Clean Energy Harvesting Research Articles

Designing Nanoengineered Photocatalysts for Hydrogen Generation by Water Splitting and Conversion of Carbon Dioxide to Clean Fuels.

Semiconductor photocatalysis has received tremendous attention in the past decade as it has shown great promise in the context of clean energy harvesting for environmental remediation. Sunlight is an inexhaustible source of energy available to us throughout the year, although it is rather dilutely dispersed. Semiconductor based photocatalysis presents one of the best ways to harness this source of energy to carry out chemical reactions of interest that require external energy input. Photocatalytic hydrogen generation by splitting of water, CO2 mitigation, and CO2 conversion to green fuel have therefore become the highly desirable clean and sustainable processes for a better tomorrow. Although numerous efforts have been made and continue to be expended to search and develop new classes of photocatalyst materials in recent years, several significant challenges still remain to be resolved before photocatalysis can reach its commercial potential. Therefore, major attention is required towards improving the efficiencies of the existing photocatalysts by further manipulating them and parallelly employing newer strategies for novel photocatalyst designs. This personal account aims to provide a broad overview of the field primarily invoking examples of our own research contributions in the field, which include photocatalytic hydrogen generation and CO2 reduction to value added chemicals. This account reviews the state-of-the-art research activities and scientific possibilities which a functional material can offer if its properties are put to best use through goal-oriented design by combining with other compatible materials. We have addressed fundamental principles of photocatalysis, different kind of functional photocatalysts, critical issues associated with them and various strategies to overcome the related hurdles. It is our hope that this current personal account will provide a platform for young researchers to address the bottleneck issues in the field of photocatalysis and photocatalysts with a sense of clarity, and to find innovative solutions to resolve them by a prudent choice of materials, synthesis protocols, and approaches to boost the photocatalysis output. We emphasize that a targeted or goal-directed photocatalyst nanoengineering as perhaps the only way to realize an early success in this multiparametric domain.

Investigation of the Temperature Compensation of Piezoelectric Weigh-In-Motion Sensors Using a Machine Learning Approach.

Piezoelectric ceramics have good electromechanical coupling characteristics and a high sensitivity to load. One typical engineering application of piezoelectric ceramic is its use as a signal source for Weigh-In-Motion (WIM) systems in road traffic monitoring. However, piezoelectric ceramics are also sensitive to temperature, which affects their measurement accuracy. In this study, a new piezoelectric ceramic WIM sensor was developed. The output signals of sensors under different loads and temperatures were obtained. The results were corrected using polynomial regression and a Genetic Algorithm Back Propagation (GA-BP) neural network algorithm, respectively. The results show that the GA-BP neural network algorithm had a better effect on sensor temperature compensation. Before and after GA-BP compensation, the maximum relative error decreased from about 30% to less than 4%. The sensitivity coefficient of the sensor reduced from 1.0192 × 10−2/°C to 1.896 × 10−4/°C. The results show that the GA-BP algorithm greatly reduced the influence of temperature on the piezoelectric ceramic sensor and improved its temperature stability and accuracy, which helped improve the efficiency of clean-energy harvesting and conversion.

Textile-Based Asymmetric Hierarchical Systems for Constant Hydrovoltaic Electricity Generation

A textile-based evaporation-driven moist-electric generators process the micro-nano hierarchical capillary system and asymmetric conducting polymer coating, which generate the power constantly and efficiently under fully wetted. The output of the generator up to 0.65 V and 8 μA and big enough to drive the LED devices by integrating several samples. • Flexible textile EMEG based on asymmetric micro-nano hierarchical capillary system. • Water flows in the proposed EMEG under capillary action without external power. • Appropriate voltages (0.65 V) and currents (8 μA) were generated on a small sample. • A fully wetted/totally immersed EMEG maintains its electrical output due to its asymmetry. • The output is enhanced by integrating multiple units, powering LED devices. Converting natural resources into electricity is an essential part of the transition to sustainable energy generation. Evaporation-driven moist-electric generators (EMEGs) are an emergent technology and show great potential for harvesting clean energy. In this paper, we report a flexible textile EMEG based on the decoration of an asymmetric micro-nano hierarchical capillary system on the cotton fabric. When water droplets encounter this textile EMEG, the water flows spontaneously under capillary action without requiring an external power supply, resulting in a constant generation of voltages up to 0.65 V and currents up to 8 μA on a small piece of sample with size of 2 cm × 5.5 cm × 0.2 mm (0.16 mL of water can induce a constant electric output for more than 3600 s). More importantly, even when fully wetted or totally immersed in water, the EMEG can maintain its electrical output owing to its inherent electrochemical asymmetry. Furthermore, the output can be enhanced by integrating multiple units, generating sufficient power to drive LED devices, while the energy can also be stored in supercapacitors. This study is of high value for designing of versatile electric generator to harvest clean energy constantly.

Defect-rich engineering of Ni-incorporated tungsten oxides micro-flowers on carbon cloth: A binder-free electrode for highly efficient hydrogen evolution reaction

Hydrogen generated by electrocatalysis water splitting is a promising way to harvest clean energy. However, exploring the cheap and highly efficient electrocatalysts with Pt-like activity for hydrogen evolution reaction (HER) remains great challenges. Herein, we report hierarchical Ni-incorporated oxygen vacancies-rich tungsten oxides micro-flowers on 3D conductive carbon cloth support (denoted as Ni–W H2-550) as a binder-free electrode for high efficient hydrogen evolution. The binder-free 3D structure and the synergistic effect between Ni-incorporated and rich oxygen vacancies can regulate the electronic structure, facilitate the electron transfer, and enlarge the exposed active sites. The as-prepared Ni–W H2-550 exhibits a low overpotential of 25 mV at 10 mA cm−2 with robust stability in alkaline electrolyte solution over 20 h. This study opens up a concise strategy toward the preparation of the low-cost and highly efficient electrocatalyst for HER.

Energy generation in public buildings using piezoelectric flooring tiles; A case study of a metro station

The building sector is benefitting from the significant advancements in clean energy harvesting technologies. The function of building products is witnessing a huge leap to extend beyond mere functional requirements to account for the environmental benefit as well. Piezoelectric flooring tiles are amongst the most promising for indoor energy generation especially in public buildings with great occupancy patterns and intensity. Hence, this study presents a comprehensive review of literature for the use of piezoelectric. The next step deducted parameter integration for the proper selection of piezoelectric tiles. This determined its successful application in the building industry-especially the transportation section which has a notable contribution to energy consumption and emission release. These were divided into factors related to the project type and location, as well as proper selection of the piezoelectric tile product. This hypothesis was tested in the case study. Hence, the application of piezoelectricity was investigated in a Metro station in a core urban area in Egypt, with an estimate of almost 57,000 daily passengers. The selection of the metro line and station as well as the location of installing the tiles was based on the highest passenger density class which provided the greatest step-footage. Furthermore, the selection of the number and type of piezoelectric tiles was determined based on the current project's energy consumption. The study compared the two shortlisted types of tiles in terms of their power generation capacity, initial capital cost, lifespan and expected savings. The results showed that twelve tiles were needed to generate the station's needs for electric energy using Sustainable Energy Floor tiles while only eight tiles were needed using Waynergy piezoelectric tiles. The results also showed a decrease in energy consumption and carbon emissions.

Development of a geothermal-flash organic Rankine cycle-based combined system with solar heat upgrade

In this paper, a new concept of clean energy harvesting from solar energy source is explored in which a fluctuating nature of solar energy source is enhanced with a geothermal energy source. Due to solar radiation's diffuse and fluctuating character, an expensive thermal storage system is required in a solar-only system. On the other hand, due to the relatively low-temperature level of geothermal brine, the flash Rankine power plant has low energy efficiency. The method used in the present study is system integration in which solar thermal energy enhances brine temperature and superheats steam for improved power generation efficiency. Synergistically, the geothermal power cycle eliminates the need for a solar thermal energy storage system, and thus, it reduces capital costs. A geothermal flash Rankine cycle is considered, which is cascaded with an organic Rankine cycle and heat recovery unit for cogeneration. Three types of organic Rankine cycles are investigated with various working fluids for regular, retrograde and transcritical configurations. The transcritical configuration, operating with Perfluorocarbon (C3F8), is found the best working fluid. The maximum exergy destruction in the organic Rankine cycle takes place in the turbine with 48%, whereas at the source side heat exchanger, this is 30%. After flashing, the vapour quality influences power generation efficiency, which shows a maximum vapour quality of around 10% for the case studied. Nevertheless, the maximization of cogenerated exergy rate happens at higher flashing vapour quality than the maximization of exergy efficiency for overall cogeneration application. The exergy efficiency for cogeneration is better during nighttime, for instance, 68% versus noontime 40%, because with solar energy input, there is large exergy destruction at solar collectors. However, during the peak solar radiation at noontime, the cogenerated exergy is more than double that of nighttime, showing an enhanced power generation. This concludes that the proposed integration is effective and creates a higher revenue stream potential than the two technologies working independently.

Continuous Energy Harvesting from Ubiquitous Humidity Gradients using Liquid-Infused Nanofluidics.

Humidity-based power generation that converts internal energy of water molecules into electricity is an emerging approach for harvesting clean energy from nature. Here it is proposed that intrinsic gradient within a humidity field near sweating surfaces, such as rivers, soil, or animal skin, is a promising power resource when integrated with liquid-infused nanofluidics. Specifically, capillary-stabilized ionic liquid (IL, Omim+ Cl- ) film is exposed to the above humidity field to create a sustained transmembrane water-content difference, which enables asymmetric ion-diffusion across the nanoconfined fluidics, facilitating long-term electricity generation with the power density of ≈12.11 µW cm-2 . This high record is attributed to the nanoconfined IL that integrates van der Waals and electrostatic interactions to block movement of Omim+ clusters while allowing for directional diffusion of moisture-liberated Cl+ . This humidity gradient triggers large ion-diffusion flux for power generation indicates great potential of sweating surfaces considering that most of the earth is covered by water or soil.

Natural cotton-based triboelectric nanogenerator as a self-powered system for efficient use of water and wind energy

With the challenges of the energy crisis and related environmental issues, the development and utilization of renewable energy have become a mandatory requirement for the sustainable development of modern society. Recently, triboelectric nanogenerators (TENGs) have been widely utilized in renewable energy sources harvesting, such as solar power, wind power, hydropower and so on. Here, a wheel-disk-shaped TENG based on natural pollution-free cotton is reported for simultaneously harvesting wind and water energy. 8.9 µA of short-circuit current and 782 V of open-circuit voltage are obtained by cotton assemble triboelectric nanogenerator (C-TENG) under a rotation speed of 210 r/min. The maximum peak power can reach 1.89 mW at a matched load resistance of 330 MΩ. Moreover, C-TENG can be used as a self-powered system to power electronic devices and sensing wind speed. This work not only presents a feasible solution for sustainable and clean energy harvesting, but also provides a reliable self-powered sensor for environmental monitoring.

Stretchable polyurethane composite foam triboelectric nanogenerator with tunable microwave absorption properties at elevated temperature

Nowadays, the integration of multiple functions such as harvesting clean energy and electromagnetic protection into single material has attracted great interest. Herein, a stretchable composite foam-based triboelectric nanogenerator (CF-TENG) with tunable microwave absorption (MA) capacity was developed by assembling self-foaming polyurethane (PU), tadpole-like [email protected]3O4 nanoparticles (NPs) and conductive wires. The CF-TENG with a volume of ∅120 mm × 3 mm can generate a maximum output power of 147.9 μW, corresponding to a power density of 1.3 µW/cm2 and easily illuminate 35 commercial light-emitting diodes (LEDs) under periodically vertical contact and separation mode, which exhibits high efficiency in energy-harvesting. Besides, the excellent MA properties and relevant mechanisms at elevated temperatures from 253 K to 333 K were investigated in detail. With an ultralow filler loading of 15 wt%, the minimum reflection loss (RLm) value at 253 K could reach −68.5 dB at 10.97 GHz and effective absorption bandwidth (EAB) below −10 dB achieved 4.37 GHz at a thickness of 2.55 mm. Temperature rise would be conducive to broadening the EAB and shifting the matching frequency towards a higher frequency band. Such a remarkable MA performance originated mainly from the dielectric-magnetic dual loss, well-matched impedance, and multiple reflections. To this end, this CF-TENG with electromagnetic protection property combining the ability to scavenge mechanical energy from ambient vibrations opens a new set of prospective applications in wearable electronics and the next-generation energy systems under invisible harsh environments.

Triboelectric nanogenerator-integrated structural supercapacitor with in situ MXene-dispersed N-doped Zn–Cu selenide nanostructured woven carbon fiber for energy harvesting and storage

A woven carbon fiber (WCF)-based triboelectric nanogenerator (TENG)-cum-structural supercapacitor is an excellent multifunctional device for clean energy harvesting and storage. This type of device has high load-bearing capacity and functions smoothly under severe outdoor conditions. Herein, WCF-based multifunctional TENG is reported that generated 8.9 W m−2 power with 84% energy conversion efficiency. The energy generated by the TENG was simultaneously stored in a connected supercapacitor that provide 1.93 Wh kg−1 of energy density and delivers 39.23 W kg−1 of power density. The specific surface area of the WCF was enhanced several hundred-fold by coating with an N-doped Zn–Cu selenide nanoporous material, thereby enabling higher energy generation and elevated storage capacity of the device. The TENG use a polyester-based solid polymer electrolyte as the negative electrode and polydimethylsiloxane-coated WCF as the positive electrode. The device has a very high coulombic efficiency with high mechanical strength and ability to resist massive impact. An application of the multifunctional device was demonstrated. These types of multifunctional devices have great potential in the self-charging automobile, aerospace, sensor, and electronics sectors.

Low-Voltage DC-DC Converter for IoT and On-Chip Energy Harvester Applications

The power saving issue and clean energy harvesting for wireless and cost-affordable electronics (e.g., IoT applications, sensor nodes or medical implants), have recently become attractive research topics. With this in mind, the paper addresses one of the most important parts of the energy conversion system chain – the power management unit. The core of such a unit will be formed by an inductorless, low-voltage DC-DC converter based on the cross-coupled dynamic-threshold charge pump topology. The charge pump utilizes a power-efficient ON/OFF regulation feedback loop, specially designed for strict low-voltage start-up conditions by a driver booster. Taken together, they serve as the masters to control the charge pump output (up to 600 mV), depending on the voltage value produced by a renewable energy source available in the environment. The low-power feature is also ensured by a careful design of the hysteresis-based bulk-driven comparator and fully integrated switched-capacitor voltage divider, omitting the static power consumption. The presented converter can also employ the on-chip RF-based energy harvester for use in a wireless power transfer system.

Novel Recycled Triboelectric Nanogenerator Based on Polymer‐Coated Trash Soda Can for Clean Energy Harvesting

AbstractResearchers are striving to find the best possible ways to decompose or recycle generated waste to create a pollution‐free environment. Besides the problem of waste pollution, efficient energy generation is another challenging issue across the world. To counter both these problems in a single shot, a unique strategy of reusing and recycling trash soda cans and disposable plastic cups in a simple function change (Funchange) triboelectric nanogenerator (TENG) with a surplus advantage of no chemical processing is presented. The Funchange TENG device presents an excellent output performance with an open circuit voltage, short circuit current, and instantaneous power of 519 V, 82 µA, and 12.25 mW, correspondingly. Further, the fabricated nanogenerator exhibits excellent stability for about 72 000 cycles. This approach of applying trash materials for ultrarobust, high‐performance TENG will pave the path toward sustainable, facile, clean, and environmentally friendly energy scavenging.

Dual-Doping and Synergism toward High-Performance Seawater Electrolysis.

Hydrogen (H2 ) production from direct seawater electrolysis is an economically appealing yet fundamentally and technically challenging approach to harvest clean energy. The current seawater electrolysis technology is significantly hindered by the poor stability and low selectivity of the oxygen evolution reaction (OER) due to the competition with chlorine evolution reaction in practical application. Herein, iron and phosphor dual-doped nickel selenide nanoporous films (Fe,P-NiSe2 NFs) are rationally designed as bifunctional catalysts for high-efficiency direct seawater electrolysis. The doping of Fe cation increases the selectivity and Faraday efficiency (FE) of the OER. While the doping of P anions improves the electronic conductivity and prevents the dissolution of selenide by forming a passivation layer containing P-O species. The Fe-dopant is identified as the primary active site for the hydrogen evolution reaction, and meanwhile, stimulates the adjacent Ni atoms as active centers for the OER. The experimental analyses and theoretical calculations provide an insightful understanding of the roles of dual-dopants in boosting seawater electrolysis. As a result, a current density of 0.8 A cm-2 is archived at 1.8 V with high OER selectivity and long-term stability for over 200 h, which surpasses the benchmarking platinum-group-metals-free electrolyzers.

Electricity generation from ionic solution flowing through packed three-dimensional graphene powders

Herein, we demonstrate a distinctive energy harvesting method that electricity can be generated from the ionic solution flowing through the interstices between packed three-dimensional graphene powders. A constructed electrokinetic nanogenerator with an effective flow area of ∼0.34 cm2 can generate a large current of 91.33 nA under 10–6 M NaCl solution with a flow rate of 0.4 ml min−1, corresponding to a maximum power density of 0.45 μW m−2. Besides, it shows a good linear relationship between the streaming current and the flow rate, suggesting that it could be used as a self-powered micro-flowmeter. These results provide a convenient way for clean energy harvesting and show a bright future for self-powered systems.

A Brief Guide to the Structure of High-Temperature Molten Salts and Key Aspects Making Them Different from Their Low-Temperature Relatives, the Ionic Liquids.

High-temperature molten salt research is undergoing somewhat of a renaissance these days due to the apparent advantage of these systems in areas related to clean and sustainable energy harvesting and transfer. In many ways, this is a mature field with decades if not already a century of outstanding work devoted to it. Yet, much of this work was done with pioneering experimental and computational setups that lack the current day capabilities of synchrotrons and high-performance-computing systems resulting in deeply entrenched results in the literature that when carefully inspected may require revision. Yet, in other cases, access to isotopically substituted ions make those pioneering studies very unique and prohibitively expensive to carry out nowadays. There are many review articles on molten salts, some of them cited in this perspective, that are simply outstanding and we dare not try to outdo those. Instead, having worked for almost a couple of decades already on their low-temperature relatives, the ionic liquids, this is the perspective article that some of the authors would have wanted to read when embarking on their research journey on high-temperature molten salts. We hope that this will serve as a simple guide to those expanding from research on ionic liquids to molten salts and vice versa, particularly, when looking into their bulk structural features. The article does not aim at being comprehensive but instead focuses on selected topics such as short- and intermediate-range order, the constraints on force field requirements, and other details that make the high- and low-temperature ionic melts in some ways similar but in others diametrically opposite.

Multifunctional and superhydrophobic cellulose composite paper for electromagnetic shielding, hydraulic triboelectric nanogenerator and Joule heating applications

• Multifunctional and superhydrophobic cellulose composite paper (CCP) is fabricated. • CCP shows a high EMI shielding effectiveness and electrical conductivity. • The superhydrophobic surface is used as the hydraulic triboelectric nanogenerator. • Surface temperature of CCP can reach 140 °C with a applied voltage of 6 V. Cellulose-based materials have attracted tremendous interest recently due to their fascinating merits of renewability, biodegradability, and low cost, holding great promise in electromagnetic protection, clean energy harvesting, and thermal management. However, the simple and effective integration of multiple functions into single cellulose material remains a challenge. Herein, we report the fabrication of a multifunctional and superhydrophobic cellulose composite paper (CCP) via coated MXene modified by in-situ polymerized polypyrrole and PDMS/candle soot on the opposite surface of the paper. CCP exhibits high-performance electromagnetic interference shielding effectiveness (~40 dB) while maintaining high electrical conductivity (1467 S/m). Moreover, the superhydrophobic surface of CCP can be used as the hydraulic triboelectric nanogenerator (H-TENG) to harvest water energy due to the liquid–solid contact triboelectrification and electrostatic induction. The hydraulic triboelectric energy can be captured and released when water droplets drop from a height of 2 cm and roll at a tilt angle of 20°, the output current can reach a peak of 0.8 nA. Furthermore, the surface saturation temperature of CCP can reach 140 °C with a low applied voltage of 6 V enabled by the Joule effect. Thus, CCP holds great potentials in applications of integrated smart electronics, clean energy harvesting, and thermal management.

Fabrication of superhydrophobic photothermal conversion fabric via layer-by-layer assembly of carbon nanotubes

Photothermal conversion material that generates thermal energy from sunlight is expected to be a promising technology for harvesting and conversion of clean solar energy. However, its photothermal conversion will be affected due to the surface contamination by dirt in outdoor applications, which greatly reduces the solar energy absorption. Herein, a superhydrophobic photothermal conversion fabric was fabricated through layer-by-lay self-assembly of carbon nanotubes (CNTs) on the surface of fibers, and followed by post-treatment with polydimethylsiloxane (PDMS). The CNTs not only impart to the fabric high photothermal conversion capability, but also construct roughening structures on the fiber surface. Consequently, the as-prepared fabric could be rapidly heated to 89.8 °C under one sun (1 kW/m2) irradiation, and showed excellent superhydrophobicity with contact angle 165° ± 0.9° and rolling angle 0.6° ± 0.2°. Meanwhile, the fabric possessed excellent stability to organic solvent, acid/alkali solutions, and UV irradiation. Importantly, the superhydrophobic self-cleaning property prevents the photothermal coating from contamination to guarantee the durability of the photothermal conversion efficiency.

Self-powered and plant-wearable hydrogel as LED power supply and sensor for promoting and monitoring plant growth in smart farming

Synopsis: Smart farming system is built by a versatile conductive hydrogel: clean energy sources can be harvested by our nano energy generator device and stored in the hydrogel supercapacitors to power up the light fertilizer for plant growth promotion, which is monitored by the wireless wearable sensors. • Multifunctional hydrogel for plant (vegetable, fruits) wearable sensor. • Self-powered hydrogel for green agriculture. • Hydrogel sensor monitoring and promoting fruit growth. • The gel collecting energy from wind, rain and sounds for light “fertilizer”. • Plant-device interaction on the gel. Significant energy is consumed to produce the highest-yielding agriculture, which increases greenhouse gas emission and leads to climate change. Smart farming is expected to allow to enhance efficiency and sustainability via site-specific monitoring and managing of crops. This study is a first of its kind development of versatile double-network hydrogel that can serve as: 1) a clean energy harvesting device for self-powered light fertilizer for plants, 2) a supercapacitor for energy storage, 3) plant growth sensor, and 4) an ammonia sensor. Polyacrylic acid double-networked with the conductive nanofiller reduced graphene oxide and then coated with polyaniline are incorporated with double networking (PAA-RGO-PANI, PRP) that significant improved mechanical stress from 300 KPa to 1050Kpa. The excellent stretchability (650%) and strength makes it suitable for agriculture-purposed plant-wearable senor that satisfies the plant growth. The electrical performance of the triboelectric energy harvester (PRP-TENG) provides high power density at 424 mW/m 2 from sound wave, wind, and mechanic pressure. The PAA-RGO-PANI supercapacitor can maintain a stable capacitance at 2330 mF cm −2 after 5000 cycles. The self-powered system combined with PRP-TENG and supercapacitor shows great potential in modern agriculture system.

Recent Advancement of Sustainable and Renewable Energy in Osmotic Power Generation

Investment in clean energy is demand in this century due to abundance of CO2 accumulation in the world to cause several environmental issues. Therefore, harvesting clean energy may assist in reducing carbon footprint in the world to create a green environment for sustainable living. The salinity gradient energy is one of the clean energies with the concept of mixing both salt concentration water from the ocean and fresh water from the river to create an osmotic pressure to power-up the generator for the production of electrical energy. Salinity different between the oceanic salt water and fresh water could produce an equilibrium osmotic pressure that achieve up to 27 bars equivalent from resulting pressure under the water for 200 to 300 meters. The potential of the power production through osmosis power generator is capture at the value of 2000 TWh per year, where in 2018 the world energy consumption was growing 2.3, in which twice the number compare to the average rate of the growth. The major energy consumption is contributed from fossil fuel and consequently resulted from emissions of CO2 increased to 33.1 Gt to the atmosphere. This work explained the advantage of using salinity gradient energy and the fundamental principle of blue energy from pressure-retarded osmosis (PRO). Thus, the osmotic power by using different salinity gradient to create energy is widely known as blue energy, in which it is green and sustainable to produce electricity to the local communities. © 2021, Chulalongkorn University, Faculty of Fine and Applied Arts. All rights reserved.

Graphene Oxide Incorporated Antifouling Thin Film Composite Membrane for Application in Desalination and Clean Energy Harvesting Processes

Graphene Oxide Incorporated Antifouling Thin Film Composite Membrane for Application in Desalination and Clean Energy Harvesting Processes