Indium-Doping-Induced Nanocomposites with Improved Oxygen Reaction Activity and Durability for Reversible Protonic Ceramic Electrochemical Cell Air Electrodes

Reversible protonic ceramic electrochemical cells (R-PCECs) are very promising as energy conversion and storage devices with high efficiency at intermediate temperatures (500–700 °C). Unfortunately, the sluggish reaction kinetics on air electrodes severely hamper the commercial application of R-PCECs. In this work, an In-doped PrBaCo₂O_5+δ air electrode is developed with a designed formula of PrBaCo_1.9In_0.1O_5+δ, which however consists of a dominated double perovskite PrBa_0.95Co_1.85In_0.09O_5+δ and a minor cubic perovskite BaCo_0.85In_0.15O_3-δ phase, as suggested by the XRD refinements. The formation of nanocomposites induced by the In-doping has markedly improved the activity of oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), due likely to the increased oxygen vacancies, enhanced the oxygen surface exchange and bulk diffusion capabilities when compared to the bare PrBaCo₂O_5+δ. Excellent electrochemical performances in fuel cell (FC) mode (2.25 W cm⁻²) and electrolysis cell (EC) mode (−4.41 A cm⁻² at 1.3 V) are achieved on the single cells with such nanocomposite air electrodes at 700 °C. In addition, promising durability tests of cells in modes of FC (100 h), EC (100 h), and cycling (210 h) are demonstrated at 600 °C. This In-doped strategy provides a novel approach to developing new air electrode materials.