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The electrocatalytic oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) are the core reactions in reversible zinc-air batteries but are kinetically challenging because of their complex multielectron transfer process. In this case, the exploration and rational design of non-precious bifunctional oxygen electrocatalysts with dense active sites and optimized electronic structures can facilitate favorable 4e-transfer. In this study, we report a highly reversible bifunctional electrocatalyst for flexible Zn-air batteries featuring pyridinic-N exclusively enriched carbon-nanotube-encased nickel-iron (NiFe) interfacial alloy nanoparticles derived from an LDH template on knitted carbon fiber cloth. The NiFe nanoparticles were catalytically released from NiFe-MOFs to form CNT tentacles when pyrolyzed in an inert atmosphere. XPS and XAS studies revealed the dominant presence of pyridinic-N, which reduces electron localization around NiFe centers and improves the interaction with oxygenated species. As a result, NiFe-N-CNT-KCC catalysts exhibited a low operating overpotential (h10) of 173 mV for the OER and a half-wave potential (E1/2) of 0.87 V for the ORR, which are superior to benchmark electrocatalysts. As an air cathode for zinc-air batteries, the NiFe-N-CNT-KCC-based battery showed an excellent electrochemical performance, with an open circuit voltage (OCV) of 1.55 V, high power density of 153 mW cm-2, excellent specific capacity of 793.2 mA h g-1, and long-term stability. Impressively, a solidstate flexible zinc-air battery with the NiFe-N-CNT-KCC cathode showed an admirable rate performance and exceptional mechanical stability under arbitrary bending and twisting conditions, showing great potential for practical implementation in next-generation high-power and high-energydensity batteries wearable applications. [ABSTRACT FROM AUTHOR]

A functionally graded membrane (FGM) with a special spiral-structured cellulose acetate (CA) membrane was prepared by electrospinning under different collection distances. The membrane morphology was analyzed by scanning electron microscopy (SEM). FESEM images revealed that the high concentration shows the formation of fibers with an irregular diameter, with a large diameter distribution range. The fiber collected at a short distance of 10 cm experiences the strong electrostatic force, resulting in the short flight time for the polymer jet. This causes the bending instability of the polymer jet forming the comparatively thick fiber diameters, whereas the fiber collected at 15 cm shows the presence of a smooth, homogeneous diameter. Furthermore, the water flux of the membrane was determined using 50 mL of Amicon stirred cells. The fiber collected at different distances showed diameter variation, which is used to design a special spiral structure on the membrane by auto-moving the collector between the fixed distances of 10–20 cm. This technique will reveal a new approach for the fabrication of a special spiral structure on the nanofibrous membrane for different biomedical applications from different polymers. Meanwhile, the fabricated FGM with a special spiral-structure CA membrane demonstrates high water permeation flux. [ABSTRACT FROM AUTHOR]

The rational design and steering of earth-abundant, efficient, and stable electrocatalysts for hydrogen generation is highly desirable but challenging with catalysts free of platinum group metals (PGMs). Mass production of high-purity hydrogen fuel from seawater electrolysis presents a transformative technology for sustainable alternatives. Here, a heterostructure of molybdenum selenide-nickel selenide (Mo 3 Se 4 -NiSe) core-shell nanowire arrays constructed on nickel foam by a single-step in situ hydrothermal process is reported. This tiered structure provides improved intrinsic activity and high electrical conductivity for efficient charge transfer and endows excellent hydrogen evolution reaction (HER) activity in alkaline and natural seawater conditions. The Mo 3 Se 4 -NiSe freestanding electrodes require small overpotentials of 84.4 and 166 mV to reach a current density of 10 mA cm -2 in alkaline and natural seawater electrolytes, respectively. It maintains an impressive balance between electrocatalytic activity and stability. Experimental and theoretical calculations reveal that the Mo 3 Se 4 -NiSe interface provides abundant active sites for the HER process, which modulate the binding energies of adsorbed species and decrease the energetic barrier, providing a new route to design state-of-the-art, PGM-free catalysts for hydrogen production from alkaline and seawater electrolysis., (© 2023 Wiley-VCH GmbH.)