Phycocyanin and cellulose nanofibril-based biodegradable triboelectric-piezoelectric hybrid nanogenerators with high-output performance

Cellulose nanofibrils (CNFs) are high aspect ratio, natural nanomaterials with high mechanical strength-to-weight ratio and promising reinforcing dopants in polymer nanocomposites. In this study, we used CNFs and oxidized CNFs (TOCNFs), prepared by a 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO)-mediated oxidation process, as reinforcing agents in poly(vinylidene fluoride) (PVDF). Using high-shear mixing and doctor blade casting, we prepared free-standing composite films loaded with up to 5 wt % cellulose nanofibrils. For our processing conditions, all CNF/PVDF and TOCNF/PVDF films remain in the same crystalline phase as neat PVDF. In the as-prepared composites, the addition of CNFs on average increases crystallinity, whereas TOCNFs reduces it. Further, addition of CNFs and TOCNFs influences properties such as surface wettability, as well as thermal and mechanical behaviors of the composites. When compared to neat PVDF, the thermal stability of the composites is reduced. With regards to bulk mechanical properties, addition of CNFs or TOCNFs, generally reduces the tensile properties of the composites. However, a small increase (~18%) in the tensile modulus was observed for the 1 wt % TOCNF/PVDF composite. Surface mechanical properties, obtained from nanoindentation, show that the composites have enhanced performance. For the 5 wt % CNF/PVDF composite, the reduced modulus and hardness increased by ~52% and ~22%, whereas for the 3 wt % TOCNF/PVDF sample, the increase was ~23% and ~25% respectively.

Hybrid Energy-Harvesting Systems Based on Triboelectric Nanogenerators

The fabrication of nanogenerators is most promising for the worldwide energy crisis situation. Nowadays, piezoelectric nanogenerators (PENGs) and triboelectric nanogenerators are getting immense recognition in the energy field. Herein, piezoelectric and triboelectric effects are combined in a fabricated piezo–tribo hybrid nanogenerator (HNG) for better output performance. A few layered MoS2 on Cu foil via electrodeposition process is deposited and then ZnO is incorporated through electrodeposition, followed by spin coating of poly(vinylidene fluoride) (PVDF) as piezoelectric material. Incorporation of ZnO increases both the piezoelectric property of the PENG and the triboelectric performance. The PVDF/MoS2@ZnO‐based HNG shows astonishing results of open‐circuit voltage (≈140 V) and short‐circuit current (≈4.6 μA) with 256 μW cm−2 power density under piezo‐tribo imparting, which is even better than most ultramodern and complex cleanroom processed nanogenerators. With excellent output performance, this HNG is also capable of harvesting energy from various mechanical and biological movements like walking, heel pressing, elbow bending, and machine vibration. It can lighten up 33 LEDs connected in series and can power up electronic devices like a calculator and wristwatch. The PENG is also biocompatible and sensitive toward physiological signal monitoring, which can be useful for potential biomedical applications.

High-performance triboelectric-electromagnetic hybrid nanogenerator using dual-functional flexible neodymium iron boron/ethyl cellulose (NdFeB/EC) composite films for wind energy scavenging

Cellulose nanofibril (CNF) materials are candidates for the sustainable development of high mechanical performance nanomaterials. Due to inherent hydrophilicity and limited functionality range, most applications require chemical modification of CNF. However, targeted transformations directly on CNF are cumbersome due to the propensity of CNF to aggregate in non-aqueous solvents at high concentrations, complicating the choice of suitable reagents and requiring tedious separations of the final product. This work addresses this challenge by developing a general, entirely water-based, and experimentally simple methodology for functionalizing CNF, providing aliphatic, allylic, propargylic, azobenzylic, and substituted benzylic functional groups. The first step is NaIO4 oxidation to dialdehyde-CNF in the wet cake state, followed by oxime ligation with O-substituted hydroxylamines. The increased hydrolytic stability of oximes removes the need for reductive stabilization as often required for the analogous imines where aldehyde groups react with amines in water. Overall, the process provides a tailored degree of nanofibril functionalization (2–4.5 mmol/g) with the possible reversible detachment of the functionality under mildly acidic conditions, resulting in the reformation of dialdehyde CNF. The modified CNF materials were assessed for potential applications in green electronics and triboelectric nanogenerators.

The properties of composite materials are strongly influenced by both the physical and chemical properties of their individual constituents, as well as the interactions between them. For nanocomposites, the incorporation of nano-sized dopants inside a host material matrix can lead to significant improvements in mechanical strength, toughness, thermal or electrical conductivity, etc. In this work, the effect of cellulose nanofibrils on the structure and mechanical properties of cellulose nanofibril poly(vinylidene fluoride) (PVDF) composite films was investigated. Cellulose is one of the most abundant organic polymers with superior mechanical properties and readily functionalized surfaces. Under the current processing conditions, cellulose nanofibrils, as-received and 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO) oxidized, alter the crystallinity and mechanical properties of the composite films while not inducing a crystalline phase transformation on the 𝛾 phase PVDF composites. Composite films obtained from hydrated cellulose nanofibrils remain in a majority 𝛾 phase, but also exhibit a small, yet detectable fraction of 𝛼 and ß PVDF phases.

As a functional polymer material, poly(vinylidene fluoride) has attracted broad attention due to its outstanding electroactive properties. The electroactive properties of poly(vinylidene fluoride) depend greatly on its crystalline structure, which in turn depends on the processing conditions. In our recent study, poly(vinylidene fluoride) films were prepared by a solution crystallization method, and the effect of evaporation temperatures on the crystalline phase, crystallinity, and morphology of poly(vinylidene fluoride) was investigated. The results reveal that evaporation temperature is the key factor when studying crystalline structure of poly(vinylidene fluoride). Low temperatures can facilitate the nucleation of β-phase; however, they are disadvantageous for the crystal nucleation and crystal growth. It was also found that the dielectric and ferroelectric properties are closely related to the crystallinity of β-phase of poly(vinylidene fluoride) films. Moreover, the porous structure formed in low evaporation temperatures can lead to a decline in dielectric property and breakdown strength. The films fabricated at 80 °C owned the highest crystallinity of β-phase (49%) and presented the maximum εr (12.5, 103 Hz) and Pr (7 µC/cm2), suggesting that the optimum temperature to prepare poly(vinylidene fluoride) films with excellent electroactive properties is 80 °C.

Melt compounding of poly (3-hydroxybutyrate-co-3-hydroxyvalerate)/nanofibrillated cellulose nanocomposites

High-performance flexible triboelectric nanogenerator based on porous aerogels and electrospun nanofibers for energy harvesting and sensitive self-powered sensing

The rational design of three-dimensional (3D) piezoelectric architectural units represents a cutting-edge approach for fabricating highly sensitive piezoelectric materials. However, the precise control over the formation of piezoelectric crystals during the construction of 3D polymer architectures remains a formidable challenge. Here, we report a novel strategy that enables the induction of dominant polar forms while simultaneously constructing their 3D architectures. Utilizing porous cellulose templates, poly(vinylidene fluoride) (PVDF) was self-assembled from solution into microspheres with diameters approximately 3 μm. During this self-assembly process, hydrogen bonding and dipole interactions between PVDF molecules and the cellulose template could facilitate the nucleation and growth of the polar forms. By manipulating the porous structure of cellulose, we successfully achieved two distinct spatial arrangements of PVDF polar microspheres: a homogeneous distribution of PVDF polar microspheres interspersed among the cellulose nanofibrils, and the aggregation of PVDF polar microspheres on the cell wall of the template. Our findings reveal that the former arrangement demonstrates superior piezoelectric sensitivity, boasting a piezoelectric voltage constant of 0.42 V·m/N at a low mass density of 0.3 g/cm3─approximately three times greater than that of the pure PVDF and the cellulose template alone. The remarkable piezoelectric sensitivity observed in the 3D porous PVDF/cellulose composite stems from the fact that the compressive stress applied to the polar microspheres induces a substantial effective electric displacement in the direction of the compressive force. This study opens the door to a new class of rationally designed piezoelectric sensors for wearable human-computer interaction applications.

Utilizing the elementary building blocks of plant cell walls, cellulose nanofibrils (CNFs), can give final materials excellent mechanical properties. For instance, CNF-based wet-spun fibers exhibit superior mechanical properties, surpassing their source materials, plant fibers. Such high mechanical performance is closely related to CNFs’ orientation; thus, most previous research has focused on optimizing spinning rates or introducing post-stretching to enhance this parameter. In this study, the effects of the CNF surface properties on CNF orientation were investigated, which are often neglected in the literature: 1) during extrusion, the CNF surface properties affect the rheological behaviors of the spinning suspension, which in turn influences CNFs’ orientation potential; 2) during coagulation, they govern the affinity between CNFs and antisolvents, thereby determining the shrinkage of CNF gels; 3) during drying, they directly impact capillary forces induced by the evaporation of antisolvents, which significantly determine the CNF orientation in the end products. Overall, this fundamental study provides deeper insights into the assembling behavior of colloidal nanoparticles such as CNFs, which can advance the development of high-performance man-made fibers.

Li-ion batteries are today essential for portable electronic devices as a main power source. Flexible Li-ion batteries have attracted great attention and could be very useful in the emerging fields of flexible, wearable, implantable and bendable electronic devices. Nano-fibrillated cellulose (NFC), with a high aspect ratio (length/diameter) of the nanofibrils, has shown to be a promising binder material for flexible Li-ion batteries [i] [ii]. As a reinforcement component, it gives flexible electrodes good mechanical properties. In addition, the process of making the flexible electrodes is water-based, eliminating the toxicity problem of using conventional poly(vinylidene fluoride) (PVDF) as binder. However, capacity fading limits the stability of the flexible electrodes during repeated cycling. Side reactions on the graphite negative electrodes could be the reason for the capacity loss. Li4Ti5O12(LTO), with a high potential of 1.55 V versus Li metal, could be an alternative to graphite for flexible negative electrodes, reducing the reactivity with the electrolyte. In this work, the electrochemical performance, such as specific capacity and columbic efficiency (CE), and mechanical properties of flexible LTO anode electrodes using NFC as binder are investigated. Fig 1 shows the photograph of LTO electrode, illustrating the flexibility. Fig. 1 Photograph of flexible Li4Ti5O12 negative electrode. [i] S.Leijonmarck, et al. Flexible nano-paper-based positive electrodes for Li-ion batteries-Preparation process and properties, Nano Energy, 2013, 2, 794–800. [ii] S.Leijonmarck, et al. Single-paper flexible Li-ion battery cells through a paper-making process based on nano-fibrillated cellulose, Journal of Materials Chemistry A, 2013, 1, 4671-4677. Figure 1

The need for technological innovation in competitive sports is crucial for self-monitoring and smart decision making. In this work, we demonstrate how intelligent sports and smart decision making can be achieved in cricket and boxing using lithium-modified zinc titanium oxide (LZTO) nanofibers based on piezoelectric nanogenerators (PENGs) and triboelectric nanogenerators (TENGs). Zinc titanium oxide (ZTO) nanofibers synthesized using electrospinning followed by a calcination technique are modified with lithium to increase the output of the nanogenerator. An optimized PENG is fabricated using 25 wt % loading of LZTO (d33 = 214 pm/V) in a poly(vinylidene fluoride) (PVDF) matrix as a double-layered structure and yields an open-circuit voltage (Voc) of 35 V and a short-circuit current (Isc) of 1.6 μA by manual tapping. To fabricate the TENG, Kapton and LZTO are used as negative and positive tribolayers, while Cu and adhesive polymer tape are used as the electrode and spacer, respectively. Furthermore, a hybrid nanogenerator (HNG) is fabricated by combining the PENG and TENG to produce a rectified voltage, current, and power density of up to 75 V, 3.2 μA, and 240 μW/cm2, respectively. These HNGs are integrated with a punching bag and demonstrated to differentiate among the six types of punches in boxing. Furthermore, PENGs are used in cricket to monitor the number of balls middled on the bat during practice and the contact of the ball with the bat and stumps for smart decision making. All kinds of lab-scale testing are done for these applications, which pave a way for exploring the frontiers in nanogenerator applications in sports as maintenance-free and self-powered sensing technology.

Polyvinyl alcohol (PVOH) and its nanofibrillated cellulose (NFC) reinforced nanocomposites were produced and foamed and its properties—such as the dynamic mechanical properties, crystallization behavior, and solubility of carbon dioxide (CO2)—were evaluated. PVOH was mixed with an NFC fiber suspension in water followed by casting. Transmission electron microscopy (TEM) images, as well as the optical transparency of the films, revealed that the NFC fibers dispersed well in the resulting PVOH/NFC nanocomposites. Adding NFC increased the tensile modulus of the PVOH/NFC nanocomposites nearly threefold. Differential scanning calorimetry (DSC) analysis showed that the NFC served as a nucleating agent, promoting the early onset of crystallization. However, high NFC content also led to greater thermal degradation of the PVOH matrix. PVOH/NFC nanocomposites were sensitive to moisture content and dynamic mechanical analysis (DMA) tests showed that, at room temperature, the storage modulus increased with decreasing moisture content. The solubility of CO2 in the PVOH/NFC nanocomposites depended on their moisture content and decreased with the addition of NFC. Moreover, the desorption diffusivity increased as more NFC was added. Finally, the foaming behavior of the PVOH/NFC nanocomposites was studied using CO2 and/or water as the physical foaming agent(s) in a batch foaming process. Only samples with a high moisture content were able to foam with CO2. Furthermore, the PVOH/NFC nanocomposites exhibited finer and more anisotropic cell morphologies than the neat PVOH films. In the absence of moisture, no foaming was observed in the CO2-saturated neat PVOH or PVOH/NFC nanocomposite samples.

For several decades, the development of potential flexible electronics, such as electronic skin, wearable technology, environmental monitoring systems, and the internet of Things network, has been emphasized. In this context, piezoelectric nanogenerators (PENGs) and triboelectric nanogenerators (TENGs) are highly regarded due to their simple design, high output performance, and cost-effectiveness. On a smaller scale, self-powered sensor research and development based on piezo-triboelectric hybrid nanogenerators have lately become more popular. When a material in the TENG is a piezoelectric material, these two distinct effects can be coupled. Herein, we developed a multimode hybrid piezo-triboelectric nanogenerator using the CsPbI3-PVDF composite. The addition of CsPbI3 to PVDF significantly enhances its electroactive phase and dielectric property, thereby enhancing its surface charge density. 5 wt % CsPbI3 incorporation in poly(vinylidene difluoride) (PVDF) results in a high electroactive phase (FEA) value of >90%. Moreover, CsPbI3-PVDF composite-based PENGs were fabricated in three modes, viz., nanogenerators in contact-separation mode (TECS), single electrode mode (TESE), and sliding mode (TES), and the output performance of all the devices was investigated. The fabricated TECS, TESE, and TES reveal peak output powers of 3.08, 1.29, and 0.15 mW at an external load of 5.6 MΩ. Through analysis of the contact angle measurement and experimental quantification, the hydrophilicity of the composite film has been identified. The hydrophobicity and moisture absorption capacity of CsPbI3-PVDF film make it an attractive option for self-powered humidity monitoring. The TENGs effectively powered several low-powered electronic devices with just a few human finger taps. This study offers a high-performance PTENG device that is reliant on ambient humidity, which is a helpful step toward creating a self-powered sensor.