Enhancing Oxygen Reduction Activity and Cr Tolerance of Solid Oxide Fuel Cell Cathodes by a Multiphase Catalyst Coating

Abstract

Intermediate temperature solid oxide fuel cells (IT‐SOFCs) are cost‐effective and efficient energy conversion systems. The sluggish oxygen reduction reaction (ORR) and the degradation of cathodes are critical challenges to the commercialization of IT‐SOFCs. Here, a highly efficient multiphase (MP) catalyst coating, consisting of Ba1−xCo0.7Fe0.2Nb0.1O3−δ (BCFN) and BaCO3, to enhance the ORR activity and durability of the state‐of‐the‐art lanthanum strontium cobalt ferrite (La0.6Sr0.4Co0.2Fe0.8O3−δ, LSCF) cathode is reported. The conformal MP catalyst‐coated LSCF cathode shows a polarization resistance (Rp) of 0.048 Ω cm2 at 650 °C, about one order of magnitude smaller than that of the bare LSCF. In an accelerated Cr‐poisoning test, the degradation rate of the catalyst‐coated LSCF electrode is 10−3 Ω cm2 h−1 (0.59% h−1) over 200 h, only one fifth of the degradation rate of the bare LSCF electrode at 750 °C. In addition, anode‐supported single cells with the MP catalyst‐coated LSCF cathode show a dramatically enhanced peak power density (1.4 W cm−2 vs 0.67 W cm−2 at 750 °C) and increased durability against Cr and H2O. Both experimental results and density functional theory‐based calculations indicate that the BCFN phase improves the ORR activity while the BaCO3 phase enhances the stability of the LSCF cathode.

An Efficient Bifunctional Air Electrode for Reversible Protonic Ceramic Electrochemical Cells

“…In our previous work, we developed a series of effective catalyst coatings on the surface of LSCF electrodes via a low-cost surface modification process. [18,[28][29][30] The coatings enhanced the ORR activity and durability of LSCF dramatically on oxygenion electrolyte-based fuel cells by increasing the surface oxygen exchange kinetics and inhibiting the surface Sr-segregation. While the enhancement of the reaction kinetics via surface modification has been extensively demonstrated for SOCs based on oxygen ion conductors, similar effects for R-PCECs have yet to be explored.…”

Surface Regulating of a Double‐Perovskite Electrode for Protonic Ceramic Fuel Cells to Enhance Oxygen Reduction Activity and Contaminants Poisoning Tolerance

“…[23] It is suggested that cathodic polarization accelerated the Cr-poisoning by the fast Mn 2+ diffusion in LSM and the fast Sr diffusion in LSCF. [5,12] To improve the Cr tolerance of the cathode for an O-SOFC, a surface modification of electrodes with a rationally designed catalyst coating has been extensively adopted. [1,12,32,33] For example, Sr-free K 2 NiF 4 -type rare-earth nickelate catalyst coating, La 2 NiO 4+δ, [34] Nd 2 NiO 4+δ, and Pr 2 NiO 4+δ, [33] have been considered to be more Cr resistant.…”

“…[5,12] To improve the Cr tolerance of the cathode for an O-SOFC, a surface modification of electrodes with a rationally designed catalyst coating has been extensively adopted. [1,12,32,33] For example, Sr-free K 2 NiF 4 -type rare-earth nickelate catalyst coating, La 2 NiO 4+δ, [34] Nd 2 NiO 4+δ, and Pr 2 NiO 4+δ, [33] have been considered to be more Cr resistant. In addition, Chen et al reported the better ORR activity and Cr tolerance of LSCF by applying a conformal catalyst coating on the cathode such as BaO, La 0.8 Ca 0.2 FeO 3 , La 0.8 Ca 0.2 Ni 0.4 Fe 0.6 O 3 , Pr 0.75 Ca 0.2 MnO 3 , Pr 0.8 Ca 0.2 FeO 3 , and a hybrid catalyst of PrNi 0.5 Mn 0.5 O 3 and PrO x .…”

“…[5][6][7][8][9] Shao et al designed a self-assembled triple conducting nanocomposite cathode BaCo 0.7 (Ce 0.8 Y 0.2 ) 0.3 O 3-δ for PCFCs, producing a peak power density of 0.508 W cm -2 without noticeable performance degradation for over 812 h at 550 °C in clean air without any contaminations. [10] Under practical operating conditions, one of the most severe degradations occurring on the cathode is its poor durability, resulting from the poisoning effect by contaminants, [11][12][13][14] which is therefore of great significance in a commercial PCFCs stack. Under the practical operation conditions, vaporized gaseous Cr species (e.g., CrO 3 and CrO 2 (OH) 2 ), generated from the oxidation of chromium scale of the interconnect (e.g., SUS430 and Crofer22APU stainless steels) in the system, can readily react with segregated BaO and SrO to form insulating phases, such as BaCrO 4 , SrCrO 4 , and Cr 2 O 3 .…”

Protonic Conduction in La2NiO4+δ and La2‐xAxNiO4+δ (A = Ca, Sr, Ba) Ruddlesden–Popper Type Oxides

“…[3] Despite significant advances in recent years, [4,5] the performance of PCECs still suffers from limiting performance of the positive electrode-hereafter positrode-where the oxygen reduction reaction and oxygen evolution reaction-hereafter water oxygen redox reaction (WORX) for PCECs-take place. Generally, cathode materials for SOFCs, such as La 0.6 Sr 0.4 CoO 3-δ (LSC), [6] La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3-δ (LSCF), [7] and Ba 0.5 Sr 0.5 Co 0.8 Fe 0.2 O 3-δ (BSCF) [8] are mixed electron hole and oxide ion conductors, with negligible proton conduction. If used in a PCEC, the WORX is therefore restricted to the three-phase boundary, where the electrolyte, positrode, and gas phase meet, resulting in large kinetic overpotential polarization.…”