**Fe-Doping in Double Perovskite PrBaCo2(1-x)Fe2xO6-**δ**: Insights into Structural and Electronic Effects to Enhance Oxygen Evolution Catalyst Stability**

**Bae-Jung Kim 1,\*, Emiliana Fabbri 1,\*, Ivano E. Castelli 2, Mario Borlaf 3, Thomas Graule 3, Maarten Nachtegaal <sup>1</sup> and Thomas J. Schmidt 1,4**


Received: 19 February 2019; Accepted: 12 March 2019; Published: 14 March 2019

**Abstract:** Perovskite oxides have been gaining attention for its capability to be designed as an ideal electrocatalyst for oxygen evolution reaction (OER). Among promising candidates, the layered double perovskite—PrBaCo2O6-<sup>δ</sup> (PBC)—has been identified as the most active perovskite electrocatalyst for OER in alkaline media. For a single transition metal oxide catalyst, the addition of Fe enhances its electrocatalytic performance towards OER. To understand the role of Fe, herein, Fe is incorporated in PBC in different ratios, which yielded PrBaCo2(1-*x*)Fe2*x*Co6-<sup>δ</sup> (*x* = 0, 0.2 and 0.5). Fe-doped PBCF's demonstrate enhanced OER activities and stabilities. Operando X-ray absorption spectroscopy (XAS) revealed that Co is more stable in a lower oxidation state upon Fe incorporation by establishing charge stability. Hence, the degradation of Co is inhibited such that the perovskite structure is prolonged under the OER conditions, which allows it to serve as a platform for the oxy(hydroxide) layer formation. Overall, our findings underline synergetic effects of incorporating Fe into Co-based layered double perovskite in achieving a higher activity and stability during oxygen evolution reaction.

**Keywords:** Fe-substitution; operando X-ray absorption spectroscopy; oxygen evolution reaction; double perovskite catalysts; oxy(hydroxide)
