1. Introduction

The utilization of common fossil fuel energy source pollutes the environment and lessen their availability in nature. A lot of energy resources including wind energy, wave energy, and biomechanical energy harvesting have been wasted in nature [1]. The researchers have attracted a lot of attention for utilizing these wasted energy resources into useful form as an alternative way to reduce environmental pollution. Apart from that, the rapid growth of wearable and flexible electronic devices in this era requires a continuous power supply. Hence, batteries are the appropriate choice for continuous power supply to these wearable devices [2]. But their drawbacks include toxicity and less lifetime. To overcome these limitations, the scientific community has attracted wide attention to harvesting the wasted energy into useful form (electrical) [3]. In this regard, Z.L. Wang demonstrated a novel concept of triboelectric nanogenerators (TENG) based on electrostatic induction and contact electrification to harness the waste energy (mechanical, ocean, wind, and wave) into useful (electrical) forms [4-6]. Additionally, TENG has attracted researchers owing to its simple fabrication process, low cost, and high electrical output [7]. It can be operated in various modes like lateral sliding, contact separation, single electrode, and freestanding mode [8-10]. Apart from that, a wide range of structural innovations have also been reported in TENG, such as contact separation, single electrode mode, vibrational energy harnessing, and biomechanical energy harvesting [11-15]. In this regard, Kim et al reported and fabricated a hybrid energy harvester using magnetic nanoparticles [16]. Till now a wide range of novel materials (2D materials, biomaterials, MOFs, and polymers) have been utilized as friction layers for the fabrication of eco-friendly and biocompatible TENG devices [17-24].

In the previous few years, there are a lot of reviews have been summarized regarding the material’s selection and theoretical modelling in TENG devices [25]. Apart from that, several reviews have been reported regarding the practical application of TENG [26]. The motivation behind this review is not only to summarize the recycled and natural oceanic bio-waste materials based TENG but also the structural innovation in TENG devices. This review explains the potential of recycled and bio-waste materials as a friction layer for the fabrication of TENG devices. Moreover, the importance of natural, cost-effective, and oceanic bio-based materials in TENG and their electrical performances are also discussed. Structural innovations also play a vital role to develop the highly efficient, eco-friendly TENG to harvest biomechanical energy. The review also specifies the role of structural developments and directionless contact-separation generation of energy including vibrational and biomechanical energy harvesting. The schematic overview of TENGs based on recycled/bio-waste materials, and structural developments in TENG devices is shown in Figure 1.

Fig. 1

Overview of TENG devices based on natural, recycled and bio-waste materials, and structural developments in TENG devices.

2. Powder and particle based TENG.

2.1 Recycled bio-waste-based TENG

The selection of the appropriate recycled materials as a friction layer in TENG devices has attracted wide attention towards researchers to reduce environmental pollution. Therefore, the utilization of recycled bio-waste natural materials for green and cost-effective energy harvesting applications is an urgent demand. In this regard, Saqib et al in 2020 reported a cost-effective bio-waste peanut shell powder (PSP) based TENG device [27] as shown in Figure 2a. The PSP-based TENG was fabricated utilizing non-toxic and low-cost PSP as an electropositive insulting layer while polyethylene terephthalate (PET) was employed as an electronegative insulting layer as depicted in Figure 2a. For the fabrication of the electropositive layer of the TENG, the PSP powder was appropriated uniformly on the aluminium (Al) electrode, and the pictorial image of the PSP thin film is shown in Figure 2b(i) [27]. Moreover, the surface roughness and morphology of the PSP film were investigated by optical microscopic and scanning electron microscopy (SEM) images (20 μm) as demonstrated in Figure 2b (ii-iii). To investigate the output performance of the TENG device, instantaneous power, voltage, and current were measured. The obtained power of the proposed device was 1.3 mW at 13 MΩ external resistance as demonstrated in Figure 2c. Apart from that, the voltage of the device was examined in various humid environments (43, 51, 63, 68, 75%) as demonstrated in Figure 2d. It can be observed that the voltage of the device was decreased as an increase in the relative humidity due to the absorption of molecules of water on the surface of the PSP film. Finally, PSP-based TENG was utilized to power electronic devices like calculators and light emitting diodes (LEDs) as depicted in Figure 2e. Later in 2021, Shaukat and co-workers reported recycled sunflower husks powder (SFP)-based TENG to harness the biomechanical energy in nature [28]. Sunflower husks contain cellulose (48.4%), lignin (17.0%), and an abundance of hydroxyl groups which can be a good candidate to donate the electrons during triboelectrification [28]. Initially, sunflower husks are transformed into fine powder having the size of 25 μm as shown in Figure 2f (ii). SFP was uniformly deposited onto the Al film as electropositive layer to fabricate the TENG as shown in Figure 2f (iii) [28]. To examine that SFP was uniformly deposited onto the Al substrate or not, optical microscopic image was taken as shown in Figure 2f (iv) which clearly indicates the uniformity of SFP. The TENG (5 cm × 5 cm) was fabricated utilizing SFP and PET as dielectric layers as demonstrated in Figure 2g. The maximum (instantaneous) power of the device was measured to investigate the electrical performance and it demonstrated up to 1200 μW at 3 MΩ external resistance as depicted in Figure 2h. It can be examined that SFP has a strong ability to donate the electrons during triboelectrification. Apart from that, electrical performance (voltage) of TENG was examined in various humid conditions as demonstrated in Figure 2i. The output performance was degraded after 60%RH. Hence SFP-TENG can operate in ambient conditions. Moreover, SFP-TENG was demonstrated to power the microelectronic devices including calculator, stopwatch, and (LEDs) (153) as depicted in Figure 2 (j, k). In 2022, Saqib et al reported the comparative analysis of the electrical performance of TENG devices based on various waste fruit shells including walnut (WFS), almond (AFS), and pistachio (Pi-WFS) as electropositive friction layer shown in Figure 2l [29]. For the fabrication of three different TENG devices, polytetrafluoroethylene (PTFE) was employed as an electronegative layer while waste fruit shells (walnut, almond, and pistachio) were employed as electropositive layers as shown in Figure 2m [29]. To investigate the surface morphology and roughness of the waste fruit shells based tribopositive films, SEM images were taken to ensure the average particle size of ~25 μm as illustrated in Figure 2n [29]. Moreover, the electrical behaviour of three TENG devices was evaluated by measuring power densities as shown in Fig. 2o [29], The Pi-WFS-based TENG generated a very high power of 416 μW/cm² as compared to WFS and AFS-based TENG devices. The high performance is due of the presence of an abundance of oxygen functional groups in Pi-WFS. Moreover, waste fruit shellsbased TENG devices were further utilized to power the electronic devices like LEDs (185) as depicted in Figure 2p. Thus, excellent performance, cost-effectiveness and environmentally friendly TENG device based on recycled bio-wastes can provide a pathway towards self-powered devices.

Fig. 2

(a) Stepwise preparation of electropositive PSP-film, and the fabrication of TENG device [27], Figure 2a-e reproduced with permission from American Chemical Society, Copyright [2020], (b) optical microscopic and SEM images of electropositive film [27], (c) output power of PSP based TENG device, (d) output voltage of TENG against relative humidity (RH) [27], (e) TENG device was utilized to drive the electronic calculator and LEDs [27], (f) step by step preparation of SFP film [28], Figure 2f-k reproduced with permission from Elsevier, Copyright [2021], (g) schematic representation of TENG based on SFP [28], (h) output power of TENG based on SFP [28], (i) voltage of TENG based on SFP against relative humidity (RH) [28], (j, k) the TENG was demonstrated for electronic calculator, stopwatch, and LEDs [28], (l) pictorial image of powders of waste fruit shells (almond, pistachio, and walnut) [29], Figure 2l-p reproduced with permission from Elsevier, Copyright [2022], (m) schematic demonstration of TENG based on waste fruit shells [29], (n) SEM image of electropositive films of waste fruit shells [29], (o) output power of TENG devices based on waste fruit shells (almond, pistachio, and walnut) [29], and (p) TENG device was demonstrated for powering the LEDs [29].

2.2 Natural and Ocean materials based TENG

Natural, cost-effective, and oceanic bio-based materials have attracted great attention towards researchers as a friction layer in TENG due to their biocompatibility. In this Feng et al reported biodegradable and low-cost leaf powder-based TENG using a cost-effective technique [30]. Figure 3a demonstrated the fabrication process of leaves (electropositive layer) based TENG [30]. The microfibrous structure of leaves can be observed from the SEM image as shown in Figure 3b while optical microscopic image (1 cm) of leaves powder-based electropositive film is depicted in Figure 3c [30]. After that, the electrical behaviour (voltage) of the leaf powder based TENG was evaluated. The voltage of 600 V was achieved as compared to fresh leaf-based TENG as shown in Figure 3d. Moreover, the output power of the PLL modified leaf powder based TENG reached up to 1.79 mW at 11 MΩ external resistance as shown in Figure 3e. In addition, Figure 3f demonstrated the stability of the PLL modified leaf based TENG device ensuring stable performance up to 135,000 cycles. Moreover, tree-based TENG device was also developed to harness the wind energy as shown in Figure 3g. The open-circuit voltage of tree-based TENG reached up to 6.2 V as illustrated in Fig. 3g. Apart from that, Saqib et al proposed a natural oceanic seagrass (bio-based materials) based TENG using simple fabrication technique [31]. The schematic diagram of TENG and the flow of the seagrass treatment is shown in Figure 3h [31]. Two distinct types such as (Zostera marina and Phyllospadix japonicas) were chosen for the fabrication of TENG devices and pictorial images, SEM of the seagrasses (~ 50 μm) and optical microscopic images, are shown in Figure 3i [31]. The seagrasses demonstrated the micro-roughness having aligned segments of 20 μm. After that, the electrical behaviour of the powder seagrasses-based proposed TENG devices was evaluated and Phyllospadix japonicus seagrass film/PET-based TENG shows a voltage of 280 V and a current of 40 μA as depicted in Figure 3 (j, k). Apart from that, the stability of TENG was tested for 5 days ensuring stable electrical performance as demonstrated in Figure 3l. Finally, the TENG was utilized for powering the LEDs (150) as depicted in Figure 3m. Hence, bio-compatible, and costeffective seagrass play a vital role for the fabrication of efficient TENG devices [31].

Fig. 3

(a) Schematic representation of fabrication of TENG based on leaf powder [30], Figure 3a-g reproduced with permission from Elsevier, Copyright [2019], (b) SEM image of fresh leaf [30], (c) pictorial image of electropositive electrode based on leaf powder [30], (d) output voltage of leaf powder based TENG [30], (e) output power, (f) stability of the PLL-modified leaf based TENG device[30], (g) pictorial image of tree TENG and its output voltage [30], (h) Schematic diagram of treatment of seagrass and fabrication of TENG device [31], Figure 3h-m reproduced with permission from Elsevier, Copyright [2021], (i) pictorial images, optical microscopic images, and SEM images of distinct Phyllospadix japonicus and Zostera marina seagrasses [31], (j,k) output performance of the seagrass powder based TENG, (l) stability of the TENG device [31], (m) fabricated TENG was utilized for powering the LEDs [31].

2.3 Particle based TENG.

TENG devices operate on conventional contact separation mode and convert the one-directional input mechanical energy into electrical form. However, few studies reported on direction-less contact-separation generation of energy including vibrational and biomechanical energy harvesting. In this regard, in 2022, Saqib and co-workers reported a directionless and weight-less triboelectric nanogenerator (P-TENG) by incorporating cellulose particles inside the gelatine capsule (degradable) for multidirectional energy harvesting [32]. The schematic demonstration of fabrication of the proposed lightest weight TENG is shown in Figure 4a in which cellulose act as an electropositive and gelatine capsule act as an electronegative part [32]. The P-TENG can harvest biomechanical energy efficiently in nature [32]. Moreover, SEM images were taken to investigate the morphology and average size (6 μm) of cellulose particles and gelatine capsules at 200 μm and 100 μm magnification [32]. The output (electrical) performance of the P-TENG was evaluated through a uniform stepping force. It can be seen from Figure 4c that the maximum value of the current is obtained when a 20% ratio of cellulose particles was incorporated inside the gelatine capsule. When the devices are staked from (1-16), the current of the P-TENG increases from (409 - 1326 nA) as depicted in Figure 4e. Moreover, the power of the single-unit P-TENG device was also evaluated as shown in Figure 4d. The 5 μW peak power was obtained at the external load resistance (70 MΩ) respectively. Finally, P-TENG was evaluated for random vibrationbased energy harnessing. The P-TENG was fixed to different parts of the body (arm, shoe etc) and electrical per- formance was evaluated as shown in Figure 4f. Hence PTENG can harvest the biomechanical energy efficiently. Moreover, in 2015, Kim et al reported a P-TENG device based on the internal vibration of PTFE powder inside the cylinder along with a novel structural design [33]. Figure 4g represents the schematic diagram of P-TENG. Two Al plates act as bottom and top electrodes with a diameter of 5 cm. An acrylic rigid cylinder was attached between the two Al plates. Moreover, the conductive copper tapes (four pieces) were affixed to the outer area of the cylinder [33]. The PTFE powder with a larger size having a diameter of 2 μm was contained in the cylinder for the internal vibration. Moreover, the SEM images of Al was investigated as illustrated in Figure 4 (h, i). Moreover, the electrodynamic shaker was utilized to measure the electrical performance of P-TENG. Various volume ratios of the PTFE powder were inserted into the cylinder to find the optimized conditions of the powder. The 50% volume ratio of PTFE powder-based TENG device shows the maximum electrical performance (voltage and current) as shown in Figure 4j. Apart from that, output current density of the 50% volume ratio-based TENG device at the 3 Hz frequency was measured. The output voltage increases with the increases in the resistance while the current shows a decreasing trend as the external resistance increases from 10⁷ - 10⁹ as shown in Figure 4k. Additionally, a small P-TENG was fabricated by inserting the PTFE powder (50% ratio) into the straw (6 mm diameter) to investigate the fluid like behaviour of the PTFE powder as shown in Figure 4l. Hence, small PTENG was vibrated into the vertical motion at 3 Hz frequency. The output current was measured as shown in Figure 4m. Moreover, the Figure 4n shows the electrical performance of P-TENG when it was vibrated along different axis (x-axis, y-axis, and z-axis). Finally, P-TENG was utilized to powering the 240 LEDs as depicted in Figure 4o. Hence, fabrication of small and lightest weight P-TENG is a viable route towards the self-powered systems [33].

Fig. 4

(a) Schematic diagram of cellulose and gelatine chemical structure and fabrication of particle TENG[32], Figure 4a-f reproduced with permission from Elsevier, Copyright [2022], (b) SEM images of cellulose particles and gelatine capsule at 100 μm and 200 μm [32], (c) the maximum output current of P-TENG at 20% ratio of cellulose particles [32], (d) output power of 20% ratio of cellulose particles based P-TENG [30], (e) the current against the various units of P-TENG [32], (f) the output voltage of P-TENG attached with different human body parts (arm, shoe, placed in bag, and placed with pen) [32], (g) schematic representation of fabricated P-TENG based on PTFE powder[33], Figure 4g-o reproduced with permission from American Chemical Society, Copyright [2015], (h) SEM image of Al (aluminium) electrode [33], (i) SEM image of Al electrode at high magnification [33], (j) maximum electrical performance (Voltage and Current) of P-TENG based on various volume ratios of PTFE powder [33], (k) maximum output current density of P-TENG with 50% ratio of PTFE powder [33], (l) Schematic representation of small P-TENG [33], (m) electrical performance of small P-TENG [33], (n) Electrical performance of P-TENG during the 3-D motion (x-axis, y-axis, z-axis) [33], and (o) pictorial image of powering 240 LEDs during vertical motion [33].

3. Conclusions

In this review, the advancements in recycled and biowaste materials as a positive friction layer and structural innovations for the development of TENG devices are explained in detail. First, the introduction section briefly explained the fundamentals of TENG, its working modes, and its operating mechanisms. Moreover, utilization of the recycled and bio-waste materials is an effective approach to enhance the TENG output performances. Natural, costeffective, and oceanic bio-based materials have attracted great attention towards researchers as a friction layer in triboelectric nanogenerators owing to their biocompatibility. Therefore, bio-compatible, and cost-effective oceanic biomaterials are well explored to increase the performance of TENG. The structural improvements also play a vital role to develop the highly efficient TENG device. Finally, multi-directional and irregular motions based TENG is a novel strategy to develop a highly efficient TENG device for biomechanical energy harvesting.

Acknowledgements

Acknowledgments

This work was supported by the National Research Foundation of Korea (NRF) grants funded by the Ministry of Science, ICT and Future Planning (MSIT) (2022R1 A2C4002037 and 2022R1A4A3032923). This work was also supported by the Commercialization Promotion Agency for R&D Outcomes (COMPA) grant funded by the Korean Government (MSIT) (RS-2023-00304743).

Conflict of Interest

REFERENCES

• 1. G. Khandelwal, N. P. M. J. Raj and S. Kim: Adv. Energy Mater., 11 (2021) 2101170. Article
• 2. Z. L. Wang: Faraday Discuss., 176 (2014) 447. ArticlePubMed
• 3. M. S. Kwak, K.-W. Lim, H. Y. Lee, M. Peddigari, J. Jang, C. K. Jeong, J. Ryu, W.-H. Yoon, S. N. Yi and G.-T. Hwang: Nanoscale, 13 (2021) 8418. ArticlePubMed
• 4. F.-R. Fan, Z.-Q. Tian and Z. L. Wang: Nano Energy, 1 (2012) 328. Article
• 5. H. E. Lee, J. H. Park, D. Jang, J. H. Shin, T. H. Im, J. H. Lee, S. K. Hong, H. S. Wang, M. S. Kwak, M. Peddigari, C. K. Jeong, Y. Min, C. H. Park, J.-J. Choi, J. Ryu, W.-H. Yoon, D. Kim, K.J. Lee and G.-T. Hwang: Nano Energy, 75 (2020) 104951. Article
• 6. H. Ko, Y. Lim, S. Han, C. K. Jeong and S. B. Cho: ACS Energy Lett., 6 (2021) 2792. Article
• 7. Y. A. Mezenov, A. A. Krasilin, V. P. Dzyuba, A. Nominé and V. A. Milichko: Adv. Sci., 6 (2019) 1900506. ArticlePubMedPMC
• 8. Z. L. Wang, L. Lin, J. Chen, S. Niu and Y. Zi: Triboelectric Nanogenerator, (2016) 49. Article
• 9. S. Niu, Y. Liu, X. Chen, S. Wang, Y. S. Zhou, L. Lin, Y. Xie and Z. L. Wang: Nano Energy, 12 (2015) 760. Article
• 10. W. Akram, Q. Chen, G. Xia and J. Fang: Nano Energy, 106 (2023) 108043. Article
• 11. Z. L. Wang: ACS Nano, 7 (2013) 9533. ArticlePubMed
• 12. G. Khandelwal, N. P. M. J. Raj and S.-J. Kim: Nano Today, 33 (2020) 100882. Article
• 13. S. Niu, S. Wang, L. Lin, Y. Liu, Y. S. Zhou, Y. Hu and Z. L. Wang: Energy Environ. Sci., 6 (2013) 3576. Article
• 14. H. S. Wang, T. H. Im, Y. Bin Kim, S. H. Sung, S. Min, S. H. Park, H. E. Lee, C. K. Jeong, J. H. Park and K. J. Lee: APL Mater., 9 (2021) 061112. Article
• 15. C. Sohn, J. J. Lee, K. Kim and C. K. Jeong: ECS J. Solid State Sci. Technol., 11 (2022) 055006. Article
• 16. V. Vivekananthan, A. Chandrasekhar, N. R. Alluri, Y. Purusothaman, G. Khandelwal, R. Pandey and S.-J. Kim: Nano Energy, 64 (2019) 103926. Article
• 17. R. A. Shaukat, Q. M. Saqib, J. Kim, H. Song, M. U. Khan, M. Y. Chougale, J. Bae and M. J. Choi: Nano Energy, 96 (2022) 107128. Article
• 18. F. F. Hatta, M. A. S. M. Haniff and M. A. Mohamed: Int. J. Energy Res., 46 (2022) 544. Article
• 19. S. R. Patil, M. Y. Chougale, J. Kim, R. A. Shaukat, M. Noman, Q. M. Saqib, M. U. Khan, T. D. Dongale and J. Bae: Energy Technol., 10 (2022) 2200876. Article
• 20. S. S. Won, M. Kawahara, C. W. Ahn, J. Lee, J. Lee, C. K. Jeong, A. I. Kingon and S. Kim: Adv. Electron. Mater., 6 (2020) 1900950. Article
• 21. L. Lapčinskis, A. Linarts, K. Mālnieks, H. Kim, K. Rubenis, K. Pudzs, K. Smits, A. Kovaļovs, K. Kalniņš, A. Tamm, C. K. Jeong and A. Šutka: J. Mater. Chem. A. Mater., 9 (2021) 8984. Article
• 22. M. Y. Chougale, Q. M. Saqib, M. U. Khan, R. A. Shaukat, J. Kim, D. Dubal and J. Bae: Adv. Sustain. Syst., 5 (2021) 2100205. Article
• 23. M. Y. Chougale, M. U. Khan, J. Kim, J. Cosgrove, R. A. Shaukat, Q. M. Saqib, M. Banjade, S. R. Patil, C. Brown, D. Dubal and J. Bae: Nano Energy, 111 (2023) 108399. Article
• 24. M. Y. Chougale, Q. M. Saqib, M. U. Khan, R. A. Shaukat, J. Kim and J. Bae: Adv. Sustain. Syst., 5 (2021) 2100161. Article
• 25. D. Choi, Y. Lee, Z.-H. Lin, S. Cho, M. Kim, C. K. Ao, S. Soh, C. Sohn, C. K. Jeong, J. Lee, M. Lee, S. Lee, J. Ryu, P. Parashar, Y. Cho, J. Ahn, I.-D. Kim, F. Jiang, P. S. Lee, G. Khandelwal, S.-J. Kim, H. S. Kim, H.-C. Song, M. Kim, J. Nah, W. Kim, H. G. Menge, Y. T. Park, W. Xu, J. Hao, H. Park, J.-H. Lee, D.-M. Lee, S.-W. Kim, J. Y. Park, H. Zhang, Y. Zi, R. Guo, J. Cheng, Z. Yang, Y. Xie, S. Lee, J. Chung, I.-K. Oh, J.-S. Kim, T. Cheng, Q. Gao, G. Cheng, G. Gu, M. Shim, J. Jung, C. Yun, C. Zhang, G. Liu, Y. Chen, S. Kim, X. Chen, J. Hu, X. Pu, Z. H. Guo, X. Wang, J. Chen, X. Xiao, X. Xie, M. Jarin, H. Zhang, Y.-C. Lai, T. He, H. Kim, I. Park, J. Ahn, N. D. Huynh, Y. Yang, Z. L. Wang, J. M. Baik and D. Choi: ACS Nano, 17 (2023) 11087. ArticlePubMed
• 26. X. Cao, Y. Xiong, J. Sun, X. Xie, Q. Sun and Z. L. Wang: Nano-Micro Lett., 15 (2023) 14. ArticlePubMedPMC
• 27. Q. M. Saqib, R. A. Shaukat, M. U. Khan, M. Chougale and J. Bae: ACS Appl Electron Mater., 2 (2020) 3953. Article
• 28. R. A. Shaukat, Q. M. Saqib, M. U. Khan, M. Y. Chougale and J. Bae: Energy Rep., 7 (2021) 724. Article
• 29. Q. M. Saqib, M. Y. Chougale, M. U. Khan, R. A. Shaukat, J. Kim, K. S. Bhat and J. Bae: Mater. Today Sustainability, 18 (2022) 100146. Article
• 30. Y. Feng, L. Zhang, Y. Zheng, D. Wang, F. Zhou and W. Liu: Nano Energy, 55 (2019) 260. Article
• 31. Q. M. Saqib, M. Y. Chougale, M. U. Khan, R. A. Shaukat, J. Kim, J. Bae, H. W. Lee, J.-I. Park, M. S. Kim and B. G. Lee: Nano Energy, 89 (2021) 106458. Article
• 32. Q. M. Saqib, R. A. Shaukat, M. Y. Chougale, M. U. Khan, J. Kim and J. Bae: Nano Energy, 100 (2022) 107475. Article
• 33. D. Kim, Y. Oh, B.-W. Hwang, S.-B. Jeon, S.-J. Park and Y.-K. Choi: ACS Nano, 10 (2016) 1017. ArticlePubMed

Figure & Data

References

Citations

Citations to this article as recorded by