**1.1 Synthesis of siloxene and its structural types**

Siloxene is prepared by deintercalation of Ca2+ from CaSi2 under concentrated hydrochloric acid. Briefly, the required amount of CaSi2 powder and HCl acid stirred in the ice-cold condition under the inert gas atmosphere for 2-4 days (**Figure 1**). During this reaction, the deintercalation of Ca layers and functionalization of Si

**Figure 1.**

*Siloxene synthesis process (reproduced from [11] with permission from Elsevier).*

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*Novel Two-Dimensional Siloxene Material for Electrochemical Energy Storage and Sensor…*

sheets can be occurred simultaneously and formed the siloxene structure. The following equation can describe the common formation mechanism of siloxene from

In general, the siloxene stoichiometric ratio of Si:H:O is 2:2:1. Based on the exfoliation and deintercalation conditions such as reaction time, the concentration of the acidic medium, and temperature, siloxene can be classified into two major types. (1) Weiss, and (2) Kautsky type siloxene structures [18]. In Weiss type siloxene (Si6(OH)3H3), the six-membered Si6 rings connected with alternative Si-H and Si-OH bonds, whereas Kautsky type siloxene (Si6O3H6), the Si6 rings connected by Si-O-Si bridge (**Figure 2**). It is noteworthy that the crystalline silicon (common impurity) in CaSi2 may affect the siloxene structure formation [19], which deviates

Due to the unique 2D structure and the abundant functional groups of siloxene, it can be applied in various applications such as optoelectronics, catalysis, water splitting, etc. Theoretical investigations of the siloxene have shown the high possibilities in different electrochemical applications [20]. However, because of limited knowledge of siloxene's electrochemistry, only a few works have been reported on the electrochemical application of siloxene so far. The siloxene has been mainly employed in supercapacitors and batteries as an electrode material and detection of

Though siloxene was discovered in 1863, it has recently received considerable attention in the electrochemical energy storage application. The researchers have been focused on siloxene based electrode materials for energy storage and conversion application. Due to the increases in energy consumption and the non-renewable sources decreasing gradually, the development of high-efficiency energy storage devices is highly demanded. Electrochemical or supercapacitors are the perfect choice for high-performance devices as the results of its high-power density and long cyclic lifetime [21]. Compared with the commercial activated carbon-based supercapacitors, the integration of Si-based materials with the current microelectronic technology can lead to higher performance in energy storage devices because of its high theoretical capacity (3579 mA hg−1). However, Si-based materials such as silicon carbide (SiC), Si nanowire, porous silicon have been employed as electrode materials in supercapacitor application, the functionalization of the one-atom-thick Si layers with interconnected Si6 rings can accommodate

Krishnamoorthy et al. have reported the siloxene based symmetric supercapacitor (SSC) application in 2018 [1]. The Kautsky-type of siloxene structure prepared by deintercalation of calcium from CaSi2 and confirmed its Si-O-Si bridges Si6 rings interconnection by Fourier transform infrared spectroscopy.

3 63 3 3 *CaSi HCl H O Si O H CaCl H* <sup>2</sup> + + → + +↑ 2 63 6 2 2 (1)

*DOI: http://dx.doi.org/10.5772/intechopen.93958*

from the structures mentioned above.

**2. Electrochemical application of siloxene**

biomarkers in electrochemical biosensors.

the better performance in supercapacitors [1].

*2.1.1 Siloxene based supercapacitors*

**2.1 Supercapacitors**

CaSi2 [11].

**Figure 2.** *Different types of Siloxene structure [19].*

*Novel Two-Dimensional Siloxene Material for Electrochemical Energy Storage and Sensor… DOI: http://dx.doi.org/10.5772/intechopen.93958*

sheets can be occurred simultaneously and formed the siloxene structure. The following equation can describe the common formation mechanism of siloxene from CaSi2 [11].

$$\text{\textbulletCaSi}\_2 + \text{\textbulletHCl} + \text{\textbulletH}\_2\text{O} \rightarrow \text{Si}\_6\text{O}\_3\\H\_6 + \text{\textbulletCaCl}\_2 + \text{\textbulletH}\_2\uparrow\tag{1}$$

In general, the siloxene stoichiometric ratio of Si:H:O is 2:2:1. Based on the exfoliation and deintercalation conditions such as reaction time, the concentration of the acidic medium, and temperature, siloxene can be classified into two major types. (1) Weiss, and (2) Kautsky type siloxene structures [18]. In Weiss type siloxene (Si6(OH)3H3), the six-membered Si6 rings connected with alternative Si-H and Si-OH bonds, whereas Kautsky type siloxene (Si6O3H6), the Si6 rings connected by Si-O-Si bridge (**Figure 2**). It is noteworthy that the crystalline silicon (common impurity) in CaSi2 may affect the siloxene structure formation [19], which deviates from the structures mentioned above.
