A Cobalt‐Free Multi‐Phase Nanocomposite as Near‐Ideal Cathode of Intermediate‐Temperature Solid Oxide Fuel Cells Developed by Smart Self‐Assembly

Abstract

An ideal solid oxide fuel cell (SOFC) cathode should meet multiple requirements, i.e., high activity for oxygen reduction reaction (ORR), good conductivity, favorable stability, and sound thermo‐mechanical/chemical compatibility with electrolyte, while it is very challenging to achieve all these requirements based on a single‐phase material. Herein, a cost‐effective multi‐phase nanocomposite, facilely synthesized through smart self‐assembly at high temperature, is developed as a near‐ideal cathode of intermediate‐temperature SOFCs, showing high ORR activity (an area‐specific resistance of ≈0.028 Ω cm2 and a power output of 1208 mW cm−2 at 650 °C), affordable conductivity (21.5 S cm−1 at 650 °C), favorable stability (560 h operation in single cell), excellent chemical compatibility with Sm0.2Ce0.8O1.9 electrolyte, and reduced thermal expansion coefficient (≈16.8 × 10−6 K−1). Such a nanocomposite (Sr0.9Ce0.1Fe0.8Ni0.2O3–δ) is composed of a single perovskite main phase (77.2 wt%), a Ruddlesden–Popper (RP) second phase (13.3 wt%), and surface‐decorated NiO (5.8 wt%) and CeO2 (3.7 wt%) minor phases. The RP phase promotes the oxygen bulk diffusion while NiO and CeO2 nanoparticles facilitate the oxygen surface process and O2− migration from the surface to the main phase, respectively. The strong interaction between four phases in nanodomain creates a synergistic effect, leading to the superior ORR activity.

High‐Performance Perovskite Composite Electrocatalysts Enabled by Controllable Interface Engineering

“…In prior studies, [26][27][28][29] perovskite-based composites were selfassembled from the calcination of their precursory materials with the nominal compositions being cation-stoichiometric. For example, by calcining a nominal RP precursor under a temperature lower than that expected for pure RP phase formation, Zhu et al obtained a composite material containing multiple phases.…”

“…[23][24][25] However, the fabrication of such composites involves sophisticated engineering of a perovskite, sometimes leveraging the solubility limit of elements within the perovskite structure, with methods to date having poor controllability and reproducibility. [23][24][25] We recently demonstrated several perovskite/perovskite composite systems, notably SP/SP, [26] SP/DP, [27] and SP/ RP [28,29] composites, found to form by self-assembly during calcination of a cation-stoichiometric perovskite precursor. Such self-assembly formation could potentially lead to better interfacial contact between the composite phases, improving the OER performance compared to single-phase counterparts.…”

“…However, it remains unclear whether the enhanced performance arises solely as a result of interface engineering, and how this contributes to OER enhancement, or if this enhancement has some contribution as a result of the compositional variation of phases from their single-phase counterparts in the perovskite-based composite, where composition is found to depend on synthesis conditions. [26][27][28][29] Here, we report a cation deficiency-promoted phase separation method for the strategic in situ formation of strongly interacting dual-phase perovskite oxide composites, with the ability to achieve accurate control over the composition, structure, and content of the component phases. Such a well-designed composite system serves as a platform to explore the origin of catalytic enhancement on perovskite composite catalysts, by which we demonstrate incontrovertible evidence supporting the key role played by the interfacial interaction of the composite catalysts in facilitating the oxygen ionic transport to enhance the lattice-oxygen participated OER kinetics.…”

A novel electrode with multifunction and regeneration for highly efficient and stable symmetrical solid oxide cell

“…It is much lower than those reported results as shown in Table S2. According to literature [26,32,36], The Rp mainly includes two parts. High frequency part corresponds to charge transfer process (R1) mainly including oxygen ion transportation processes in the electrolyte, electrolyte-electrode interface and the electrodes.…”

“…Moreover, Fe-based perovskites have matching thermal expansion coefficients (TEC) with YSZ or Gd0.1Ce0.9O2-δ (GDC), which can enhance the stability of the electrode and electrolyte interface [22,23]. Fe-based perovskites doped with alkaline-earth metal cations have exhibited good electrochemical performance in SOCs [23,25,26]. Bian et al investigated La0.6Ce0.1Sr0.3Fe0.9Ni0.1O3-δ as electrodes of SSOFC and the cell exhibited excellent peak power density of 900 mW cm -2 at 850 °C in wet H2 [27].…”