# Expanding Horizons: Taking Advantage of Graphene's Surface Area for Advanced Applications
## 4 Surface Area in Supercapacitors and Lithium-Ion Batteries
### Surface Area and Electrode Capacitance  
[PERSON] et al. [39] conducted a study on capacitive deionization with asymmetric electrodes, where they compared the electrode capacitance with the electrode surface area. They used a 10 mM solution of zinc acetate dihydrate to prepare a solution in deionized water. After being cleaned and immersed in the zinc acetate solution for 20 min, an activated carbon cloth (ACC) was dried for 30 min at 100 \({}^{\circ}\)C in an oven. To confirm that a thick layer of zinc ions was formed on the ACC surface, this procedure was repeated three times. Figure 6A illustrates the electrochemical impedance spectroscopy for AA and ZnO-ACC, and Figure 6B illustrates the desalination performance of the symmetric and asymmetric arrangements of the ZnO-ACC and ACC electrodes. The zinc-coated ACC was then subjected to calcination at 350 \({}^{\circ}\)C for 5 h to produce ACC surfaces with seeded ZnO nanoparticles. By analyzing Nyquist plots, the electrode-specific capacitance valueswere confirmed. It was clear that in contrast to the uncoated ACC electrodes, the electrodes coated with ZnO nanorods (ZnO NR) on an ACC displayed unique electrochemical properties. Notably, the ACC sensors coated with ZnO NR showed reduced series electrode resistance and increased charge transfer resistance. The Nyquist plots were used to extract important electrical properties, such as coating capacitance, double-layer capacitance, and pore resistance, using a modified Randles equivalent circuit model. After coating the ACC with ZnO NRs, the results showed a significant increase in coating capacitance, from 12.36 mF to 600 mF, for a 1 cm\({}^{2}\) electrode [40], along with a slight rise in the combined layer capacitance, from 4 F to 4.6 F. The transfer resistance of the ZnO NR-ACC electrodes exhibited a significant elevation when compared to the uncoated ACC electrodes. This heightened resistance posed an additional impediment to undesirable Faradaic currents and simultaneously amplified the electrode pore resistance [39; 41]. The Warburg impedance curve showed a delayed response from the ZnO NR-ACC electrode surface, suggesting that, even at lower frequencies, ions could readily reach the electrode surface. This was explained by the uniformly dispersed electric field and the ZnO NRs' adsorption-accessible surface. When the ZnO NR-coated ACC electrodes were paired with the uncoated ACC electrodes as counter electrodes, they exhibited distinct physical, chemical, and electrical properties. The electrodes were set up in three distinct configurations to examine the main factor affecting salt adsorption in an asymmetric capacitive deionization (CDI) cell [56; 57; 58]. The results revealed that capacitance, rather than the surface area, played the dominant role. When compared to the symmetric ACC electrode devices, the ZnO NR-coated symmetric ACC electrode devices continuously showed a greater specific salt removal capability. However, when the symmetry of the electrodes was disrupted, the salt adsorption capacity decreased significantly [59; 60; 61]. A comparable investigation into large-scale pattern-generation graphene sheets for transparent electrodes was conducted by [PERSON] et al. [42]. They created a simple technique that uses CVD on nickel layers to produce and transfer stretchable, high-quality graphene films on a large scale. By varying the thickness of the catalytic metals, growth time, and UV treatment duration, the number of layers in these patterned films can be easily transferred to stretchable substrates using straightforward contact procedures. Scaling up production is possible because the only restriction on the film's dimensions is the size of the CVD growing chamber. These graphene films' remarkable optical, electrical, and mechanical qualities create opportunities for use in flexible, stretchable, and foldable transparent electronics on a wide scale [43; 44].