One of the main challenges for advanced metallic nanoparticles (NPs) supported functional perovskite catalysts is the simultaneous achievement of a high population of NPs with uniform distribution as well as long-lasting high performance. These are also the essential requirements for optimal electrode catalysts used in solid oxide fuel cells and electrolysis cells (SOFCs and SOECs). Herein, we report a facile operando manufacture way that the crystal reconstruction of double perovskite under reducing atmosphere can spontaneously lead to the formation of ordered layered oxygen deficiency and yield segregation of massively and finely dispersed NPs. The real-time observation of this emergent process was performed via an environmental transmission electron microscope. Density functional theory calculations prove that the crystal reconstruction induces the loss of coordinated oxygen surrounding B-site cations, serving as the driving force for steering fast NP growth. The prepared material shows promising capability as an active and stable electrode for SOFCs in various fuels and SOECs for CO2 reduction. The conception exemplified here could conceivably be extended to fabricate a series of supported NPs perovskite catalysts with diverse functionalities.

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catalysts with low-cost and earth-abundant materials. [5][6][7][8][9][10] In terms of achieving the best performances, the HER is usually carried out in an acidic environment while the OER in an alkaline condition. Nevertheless, practical utilization of these electrodes in an integrated electrolysis device has been hindered since the HER and OER catalysts usually require very different pH values in order to produce long lifetimes and high activities. In this context, a bifunctional electrocatalyst with high activities for both the OER and HER in an identical condition is desired. [10][11][12][13] Most state-of-the-art water splitting catalyst researches have been focused on the development of nonprecious metal catalysts that are competitive to precious metals. [5][6][7][8][9][10][14][15][16][17][18] As a result, perovskites are being spotlighted as promising candidates due to their favorable compositional flexibility and good stability in a wide range of electrochemical window, thus enabling easy modification of their catalytic properties. Ba 0.5 Sr 0.5 Co 0.8 Fe 0.2 O 3-δ (BSCF) has been introduced as an excellent OER catalyst, whose catalytic activity for water oxidation is one order higher than that of IrO 2 in alkaline conditions. [16][17][18] Furthermore, Xu et al. proved BSCF is capable of catalyzing HER in alkaline conditions. [15] They also found that its HER catalytic performance and durability can be drastically improved via proper A-site Pr-doping. Nevertheless, surface amorphous phases in Pr-doped BSCF were still found after the durability test. It was reported that a smaller size mismatch between the host and dopant cations in the A-site has a remarkable effect on rationalizing the stabilities and activities of cubic BSCF. [19,20] Consequently, we predict that the La-doped BSCF would possess better robustness than Pr-doped BSCF (note that the sequence of ion radiuses is Ca 2+

To date, most investigations of Ni-Fe bimetallic catalysts for solid oxide fuel cells (SOFCs) have focused on materials with micro-scale particle sizes, which severely restrict their catalytic activity. In this study, we fabricated a Ni- and/or Fe-doped A-site-deficient LaSrCrO3 perovskite (A-LSC) bimetallic anode material on which the in situ exsolution of uniformly dispersed nano Ni, Fe and Ni-Fe alloy with an average particle size of 25 to 30 nm was facilitated by the introduction of A-site deficiency under a reducing atmosphere. The dopants were shown to significantly enhance the electrical conductivity of the material by many orders of magnitude. Further characterization of the bimetallic material showed that the addition of Fe changed the reduction behavior and increased the amount of oxygen vacancies in the material. Fuel cell performance tests demonstrated that the prepared bimetallic anode catalyst with a highly catalytically active nano Ni-Fe alloy promoted the electrochemical performance in 5000 ppm H2S-syngas and improved the carbon deposition resistance compared to a monometallic anode catalyst.