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In this work, g-C3N4 / 3 % rGO nanocomposite was synthesized as a photo-catalyst in order to usein the Li-ion oxygen battery. The aim was to reduce the high charging potential of the battery by the photoassistance. The synthesis of nanocomposite was carried out by thermal decomposition of melamine which wasinitially mixed with the required amount reduced graphene oxide (rGO). The rGO had dual competing actions inthe nanocomposite. The first action was to reduce the optical band gap of the semiconductor nanocomposite thatthe photo-catalyst properties of the nanocomposite were improved. Secondly, rGO degradated the visible lightutilization of the nanocomposite since it favorably absorbed incident light instead of g-C3N4. The photo-assistedcharging tests indicated that the synthesized nanocomposite reduced the charging potential and improved thecyclic discharge-charge performance of the Li-ion oxygen battery.

Graphene is a two-dimensional, honeycomb-structured material consisting of a uniform monolayerof carbon atoms. Most scientists believe that graphene has revolutionary properties and research on graphene isincreasing exponentially. It is considered as an alternative material that can replace silicon according to itsproperties, and graphene is called the supermaterial of the next century. On the other hand, some applications ofgraphene require the rearrangement of electronic properties. The chemical doping method is one of the mostfrequently used methods for this arrangement. In this study, nitrogen-doped graphene was synthesized bychemical vapor deposition (CVD) method. Urea was used as a nitrogen-doping source. Different amounts ofurea were used to optimize the chemical nitrogen doping process. Raman spectroscopy was used for thecharacterization of the synthesized nitrogen-doped graphene. During the experiments, light (400-700 nmwavelength) was sent to the nitrogen-doped graphene surface with a solar simulator (A-type 150W, 1-3 SUN,Xenon lamp, 1.5 AM Filter). The photo-catalytic properties of the samples were measured by the potentiostatictechnique.

The development of high energy density batteries has been rapidly advanced by the increasingenergy demand of the modern world. The lithium-air batteries have great interest due to their having the highestenergy density compared to the other battery technologies. However, the large implementation of lithium-airbatteries is hindered using metallic Li anode, leading to low coulombic efficiency, low energy efficiency andsafety problems. In this study, to improve the performances of these batteries, we designed the lithium-airbattery by integrating the Li-Si based alloy anode and photo-catalyst loading porous carbon cathode. The resultsshow that the designed lithium-air battery has low over potential through the extended cycling stability. Theworking voltage of the cell is below 2.5 V. This study indicates that the developed the lithium-air battery withhigher coulombic efficiency and lower polarization values is the alternatives to the conventional lithium-airbatteries, which comprise metallic Li anode and carbon-based cathode.

Graphene was synthesized by the chemical vapor deposition (CVD). Initially ratios of Ar, H2 and CH4 gases were optimized to get a single layer graphene by CVD. Raman characterizations showed that the optimized synthesis conditions provided I2D/IG ratio as 3 that this ratio indicated the formation of the single layer graphene. The synthesized single layer graphene was mixed with melamine at the certain ratios to obtain the graphene/graphitic-C3N4 (g-C3N4) semiconductor composites. All the synthesized composites were prepared as the photo-electrode to be used in the photo-assisted charging of the lithium-ion oxygen battery. The photo-current levels produced by the photo-electrodes were determined by the linear sweep voltammetry technique.

High entropy oxides are a new class of materials with a single-phase structure consisting of five or more components. Due to their high structural stability and electrochemical performance, they have attracted a lot of attention in recent years. In this study, high entropy oxides with the composition ((FeNiCrMn)1-xCox)3O4 (x=0.1, 0.2, 0.3) were synthesized using the solid state method and their electrochemical performances as anode material for lithium-ion battery were investigated. Spinel crystal structured of high entropy oxides were characterized by X-ray diffraction (XRD) technique. The electrochemical performance of anodes were evaluated by assembling CR2016 type coin cell. As a result of galvanostatic charge/discharge experiments the initial discharge capacities of ((FeNiCrMn)1-xCox)3O4 (x=0.1, 0.2, 0.3) anodes at a current density of 50 mA g-1 werecalculated as 1993 mA h g-1, 1651 mA h g-1 and 1706 mA h g-1, respectively. Among the synthesized high entropy oxide anodes, the ((FeNiCrMn)0.9Co0.1)3O4 anode shows high initial discharge capacity, while their capacity retention rates at the end of 10th cycle were calculated as 53.9%, 55.1%, 59.7%. This study clearly indicates that the electrochemical performances of high entropy oxide anodes are affected by the Co content.

The low-cost electro-catalysts are very crucial for the lithium-ion oxygen battery electrodes. In this work porous reduced graphene oxide (rGO) was synthesized by the chemical methods and mixed with melamine to obtain rGO/graphitic-C3N4 (g-C3N4) composite which compose of 50% rGO and 50% g-C3N4. SEM, XRD and FTIR characterizations showed that the synthesized composite structure reflected most of the features of the rGO structure. The synthesized rGO/g-C3N4 composite was prepared as the cathode for the Li-ion-oxygen battery and its discharge/charge performance was determined. The composite cathode demonstrated a distinctive performance since g-C3N4 catalyzed both the oxygen reduction and oxygen evolution reactions during the discharging and charging. This work showed that rGO/g-C3N4 composite electrode was quite promising as the cost-effective cathode for the Li-ion-oxygen batteries.

High entropy oxides (HEOs) are attractive as a negative electrode material for lithium-ion batteries because of the high specific capacities and cycling stabilities. Moreover, they offer a wide range of compositional variation to reach the desired electrochemical performances. In this study, we synthesized the Mgx(CoNiZnLi)100-xO high entropy oxides using conventional solid state reaction technique and examined their electrochemical properties in lithium-ion cells as anode material. The structural properties of as-synthesized Mg5(CoNiZnLi)95O and Mg35(CoNiZnLi)65O HEOs were investigated using X-ray diffraction (XRD) technique, which showed that all the oxides have single-phase rock-salt structure. When tested as anode material in lithium-ion cell, Mg5(CoNiZnLi)95O anode exhibits higher initial discharge capacity than Mg35(CoNiZnLi)65O electrode. However, the Mg35(CoNiZnLi)65O electrode shows the higher cycling stability than Mg5(CoNiZnLi)95O electrode at the further cycle period. This work offers an approach to control the electrochemical properties of HEO based anodes by tuning active and inactive cation contents in the structure.

High-entropy oxides (HEOs), which are new class of single-phase solid solution materials, have recently attracted as electrode material due to their Li-ion storage properties. In this work Mg0.2Co0.2Ni0.2Zn0.2Li0.1Cu0.1O high entropy oxide was synthesized by conventional solid state method to evaluate its electrochemical performances as anode in the Li-ion battery. The structure of the synthesized Mg0.2Co0.2Ni0.2Zn0.2Li0.1Cu0.1O was characterized by using X-ray diffraction and field emission - scanning electron microscope techniques. The synthesized high entropy oxide was observed to have single phase rock salt crystal structure. The electrochemical performance of the anode was evaluated by assembling CR2016 type coin cell. Galvanostatic charge/discharge tests showed that the Mg0.2Co0.2Ni0.2Zn0.2Li0.1Cu0.1O anode delivers a high initial discharge capacity of 1668 mA h g-1 at a current of 200 mAg-1. The capacity cyclic stability was observed as also satisfactory. These performance values show that the Mg0.2Co0.2Ni0.2Zn0.2Li0.1Cu0.1O high entropy oxide has good potential to be used as anode in Li-ion batteries.

High entropy oxides (HEOs) are attractive as a negative electrode material for lithium-ion batteries (LIBs), because of the high specific capacities and cycling stabilities. Moreover, they offer a wide range of compositional variation to reach the desired electrochemical performances. In this study, we synthesized the Co5(MgNiZnLi)95O and Co35(MgNiZnLi)65O high entropy oxides using conventional solid state reaction technique and examined their electrochemical properties in lithium-ion cells as anode material. The structural properties of as-synthesized high entropy oxides were investigated using X-ray diffraction (XRD) technique, which showed that all the oxides have single-phase rock-salt structure. The increase in the Co content from 5% to 35%, the high entropy oxide based anodes resulted in improved discharge capacity due to the different oxidation states in Co ions. This work indicates that the compositional and elemental valences are very crucial to design and achieve novel high performance high entropy oxide based anode materials for lithium-ion batteries.

The cryogenic treatment is a method frequently used in the development of the wear resistance of alloy steels due to the increase in their hardness driven by the mechanisms such as the conversion of retained austenite to martensite and the formation of secondary carbides. In recent studies, it has been reported that besides the hardening mechanisms, the cryogenic treatment can also improve the mechanical properties of the alloys by reducing the residual stresses and modifying the microstructure. This research aims to investigate the impact of deep cryogenic process (-196°C) on the microstructures of medium carbon spring steels contain various alloying elements. The conventional heat treatment (CHT) and the deep cryogenic treatment (DCT) procedures were applied to the spring steels which have various alloying elements. Hardness, tensile and notch toughness tests were performed to determine the mechanical properties. Consequently, the aim is to determine the applicability of the cryogenic treatment in the improvement of the mechanical properties of medium carbon spring steels.

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-x)LixO (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-x)LixO HEO anodes, in the structure. The more the oxygen vacancy concentration in the anode, the higher the discharge capacity in the LIB. The (MgCoNiZn)(0.65)Li0.35O 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.

Presently intercalation type graphite anode electrodes were being used mainly in the commercial Li-ion batteries. Graphite electrodes, however, have reached their theoretical capacity values ( 372 mAhg-1). Therefore large amount of studies on the synthesis of the novel electrode types were conducted all over the world. One of the novel electrode groups is conversion type electrode. The high entropy design approach is especially utilized in this multi-component oxide electrode synthesis. In this study a new high entropy oxide (Mg0.2Co0.2Ni0.2Zn0.2Li0.2)O was synthesized for the first time in the literature by mixing and grinding of the oxide powders, followed by solid-state reaction at 1000 ºC. The microstructure of the material was characterized using XRD and FESEM-EDX methods, showing single-phase rocksalt structure. The electrochemical performances of the synthesized (Mg0.2Co0.2Ni0.2Zn0.2Li0.2)O as anode material for Li-ion batteries was determined using LIR2016 coin cell. The results showed that (Mg0.2Co0.2Ni0.2Zn0.2Li0.2)O, which has good potential to be used as anode in lithium-ion batteries, had the highest capacity value in 1.0 M LiTFSI-DME electrolyte (1725 mAhg-1).