Developing high-performance and low-cost electrocatalysts for oxygen reduction reaction (ORR) is still a great challenge for Al–air batteries. Herein, CeO2, a unique ORR promoter, was incorporated into ketjenblack (KB) supported Co3O4 catalyst. We developed a facile two-step hydrothermal approach to fabricate Co3O4–CeO2/KB as a high-performance ORR catalyst for Al–air batteries. The ORR activity of Co3O4/KB was significantly increased by mixing with CeO2 nanoparticles. In addition, the Co3O4–CeO2/KB showed a better electrocatalytic performance and stability than 20 wt % Pt/C in alkaline electrolytes, making it a good candidate for highly active ORR catalysts. Co3O4–CeO2/KB favored a four-electron pathway in ORR due to the synergistic interactions between CeO2 and Co3O4. In full cell tests, the Co3O4–CeO2/KB exhibited a higher discharge voltage plateau than CeO2/KB and Co3O4/KB when used in cathode in Al–air batteries.Keywords: adsorption of oxygen; Al−air batteries; Co3O4−CeO2/C; hydrothermal; oxygen reduction reaction; synergistic effects;

A novel template-free strategy was developed to synthesize a series of iron and nitrogen co-doped carbon materials (Fe-N-C) with different structures and active sites for oxygen reduction reaction (ORR). These catalysts with well-defined structures not only possess remarkable ORR activity but also provide unique models for probing active sites of Fe-N-C composites. Among these catalysts, the unique Fe1-N-G consisting of N-doped graphene-like nanosheets, carbon nanotubes and iron-based nanoparticles encapsulated in graphitic carbon layers showed the highest ORR activity with the half-wave potential of ~0.86 V, even outperforming the commercial 20 wt% Pt/C. This catalyst also exhibited better durability and discharge performance in practical Al-air batteries than the commercial Pt/C. It is worth noting that the BET surface area of Fe1-N-G is much smaller than that of N-G and Fe0.1-N-G. The superior electrocatalytic activity should be mainly attributed to the synergistic effect between non-crystalline FeNxCy moieties and the iron-based nanoparticles towards ORR in Fe1-N-G catalyst.Download high-res image (137KB)Download full-size image

•TiO2-δ nanocrystals encased into the porous carbon framework were fabricated.•Defects were introduced by magnesium reduction of MIL-125(Ti) precursor.•SIBs using TiO2-δ/C anode exhibit excellent sodium storage performance.Inferior electronic conductivity and sluggish sodium ion diffusion are still two big challenges for TiO2 anode material for Na ion batteries (SIBs). Herein, we synthesize TiO2/C composites by the pyrolysis of MIL-125(Ti) precursor and successfully introduce defects to TiO2/C composite by a simple magnesium reduction. The as-prepared defect-rich TiO2-δ/C composite shows mooncake-shaped morphology consisting of TiO2-δ nanocrystals with an average particle size of 5 nm well dispersed in the carbon matrix. When used as a SIBs anode, the defect-rich TiO2-δ/C composite exhibits a high reversible capacity of 330.2 mAh g−1 at 50 mA g−1 at the voltage range of 0.001–3.0 V and long-term cycling stability with negligible decay after 5000 cycles. Compared with other four TiO2/C samples, the electrochemical performance of defect-rich TiO2-δ/C is highly improved, which may benefit from the enhanced electronic/ionic conductivities owing to the defect-rich features, high surface area rendering shortened electronic and ionic diffusion path, and the suppress of the TiO2 crystal aggregation during sodiation and desodiation process by the carbon matrix.Download high-res image (395KB)Download full-size image

Rutile TiO2 is seldom studied as anode material for Na-ion battery for its much poorer Na storage performance than anatase phase. Herein, strategies of carbon coating and nitrogen doping are proposed and achieved together by a facile ball milling method followed by a high temperature sintering process to improve its electrochemical properties. The feature of this work lies in the dual N doping, not only to the carbon layers but also to the TiO2 lattice, resulting in sufficient oxygen vaccancies and defects in TiO2/C. Although the pristine TiO2 prepared by the similar method shows only 10 mAh g−1 capacity, the Na storage performance of N-doped TiO2/C is significantly enhanced. It demonstrates a high reversible discharge capacity of 211.2 mAh g−1 at 16.8 mA g−1 (0.1C). Moreover, a capacity retention of 92.3% is achieved after 500 cycles at 168 mA g−1 (1C), verifying ultrahigh reversible capacity and excellent cycling performance for rutile TiO2. The excellent Na storage performance of N-doped TiO2/C should be ascribed to the improved electronic and ionic conductivity resulting from dual N-doping strategy and shortened Na ion diffusion length due to the particle downsizing.Download high-res image (183KB)Download full-size image

Here we report a hybrid of MnOx–CeO2/Ketjenblack as a novel catalyst for oxygen reduction reaction (ORR) by a facile strategy. This hybrid exhibits comparable activity and better stability towards ORR than the commercial 20 wt% Pt/C due to the synergistic effect.

High-performance, low cost catalyst for oxygen reduction reaction (ORR) remains a big challenge. Herein, nanostructured NiCo2O4/CNTs hybrid was proposed as a high-performance catalyst for metal/air battery for the first time. The well-formed NiCo2O4/CNTs hybrid was studied by steady-state linear polarization curves and galvanostatic discharge curves in comparison with CNTs-free NiCo2O4 and commercial carbon-supported Pt. Because of the synergistic effect, NiCo2O4/CNTs hybrid exhibited significant improvement of catalytic performance in comparison with NiCo2O4 or CNTs alone, even outperforming Pt/C hybrid in ORR process. In addition, the benefits of Ni incorporation were demonstrated by the improved catalytic performance of NiCo2O4/CNTs compared to Co3O4/CNTs, which should be attributed to improved electrical conductivity and new, highly efficient, active sites created by Ni cation incorporation into the spinel structure. NiCo2O4/CNTs hybrid could be used as a promising catalyst for high power metal/air battery.

Poor cycling performance is still the big challenge for aqueous rechargeable lithium batteries (ARLBs), in which the instability of the anode is considered to be the main issue. In this work, NaV6O15 nanoflakes were synthesized by a two-step approach and a NaV6O15//LiMn2O4 ARLB system with superior cycling performance was constructed. The galvanostatic charge–discharge result demonstrates an initial discharge capacity of 110.7 mA h g−1 (based on anode mass) at 150 mA g−1 and the capacity retention of ca. 90% and 80% at 300 mA g−1 after 100 and 400 cycles, respectively. Such superior cycling performance of ARLBs is mainly due to the intrinsic 3-D tunneled structure of NaV6O15, nanoflake morphology and relatively stable electrode surface, as verified by the X-ray diffraction (XRD), electrochemical impedance spectroscopy (EIS), and scanning electron microscopy (SEM) results of the tested electrodes. Moreover, a simple single-phase reaction mechanism during the lithium ion insertion/extraction process is observed for NaV6O15 by XRD analysis.

In this work, a novel electrocatalyst, Mn0.3Ce0.7O2, with relatively high power performance has been, for the first time, proposed for metal/air batteries. The as-prepared samples are well characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), inductively coupled plasma (ICP) and nitrogen sorption experiments. Meanwhile, electrocatalytic activity towards the reduction of oxygen of Mn0.3Ce0.7O2 is compared with those of the pure MnO2 and CeO2. It is observed that the Mn0.3Ce0.7O2 solid solution is well formed after the calcination. Electrochemical results show that Mn0.3Ce0.7O2 exhibits much higher electrocatalytic activity in the oxygen reduction reaction (ORR) than pure MnO2 under high discharge current density, which is probably attributed to the effective activation of molecular oxygen over the Mn0.3Ce0.7O2 solid solution and higher surface area.

•Mg2Ni alloy was rapidly quenched in a static magnetic field.•The as-prepared alloy has directional columnar structures and high internal strain.•High quenching rate goes against the formation of directional columnar crystals.•The as-prepared alloy exhibits improved electrochemical performance.Mg2Ni alloy prepared by vacuum induction melting is rapidly quenched in the presence of an external magnetic field. The effects of magnetic field on the microstructure and electrochemical hydrogen storage behavior of Mg2Ni alloy are well investigated for the first time. X-ray diffraction (XRD), scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS) studies show that the applied magnetic field results in a preferred orientation growth during the rapid solidification of alloy melt, which induces the generation of columnar crystals. Meanwhile, decreased grain size and increased internal strain are noted for this alloy, as well as the eliminated composition segregation. It is found on the charge–discharge experiments that the as-prepared alloy displays an increased capacity and improved cycle stability compared to the alloys without magnetic field treatment. The potentiodynamic polarization results indicate that the Mg2Ni alloy exhibits relatively high corrosion resistance against the alkaline solution. Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) results demonstrate enhanced electrochemical kinetics for the treated Mg2Ni alloy, consistent with the enhanced electrochemical properties.

The effect of static magnetic field treatment for synthesis of Mg2Ni0.8Mn0.2 alloys during rapid quenching was investigated in this paper. X-ray diffraction (XRD) and scanning electron microscope (SEM) results show that the transversal static magnetic field can effectively refine the grain size, producing nanocrystalline inside. This distinct phenomenon is probably attributed to the Lorentz force suppressing the crystallization of the hydrogen storage alloys and the thermoelectric effect. Mainly due to the grain refinement, the discharge capacity of Mg2Ni0.8Mn0.2 alloy is raised from 79 to about 200 mA h g−1. It is confirmed that Mg2Ni0.8Mn0.2 alloy by magnetic field assisted approach possesses enhanced electrochemical kinetics and relatively high corrosion resistance against the alkaline solution, thus resulting in higher electrochemical properties.

In this study, AlF3 was successfully coated on the surface of LiV3O8 nanosheets, as verified by transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDX). AlF3 coated LiV3O8 exhibited the significantly improved cycling stability with the capacity retention of ca. 91% over 50 cycles at 150 mA g− 1, while that of the bare one was only 61%. When cycling at 55 °C, the bare electrode delivered a much larger capacity loss (44.8%) in comparison with that (19.1%) of the coated one. On the basis of the XRD, CV and EIS results, it was suggested that the AlF3 coating layer could protect the bulk material well and facilitate the kinetics of Li-ion diffusion, leading to smaller electrochemical impedance, thus resulted in improvement of cycling stability for LiV3O8.Highlights► AlF3 was successfully coated on the surface of LiV3O8 nanosheets. ► AlF3 coated LiV3O8 exhibited the significantly improved cycling stability. ► Electrochemical property of the coated one at elevated temperature was improved. ► AlF3 layer could protect the bulk material well.

Poor cycling performance is still the big challenge for aqueous rechargeable lithium batteries (ARLBs), in which the instability of the anode is considered to be the main issue. In this work, NaV6O15 nanoflakes were synthesized by a two-step approach and a NaV6O15//LiMn2O4 ARLB system with superior cycling performance was constructed. The galvanostatic charge–discharge result demonstrates an initial discharge capacity of 110.7 mA h g−1 (based on anode mass) at 150 mA g−1 and the capacity retention of ca. 90% and 80% at 300 mA g−1 after 100 and 400 cycles, respectively. Such superior cycling performance of ARLBs is mainly due to the intrinsic 3-D tunneled structure of NaV6O15, nanoflake morphology and relatively stable electrode surface, as verified by the X-ray diffraction (XRD), electrochemical impedance spectroscopy (EIS), and scanning electron microscopy (SEM) results of the tested electrodes. Moreover, a simple single-phase reaction mechanism during the lithium ion insertion/extraction process is observed for NaV6O15 by XRD analysis.

In this work, a novel electrocatalyst, Mn0.3Ce0.7O2, with relatively high power performance has been, for the first time, proposed for metal/air batteries. The as-prepared samples are well characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), inductively coupled plasma (ICP) and nitrogen sorption experiments. Meanwhile, electrocatalytic activity towards the reduction of oxygen of Mn0.3Ce0.7O2 is compared with those of the pure MnO2 and CeO2. It is observed that the Mn0.3Ce0.7O2 solid solution is well formed after the calcination. Electrochemical results show that Mn0.3Ce0.7O2 exhibits much higher electrocatalytic activity in the oxygen reduction reaction (ORR) than pure MnO2 under high discharge current density, which is probably attributed to the effective activation of molecular oxygen over the Mn0.3Ce0.7O2 solid solution and higher surface area.

Here we report a hybrid of MnOx–CeO2/Ketjenblack as a novel catalyst for oxygen reduction reaction (ORR) by a facile strategy. This hybrid exhibits comparable activity and better stability towards ORR than the commercial 20 wt% Pt/C due to the synergistic effect.