Ubiquitous Energy Research Articles

An Emerging Family of Piezocatalysts: 2D Piezoelectric Materials.

Piezocatalysis is an emerging technique that holds great promise for the conversion of ubiquitous mechanical energy into electrochemical energy through piezoelectric effect. However, mechanical energies in natural environment (such as wind energy, water flow energy, and noise) are typically tiny, scattered, and featured with low frequency and low power. Therefore, a high response to these tiny mechanical energies is critical to achieving high piezocatalytic performance. In comparison to nanoparticles or 1D piezoelectric materials, 2D piezoelectric materials possess characteristics such as high flexibility, easy deformation, large surface area, and rich active sites, showing more promise in future for practical applications. In this review, state-of-the-art research progresses on 2D piezoelectric materials and their applications in piezocatalysis are provided. First, a detailed description of 2D piezoelectric materials are offered. Then a comprehensive summary of the piezocatalysis technique is presented and examines the piezocatalysis applications of 2D piezoelectric materials in various fields, including environmental remediation, small-molecule catalysis, and biomedicine. Finally, the main challenges and prospects of 2D piezoelectric materials and their applications in piezocatalysis are discussed. It is expected that this review can fuel the practical application of 2D piezoelectric materials in piezocatalysis.

Direct-current output of silicon–organic monolayer–platinum Schottky TENGs: Elusive friction-output relationship

Triboelectric nanogenerators (TENGs) are an emerging energy harvesting technology able to convert ubiquitous mechanical energy into electricity. Friction, static charging and flexoelectricity are all involved in the mechanism underpinning TENG operation, but their relative contribution has remained elusive. Here we used dynamic and static conductive atomic force microscopy (C-AFM) measurements on monolayer-modified silicon crystals to detect evidence of a relationship between friction and zero-bias current, and between pressure and the direction of the putative flexovoltage. We demonstrate that a static electricity-related tribovoltage is probably responsible for a friction excess, and that surprisingly this friction excess is found to be dependent on the doping level and type of the silicon substrate. Such friction excess is however no longer measurable once current is allowed to flow across the junction. This observation points to an electrostatic origin of friction in silicon-based Schottky TENGs, and suggests that the zero external bias DC current is at least in part an electronic flow to neutralize static charges. Further, the sign of the zero-bias current, but not its magnitude, is independent of the semiconductor doping type, which is again suggestive of surface statics being a main contributor to the zero-bias output rather than exclusively a space-charge effect. We also reveal the presence of a junction flexovoltage under pressures common in AFM experiments (GPa), even for negligible lateral friction. In a static Pt–monolayer–n-type Si junction the flexovoltage carries the same sign as the tribovoltage, and can reach such magnitude to overwrite external voltages as high as 2 V. The immediate implication is that the flexovoltage is likely to have i) a strong contribution to the zero-bias output of a n-Si Schottky TENG, ii) a negative effect on the output of a p-Si TENG, and iii) its detection can be straightforward, as we discovered that flexoelectricity manifests as an “inverted diode”: a n-type Si–platinum diode with negligible current even when the n-type material is negatively biased as long as the “static” diode remains under a large normal pressure.

High Performance Rotary‐Structured Triboelectric‐Electromagnetic Hybrid Nanogenerator for Ocean Wind Energy Harvesting

AbstractModern ship is an important transportation and even military equipment on the ocean, which has ubiquitous ocean wind energy with high‐speed and stable wind direction. However, much higher‐speed wind energy during the movement of the ship is often abandoned. Triboelectric nanogenerator (TENG) that can generate electrical energy by scavenging ambient mechanical energy is one of the emerging energy harvesting technologies. By coupling the TENG and electromagnetic generators (EMG), a high‐performance rotary‐structured triboelectric‐electromagnetic hybrid nanogenerator (RS‐HG) is designed in this study. By introducing a matched inductor in the paired energy management circuit (EMC), the charging efficiency of RS‐TENG can be effectively enhanced by 15 times compared to that without EMC. At a simulated wind speed of 15 m s−1, the peak power of lateral TENG (L‐TENG), top TENG (T‐TENG) and EMG are 7.54, 7.85, and 22.5 mW, respectively. The demonstrated RS‐HG comprising two RS‐TENGs and one EMG can readily charge a 1 mF capacitor to 8 V within 15 s under the wind speed of 15 m s−1 and continuously power the electronic devices. Moreover, the RS‐HG can also successfully charge a smartphone through the step‐down and voltage stabilization module to further expand its application scenarios. The applications of powering portable electronics reveal the huge prospects of hybrid nanogenerators in energy harvesting and self‐powered environmental monitoring during navigation.

3D-Printed Thermoplastic Polyurethane Electrodes for Customizable, Flexible Lithium-Ion Batteries with an Ultra-Long Lifetime.

3D printing technology has demonstrated great potential in fabricating flexible and customizable high-performance batteries, which are highly desired in the forthcoming intelligent and ubiquitous energy era. However, a significant performance gap, especially in cycling stability, still exists between the 3D-printed and conventional electrodes, seriously limiting the practical applications of 3D-printed batteries. Here, for the first time, a series of thermoplastic polyurethane (TPU)-based 3D-printed electrodes is developed via fused deposition modeling for flexible and customizable high-performance lithium-ion batteries. The TPU-based electrode filaments in kilogram order are prepared via a facile extrusion method. As a result, the electrodes are well-printed with high dimensional accuracy, flexibility, and mechanical stability. Notably, 3D-printed TPU-LFP electrodes exhibit a capacity retention of 100% after 300 cycles at 1C, which is among the best cycling performance of all the reported 3D-printed electrodes. Such excellent performance is associated with the superb stress cushioning properties of the TPU-based electrodes that can accommodate the volume change during the cycling and thus significantly prevent the collapse of 3D-printed electrode structures. The findings not only provide a new avenue to achieve customizable and flexible batteries but also guide a promising way to erase the performance gap between 3D-printed and conventional lithium-ion batteries.

A Bistable Triboelectric Nanogenerator for Low-Grade Thermal Energy Harvesting and Solar Thermal Energy Conversion.

Converting ubiquitous ambient low-grade thermal energy into electricity is of great significance for tackling the fossil energy shortage and environmental crisis but poses a considerable challenge. Here, a novel thermal-driven triboelectric nanogenerator (TD-TENG) is developed, which utilizes a bimetallic beam with a bi-stable dynamic feature to induce continuous mechanical oscillations, and the mechanical motion is then converted into electric power using a contact-separation TENG. The thermal process inside the device is systematically investigated and effective thermal management is conducted accordingly. After optimization, the TD-TENG can produce a power density of 323.9mWm-2 at 59.5°C, obtaining the highest record of TENG-based thermal energy harvesters. Besides, the first prototype of TENG-based solar thermal harvester is successfully demonstrated, with a power density of 364.4mWm-2 . Moreover, the TD-TENG can harvest and dissipate the heat at the same time, exhibiting great potential in over-heated electronics protection as well as architectural energy conservation. Most importantly, the operation temperature range of the TD-TENG is tunable by adjusting the bimetal parameters, allowing the device a wide and flexible working thermal gradient. These unique properties validate the TD-TENG is a simple, feasible, cost-effective, and high-efficient low-grade thermal energy harvester.

Water-Resistant Thermoelectric Ionogel Enables Underwater Heat Harvesting

The energy crisis is one of the most critical and urgent problems in modern society; thus, harvesting energy from ubiquitous low-grade heat energy with thermoelectric (TE) materials has become an available strategy in sustainable development. Recently, emerging ionic TE materials have been widely used to harvest low-grade heat energy, owing to their excellent performance in high ionic Seebeck coefficient, low thermal conductivity, and mechanical flexibility. However, the instability of ionic conductive materials in the underwater environment seriously suppresses underwater energy-harvesting, resulting in a waste of underwater low-grade heat energy. Herein, we developed a water-resistant TE ionogel (TEIG) with excellent long-term underwater stability utilizing a hydrophobic structure. Due to the hydrophobic polymer network and hydrophobic ionic liquid (IL), the TEIG exhibits high hydrophobicity and antiswelling capacity, which meets the requirement of environment stability for underwater thermoelectric application. Furthermore, the water resistance endows the TEIG with great thermoelectric performances in the underwater environment, including satisfactory ionic Seebeck coefficient, outstanding durability, and superior salt tolerance. Therefore, this investigation provides a promising strategy to design water-resistant TE materials, enabling a remarkable potential in harvesting low-grade heat energy under water.

Analysis of Influencing Parameters Enhancing the Plucking Efficiency of Piezoelectric Energy Harvesters.

The integration of energy harvesting systems into sensing technologies can result in novel autonomous sensor nodes, characterized by significant simplification and mass reduction. The use of piezoelectric energy harvesters (PEHs), particularly in cantilever form, is considered as one of the most promising approaches aimed at collecting ubiquitous low-level kinetic energy. Due to the random nature of most excitation environments, the narrow PEH operating frequency bandwidth implies, however, the need to introduce frequency up-conversion mechanisms, able to convert random excitation into the oscillation of the cantilever at its eigenfrequency. A first systematic study is performed in this work to investigate the effects of 3D-printed plectrum designs on the specific power outputs obtainable from FUC excited PEHs. Therefore, novel rotating plectra configurations with different design parameters, determined by using a design-of-experiment methodology and manufactured via fused deposition modeling, are used in an innovative experimental setup to pluck a rectangular PEH at different velocities. The obtained voltage outputs are analyzed via advanced numerical methods. A comprehensive insight into the effects of plectrum properties on the responses of the PEHs is attained, representing a new and important step towards the development of efficient harvesters aimed at a wide range of applications, from wearable devices to structural health monitoring systems.

Integrated Piezo-Triboelectric Nanogenerators-Based Self-Powered Flexible Temperature and Pressure Sensor

Efficient harvesting of ubiquitous ambient mechanical energy using various types of nanogenerators (NGs) has attracted considerable interest in recent years. Herein, we present a textile triboelectric nanogenerator (T-TENG) using Polytetrafluoroethylene (PTFE) and Nylon based counter-surfaces in fabric form (both fixed to conductive fabric electrodes). T-TENG performance is enhanced by exposing PTFE film with Argon plasma. The output voltage of the plasma treated devices increased by a factor of ~10, and their short circuit current density increased by a factor of ~9 (compared to pristine non-plasma treated devices). Additionally, we demonstrate that the fabricated T-TENG can be used as a self-powered temperature sensor, tested in the 25-90 °C range. The T-TENG output voltage decreased linearly with increasing temperature exhibiting a sensitivity of ~ 1%/(°C). Further, we integrated a flexible piezoelectric nanogenerator (PENG) on top of the T-TENG to detect the contact forces. The PENG output is also used to compensate the pressure dependent output of TENG underneath, and allows distinct temperature and pressure measurements. The excellent results observed here show the potential of T-TENGs for use as self-powered sensors in applications such as health monitoring, wearables and interactive systems.

Water splitting with silicon p-i-n superlattices suspended in solution.

Photoelectrochemical (PEC) water splitting to produce hydrogen fuel was first reported 50 years ago1, yet artificial photosynthesis has not become a widespread technology. Although planar Si solar cells have become a ubiquitous electrical energy source economically competitive with fossil fuels, analogous PEC devices have not been realized, and standard Si p-type/n-type (p-n) junctions cannot be used for water splitting because the bandgap precludes the generation of the needed photovoltage. An alternative paradigm, the particle suspension reactor (PSR), forgoes the rigid design in favour of individual PEC particles suspended in solution, a potentially low-cost option compared with planar systems2,3. Here we report Si-based PSRs by synthesizing high-photovoltage multijunction Si nanowires (SiNWs) that are co-functionalized to catalytically split water. By encoding a p-type-intrinsic-n-type (p-i-n) superlattice within single SiNWs, tunable photovoltages exceeding 10 V were observed under 1 sun illumination. Spatioselective photoelectrodeposition of oxygen and hydrogen evolution co-catalysts enabled water splitting at infrared wavelengths up to approximately 1,050 nm, with the efficiency and spectral dependence of hydrogen generation dictated by thephotonic characteristics of the sub-wavelength-diameter SiNWs. Although initial energy conversion efficiencies are low, multijunction SiNWs bring the photonic advantages of a tunable, mesoscale geometry and the material advantages of Si-including the small bandgap and economies of scale-to the PSR design, providing a new approach for water-splitting reactors.

Analysis of a Combined Solar Drying System for Wood-Chips, Sawdust, and Pellets

The future of conventional fuels has limited sustainability and creates disquietude because of the ubiquitous energy crisis worldwide. The judicious use of biomass or wood-based fuels is inevitable. The quality of wood fuels depends on the moisture content, and subsequently, solar drying solutions can play a vital role in adequately storing and controlling moisture in the fuels. In the present study, a novel forced convection cabinet-type solar dryer was developed and investigated for its thermal performance. An artificial neural network (ANN model) was created to predict the final moisture content of the drying system. The drying behavior of three distinct wood fuels, i.e., woodchips, sawdust, and pellets, was kept under observation to plot the drying curve based on their calculated moisture ratio. The dryer reached a maximum temperature of 60 °C while maintaining a temperature gradient of 10–20 °C. The maximum thermal energy and exergy efficiency was recorded as 55% and 51.1%, respectively. The ANN-optimized model was found suitable with reasonable values of coefficient of correlation (R) for the model.

Recent advances in interfacial solar vapor generation: clean water production and beyond

This review summarizes the recent progress in interfacial solar vapor generation, which was first proposed in 2014. The technique shows great potential for decentralized desalination applications using ubiquitous and renewable solar energy.

Electromechanical Properties of a Hybrid Broadband Wind Energy Harvester for Smart Agriculture Monitoring in the Loess Plateau

Wind, as a ubiquitous energy, is an important power source for intelligent monitoring systems in smart agriculture applications, and its efficient collection can greatly improve the long-term performance of monitoring systems. However, it is difficult to achieve the broadband and efficient harvesting of wind energy using the existing energy collection technology. Herein, a broadband energy conversion device (ECD), consisting of a triboelectric nanogenerator (TENG) and an electromagnetic generator (EMG), is proposed for wind energy collection under different wind speeds. The introduction of an optimized Scotch yoke mechanism greatly improves the utilization of wind energy by the TENG, thus reducing energy dissipation. Moreover, the addition of a deflector into the fan greatly reduces the start-up wind speed and improves the ability of the device to capture breeze energy. By doping multi-walled carbon nanotubes, the output voltage and current of the TENG can be improved by 108.89% and 116.61%, respectively. Furthermore, the adopted all-directional conductive foam can greatly prolong the service life of the ECD. The peak power of the ECD is 68.49 mW at 9.6 m/s, with the EMG and TENG producing approximately 64.80 mW and 3.69 mW, respectively. The proposed ECD provides a new technical strategy for the practical application of wind energy harvesters.

Design and implementation of a novel multi-faceted-efficient pneumatic dual-axis solar tracker

PurposePhotovoltaic (PV) systems are experiencing exponential growth due to environmental concerns, unlimited and ubiquitous solar energy, and starting-to-make-sense panel costs. Alongside designing more efficient solar panels, installing solar trackers and special circuitry for optimizing power delivery to the load according to a maximum power point tracking (MPPT) algorithm are other ways of increasing efficiency. However, it is critical for any efficiency increase to account for the power consumption of any amendments. Therefore, this paper aims to propose a novel tracker while using MPPT to boost the PV system's actual efficiency accounting for the involved costs.Design/methodology/approachThe proposition is an experimental pneumatic dual-axis solar tracker using light-dependent resistor (LDR) sensors. Due to its embedded energy storage, the pneumatic tracker offers a low duty-cycle operation leading to tracking energy conservation, fewer maintenance needs and scalability potential. While MPPT assures maximum load power delivery, the solar PV's actual delivered power is calculated for the first time, accounting for the solar tracking and MPPT power costs.FindingsThe experiments' results show an increase of 37.6% in total and 35.3% in actual power production for the proposed solar tracking system compared to the fixed panel system, with an MPPT efficiency of 90%. Thus, the pneumatic tracking system offers low tracking-energy consumption and good actual power efficiency. Also, the newly proposed pneumatic stimulant can significantly simplify the tracking mechanism and benefit from several advantages that come along with it.Originality/valueTo the best of the authors’ knowledge, this work proposes, for the first time, a single-motor pneumatic dual-axis tracker with less implementation cost, less frequent operation switching and scalability potential, to be developed in future works. Also, the pneumatic proposal delivers high actual power efficiency for the first time to be addressed.

Flexible hydrogel with a coupling enhanced thermoelectric effect for low-grade heat harvest

Harvesting abundant and ubiquitous low-grade thermal energy and simultaneously converting it into electrical energy hold the potential of solving the existing energy crisis. Advances in thermoelectric materials now allow thermoelectric ionogel electrolyte to enhance the energy conversion and storage capacities under a thermal gradient. Here, we report an ionic thermoelectric (i-TE) material based on polyacrylamide (PAM) carboxymethyl cellulose (CMC) double network gel substrate with flexible and high thermal-electrical conversion properties. By combining the thermodiffusion effect of lithium sulfate (Li2SO4) ions and the thermogalvanic effect of [Fe(CN)64−/Fe(CN)63−], which achieved a coupled ionic Seebeck effect of up to 11.58 mV/K, exhibiting a high ionic conductivity (18.4 mS cm−1) and low thermal conductivity (0.47 W m−1/K), resulting in a high ionic power factor (198.2 μW m−1K−2) at room temperature. It exhibited an excellent tensile property (634%) and adhesion, and avoids electrolyte leakage to a large extent. Moreover, the application in ionic capacitors also demonstrates the superior thermoelectric conversion capability of i-TE gels. We believe that i-TE materials will pave a new pathway for low-grade thermal harvesting and self-driven flexible wearable electronics.

Printed Organic Photovoltaic Modules on Transferable Ultra‐thin Substrates as Additive Power Sources

Thin-film photovoltaics with functional components on the order of a few microns, present an avenue toward realizing additive power onto any surface of interest without excessive addition in weight and topography. To date, demonstrations of such ultra-thin photovoltaics have been limited to small-scale devices, often prepared on glass carrier substrates with only a few layers solution-processed. We demonstrate large-area, ultra-thin organic photovoltaic (PV) modules produced with scalable solution-based printing processes for all layers. We further demonstrate their transfer onto light-weight and high-strength composite fabrics, resulting in durable fabric-PV systems ∼50 microns thin, weighing under 1 gram over the module area (corresponding to an area density of 105 g m-2 ), and having a specific power of 370 W kg-1 . Integration of the ultra-thin modules onto composite fabrics lends mechanical resilience to allow these fabric-PV systems to maintain their performance even after 500 roll-up cycles. This approach to decouple the manufacturing and integration of photovoltaics enables new opportunities in ubiquitous energy generation.

Surface Analysis of Pristine and Cycled NMC/Graphite Lithium-Ion Battery Electrodes: Addressing the Measurement Challenges.

Lithium-ion batteries are the most ubiquitous energy storage devices in our everyday lives. However, their energy storage capacity fades over time due to chemical and structural changes in their components, via different degradation mechanisms. Understanding and mitigating these degradation mechanisms is key to reducing capacity fade, thereby enabling improvement in the performance and lifetime of Li-ion batteries, supporting the energy transition to renewables and electrification. In this endeavor, surface analysis techniques are commonly employed to characterize the chemistry and structure at reactive interfaces, where most changes are observed as batteries age. However, battery electrodes are complex systems containing unstable compounds, with large heterogeneities in material properties. Moreover, different degradation mechanisms can affect multiple material properties and occur simultaneously, meaning that a range of complementary techniques must be utilized to obtain a complete picture of electrode degradation. The combination of these issues and the lack of standard measurement protocols and guidelines for data interpretation can lead to a lack of trust in data. Herein, we discuss measurement challenges that affect several key surface analysis techniques being used for Li-ion battery degradation studies: focused ion beam scanning electron microscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, and time-of-flight secondary ion mass spectrometry. We provide recommendations for each technique to improve reproducibility and reduce uncertainty in the analysis of NMC/graphite Li-ion battery electrodes. We also highlight some key measurement issues that should be addressed in future investigations.

Wind‐Driven Bidirectional Fluttering Triboelectric Nanogenerator Via Dual Flagpole and Slot Structure Design

AbstractRecently, as fossil fuel reserves have decreased and energy requirements have increased worldwide, wind energy, which has various advantages, such as ubiquitous, sustainable, clean, and infinite energy capacitance, has attracted increasing attention. In particular, wind‐driven fluttering‐type triboelectric nanogenerators (TENGs), which can utilize mechanical movement induced by wind energy based on the coupling of the triboelectric effect and electrostatic induction, have been widely studied. However, previous studies have not discussed structural device designs to harvest bidirectional wind energy. Herein, a wind‐driven bidirectional fluttering triboelectric nanogenerator (WBF‐TENG) is reported, which has a dual flagpole and slot structure design to generate electrical output against wind blowing from both directions. Considering natural wind flow in random direction, WBF‐TENG is more effective compared with the previous unidirectional fluttering TENGs. The electrical output of the WBF‐TENG is quantitatively measured and analyzed in terms of the peak and root mean square outputs depending on various design parameters and wind velocities. The findings demonstrated that the WBF‐TENG can be utilized as a swing safety light by continuously turning on 76 LEDs when riding a swing during right and left direction movements. Furthermore, the WBF‐TENG can scavenge omnidirectional wind energy by vertically stacking two devices.

Design of metallic phase WS2/cellulose nanofibers composite membranes for light-boosted osmotic energy conversion

Osmotic energy reserves in estuaries, coupled with the ubiquitous solar energy, could be harnessed through emerging nanofluidic membranes to reduce the energy crisis. Herein, we mixed WS2 with high concentration of metal phase and cellulose nanofiber (CNF) to fabricate composite membranes by vacuum filtration. Incorporated CNF as space charge donors increases the ion flux through the enlarged interlayer spacing in the WS2/CNF composite membrane. By simulating seawater and river water, the power density of the composite membrane reached to 1.99 W m−2. Furthermore, due to the photoelectric characteristics of WS2, the composite membrane exhibits photoresponsivity, which generated a photocurrent of 177 nA through illumination. Taking the advantage of the optoelectronic properties of the composite membrane, the power density under illumination is twice than that of the dark state. Based on the results, this material design strategy can enhance the ion transport in nanofluidic membranes for efficient generation of clean energy.

Solar Energy in Space Applications: Review and Technology Perspectives

AbstractSolar cells (SCs) are the most ubiquitous and reliable energy generation systems for aerospace applications. Nowadays, III–V multijunction solar cells (MJSCs) represent the standard commercial technology for powering spacecraft, thanks to their high‐power conversion efficiency and certified reliability/stability while operating in orbit. Nevertheless, spacecraft companies are still using cheaper Si‐based SCs to amortize the launching costs of satellites. Moreover, in recent years, new SCs technologies based on Cu(In,Ga)Se2(CIGS) and perovskite solar cells (PSCs) have emerged as promising candidates for aerospace power systems, because of their appealing properties such as lightweightness, flexibility, cost‐effective manufacturing, and exceptional radiation resistance. In this review the current advancements and future challenges of SCs for aerospace applications are critically discussed. In particular, for each type of SC, a description of the device's architecture, a summary of its performance, and a quantitative assessment of the radiation resistance are presented. Finally, considering the high potential that 2D‐materials (such as graphene, transition metal dichalcogenides, and transition metal carbides, nitrides, and carbonitrides) have in improving both performance and stability of SCs, a brief overview of some important results concerning the influence of radiation on both 2D materials‐based devices and monolayer of 2D materials is also included.

Asynchronous Wind Turbine Generator: Output Power Evaluation

In addition to photovoltaic (PV) power plants, wind turbine generators represent the most ubiquitous renewable energy use today. The stochastic and intermittent character of wind as a key source of electricity is one of the fundamental challenges associated with wind turbines WT. This paper describes an induction generator used in wind turbines. The implemented Turbine utilizes a straightforward output power against wind speed relationship to convert wind speed to turbine output power. When the wind speed is below or above the cut-in speed, the turbine produces no real power. Constantly, the machine consumes reactive power. This implemented block compensates for the machine's reactive power demand. Local load consumption is 75 kW. The electricity grid makes up for any shortage in wind turbine generation. When the generator's output exceeds 75 kW, the excess energy is exported to the grid.