Well-dispersed trimetallic-alloyed PdSnCo nanocrystals with an average size of 7 nm are supported on nitrogen-doped reduced graphene (NG) nanosheets by a solvothermal method. The PdSnCo/NG nanocatalyst is characterized by scanning electron microscopy, energy dispersive spectroscopy, transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. As a result, the PdSnCo/NG exhibits high catalytic activity toward oxygen reduction reaction and high electrochemical stability in alkaline medium, compared to commercial 10% Pd black, binary PdSn/NG, and PdCo/NG. Moreover, PdSnCo/NG nanocatalyst shows high discharge capacity of 6750 mAh g−1, low charge voltage and predominant cycleability for lithium-air batteries.

•An amorphous oxygen-deficient TiO2-x thin layer on CNTs was synthesized by ALD.•The CNTs@TiO2-x is employed as cathode material for lithium-air battery.•The cathode shows significant improvement in discharge capacity and durability.•The mechanisms of electrode reactions for CNTs@TiO2-x cathode are proposed.The amorphous oxygen-deficient TiO2-x thin layer coated carbon nanotubes (CNTs) are synthesized by atomic layer deposition and employed as cathode materials for lithium-air battery. The cathode demonstrates high electrocatalytic activity toward electrode reactions, resulting from the introduction of oxygen-deficient TiO2-x into the nanocomposites. It is found that the intrinsically isotropic nature of amorphous TiO2 which a certain amount of Ti3.5+ and Ti3+ can improve the catalytic activity. Consequently, the battery with the corresponded CNT@TiO2-x cathode shows high discharge/charge capacities and good cycling performance, which the cyclic retention of more than 90 cycles are achieved, while with the pristine CNTs only 50 cycles are obtained. This study provides an approach to fabricate cathode materials for lithium-air battery and moreover clarifies the influence of oxygen vacancies of TiO2 on the electrochemical performance.

•Ru/N-CNFs@TiO2 nanocomposite is prepared by electrospinning and ALD.•The Ru/N-CNFs@TiO2 is employed as cathode material for Li-O2 battery.•The cathode shows significant improvement in discharge capacity and durability.•DFT calculation is used to reveal the mechanisms of electrode reactions.Flexible Li-O2 batteries have attracted worldwide research interests and been considered to be potential alternatives for the next-generation flexible devices. Nitrogen-doped carbon nanofibers (N-CNFs) prepared by electrospinning are used as flexible substrate and an amorphous TiO2 layer is coated by atomic layer deposition (ALD) and then decorated with Ru nanoparticles. The Ru/N-CNFs@TiO2 composite is directly used as a free-standing electrode for Li-O2 batteries and the electrode delivers a high specific capacity, improved round-trip efficiency and good cycling ability. The superior electrochemical performance can be attributed to the amorphous TiO2 protecting layer and superior catalytic activity of Ru nanoparticles. Based on density functional theory (DFT) calculations from first principles, the carbon electrode after coating with TiO2 is more stable during discharge/charge process. The analysis of Li2O2 on three different interfaces (Li2O2/N-CNFs, Li2O2/TiO2, and Li2O2/Ru) indicates that the electron transport capacity was higher on Ru and TiO2 compared with N-CNFs, therefore, Li2O2 could be formed and decomposed more easily on the Ru/N-CNFs@TiO2 cathode. This work paves a way to develop the free-standing cathode materials for the future development of high-performance flexible energy storage systems.

Ternary PdNiM (M = Cu or Sn) alloys are supported on nitrogen-doped graphene (NG) by a simple chemical reduction method. PdNiM (M = Cu or Sn) are used as nanocatalysts for the oxygen reduction reaction (ORR) in an alkaline electrolyte. The nanocatalysts are characterized by scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The physical properties demonstrate that PdNiM (M = Cu or Sn) nanoparticles are highly alloyed and well dispersed on NG. PdNiM (M = Cu or Sn) electrocatalysts exhibit high ORR activity and stability, which are better than 20% commercial Pd black and close to 20% commercial Pt/C. These results indicate that the addition of Sn or Cu into a PdNi-based catalyst not only reduces the level of Pd but also greatly improves the catalytic activity.

Nitrogen-doped TiO2 is in situ synthesized by plasma enhanced atomic layer deposition on carbon nanotubes (N-TiO2/CNTs). The prepared N-TiO2/CNT nanocomposites are employed as anode materials for sodium ion batteries. The specific capacity of an N-TiO2/CNT electrode is 1.45 times higher than that of a TiO2/CNT electrode at a current density of 50 mA g−1 after 200 cycles. It is demonstrated that N-TiO2/CNTs are more effective in an electrochemical Na cell due to the enhanced kinetics which results from the nitrogen-doping and the amorphous feature.

•Sulfur-doped graphene (SG) is prepared by a microwave-assisted irradiation method.•PdW alloy nanocrystals are supported on sulfur-doped graphene.•The PdW/SG is employed as an electrocatalyst for the oxygen reduction reaction.•The electrocatalyst shows a significant improvement in activity compared with Pd-SG and Pd-G.Sulfur-doped graphene (SG) is synthesized by a simple microwave irradiation method and PdW nanoparticles are grown in situ on SG. The electrocatalyst shows excellent activity for the oxygen reduction reaction (ORR) in alkaline solution and the reaction kinetics investigation shows that PdW-SG follows a four-electron transfer process in ORR, which is much better than Pd-SG or Pd-G. The improved catalytic performance may result from the changes in the electronic structure when Pd alloys with W as well as the strong interactions between the PdW nanoparticles and SG.

Si/Ni3Si-encapulated carbon nanofiber composites are synthesized by a facile one-pot electrospinning method and employed as three-dimensional network structured anode materials for lithium ion batteries. It is demonstrated that the composite exhibited increased cycling performance with a reversible capacity of 1132.4 mAh g−1 after 200 cycles, which is 45% higher compared to the bare Si. The improved battery performance is attributed to the alloying of Si with Ni, which could effectively alleviate the volume expansion during lithium insertion/extraction. In addition, the formation of one dimensional nanofiber in which Si/Ni3Si nanoparticles are well distributed not only increases the electronic conductivity, but also enhances the mechanical strength of the electrodes, resulting in increased cycle stability.

SnSbZn–carbon (SnSbZn–C)-based hybrid composite nanofibers are synthesized by electrospinning. The zero-dimensional alloy nanoparticles, SnSb and SbZn, are enclosed by one-dimensional carbon nanofibers, therefore they exhibit improved electrochemical performance as anode materials for lithium-ion batteries. For the 200th cycle, the discharge capacity remains at 663 mA h g−1 and the capacity retention is 84%, the high cycling stability can be attributed to the unique one-dimensional nanofiber structure which can accommodate the volume expansion generated during cycling, and prevent the particles from aggregating.