Functional Role of Fe-Doping in Co-Based Perovskite Oxide Catalysts for Oxygen Evolution Reaction

Abstract

Perovskite oxides have been at the forefront among catalysts for the oxygen evolution reaction (OER) in alkaline media offering a higher degree of freedom in cation arrangement. Several of highly OER active Co-based perovskites have been known to show extraordinary activities and stabilities when the B-site is partially occupied by Fe. At the current stage, the role of Fe in enhancing the OER activity and stability is still unclear. In order to elucidate the roles of Co and Fe in the OER mechanism of cubic perovskites, two prospective perovskite oxides-La0.2Sr0.8Co1-xFexO3-δ and Ba0.5Sr0.5Co1-xFexO3δ with x = 0 and 0.2-were prepared by flame spray synthesis as nanoparticles. This study highlights the importance of Fe in order to achieve high OER activity and stability by drawing relations between their physicochemical and electrochemical properties. Ex situ and operando X-ray absorption spectroscopy (XAS) was used to study the local electronic and geometric structure under oxygen evolving conditions. In parallel, density function theory computational studies were conducted to provide theoretical insights into our findings. Our findings show that the incorporation of Fe into Co-based perovskite oxides alters intrinsic properties rendering efficient OER activity and prolonged stability.

Cation insertion to break the activity/stability relationship for highly active oxygen evolution reaction catalyst

“…6a), unlike previous observations made for other highly active catalysts, such as Ba 0.5 Sr 0.5 Co 0.8 Fe 0.2 O 3−δ (refs. 17,26,30,61 ). Furthermore, negligible amount of iridium was found leached during the OER for α-Li 2 IrO 3 ( Supplementary Fig.…”

“…Numerous research efforts were therefore devoted to improving the OER kinetics by developing transition metal oxides electrocatalysts. Recent experimental results and theoretical studies pointed out that increasing the transition metal-oxygen bond covalency leads to an enhanced OER kinetics concomitant with the destabilization of the surface [12][13][14][15][16][17][18] . Screening a large variety of transition metal oxides, it could be shown that this phenomenon is related to the relative position of the Fermi level when compared to the reversible potential for water oxidation, as well as to the charge-transfer energy [19][20][21][22] .…”

Ambient Growth of Hierarchical FeOOH/MXene as Enhanced Electrocatalyst for Oxygen Evolution Reaction

“…Recently, transition metal‐based materials including oxides, hydroxides, phosphides and chalcogenides have been intensive studied as alternative OER catalysts to meet the demand of high catalytic activity and low cost . Among them, iron oxyhydroxide FeOOH becomes a promising one due to its natural abundance, environmental protection and high intrinsic activity .…”

Smart Control of Composition for Double Perovskite Electrocatalysts toward Enhanced Oxygen Evolution Reaction

“…Therefore, previous reports have focused on strategies such as the introduction of OER‐active elements into the B‐site and tailoring the oxygen defect to increase the catalytic performance. Among the transition‐metal‐based perovskite oxides (such as Mn, Fe, Co and Ni), Co‐based oxides have emerged as promising candidates owing to the outstanding OER performance of the CoO 6 octahedron . Co in a perovskite structure usually has more oxidation states (Co 2+ , Co 3+ , Co 4+ ) and spin states than Ni (Ni 2+ ) and Fe (Fe 3+ ) because the formation of high oxidation states of Ni 3+ and Fe 4+ typically require high pressures or oxidation conditions .…”

“…Among the transitionmetal-based perovskite oxides (such as Mn, Fe, Co and Ni), Cobased oxidesh ave emerged as promising candidates owing to the outstanding OER performance of the CoO 6 octahedron. [11][12][13][14][15] Co in ap erovskite structure usually has more oxidation states (Co 2 + ,C o 3 + ,C o 4 + )a nd spin states than Ni (Ni 2 + ) and Fe (Fe 3 + )b ecause the formation of high oxidation states of Ni 3 + and Fe 4 + typically require high pressures or oxidation conditions. [4,16] Co 3 + and Co 4 + cationsare beneficial for the formationo f*OH and *OOH, respectively,ina lkalinec onditions.…”