In this work, g-C 3 N 4 /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 C�C bonds formed between g-C 3 N 4 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-C 3 N 4 pointed out that the g-C 3 N 4 /3% rGO nanocomposite has the optimum light absorbance efficiency. The photoassisted charging tests indicated that the g-C 3 N 4 /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. KEYWORDS: g-C 3 N 4 /rGO, nanocomposites, photocharging, Li-ion oxygen batteries, photocatalyst

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.

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.