ABSTRACT
In this work, nitrogen (N)-doped graphene film is synthesized, as a photo-catalyst, on one side of the copper foam by chemical vapor deposition and the copper foam is directly used as an electrode after porous Pd@rGO cathode loading to the other side of the foam for the photo-assisted charging of the Li-ion oxygen battery. The amount of urea (CO(NH2)2), which is used as N atom source, is optimized to get maximum photo-anodic currents from the n-type graphene films. The optical band gap and the valance band edge potential of the optimized N-doped graphene film are determined as 2.00 eV and 3.71 VLi+/Li, respectively. X-ray photoelectron spectra provided that the atomic percent of N atoms in the graphene film is 1.34% and the graphitic, pyrrolic and pyridinic N atom percentages are 54.01%, 42.20% and 3.79%, respectively. The photo-assisted charging tests indicated that the N-doped graphene film photo-catalyst reduced the charging potential significantly even at 1000 mA g-1 (0.1 mA cm-2) current density and improved the cyclic discharge-charge performance of the Li-ion oxygen battery considerably.
ABSTRACT
In this work, we aimed to synthesize an effective nanocomposite photocatalyst for the photo-assisted charging of the Li-ion oxygen battery. Initially the graphene films were synthesized by chemical vapor deposition, and subsequently, g-C3N4/graphene nanocomposites were synthesized by thermal reduction as photocatalysts. FTIR spectra analysis showed that novel C=C bonds can form between g-C3N4 and graphene films during the synthesis process. The photocurrent measurements indicated that the presence of graphene considerably contributed to the visible light utilization and photocatalytic efficiency of g-C3N4. This contribution was also revealed by the UV-vis diffuse reflectance spectra measurements, which showed that the incremental addition of the graphene reduced the optical band gap of the nanocomposite incrementally. The photocatalyst performance of the g-C3N4/graphene nanocomposite was also observed in the photo-assisted charging tests of the Li-ion oxygen battery, and the presence of 2D graphene in the structure improved the effectiveness of g-C3N4 in the reduction of the charging potential, especially at high current densities.
ABSTRACT
In this study, a facile approach has been developed to fabricate GO/SiO2 nanosheets by the hydrolysis of tetraethyl orthosilicate (TEOS) in the graphene oxide (GO) solution with the assistance of the ultrasonication. The morphology and structure of the SiO2/GO nanosheets were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR) and Raman spectroscopy. The results showed that the covalently bonded SiO2 nanoparticles onto the GO sheets were dense and uniform. The agglomeration of the nanosheets was prevented by the ultrasonication and the layer sizes decreased throughout the synthesis process. The size and thickness of the SiO2 nanoparticles were determined by the initially and externally added TEOS amounts, respectively, on the GO surface. The anode performance of the thermally reduced rGO/SiO2 nanosheets was also observed in the Li-ion half-cell. The reversible capacity of the synthesized TrGOSN-1.5 anode was 424 mA h g-1 at a current density of 100 mA g-1.
ABSTRACT
In this work, g-C3N4/rGO nanocomposites were synthesized to use them as photocatalysts in Li-ion oxygen batteries by aiming at the reduction of the charging potential efficiently under photoassisted conditions. Fourier transform infrared (FTIR) spectra showed that novel CâC bonds formed between g-C3N4 and rGO during the decomposition of melamine and that the formation of these bonds was assumed to cause a red shift in the optical absorption band edge. The competition between the narrowing in the optical band gaps of the nanocomposites as a result of the red shift due to the presence of rGO and the degradation in the visible light utilization as a result of favorably absorbed incident light by rGO instead of g-C3N4 pointed out that the g-C3N4/3% rGO nanocomposite has the optimum light absorbance efficiency. The photoassisted charging tests indicated that the g-C3N4/3% rGO nanocomposite reduced the charging potential effectively, especially at higher current densities, and improved the cyclic discharge-charge performance of the Li-ion oxygen batteries considerably.
ABSTRACT
High-entropy oxides (HEOs), which are a new class of single-phase solid solution materials, have recently attracted significant attention as an anode material for lithium-ion batteries (LIBs). In this study, (MgCoNiZn)1-xLixO (x = 0.05, 0.15, 0.25, and 0.35) HEOs were synthesized and their electrochemical performances as the anode material were observed in LIBs. X-ray photoelectron spectroscopy (XPS) analysis showed that the increase in the lithium cation concentration causes generation of more oxygen vacancies, which greatly affected the electrochemical performance of (MgCoNiZn)1-xLixO HEO anodes, in the structure. The more the oxygen vacancy concentration in the anode, the higher the discharge capacity in the LIB. The (MgCoNiZn)0.65Li0.35O anode had 1930 mA h g-1 initial and 610 mA h g-1 stable (after 130 cycles) discharge capacities at a current density of 1000 mA g-1. This work clearly indicated that designing a HEO with abundant oxygen vacancies in the structure was a very efficient strategy to improve the electrochemical performance of the HEO electrode for LIBs.
