Tribo‐Tunneling DC Generator with Carbon Aerogel/Silicon Multi‐Nanocontacts

Abstract

Mechanical energy conversion technologies such as piezoelectric or triboelectric nanogenerators are able to harvest environmental energy (e.g., vibration, wind, tidal wave) and human body motion for powering electric vehicles, sensor networks, and wearable devices. [1][2][3] Traditional triboelectric nanogenerators (TENGs) may generate high voltage but with extremely low AC current ( J ≈ 0.01-0.1 A m −2 ) density. [1] The performance of TENGs is optimal only at high frequency due to the dielectric displacement current mechanism, while the environmental mechanical sources usually have frequencies lower than 10 Hz. [4] In contrast, the non-equilibrium tribo-tunneling phenomenon, recently discovered in the semiconductor-based Schottky moving contacts, is capable of generating a continuous DC current as high as 100 A m −2 regardless of the motion direction, and not limited by the mechanical source frequency. [3,[5][6][7][8][9][10] The tribo-tunneling transport tip-enhanced current generation, as reported by Liu et al. [3,6] using conductive-atomic force microscope (C-AFM), show that the tribo-tunneling current density ( J) output can be boosted by the nano-sized contact (tip radius R ≈ 30 nm) up to 10 6 A m −2 due to the enhanced electronic excitation and strong localized electric field E. It has been reported that a micro-tip (tip radius R ≈ 30 µm) sliding system produces a current density of 35 A m −2 while larger tip radius (R ≈ 100-300 µm) yields a current density of 10 A m −2 in the test probe sliding system. [5,6] However, scaling up the concept with micro-electromechanical systems (MEMS)-fabricated tip array is time-consuming and costly. The metal micro-tips also cause substrate surface scratching, which impacts the sustainability of the power generation. Moreover, the relatively low open-circuit voltage (V oc , 300-600 mV) of the single metal/Si sliding unit is insufficient for practical applications in electronics. To address those issues, we developed a carbon aerogel-based system in this work, which scales up the DC output and enhances the Voc output by one order via naturally formed Schottky nanocontacts.Carbon aerogel is electrically conductive, synthetic ultralight material composed of 3D network structures of interconnected amorphous carbon nanoparticles. [11] It has been widely used for nanocomposite, electrodes, desalination filters, and heterogeneous catalysis due to its large surface area. [12] In this work, Although tip-enhanced tribo-tunneling in metal/semiconductor point nanocontact is capable of producing DC with high current density, scaling up the process for power harvesting for practical applications is challenging due to the complexity of tip array fabrication and insufficient voltage output. Here, it is demonstrated that mechanical contact between a carbon aerogel and silicon (SiO 2 /Si) interface naturally forms multiple nanocontacts for tribo-tunneling current generation with an open-circuit voltage output (V OC ) reaching 2 V, and short-circuit DC current output (I SC ) of ≈15 µA. It h...

Single-Electrode Electrochemistry: Chemically Engineering Surface Adhesion and Hardness To Maximize Redox Work Extracted from Tribocharged Silicon

“…This knowledge will also provide the basis to develop devices harvesting electricity from vibrations and friction, akin to the tribo-tunneling current generation reported by metal-insulator semiconductor triboelectric contacts. [40][41][42]…”

Direct Current Triboelectric Nanogenerators

“…Furthermore, an enhanced open‐circuit voltage output can be obtained via the multiple flexible nanocontacts between a carbon aerogel and silicon (SiO 2 /Si) induces an intensified interaction between atoms at the interface (Figure 5g). [ 105 ] By sliding a carbon aerogel on a p‐type Si wafer with a thin SiO 2 layer, a direct current of 15 µA and voltage of 2 V is obtained, which is much higher than other semiconductor‐based DC system and sufficient for the practical applications. [ 90,101,104 ] Moreover, introducing transparent materials such as indium tin oxide (ITO), the performance of semiconductor‐based DC system can be enhanced by coupling electric fields induced with irradiation and friction (Figure 5h).…”

“…Reproduced with permission. [ 105 ] Copyright 2019, Wiley‐VCH. h) The schematic diagram of the tribo‐photovoltaic generator prototype based on transparent materials.…”

Tribovoltaic Effect on Metal–Semiconductor Interface for Direct‐Current Low‐Impedance Triboelectric Nanogenerators

“…However, conventional TENGs usually use organic polymer insulation materials, and the charges generated by friction tends to accumulate on the surface of the material, resulting in an alternating output . Recently, semiconductor materials began to attract researchers' interest, and a series of work has made great progress: the tribotunneling nanogenerator based on sliding metal–insulator–semiconductor (MIS) structure, the moving Schottky diode based on metal–semiconductor (MS) structure, the triboelectric cell based on PN junction structure, and other moving heterojunction nanogenerator . Thundat and Liu et al realized an ultrahigh current density MIS nanogenerator due to quantum mechanical tunneling of the ultrathin natural oxide layer .…”

“…Recently, semiconductor materials began to attract researchers' interest, and a series of work has made great progress: the tribotunneling nanogenerator based on sliding metal–insulator–semiconductor (MIS) structure, the moving Schottky diode based on metal–semiconductor (MS) structure, the triboelectric cell based on PN junction structure, and other moving heterojunction nanogenerator . Thundat and Liu et al realized an ultrahigh current density MIS nanogenerator due to quantum mechanical tunneling of the ultrathin natural oxide layer . Lin et al designed a moving Schottky diode generator with high current density output which is based on the built‐in electric field separation .…”