Bi-Functional Oxygen Electrocatalysts for Reversible Solid Oxide Cells: The Influence of A-Site Non-stoichiometry on the System (La or Ba)0.6-xSr0.4Co0.8Fe0.2O3−δ
Selective tailoring of stoichiometry in perovskite oxide generates excellent electrocatalytic activity toward redox reaction of oxygen [oxygen evolution reaction (OER) and oxygen reduction reaction (ORR)]. The redox reaction of oxygen is kinetically sluggish (spin relaxed reaction) and is the rate-l...
| Autores: | , , , , , , , , , , , |
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| Tipo de recurso: | artículo |
| Estado: | Versión aceptada para publicación |
| Fecha de publicación: | 2025 |
| País: | España |
| Institución: | Consejo Superior de Investigaciones Científicas (CSIC) |
| Repositorio: | DIGITAL.CSIC. Repositorio Institucional del CSIC |
| OAI Identifier: | oai:digital.csic.es:10261/406447 |
| Acceso en línea: | http://hdl.handle.net/10261/406447 https://www.scopus.com/inward/record.uri?eid=2-s2.0-105005768938&doi=10.1021%2facsaem.5c00803&partnerID=40&md5=65629196be936b3aa9b4d5d072de0f1c |
| Access Level: | acceso abierto |
| Palabra clave: | A-site non-stoichiometry Bifunctional electrocatalyst Oxygen defects Oxygen evolution reaction (OER) Oxygen reduction reaction (ORR) Solid oxide cell (SOC) |
| Sumario: | Selective tailoring of stoichiometry in perovskite oxide generates excellent electrocatalytic activity toward redox reaction of oxygen [oxygen evolution reaction (OER) and oxygen reduction reaction (ORR)]. The redox reaction of oxygen is kinetically sluggish (spin relaxed reaction) and is the rate-limiting step for solid oxide cells (SOCs). We have reported that introducing non-stoichiometry at the A-site in A0.6-xSr0.4Co0.8Fe0.2O3−δ imparts a bifunctional electrocatalyst for OER and ORR with excellent performance in fuel cell (FC) and electrolyzer cell (EC) mode. Two compositions, Ba0.6Sr0.4Co0.8Fe0.2O3−δ (BSCF-6482) and La0.6Sr0.4Co0.8Fe0.2O3−δ (LSCF-6482), are designed by varying the non-stoichiometry from 0.6 to 0.52 for Ba and La, respectively. X-ray photoelectron spectroscopy (XP spectroscopy), iodometric estimation, and O2-temperature-programmed desorption (O2-TPD) reveal that Ba0.54Sr0.4Co0.8Fe0.2O3−δ (BS-54) promotes oxygen surface exchange (higher β-oxygen population) and La0.54Sr0.4Co0.8Fe0.2O3−δ (LS-54) accelerates α-oxygen desorption (charge-transfer reaction). A study of the distribution of relaxation time (DRT) using EIS (electrochemical impedance spectroscopy) on cell configuration LS-54 (or BS-54)/GDC-LS-54 (or BS-54)//GDC//Pt@800 °C reveals that LS-54 has minimum electrode polarization (comprising dual processes of charge transfer and oxygen surface exchange) at both +0.8 V (OER) and −0.8 V (ORR), which resonates at 103-104 Hz. It is corroborated that α-oxygen is associated with the charge-transfer process and controls the ORR, whereas the OER is assisted by oxygen surface exchange, primarily linked with β-oxygen. Inclusion of non-stoichiometry at the A-site promotes oxygen-vacancy formation and stabilizes a lower valence state for the B-site cations. The rate-controlling steps for the OER and ORR thereby alter in LS-54 and BS-54 compared to LSCF/BSCF-6482. Electrochemical measurements show superior reversible solid oxide cell (SOC) performance of LS-54 having a current density (CD) of 1.27 A cm-2 @1.5 V and 0.66 A cm-2@0.5 V for a cell with dimensions as large as 5 cm × 5 cm. A similar cell operated with a CD of 1.0 A cm2 under standalone mode of operation in FC. This work proposes a novel strategy to demonstrate A-site non-stoichiometric La0.54Sr0.4Co0.8Fe0.2O3−δ to be a superior bifunctional electrocatalyst for both OER and ORR for SOCs. © 2025 American Chemical Society. |
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