The direct conversion of mechanical energy into electricity by nanomaterial-based devices offers potential for green energy harvesting . A conventional triboelectric nanogenerator converts frictional energy into electricity by producing alternating current (a.c.) triboelectricity. However, this approach is limited by low current density and the need for rectification . Here, we show that continuous direct-current (d.c.) with a maximum density of 10 A m can be directly generated by a sliding Schottky nanocontact without the application of an external voltage. We demonstrate this by sliding a conductive-atomic force microscope tip on a thin film of molybdenum disulfide (MoS). Finite element simulation reveals that the anomalously high current density can be attributed to the non-equilibrium carrier transport phenomenon enhanced by the strong local electrical field (10-10 V m) at the conductive nanoscale tip . We hypothesize that the charge transport may be induced by electronic excitation under friction, and the nanoscale current-voltage spectra analysis indicates that the rectifying Schottky barrier at the tip-sample interface plays a critical role in efficient d.c. energy harvesting. This concept is scalable when combined with microfabricated or contact surface modified electrodes, which makes it promising for efficient d.c. triboelectricity generation.

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Real-time, label-free detection of Gram-positive bacteria with high selectivity and sensitivity is demonstrated using an interdigitated impedimetric array functionalized with naturally produced antimicrobial peptide from class IIa bacteriocins. The antimicrobial peptide, leucocin A, was chemically synthesized and covalently immobilized on interdigitated gold microelectrodes via the interaction between the C-terminal carboxylic acid of the peptide and free amines of a preattached thiolated linker. Exposing the peptide sensor to various concentrations of Gram-positive bacteria generated reproducible impedance spectra that detected peptide-bacteria interactions at a concentration of 1 cell/μL. The peptide sensor also selectively detected Listeria monocytogenes from other Gram-positive strains at a concentration of 10(3) cfu mL(-1). The study highlights that short peptide ligands from bacteriocin class offer high selectivity in bacterial detection and can be used in developing a robust, portable biosensor device to efficiently detect pathogenic Gram-positive bacteria in food samples.

Direct-current (d.c.) electricity generation using moving Schottky contact is emerging as a new strategy for mechanical energy conversion. Here, we demonstrate the generation of d.c.tunneling current with a density of ~35 A/m 2 at a metal-insulator-semiconductor (MIS) sliding system using micro-tips. The measured current densities were found to be three to four orders of magnitude higher than that observed with the conventional polymer-based triboelectric nanogenerators (TENGs). The electromotive force ∆Vs * for the tribo-tunneling transport comes from the dynamic electronic excitation at the frictional interface rather than from the electrostatically trapped surface charges as in the case of conventional TENGs. The strong electronic excitation can give rise to a non-equilibrium interfacial charge variation ∆σm.Depending on the energy distribution of the excited electrons/holes, ∆σm subsequently dissipates non-adiabatically into tunneling current and trapped surface charges, or adiabatically into heat. These fundamental results not only enhance our understanding of the triboelectric phenomenon, but also open up new paths for the development of next-generation mechanical energy harvesting and sensing techniques. Main Text

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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...

Boosting the photovoltaic power output is the key to large-scale implementation of solar cell technologies for renewable energy applications. Traditional solar energy harvesting is limited by the costly fabrication of p-n junctions, the duration of sunlight irradiation, and theoretical output limit. In this work, Liu et al. demonstrate that the photovoltaic power output can be dramatically enhanced by mechanical friction between a metal and a semiconductor, leading to the development of a new power generation approach called tribo-photovoltaic generator. It enables highly efficient solar-mechanical energy co-harvesting in the daytime as well as mechanical energy at night. The tribo-photovoltaic effect may be utilized for co-harvesting of solar and mechanical energy in various scenarios such as ocean tidal energy harvesters, wind turbines, and aerospace energy collectors.

Aqueous zinc (Zn) chemistry features intrinsic safety, but suffers from severe irreversibility, as exemplified by low Coulombic efficiency, sustained water consumption and dendrite growth, which hampers practical applications of rechargeable Zn batteries. Herein, we report a highly reversible aqueous Zn battery in which the graphitic carbon nitride quantum dots additive serves as fast colloid ion carriers and assists the construction of a dynamic & self-repairing protective interphase. This real-time assembled interphase enables an ion-sieving effect and is found actively regenerate in each battery cycle, in effect endowing the system with single Zn2+ conduction and constant conformal integrality, executing timely adaption of Zn deposition, thus retaining sustainable long-term protective effect. In consequence, dendrite-free Zn plating/stripping at ~99.6% Coulombic efficiency for 200 cycles, steady charge-discharge for 1200 h, and impressive cyclability (61.2% retention for 500 cycles in a Zn | |MnO2 full battery, 73.2% retention for 500 cycles in a Zn | |V2O5 full battery and 93.5% retention for 3000 cycles in a Zn | |VOPO4 full battery) are achieved, which defines a general pathway to challenge Lithium in all low-cost, large-scale applications.