A New Durable Surface Nanoparticles‐Modified Perovskite Cathode for Protonic Ceramic Fuel Cells from Selective Cation Exsolution under Oxidizing Atmosphere

A high‐performance cathode of a protonic ceramic fuel cell (PCFC) should possess excellent oxygen reduction reactivity, high proton/oxygen‐ion/electron conductivity, and sufficient operational stability, thus requiring a delicate tuning of both the bulk and surface properties of the electrode material. Although surface modification of perovskites with nanoparticles from reducing‐atmosphere exsolution has been demonstrated effective at improving the electrochemical anodic oxidation, such nanoparticles would easily re‐incorporate into the perovskite lattice causing a big challenge for their application as a cathode. Here, a durable perovskite‐based nanocomposite cathode for PCFCs is reported, which is facilely prepared via the exsolution of nanoparticles in an oxidizing atmosphere. Through composition and cation nonstoichiometry manipulation, a precursor with the nominal composition of Ba0.95(Co0.4Fe0.4Zr0.1Y0.1)0.95Ni0.05O3−δ (BCFZYN‐095) is designed, synthesized, and investigated, which, upon calcination, gives rise to the formation of a perovskite‐based nanocomposite comprising a major perovskite phase and a minor NiO phase enriched on the perovskite surface. The major perovskite phase enabled by the proper cation nonstoichiometry manipulation promotes bulk proton conduction while the NiO nanoparticles facilitate the oxygen surface exchange process, leading to a superior cathodic performance with a maximum peak power density of 1040 mW cm−2 at 650 °C and excellent operational stability of 400 h at 550 °C. The major perovskite phase, m‐BCFZYN‐095, in BCFZYN‐095 has high proton conductivity, and NiO nanoparticles on the surface effectively improve the oxygen surface exchange rate, thereby simultaneously increasing proton and oxygen ion conductivities of the BCFZYN‐095 composite. Consequently, favorable peak power densities of a protonic ceramic fuel cell with the BCFZYN‐095 composite cathode in H2 are obtained.