Rechargeable metal–air batteries and water splitting are highly competitive options for a sustainable energy future, but their commercialization is hindered by the absence of cost-effective, highly efficient and stable catalysts for the oxygen evolution reaction. Here we report the rational design and synthesis of a double perovskite PrBa0.5Sr0.5Co1.5Fe0.5O5+δ nanofiber as a highly efficient and robust catalyst for the oxygen evolution reaction. Co-doping of strontium and iron into PrBaCo2O5+δ is found to be very effective in enhancing intrinsic activity (normalized by the geometrical surface area, ∼4.7 times), as validated by electrochemical measurements and first-principles calculations. Further, the nanofiber morphology enhances its mass activity remarkably (by ∼20 times) as the diameter is reduced to ∼20 nm, attributed to the increased surface area and an unexpected intrinsic activity enhancement due possibly to a favourable eg electron filling associated with partial surface reduction, as unravelled from chemical titration and electron energy-loss spectroscopy.

Hybrid supercapacitors consisting of a battery-type faradaic electrode/capacitive electrode couple could achieve significantly improved energy density compared to that of the state-of-theart supercapacitors due to the extended voltage window and introduction of a battery-type electrode with high capacity. However, their commercial application is still hampered by lacking of proper electrode materials and structures. Here, a series of Co x Ni 1-x (OH) 2-reduced graphene oxide (rGO) nanocomposites are derived from a facile process at room temperature using hydrous hydrazine and different ratios of Co(II) to Ni(II) to tune the composition and morphology. In particular, an architectural composite electrode consisting of porous Co x Ni 1x (OH) 2 disks wrapped by rGO achieves high capacity, rate capability (743 and 545 C g-1 at 1 A g-1 and 20 A g-1 , respectively), and long cycling life. When coupled with a p-phenylenediamine (PPD)-modified rGO, the resulting hybrid supercapacitor exhibits superior energy densities of 72 and 44 W h Kg-1 at a power density of 797 W Kg-1 and 16.7 kW Kg-1 , respectively, and excellent cycling stability for 20,000 cycles at 20 A g-1 , implying that it is a very promising device for portable power and next-generation energy storage.

A series of porous La0.6Sr0.4Co1–xFexO3–δ (x = 0–1) nanofibers with diameters of 54–71 nm are synthesized by electrospinning using appropriate polymers and different processing parameters. When tested as a catalyst for oxygen evolution reaction (OER), an La0.6Sr0.4Co0.6Fe0.4O3–δ (LSCF6464) nanofiber catalyst (with a specific surface area of 24.2 m2 g−1) exhibits a potential (vs Ag/AgCl) of 647 mV at 10 mA cm−2disk, which is much smaller than that of a powder‐type commercial LSCF (786 mV) and also smaller than that of the state‐of‐the‐art IrO2 catalysts (660 mV). The LSCF6464 nanofiber catalyst further delivers an outstanding durability, with almost no observable change in potential at a current density of 10 mA cm−2disk for more than 3 h. In contrast, the performance of an IrO2 catalyst degrades continuously under the same testing conditions. The findings suggest that the LSCF nanofiber is a promising OER electrocatalyst for metal–air batteries and water electrolysis.