Search

Ni3S2 nanowires were synthesized in situ using a one-pot hydrothermal reaction on Ni foam (NF) for use in supercapacitors as a positive electrode, and various contents (0.3−0.6 mmol) of Co(OH)2 shells were coated onto the surfaces of the Ni3S2 nanowire cores to improve the electrochemical properties. The Ni3S2 nanowires were uniformly formed on the smooth NF surface, and the Co(OH)2 shell was formed on the Ni3S2 nanowire surface. By direct NF participation as a reactant without adding any other Ni source, Ni3S2 was formed more closely to the NF surface, and the Co(OH)2 shell suppressed the loss of active material during charging–discharging, yielding excellent electrochemical properties. The Co(OH)2–Ni3S2/Ni electrode produced using 0.5 mmol Co(OH)2 (Co0.5–Ni3S2/Ni) exhibited a high specific capacitance of 1837 F g−1 (16.07 F cm−2) at a current density of 5 mA cm−2, and maintained a capacitance of 583 F g−1 (16.07 F cm−2) at a much higher current density of 50 mA cm−2. An asymmetric supercapacitor (ASC) with Co(OH)2–Ni3S2 and active carbon displayed a high-power density of 1036 kW kg−1 at an energy density of 43 W h kg−1 with good cycling stability, indicating its suitability for use in energy storage applications. Thus, the newly developed core–shell structure, Co(OH)2–Ni3S2, was shown to be efficient at improving the electrochemical performance.

Ni-rich cathodes exhibit rapid capacity degradation upon cycling; hence, the development of Ni-rich cathode materials with a stable electrochemical performance for use in next-generation lithium-ion batteries (LIBs) are extremely challenging. In this study, boron trioxide (B2O3)-modified LiNi0.87Co0.10Al0.03O2 (NCA) compounds with high charging–discharging structural stability were prepared using the Ni0.88Co0.095Al0.025OH precursor for application in LIB cathodes. In addition, the sintering temperature of the NCA cathode material was optimized. B2O3 not only filled in the cracks that formed during the first sintering process but also effectively prevented the fragmentation and loss of cathode NCA particles during the charge–discharge process, thus improving their electrochemical properties. The coated particles exhibited sufficient structural integrity and did not exhibit severe cracking during the cycling process. The B2NCA3 cathode with 2.0 wt% B2O3 demonstrated sufficient cyclic stability and rate properties. It exhibited a high specific capacity of 184 mAh g−1 and a capacity retention of 86% after 100 cycles at 0.2 C and 25 °C.

Lotus–root–structure porous multichannel carbon nanotubes with sidewalls are used in sulfur/carbon (P–MCNT) composites as a sulfur carrier for Li–sulfur (Li S) batteries. P–MCNT is prepared by a simple electrospinning method using coaxial needles, followed by heat treatment and etching. P–MCNT developed multichannel inner pores of different sizes in an axial direction when different amounts of polymethyl methacrylate (PMMA) were added. The sidewall–holes are prepared by adding SiO2 to the electrospinning solution followed by etching. As the porosity increases, the sulfur content reaches a maximum of 78 wt%. The sulfur/P–MCNT composite for Li S batteries exhibits superior performance with a high initial discharge capacity of 1315 mAh g−1 and maintained satisfactory cyclability. This superior performance was ascribed to the morphology of the P–MCNT, which both captured sulfur and restricted its loss during the charge–discharge process. In addition, the introduction of more pores into the carbon material facilitated the diffusion of lithium ions into the electrodes and improved the interfacial charge transfer.

Porous TiO2 nanofibers (PTFs) and dense TiO2 nanofibers (DTFs) were prepared using simple electrospinning for application in dye-sensitized solar cells (DSSCs). TiO2 nanoparticles (TNPs) were prepared using a hydrothermal reaction. The as-prepared PTFs and DTFs (with a fiber diameter of around 200 nm) were mixed with TNPs such as TNP-PTF and TNP-DTF nanocomposites used in photoelectrode materials or were coated as light scattering layers on the photoelectrodes to improve the charge transfer ability and light harvesting effect of the DSSCs. The as-prepared TNPs showed a pure anatase phase, while the PTFs and DTFs showed both the anatase and rutile phases. The TNP-PTF composite (TNP:PTF = 9:1 wt.%) exhibited an enhanced short circuit photocurrent density (Jsc) of 14.95 ± 1.03 mA cm−2 and a photoelectric conversion efficiency (PCE, η) of 5.4 ± 0.17% because of the improved charge transport and accessibility for the electrolyte ions. In addition, the TNP/PTF photoelectrode showed excellent light absorption in the visible region because of the mountainous nature of light induced by the PTF light scattering layer. The TNP/PTF photoelectrode showed the highest Jsc (16.96 ± 0.79 mA cm−2), η (5.9 ± 0.13%), and open circuit voltage (Voc, 0.66 ± 0.02 V).