الفهرس | Only 14 pages are availabe for public view |
Abstract Graphene-based supercapacitors have high energy density potential which is beneficial for renewable energy related applications or electrical vehicles. However, further improvement to its energy density is possible by improving the electrode’s intrinsic capacitance. By using density functional theory (DFT), many models based on fixed-band approximation (FBA) were developed to estimate the quantum capacitance of free-standing graphene with different type of point defects. Nonetheless, these models had numerous major shortcomings that affect the accuracy of the results, making the results incomparable with experimental measurements. Therefore, another methodology based on DFT was recently developed called the interfacial capacitance model (ICM). This methodology, however, was only tested and used on pristine graphene mono/bi-layer adsorbed on copper or nickel substrates. The models didn’t include any defects which would be commonly found in graphene. Therefore, in this work we have developed 6 various models (including pristine model) of mono-layer graphene with various point-like defects such as single-vacancy, double-vacancy, and stone-wales. ICM was implemented to estimate the interfacial capacitance of each model. The results ranged from 1.692 to 1.872 F cm2 for all models with respect to the pristine model with a capacitance of 1.733 F cm2. The general trend was found that the capacitance is enhanced by 1 to 8% as long as no chemical bonds exist between the defect and the underlying copper substrate. In other words, the presence of chemical bonds was found to transform graphene’s adsorption from physisorption to chemisorption. Our results were found to be in the same order of magnitude of experimental results which ranged from 1 to 10 F cm2, depending on the tested graphene sample and type of electrolyte. The interplays between the defects and the underlying copper substrate were also discussed and investigated with the help of DOS/PDOS analysis. |