pressure points when a rider sits on the saddle of the horse and provides data through
wireless transmission to know the state of the rider while riding [28]. The power density
produced by the device was 1.25 mW/cm2 under an external load of 60 MΩ. Vijoy et al.
used room temperature cured polydimethylsiloxane (PDMS) and Cu electrodes for
producing 14 µW power across a load of 20 MΩ. A capacitance model was employed to
evaluate the use of this device as an impact detector [29]. Cao et al. developed a self-
powered pressure and strain sensor by utilizing MXene film as a single electrode mode
TENG. MXene was brushed into a pre-stretched latex substrate followed by releasing of
this substrate to obtain crumpled structures. These structures enhanced the surface
roughness leading to a higher energy-harvesting property with a power density of
2.89 µW/cm2, which was higher than the TENG based on a flat MXene film. This system
was applied to a wireless motion monitoring system to obtain feedback about the motion
state of the human body [30].
The use of MOFs in nanogenerators offers advantages like fine pore-size distribution,
ultra-high surface area, and good chemical stability [31]. In addition, there have been
multiple reports on the use of MOFs for the improvement of the performance of TENGs
[32]. From the analysis of the available reports, it can be concluded that MOFs can help in
improving the performance of nanogenerators in addition to helping in the functioning of
a wide spectrum of sensors. However, there have been limited reports utilizing MOF for
nanogenerator-powered sensors, especially in the wearable domain. This chapter aims to
summarize attempts that have been reported for the use of MOFs in wearable sensing and
nanogenerator domains so that a clear view of the present scenario can be obtained for
ascertaining future directions of research.
The performance, durability, and cost-effectiveness of TENG always depend on the
materials used for the fabrication. Dielectric polymers such as PVDF, polyaniline (PANI),
polytetrafluoroethylene (PTFE), etc., and some metals are widely studied for TENG ap
plications. Functionalizing polymers is very difficult and this limits the development of
multifunctional TENG. MOFs hold a special interest in this field owing to their ease of
functionalization by changing their metal centers and organic ligands, and offer high
surface area and flexibility. The surface functionalities of MOF-based TENG enable the
development of self-powered sensors.
Khandelwal et al. studied the triboelectric performance of zeolite imidazole framework
(ZIF) family MOFs as a positive layer and Kapton as a negative layer in vertical contact
separation mode [33]. The surface roughness of the ZIF MOF layer was measured using
atomic force microscopy (AFM) as it is a crucial factor that affects the performance of
TENG. They have synthesized different MOFs (ZIF-7, ZIF-9, ZIF-11, and ZIF-12) by using
different reagents with different concentrations. The ZIF-7 showed higher surface
roughness than other ZIF MOFs. The ZIF-7/Kapton TENG delivered the highest per
formance of 1.1 µA and 60 V and it powered a wristwatch and hydro thermometer. In
another work by the same group, a ZIF-8/Kapton TENG was developed that showed
164 V and 70 µA [34]. ZIF-8 ligand i.e., 2-methylimidazole is sensitive to tetracycline due
to the π–π interactions that take place between them that affect the output voltage of the
TENG. With an increase in tetracycline concentration, the output voltage was reduced
due to the reduction in electron density at the benzene ring of ZIF-8, as shown in
Figure 14.2(ii). This kind of selective MOF enables multifunctional wearable TENG for
power generation and sensing applications. In another work, the same group developed
ZIF-62 based TENG using benzimidazole and imidazole ligands, further demonstrating
its usage as a fitness tracker, as shown in Figure 14.2(iii) [35]. It delivered a performance
of 62 V, 14 µA, and 16 nC and by deposition stream of ions using a Zerostat 3 gun, its
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