Reversible protonic ceramic cells (RePCCs) can facilitate the global transition to renewable energy sources by providing high efficiency, scalable, and fuel‐flexible energy generation and storage at the grid level. However, RePCC technology is limited by the lack of durable air electrode materials with high activity toward the oxygen reduction/evolution reaction and water formation/water‐splitting reaction. Herein, a novel nanocomposites concept for developing bifunctional RePCC electrodes with exceptional performance is reported. By harnessing the unique functionalities of nanoscale particles, nanocomposites can produce electrodes that simultaneously optimize reaction activity in both fuel cell/electrolysis operations. In this work, a nanocomposite electrode composed of tetragonal and Ruddlesden–Popper (RP) perovskite phases with a surface enriched by CeO2 and NiO nanoparticles is synthesized. Experiments and calculations identify that the RP phase promotes hydration and proton transfer, while NiO and CeO2 nanoparticles facilitate O2 surface exchange and O2‐ transfer from the surface to the major perovskite. This composite also ensures fast (H+/O2‐/e‐) triple‐conduction, thereby promoting oxygen reduction/evolution reaction activities. The as‐fabricated RePCC achieves an excellent peak power density of 531 mW cm‐2 and an electrolysis current of −364 mA cm‐2 at 1.3 V at 600 °C, while demonstrating exceptional reversible operation stability of 120 h at 550 °C.

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Proton-conducting fuel cells (PCFCs) with a perovskite-type proton-conducting electrolyte show many advantages over conventional oxygen-ion-conducting ceramic fuel cells. Both electrode catalytic activity and electrolyte conductivity determine the performance of PCFCs. Cation non-stoichiometry has a great influence on the catalytic activity and conductivity of perovskite oxides. Here, we propose a PCFC with B-site-cation-deficient perovskites (BCDPs) for all cell components, including cathode, electrolyte, and anode. More specifically, a cell with Ba­(Co0.4Fe0.4Zr0.1Y0.1)0.95O3−δ (BCFZY-0.95) cathode, Ba­(Zr0.1Ce0.7Y0.1Yb0.1)0.95O3−δ (BZCYYb-0.95) electrolyte, and Ni–BZCYYb-0.95 anode is fabricated and tested for power generation. Electrochemical impedance spectroscopy in combination with the distribution of relaxation times verify the superior oxygen reduction reaction activity of the BCFZY-0.95 cathode compared to BaCo0.4Fe0.4Zr0.1Y0.1O3−δ and higher proton conductivity of BZCYYb-0.95 than BaZr0.1Ce0.7Y0.1Yb0.1O3−δ. At 650 °C, a BCDP cell with a thin-film electrolyte shows a high-power density of 840 mW cm–2. The cell is stably operated within the test period of 400 h of stability at 550 °C.

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Oxygen evolution reaction (OER) is a vital electrochemical process for various energy conversion and fuel production technologies. Co/Ni-rich perovskite oxides are extensively studied as promising alternatives to precious-metal catalysts; however, low-cost and earth-abundant iron (Fe)-rich perovskites are rarely investigated to date due to their poor activity and durability. This study reports an Fe-rich Sr 0.95 Ce 0.05 Fe 0.9 Ni 0.1 O 3−δ (SCFN) perovskite oxide with minor Ce/Ni co-doping in A/B sites as a high-performance OER electrocatalyst. Impressively, SCFN shows more than an order of magnitude enhancement in mass-specific activity compared to the SrFeO 3−δ (SF) parent oxide, and delivers an attractive small overpotential of 340 mV at 10 mA cm −2 , outperforming many Co/Ni-rich perovskite oxides ever reported. Additionally, SCFN displays robust operational durability with negligible activity loss under alkaline OER conditions. The increased activity and stability of SCFN can be ascribed to co-doping-induced synergistic promotion between structural and electronic modulation, where Ce doping facilitates the formation of a 3D corner-sharing cubic structure and Ni doping gives rise to strong electronic interactions between active sites, which is key to achieving a highly active long-life catalyst. Importantly, this strategy is universal and can be extended to other Fe-based parent perovskite oxides with high structural diversity.

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efficiency, low emissions, and fuel flexi bility. [1] Conventional SOFCs based on oxygenionconducting Y 0.16 Zr 0.84 O 1.92 (YSZ) electrolyte (OSOFCs), typically operate at temperatures above 800 °C, [2] which introduces several important draw backs, including high material, system, and operation costs, challenging cell com ponent compatibility, difficult sealing, and poor operational stability. Proton conducting SOFCs (also called protonic ceramic fuel cells, PCFCs) can address these issues due to their lower operation temperatures (350-650 °C). [3] The lower activation energy for proton conduction in oxides compared to oxygen conduc tion ensures a sufficiently high proton conductivity in the electrolyte at reduced temperatures. [4] Despite their great promise, the reported power outputs of PCFCs are still inferior to those of OSOFCs. One of the main reasons is the poor sintering of the electrolyte that introduces large grain boundary resistance. [3b] In addi tion, the phase reactions between NiO and cermet anode/ electrolyte during the cell fabrication process has an addi tional detrimental effect on the proton conductivity of the electrolyte. [5] As a result, for most of the reported PCFCs, the Anode-supported protonic ceramic fuel cells (PCFCs) are highly promising and efficient energy conversion systems. However, several challenges need to be overcome before these systems are used more widely, including the poor sintering of recently developed proton-conducting oxides and the decreased proton conductivity due to detrimental reactions between the nickel from anode and the electrolyte occurring during high-temperature co-sintering. Herein, a Ni doping strategy to increase the electrolyte sintering, suppress the detrimental phase reactions, and generate stable Ni nanoparticles for enhanced performance is proposed. A nickel-doped perovskite oxide is developed with the nominal composition of Ba(Zr 0.1 Ce 0.7 Y 0.1 Yb 0.1 ) 0.95 Ni 0.05 O 3−δ . Acting as a sintering aid, such a small amount of nickel effectively improves the sintering of the electrolyte. Concomitantly, reactions between nickel and the Ni-doped ceramic phase are suppressed, turning detrimental phase reactions into benefits. The nickel doping further promotes the formation of Ni nanoparticles, which enhance the electrocatalytic activity of the anode toward the hydrogen oxidation reaction and improve the charge transfer across the anode-electrolyte interface. As a result, highly efficient PCFCs are developed. The innovative anode developed in this work also shows favorable activity toward ammonia decomposition, making it highly promising for use in direct ammonia fuel cells.The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/smll.202200450.