with a reduced valence of Co ions. Post-mortem and identical location TEM analyses reveal that the Co/Fe spinel-like surface retains a stable chemical environment of the Co/Fe ions, although its structure weakens after electrochemical processing. Further, it is verified that prior to the onset of OER, the Co/Fe spinel-like surface promotes the formation of the highly active Co­(Fe)­OOH phase, which enhances the OER electrocatalytic properties of the underlying conductive BSCF perovskite. This study provides a detailed understanding of the fundamental transformations that oxide catalysts undergo during electrochemical processes and can aid in the development of novel oxide catalysts with enhanced activity.

Anodic Transformation of a Core‐Shell Prussian Blue Analogue to a Bifunctional Electrocatalyst for Water Splitting

“…[ 13 ] and Shao et al. [ 14 ] unraveled a dynamic reconstruction of the well‐known Ba 0.5 Sr 0.5 Co 0.8 Fe 0.2 O 3–δ catalyst, revealing a (Co/Fe)O(OH) active layer. It was reported that Co 3 O 4 [ 15 ] and CoO x , [ 16 ] plus NiO, [ 17 ] NiFe, [ 18 ] and NiCo oxides, [ 9 ] operate in a similar manner when an anodic potential is applied.…”

In Situ/Operando Capturing Unusual Ir6+ Facilitating Ultrafast Electrocatalytic Water Oxidation

“…From the perspective of structural design, synergistic effects can occur through the interface engineering, such as for intermetallic/interface, structurally ordered multi‐metallic compounds, core‐shell nanoparticles, heterostructures, and hybrid electrocatalysts. [ 9–11,15–17 ] However, in these systems the synergistic effects of the active sites occur restricted only on the grain boundaries or phase interfaces. Note that the previous studies on low doping levels, the charge transfer process between two phases (or two elements), and between adsorbates and the substrates were incorrectly interpreted as synergistic effects, but rather modification of electronic structure.…”

Carbonate formation lowers the electrocatalytic activity of perovskite oxides for water electrolysis

“…Surface contaminants induced by simple exposure to air are well recognized for Li-ion batteries, where the formation of lithium and nickel carbonates results in degradation, especially for Ni-rich cathode materials. 18,19 For electrocatalysts, the possible formation of such contaminants has been recognized, 20 but their effect on electrocatalytic performance has yet to be explored.…”