Ni(OH)2 derived from an MOF template was synthesized as an electrode material for supercapacitors. The electrochemical performance of the electrode was adjusted by effectively regulating the morphology of Ni(OH)2. The evolution of electrochemical performance of the electrode with morphology of Ni(OH)2 was highlighted in detail, based on which honeycomb-like Ni(OH)2 was successfully synthesized, and endowed the electrode with outstanding electrochemical performance. For the three-electrode testing system, honeycomb-like Ni(OH)2 exhibited a very high specific capacitance (1865 F·g−1 at 1 A·g−1, 1550 F·g−1 at 5 mV·s−1). Moreover, it also presented an excellent rate capability and cycling stability, due to 59.46 % of the initial value (1 A·g−1) being retained at 10 A·g−1, and 172% of initial value (first circle at 50 mV·s−1) being retained after 20,000 cycles. With respect to the assembled hybrid supercapacitor, honeycomb-like Ni(OH)2 also displayed superior electrochemical performance, with a high energy density (83.9 Wh·kg−1 at a power density of 374.8 W·kg−1). The outstanding electrochemical performance of Ni(OH)2 should be attributed to its unique honeycomb-like structure, with a very high specific surface area, which greatly accelerates the transformation and diffusion of active ions.

Ultrathin gold nanowires (AuNWs) play an important role in wearable devices, biological detection, and other fields. However, their applications in transparent conduction are limited due to high junction resistance caused by the oleyamine (OAm) ligand and structural instability caused by Rayleigh instability. A treatment method has been proposed to eliminate these two defects via a hydrogen sulfide (H2S) atmosphere and heat treatment. The nanowires are subjected to heat treatment in a hydrogen sulfide atmosphere, which induces the nanowires to fracture into gold particles (AuNPs) and evolve into a stable spider-web-like structure. As a result, the conductivity of the treated film is significantly improved, reaching 65 Ω/sq at 120 °C, 50 min, and 1000 ppm of H2S. The electrical properties of the film can be maintained for more than one month. This method suggests a promising approach to ultrathin AuNWs for excellent improvement of electronic conduction and stability, which can be used in wearable devices.

The NiO/graphene (NiO/G) composite nanofibers were successfully synthesized by simple electrospinning followed by heat treatment. They as anode materials for lithium ion batteries demonstrated the more outstanding electrochemical performance when compared with the NiO + Ni composite nanofibers as the reference. NiO/G exhibited a higher discharging/charging capacity (about 712 mAh·g−1 at the third cycle) with a coulombic efficiency of nearly 100% than NiO + Ni (547 mAh·g−1). NiO/G also demonstrated the excellent cycling stability due to its higher discharging capacity of 571 mAh·g−1 and retention rate of 78% than NiO + Ni (184 mAh·g−1 and 33%) when subject to 50 cycles at 100 mA·g−1. Moreover, its rate performance was also greatly improved when compared with NiO + Ni owing to its higher discharging capacity (305 mAh·g−1, 556 mAh·g−1) and retention rate (44%, 80%) at the current density increased from 100 mA·g−1 to 2000 mA·g−1, and then recovered to 100 mA·g−1. The outstanding electrochemical performance of the NiO/G electrode is closely related to its lower ohmic resistance (2.1 Ω)/charge transfer resistance (86.5 Ω), and stronger diffusion capability of Li+ resulting from the high specific surface area, excellent conductivity and a certain charge storage capacity of graphene.

Hollow-structured NiO + Ni nanofibers wrapped by graphene were designed and successfully fabricated via a simple method. First, solid NiO + Ni nanofibers were prepared by electrospinning followed by calcination. Here, a portion of the metallic Ni was retained to improve the electrochemical performance of NiO by adjusting the calcination temperature. Next, the nanofibers were thoroughly mixed with different amounts of graphene and calcinated once more to form hollow-structured NiO + Ni nanofibers with an extremely high specific surface via the reaction between graphene and NiO on the nanofiber surface and subsequent migration of NiO into the nanofibers. Results showed that the obtained hollow-structured NiO + Ni electrode demonstrates optimal electrochemical performance when the graphene content is controlled to 3 wt%. The first cycle discharge/charge specific capacity of the electrode peaked (1596/1181 mAh · g−1 ) at 100 mA · g−1, with a coulombic efficiency of approximately 74% (60% for 0 wt% graphene, 65% for 1 wt% graphene, and 51% for 4 wt% graphene). It also presented excellent cycling stability after 100 cycles at 100 mA · g−1 on account of its high retained discharge specific capacity (251 mAh · g−1 for 0 wt% graphene, 385 mAh · g−1 for 1 wt% graphene, 741 mAh · g−1 for 3 wt% graphene, and 367 mAh · g−1 for 4 wt% graphene). Moreover, the synthesized electrode possessed outstanding rate capability owing to its large average discharge specific capacity of approximately 546 mAh · g−1 (45 mAh · g−1 for 0 wt% graphene, 256 mAh · g−1 for 1 wt% graphene, and 174 mAh · g−1 for 4 wt% graphene) from 100 mA · g−1 to 2000 mA · g−1. The observed improvement in electrochemical performance could be attributed to the increase in active sites and decrease in charge transport distance in the hollow-structured NiO + Ni nanofibers. Excessive introduction of graphene caused a sharp loss in electrochemical performance due to the agglomeration of graphene sheets on the nanofiber surfaces.

AlCrCoNiFeCTax (x = 0, 0.5 and 1.0) high-entropy alloys coatings were synthesized on 45# steel by laser cladding. The microstructural evolution of the coatings with the change in x was analyzed in detail. The effect of Ta content on the wear behaviors of the coatings at different circumstances (in air and 3.5 wt.% NaCl solution) was especially highlighted. The microstructure presented the following change: equiaxed BCC (Body Centered Cubic) grains + fine MC (carbide, M = Al, Cr, Co and Ni) particles (x = 0) → equiaxed BCC grains + coarse TaC blocks + fine TaC particles (x = 0.5) → flower-like BCC grains + coarse TaC blocks + eutecticum (BCC + TaC) (x = 1.0). The average microhardness of the coatings demonstrated an upward tendency with increasing x due to the combination of the stronger solid solution and dispersion strengthening from the significant difference in atomic radius between Ta and Fe and the formation of TaC with an extremely high hardness. The wear rates of the coatings were gradually reduced both in air and in NaCl solution along with the increase in Ta content, which were lower than those of the substrate. The wear rates of the coatings with x = 0.5 and 1.0 in NaCl solution were slightly reduced by about 17% and 12% when compared with those in air. However, the values of the substrate and the coating without Ta in NaCl solution were sharply enhanced by 191% and 123% when compared with those in air. This indicated that the introduction of Ta contributed to the improvement in wear resistance both in air and in NaCl solution.