# Electrospinning-Based Carbon Nanofibers for Energy and Sensor Applications
## 4 Application of Carbon Nanofibers
### Sensor Applications  
#### 4.2.1 Electrochemical Sensor  
Electrochemical sensing is a popular application of carbon material. For different targets, the researchers used different measurement techniques such as voltammetry (cyclic voltammetry, differential-pulse voltammetry, square-wave voltammetry, etc.), amperometry, and potentiometry, conductivity, and impedance changes [130; 131].  
[PERSON] et al. studied the ability of Co\({}_{3}\)O\({}_{4}\) (combination of Co\({}^{2+}\) and Co\({}^{3+}\)) in the detection of trichloroacetic acid (TCA), KBrO\({}_{3}\), and NaNO\({}_{2}\) with CV measurements (Figure 18a) [132]. Although the material proved to be capable of detecting a variety of targets, it did not exhibit high sensitivity. The low surface area of simple CNFs may have limited their ability to detect a low concentration of the target chemical. The CNFs decorated with cobalt oxide nanoparticles still have high potential in the application of an electrochemical sensor for many yet-to-be-discovered targets. [PERSON] et al. developed a multichannel CNF decorated with Co\({}_{3}\)O\({}_{4}\) that could be used as a material for both a supercapacitor and an electrochemical sensor (Figure 18b) [133]. In the presence of glucose, Co\({}_{3}\)O\({}_{4}\) can be converted into CoOOH. When applying 0.55 V, the redox peak increases with the addition of more condensed glucose. The authors used the potentiometric measurement method to detect different concentrations of glucose in a solution. Due to the excellent pore volume of the multichannel carbon structure, the material exhibited a wild detection range from 1 nM up to 1 M.  
[PERSON] et al. combined the decoration of SnO\({}_{2}\) and the modification of MoS\({}_{2}\) on the carbon structure by using a glassy carbon electrode for the detection of phenacetin and indomethacin (Figure 18c) [134]. It was proven that the SnO\({}_{2}\) and MoS\({}_{2}\) can provide their own contributions to the outstanding performance of the CNFs. The present of MoS\({}_{2}\) can reduce the resistance of the carbon electrode with the electrolyte solution and it can also enhance the current peak signal. Although the detection range can reach a limit from 50 nM up to 0.5 M for indomethacin, the detection limit of phenacetin seems to be greater (from 50 nM to 7.2 M). Since the differential pulse voltammetry measurement was used for detection, the CNFs can detect the concentration very clearly [135].  
Figure 17: (**a**) MEA constructed of multichannel fibers, carbonization at high temperature [126]. (**b**) Orthogonally aligned CNFs for MEA in fuel cells [127]. (**c**) MEA from the composite of CNFs and SPEEK [128]. (**d**) MEA from the acid\(-\)treated CNFs and SPEEK [129].  
[PERSON] et al. used Hermin to embed active iron ions (Fe\({}^{3+}\)) on the surface of CNFs from the PAN precursor (Figure 18d) [136]. By controlling the voltage applied in the electrospinning process (12, 15, and 35 kV), the effects of the diameter of fibers were also investigated. The CNFs made from fibers electrospun with 15 kV exhibited the largest surface area as well as mesopore ratio, so they also showed the highest capacitive currents. The fiber was continued to be tested for bisphenol A (BPA) detection. The ultra-sensitive linear range is from 3 mM up to 1 \(\upmu\)M with outstanding selectivity. In addition, the stability and reproducibility of the material also produce remarkable results.