Recent Progress in Self-Powered Sensors Based on Liquid-Solid Triboelectric Nanogenerators

Abstract

Recently, there has been a growing need for sensors that can operate autonomously without requiring an external power source. This is especially important in applications where conventional power sources, such as batteries, are impractical or difficult to replace. Self-powered sensors have emerged as a promising solution to this challenge, offering a range of benefits such as low cost, high stability, and environmental friendliness. One of the most promising self-powered sensor technologies is the L-S TENG, which stands for liquid-solid triboelectric nanogenerator. This technology works by harnessing the mechanical energy generated by external stimuli such as pressure, touch, or vibration, and converting it into electrical energy that can be used to power sensors and other electronic devices. Therefore, self-powered sensors based on L-S TENGs-which provide numerous benefits such as rapid responses, portability, cost-effectiveness, and miniaturization-are critical for increasing living standards and optimizing industrial processes. In this review paper, the working principle with three basic modes is first briefly introduced. After that, the parameters that affect L-S TENGs are reviewed based on the properties of the liquid and solid phases. With different working principles, L-S TENGs have been used to design many structures that function as self-powered sensors for pressure/force change, liquid flow motion, concentration, and chemical detection or biochemical sensing. Moreover, the continuous output signal of a TENG plays an important role in the functioning of real-time sensors that is vital for the growth of the Internet of Things.

Keywords: active sensor; chemical sensor; flexibility sensor; liquid–solid interface; self-powered sensor; triboelectric nanogenerator.

Figure 1

Application of the L–S TENG in energy harvesting and self-powered sensors. Reproduced with permission from [28], 2014, Royal Society of Chemistry; [29], 2014, Royal Society of Chemistry; [30], 2014, American Chemical Society; [31], 2018, American Chemical Society; [32], 2016, Wiley; and [33], 2019, Elsevier.

Figure 2

(a) Schematic of the contact electrification between different phases. (b) Interaction of two atoms at the (i) equilibrium position, (ii) repulsive region, and (iii) attractive region; (iv,v) electron transfer in contact. (c) Mechanism of contact electrification at the liquid–solid interface and formation of the EDL. Reproduced with permission from [40], 2022, American Chemical Society; and [41], 2020, Wiley.

Figure 3

The working mechanism of the contact-separation mode: (i) Initial, (ii) Pressed. (iii) Releasing, (iv) Released, and (v) Pressing states, and the comparison of the measured results of the (vi) open-circuit voltage and (vii) short-circuit current densities of (a) the water-TENG proposed by Lin et al. [43] and (b) the LSTEG proposed by Yang et al. [46]. Reproduced with permission from [43], 2013, Wiley; and [46], 2018, Elsevier.

Figure 4

The working mechanism of the lateral sliding mode and the comparison of the measured results of the open-circuit voltage and short-circuit current of (a) the L-S FluTENG: (i) Fully separated, (ii) Fully contacted, (iii) Sliding out, and (iv) Sliding in states; and (b) the WTENG. Reproduced with permission from [48], 2017, Elsevier; and [47], 2018, Elsevier.

Figure 5

The working mechanism of the free-standing mode and typical voltage and current output signals of (a) the rotating water TENG: Generation of (i–iii) positive and (iv–vi) negative peak signals; and (b) the U-shaped TENG: Generation of (i–iv) positive and (v–viii) negative peak signals. Reproduced with permission from [56], 2016, Elsevier; and [20], 2017, Elsevier.

Figure 6

The working mechanism of the single-electrode mode and the typical output current signal of (a) a water-TENG with a superhydrophobic PTFE surface: (i) Precharged and (v) charged surfaces, water droplet in (ii & vi) contacting, (iii & vii) sliding, and (iv & viii) separated states with solid surface; and (b) the Wd-TENG: (i) Precharged and (vi) charged solid surfaces, water droplet in (ii & vii) contacting, (iii–iv & viii–ix) sliding, and (v & x) separated states with solid surface. Reproduced with permission from [15], 2014, Wiley; and [66], 2019, Wiley.

Figure 7

Schematic diagrams of (a–c) the droplet-based, (d–f) flow-based, and (g–i) wave-based L–S TENGs. Reproduced with permission from [45], 2019, Elsevier; [63], 2021, Science Partner Journals; [68], 2021, Wiley; [62], 2015, Springer Nature; [19], 2018, Springer Nature; [73], 2022, Elsevier; [51], 2014, American Chemical Society; [65], 2018, Wiley; and [33], 2018, Elsevier.

Figure 8

The triboelectric charge density (TECD) of different triboelectric materials. Reproduced with permission from [97], 2019, Nature Portfolio.

Figure 9

Performance characterization of the L–S TENG with different (a–d) properties of the ions, (e) pH values, and (f) temperatures of the water. Reproduced with permission from [106], 2016, Wiley; [32], 2016, Wiley; [106], 2016, Wiley; [19], 2018, Springer Science; [13], 2016, American Chemical Society; and [43], 2013, Wiley.

Figure 10

(a) Electrical response from the TENG and self-powered communication via solid–liquid–solid interactions. Inset images: (i) Morse code table, electrical responses based on magnitude and duration of the high level of (ii) & (iv) numbers and (iii) & (v) alphabets, respectively, (vi) Schematic diagram of the device, (vii) Signal waveform for Morse code’s transmission, Signal waveforms for the message (viii) “SOS” and (ix) “WHERE” and “TYUT”; (b) electrospun MS mat-based water-TENG for self-powered water temperature sensor. Inset images: (i) The setup and working mechanism, (ii) SEM images, (iii) The dependence of contact angle on water temperature, (iv) The dependence of output voltage on impacting time and water temperature, (v) Relationship between the output voltage and temperature; (c) the application of LST-TENG as a water level sensor for ship draft detecting. Inset images: (i) Experimental setup, (ii) Output voltage, (iii) The time variation of the output voltage with time and detected water level, (iv) The ship at different water level; (d) flow and level sensing via waveform-coupled liquid–solid contact electrification. Inset images: (i) Experimental setup, (ii) The dependence of the open-circuit voltage on (ii) regular flow and (iii) irregular flow, (iv) Application prospects of the device. Reproduced with permission from [114], 2022, Elsevier; [115], 2019, Elsevier; [116], 2019, Wiley; and [117], 2021, Elsevier.

Figure 11

(a) Testing setup for the U-shaped TENG as a model for dynamic pressure sensing; (b) the open-circuit voltage peak at different pressures and (c) its relationship; (d) the short-circuit current peak at different pressures and (e) its relationship. Reproduced with permission from [20], 2017, Elsevier.

Figure 12

(a) Average output voltage values generated by various NaCl solution concentrations ranging from 0 to 0.75 M, and (b) the sensitivity of the sensor during its NaCl solution concentration. A test of the selectivity of the self-powered triboelectric sensor for (c) Pb²⁺ detection by using dithizone as the surface modifying agent; (d) Cr³⁺ detection by using diphenylcarbazide as the surface modifying agent. Reproduced with permission from [32], 2016, Wiley; and [106], 2016, Wiley.

Figure 13

(a) Schematic illustration of the self-powered TENG sensor for organic concentrations and (b) the FESEM image of PTFE membrane surface; (c,d) short-circuit current for different formaldehyde concentrations; and (e,f) short-circuit current for different ethanol concentrations (percentage by volume). Reproduced with permission from [49], 2016, Elsevier.

Figure 14

(a) The working mechanism of the L–S TENG-based sensor: (i) First droplet falls, (ii) Droplet contacts the surface, (iii) Second droplet falls, and (iv) Second droplet contacts the first droplet; and (b) Isc with different liquid alcohol, acetone, NaOH liquid, NaCl liquid values; (c) schematic illustration of the L–S TENG and (d) Voc and Isc in paraffin oil/water with different aqueous solutions of HCl (0.1 mol·L⁻¹), deionized water, NaOH (0.1 mol·L⁻¹), and mixture solution of NaOH and NaCl (0.1 mol·L⁻¹). Reproduced with permission from [122], 2019, Elsevier; and [126], 2019, Wiley.