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• HSAs/ZIF-8 electrode with excellent electrochemical performances was fabricated. • DFT simulations clarify the effect of ZIF-8 on superior properties of HSAs. • Extended systems of HSAs/ZIF-based composites show enhanced HRD properties. Zeolitic imidazolate framework ZIF-8 polyhedral crystal is coated uniformly on the surface of hydrogen storage alloys (HSAs) using a simple method of wet-chemical. On the one hand, the adsorption of H 2 on ZIF-8 verified by density functional theory simulations is in favor of the suppression of side reaction of H 2 evolution, enlisting the improved discharge capacity. On the other hand, the adsorbed H 2 on ZIF-8 is able to be desorbed to H atom further adsorbed on HSAs, increasing the H concentration on electrode/electrolyte interface, which is beneficial to the enhanced electrochemical reaction rate and H diffusion rate. As a consequence, compared with the bare HSAs electrode, the HSAs/ZIF-8 hybrid electrode exhibits excellent electrochemical performances for enhanced maximum discharge specific capacity (302.6 vs. 328.2 mAh g–1) and superior high-rate dischargeability (capacity retention increases from 13.5 to 30.2% at a discharge current density of 3000 mA g–1). Furthermore, another ZIF-based system of HSAs/ZIF-67 electrode shows similar electrochemical properties to the HSAs/ZIF-8 electrode; besides, the extended system of HSAs/ZIF-8-graphene hybrid electrode also exhibits enhanced rate capabililty. In this work, zeolitic imidazolate framework ZIF-8 polyhedral crystal is coated uniformly on the surface of hydrogen storage alloys (HSAs) using a simple method of wet-chemical. The composite of HSAs/ZIF-8 exhibits superior electrochemical performances and the corresponding mechanism was revealed by the density functional theory simulations. [Display omitted] [ABSTRACT FROM AUTHOR]

Metal/carbon-based materials derived from metal-organic frameworks have recently attracted great attention for oxygen reduction reaction (ORR) electrocatalysts, but poor electrical conductivity and insufficient stability owing to granular structures, as well as low production hinder their practical applications. Herein, we design and synthesize Co nanoparticles decorated on N-doped carbon nanonecklaces (Co/N-CNNs) by way of electrospinning and following carbonization. The Co/N-CNNs hybrid exhibits excellent ORR performance with a positive half-wave potential (0.865 V) and a large limiting current density (5.35 mA cm−2), even comparable to those of Pt/C. Such superior electrocatalytic properties are attributed to the distinctive necklace-like structure, which supplies high specific surface area, hierarchical porous structure, well-dispersed and covered Co nanoparticles, and hierarchical architecture of N-doped carbon. This work provides an effective strategy to fabricate ORR electrocatalysts with well-designed structure and mass production via electrospinning. In this work, a hybrid of Co nanoparticles decorated on N-doped carbon nanonecklaces (Co/N-CNNs) was constructed via electrospinning and the following carbonization. Owing to the unique structure, such as high specific surface area and hierarchical porosity, dispersed and protected Co nanoparticles, as well as N-doped hierarchical carbon architecture, the optimized Co/N-CNNs hybrid as an oxygen reduction reaction electrocatalyst displays remarkable activity, stability, and methanol tolerance, even superior to Pt/C in alkaline condition. [Display omitted] • Co/N-CNN-2 was fabricated through electrospinning. • Co/N-CNN-2 possesses a unique necklace-like structure. • Co/N-CNN-2 displays superior ORR performance. • The mechanisms behind the superior performance are clarified. [ABSTRACT FROM AUTHOR]

The main challenge for the applications of nickel-metal hydride (Ni-MH) batteries in low-temperature regions derives from the sluggish kinetics of its negative electrode materials—hydrogen storage alloys (HSAs). Here we design and fabricate a series of Co-free HSAs, exhibiting superior electrochemical reaction kinetics and low-temperature dischargeability performance. One novel candidate, La 0.95 Y 0.05 Ni 4.5 Mn 0.4 Al 0.35 , shows the highest discharge specific capacity of 283.5 mAh g−1 among reported data of AB 5 -type HSAs at a high discharge current density of 3000 mA g−1, which is 4.3 times that of the alloy synthesized with the same composition as a commercial alloy (MmNi 3.55 Co 0.75 Mn 0.4 Al 0.3) electrode (65.9 mAh g−1). Moreover, this Co-free La 0.95 Y 0.05 Ni 4.5 Mn 0.4 Al 0.35 alloy electrode can remain a discharge specific capacity of 255.8 mAh g−1 at a low temperature of 233 K while the synthesized MmNi 3.55 Co 0.75 Mn 0.4 Al 0.3 alloy electrode shows a specific capacity of only 9.5 mAh g−1. The discharge specific capacity of the above Co-free alloy electrode can reach 30.0 mAh g−1 228 K, making it a promising candidate as a negative electrode material for applications in Ni-MH batteries at ultra-low temperature. Image 1 • A series of high-performance Co-free HSAs were designed and fabricated. • One of them shows the best rate property among AB 5 -type HSAs. • The discharge capacity of the above alloy can reach 30 mAh g−1 at 228 K. [ABSTRACT FROM AUTHOR]

• PANI/HSAs electrode with excellent electrochemical performances was fabricated. • DFT simulations clarify the effect of PANI on superior properties of HSAs. • Extended systems of HSAs/PANI-based composites show enhanced HRD properties. Nanoparticle-shaped polyaniline (PANI) is coated uniformly on the surface of hydrogen storage alloys (HSAs) by in situ polymerization of aniline using an electroless method. PANI has a strong attractive interaction with hydrogen during electrochemical reactions, which has been validated by the density functional theory simulations. Moreover, it is easy to form a nickel-rich layer on HSAs surface with the presence of acid during the fast polymerization process of aniline, which is beneficial for the enhancement of electrochemical reaction kinetics. Both of which contribute to the excellent electrochemical performances of the composite of HSAs/PANI as a negative electrode material in nickel-metal hydride (Ni-MH) battery. Compared with the bare HSAs electrode, the maximum discharge capacity of the HSAs/PANI electrode increases from 302.6 to 330.8 mAh g−1 and the capacity retentions enhances from 13.5 to 30.9% at a discharge current density of 3000 mA g−1. The extended systems of HSAs/Ni-doped PANI and HSAs/graphene/PANI composites also show improved high-rate dischargeability properties. Image, graphical abstract In this work, polyaniline (PANI) was coated uniformly on the surface of hydrogen storage alloys (HSAs) by in situ polymerization of aniline using an electroless method. The composite of HSAs/PANI exhibits superior electrochemical performances and the corresponding mechanism was revealed by the density functional theory simulations. [ABSTRACT FROM AUTHOR]