Energy Conversion Concepts Research Articles

Addressing Individual Layers and Their Optical Properties in Artificial MoS2 Bilayers via Sulfur Isotope Labeling.

The physicochemical properties of van der Waals (vdW) heterostructures are driven by the delicate interactions between the individual layers in a multilayer stack. While addressing the monolayers of different compositions in the multilayer is feasible, exploring the intrinsic properties of the monolayers of the same composition within a multilayer is extremely challenging. This becomes of utmost importance in energy conversion and storage concepts based on layered vdW materials. For example, the charge distribution on the individual layers can be determined, and the behavior can be disentangled. We introduce sulfur isotope labeling as a powerful tool for separately addressing monolayers in vdW heterostructures composed of transition metal disulfides. Using chemical vapor deposition (CVD), we prepared monolayers of MoS2 using natural sulfur (NatS) and 34sulfur (34S) as precursors. Artificial bilayers were then prepared by transferring Mo34S2 onto MoNatS2. Thanks to the different masses of NatS and 34S, we were able to disentangle the spectral fingerprints of phonons and excitons in the two layers using Raman and photoluminescence microspectroscopy. Also, the charge distribution on the individual layers was revealed through Raman spectra analysis. Our work thus provides a different perspective for understanding the functionalities and optical properties of smart architecture based on transition metal chalcogenides.

Wave power calculation of a large periodic array of bottom-hinged paddle wave energy converters using Floquet–Bloch theory

In this study we consider a wave energy farm consisting of a large number of bottom-hinged paddles. The paddles are arranged in a doubly-periodic manner, with a finite number of identical rows and each row containing an infinite number of paddles. Each paddle is attached to its own damper and spring, allowing power to be generated through its pitching motion. Unlike previous studies into paddle arrays, we envisage compact arrays consisting of small devices arranged across a large number of rows. The mathematical analysis of this proposed configuration is best suited to methods that exploit the periodicity of the array. It is shown that the velocity potential everywhere within the array can be described by an expansion in terms of suitably-defined Floquet–Bloch eigenmodes and this allows the solution to the scattering problem involving waves incident upon the array to be determined by a simple low-order system of equations. The method used in this study is exact within the setting of linearised water waves and has all of the advantages of classical low-frequency multi-scale homogenisation without the low-frequency restriction. It may also be regarded as a natural extension of the well-known wide-spacing approximation without the large separation restriction. Although the focus of this paper is on the mathematical approach to the solution of the problem, we provide a range of results to illustrate the performance of this proposed wave energy converter concept.

Economic feasibility study for wave energy conversion device deployment in Faroese waters

As the world continues to battle with increasing energy demand along with the serious effects of climate change, there is a need for more reliable renewable energy sources. The objective of the present work is to study the economic feasibility for deployment of wave energy conversion devices in the Faroese coastal region. We analyze eight different wave energy conversion concepts under development at nine different nearshore locations in the Faroese coastal region. The nine different locations are classified into three coastal locations — three on the west coast, three on the east coast and three on the north coast. The eight wave energy conversion devices mostly rely on different working principles, though some of these are similar. Results show that there is quite a significant difference in the performance of the devices from coast to coast. There is also a difference between the different conversion devices as they rely on different principles and the suitability of each device varies from location to location. We also show that the Faroe Islands are a suitable location for wave energy converter deployment compared to other places. Furthermore, results show that the performance of wave energy converters in the Faroe Islands can prove to be a direct competitor to offshore floating wind energy.

Electromechanical Energy-Based 3D-Controllable Motion of Small Matter toward Tiny Machines

Is it possible to remotely operate a tiny piece of matter or a less-than-one-centimeter machine to perform a medical task in life? Especially given that in the present technology, neither the mechanism nor battery is small enough to be set up inside the structure of such a tiny machine. Yet, if the powered matter is magnetically responsive, then a magnetic field, as one of the potential power sources, can be applied to power it promisingly. Herein, the concept of electromechanical energy conversion is utilized through a specific configuration consisting of eight solenoids arranged together as a nest. The device converts electrical energy into an electromagnetic field, and finally, into mechanical energy, respectively, resulting in magnetic manipulation. Since electric energy is supplied to the configuration, eight solenoids generate the controllable magnetic field in both direction and magnitude by means of the superposition technique. The device can magnetically navigate tiny motorless matter to release mechanical energy through the 3D-controllable motion to arbitrary positions effectively and physical interactions with the surrounding environment as if operating a tiny machine. The experimental results report the feasibility of the device to control the 6-DOF locomotion of small matter precisely. The contribution of the concept based on this work leads to a promising protocol to remotely power small machines, micro-engines, micro-propellers, micro-turbines, etc.

Investigation of Pressure Chambers for Integrated Fluidic Actuators in Adaptive Slabs

A high proportion of the CO2 emissions worldwide are caused by the construction sector or are associated with buildings. Every part of the industry needs to reduce its share of emissions, so the building sector must also do its part. One possible solution for achieving this reduction in the field of load-bearing structures is the use of adaptive structures. This research focuses on adaptive slab structures, which require specific actuators to be integrated into the system. Conventional actuators are not suitable due to the prevailing requirements, namely installation space and performance. For this investigation, the actuator is divided into different functional components. A rough description of the requirements for one component, namely the energy converter, is given. Different concepts are developed, tested, and compared with numerical results. Due to the requirements, the concepts are limited to hydraulics. The authors then present a comparison of different simulation strategies for the energy converter. Overall, this paper provides a new contribution to the design of energy converter concepts for integrated hydraulic actuators in slabs, along with experimental verification of the working principle of the energy converters to meet the requirements. A simplified numerical model is proposed to estimate the behavior of the energy converter during the early design phase.

Co-design of a wave energy converter for autonomous power

A “bolt-on” wave energy converter is designed to provide power for sensors on an existing oceanographic buoy. The narrow-banded pitch/roll response of the target oceanographic buoy lends itself to a tuned-resonator design, for which we suggest a novel “pitch resonator” wave energy converter concept. Using a pseudo-spectral method, the performance of the proposed wave energy converter is modeled in the range of sea states expected to be present at the target deployment location to study the effect of flywheel inertia on performance. The results show that the system can marginally meet the desired power demands, but suggest that related design concepts may be worth consideration.

Maximizing the energy conversion of triboelectric nanogenerator through the synergistic effect of high coupling and dual-track circuit for marine monitoring

The wave energy harvesting efficiency (EHE) and electrical energy storage efficiency (ESE) significantly impact ocean power at the front-end and back-end stages, respectively. In this work, to maximize the overall energy conversion affected by these two factors, a clip-like structured pendulum coupled nanogenerator (CP-CNG) integrated with a dual-track circuit (DTC) is elaborately designed to address poor energy conversion of the TENGs for marine monitoring. The optimized EHE was realized through coupling one freestanding triboelectric nanogenerator (FR-TENG) unit and two electromagnetic generator (EMG) units into two contact-separation triboelectric nanogenerator (CS-TENG) units. The space utilization rate of CP-CNG can be as high as 91.9%. Meanwhile, increased ESE is achieved by integrating DTC as voltage regulators, which perform backend energy management for CS-TENG and EMG, respectively. It is worth noting that for a 1 mF capacitor, the stored energy via the cooperation of CP-CNG and DTC can reach 60.7 mJ in 110 s, which is about 164 times that of CS-TENG (0.37 mJ) coupling with FR-TENG and EMG and 1.6 times that of CS-TENG (36.8 mJ) with buck circuit, demonstrating excellent synergistic effects. Owing to the synergistic effect, one CP-CNG can continuously drive four thermohygrometers under simulated water wave conditions. In additional, a hazard alarm system, including an immersion sensor, Bluetooth and gateway support, can also be powered by one CP-CNG successfully. This work develops a state-of-the-art concept for maximum energy conversion of TENGs, which should have a profound impact on the design of high-performance TENGs in the future.

A 3D numerical investigation of the influence of the geometrical parameters of an I-beam attenuator OWC on its performance at the resonance period

The oscillating water column (OWC) is the oldest and most reliable concept for wave energy conversion. This paper investigates the hydrodynamic performance of one chamber of an I-Beam attenuator OWC at its natural frequency using fully nonlinear CFD. The effects of chamber geometry on the hydrodynamic performance are investigated by solving the unsteady Reynolds averaged Navier-Stokes equations using ANSYS-Fluent. Comparisons are made with experimental results in both a terminator and an attenuator orientation. The effects of PTO damping, chamber length, and chamber height on the hydrodynamic efficiency are investigated. Increasing the length of the chamber with constant PTO ratio improves the quality of the wave entering the chamber, while decreased length leads to stronger vortices. The optimum PTO coefficient is found to be close to that chosen for the experiments. Reducing the inner skirt height of the chamber significantly reduces all hydrodynamic parameters while a 20 % increase in the chamber's inner skirt height improves the efficiency of the OWC by about 15 %. Observations of the flow field make it clear that reducing the chamber's length can create vortices at the inlet of the OWC. The calculations highlight important nonlinear and viscous effects on the performance of an OWC chamber.

Multi-PTO Wave Energy Converter for Low Energetic Seas: Ensenada Bay Case.

The paper presents a wave energy converter concept to harvest energy at Ensenada Bay, Mexico. The study area can be classified as a low energy sea due to the mean wave power being around 10 kW/m; the wave conditions are significant wave height of 0.5 to 2.5 and peak period of 5 to 20 s. The wave energy converter is formed by a torus buoy and anchored to the sea bottom by four connection structures distributed every 90°. The connected structures play a piston role, and their response is leveraged to run a power take-off system, for example, a linear or hydraulic system. This work does not focus on designing the power take-off system; therefore, it is simplified as linear damping, and an iterative process calculates its value. The hydrodynamic buoy study is made on the frequency domain with Nemoh BEM solver and the power absorption on the time domain with the WEC-Sim code. The capture width ratio is used to evaluate the wave energy converter performance and is a key factor in choosing the optimal size. The wave energy converter captures an average of 20% of the available energy and is well-fixed between periods 8 and 16 s. The present study achieves its target: providing a wave energy converter system to operate under site wave conditions.

Analysis of an innovative compact point absorber wave energy converter concept suitable for small-scale power applications

In response to the need for efficient, small-scale power sources for applications such as ocean observation and navigation, this paper presents the design, modeling, fabrication, testing, and analysis of a compact point-absorber wave energy converter (PAWEC) equipped with a mechanical direct-drive power takeoff (PTO) mechanism. The motivation is to address the mismatch between the natural frequencies of conventional PAWECs and dominant ocean wave frequencies, which limits energy capture. The primary objective is to enhance the efficiency of small-scale wave energy converters (WEC) without increasing the buoy size. To achieve this, we introduce a novel design element: an added mass plate (AMP) attached to the buoy. The AMP is devised to increase the WEC added mass and natural period, thereby aligning its natural frequency with dominant ocean wave frequencies. In our case study of a scaled model (1:2.2), the AMP effectively doubled the added mass of the WEC and increased its natural period by 32%. The WEC incorporates a rack and pinion mechanical motion rectifier-type PTO to convert the heave oscillations of the buoy into unidirectional rotation. The scaled model was tested in a wave basin facility with regular waves at zero angle of incidence. The WEC with AMP achieved a maximum root mean square power of 9.34 W, a nearly 30% increase compared to the conventional configuration without AMP, which produced 7.12 W under similar wave conditions. Numerical analysis using the boundary element method in the frequency domain for regular waves confirmed these findings. Finally, it has been derived that the proposed WEC, equipped with an AMP, offers enhanced efficiency in longer wave periods without the need for a larger buoy, establishing its viability as a power source for navigational buoys. This paper also offers a comprehensive guide to experimental techniques for characterizing a PAWEC in a laboratory setting, contributing valuable insights into the wave energy community.

Investigating the effect of 5E-based STEM education in solar energy context on creativity and academic achievement of female junior high school students

Effective science teaching by providing students with the necessary knowledge, attitude and skills can prepare them to live in a community and face its challenges. One of the most important topics in science education is energy education, and STEM is a new approach that can be used for energy education. Solar energy was used as a suitable context in STEM-based energy education to investigate its impact on the learning and creativity of female students. The study population consisted of ninth-grade female students of the junior high school in Qarchak city in the academic year 2020–2021, and the sample consisted of 143 people who were selected by random sampling in two groups of control and experimental. The students in the experimental group underwent 5E-based STEM education in the concepts of energy and energy conversion for 7 sessions (35 min for each session) as distance learning. ANCOVA analysis showed that teaching science with the 5E-based STEM approach significantly increases creativity along with science and math learning performance in female students. The effect on creativity subscales is not the same and has a greater effect on originality and elaboration. Furthermore, There is an overlap of 50% between the top people (5%) in science and math with the top people (5%) in overall creativity in the experimental group. This overlap reaches its maximum value (75%) in the flexibility subscale.

Selective Discrimination between CO and H2 with Copper-Ceria-Resistive Gas Sensors.

The production of hydrogen and the utilization of biomass for sustainable concepts of energy conversion and storage require gas sensors that discriminate between hydrogen (H2) and carbon monoxide (CO). Mesoporous copper-ceria (Cu-CeO2) materials with large specific surface areas and uniform porosity are prepared by nanocasting, and their textural properties are characterized by N2 physisorption, powder XRD, scanning electron microscopy, transmission electron microscopy, and energy-dispersive X-ray spectroscopy. The oxidation states of copper (Cu+, Cu2+) and cerium (Ce3+, Ce4+) are investigated by XPS. The materials are used as resistive gas sensors for H2 and CO. The sensors show a stronger response to CO than to H2 and low cross-sensitivity to humidity. Copper turns out to be a necessary component; copper-free ceria materials prepared by the same method show only poor sensing performance. By measuring both gases (CO and H2) simultaneously, it is shown that this behavior can be utilized for selective sensing of CO in the presence of H2.

Emerging Exsolution Materials for Diverse Energy Applications: Design, Mechanism, and Future Prospects

Nanostructured catalytic materials are considered to be a favorable design concept for various energy conversion and storage systems. Nanosized metal catalysts supported on oxide scaffolds have been adopted in numerous fields, including fuel cells, gas sensors, and chemical reforming devices. Nevertheless, nanometal catalysts often suffer from durability issues. Although surface-decorated nanometal catalysts can deliver sufficient catalytic activity, some of them still exhibit durability issues in severe operating environments. Recently, nanocatalysts produced by in situ exsolution have been demonstrated to overcome the practical limitations of conventional nanometal catalysts. The exsolution is defined as a process in which a catalytically active dopant in perovskite oxide is exsolved on its surface as highly dispersed nanometal catalysts. In particular, exsolution nanocatalysts embedded on perovskite oxides exhibit higher nanoparticle densities and greater resistance to particle agglomeration than conventional nanometal catalysts. This Perspective presents an overview of recent advances in exsolution materials for energy applications including fundamental mechanisms, design strategies for host oxides, and practical applications. The future prospects of these materials and the scope for further optimization are also discussed.

A wave-to-wire analysis of the adjustable draft point absorber wave energy converter coupled with a linear permanent-magnet generator

An adjustable draft point absorber was recently proposed as a novel approach to improve power absorption with constrained power take-off (PTO) capacities. The key feature of the novel wave energy converter (WEC) concept is to adjust the buoy draft by regulating the ballast water inside the buoy, which aims to enable variation of the natural frequency of the WEC. Although previous research has shown benefits for the energy absorption stage, the impact of the draft adjustment on the power conversion efficiency and overall performance has not been examined yet. Therefore, a wave-to-wire model is established to provide an in-depth insight into the systematic performance of the adjustable draft point absorber integrated with a linear permanent magnet generator. Both a nonlinear hydrodynamic model and an analytical generator model are derived, thus the complete process from the wave power input through the whole WEC system to the usable electricity is covered. Based on the established model, wave-to-wire responses of the novel concept are obtained and analyzed. The negative effects of the draft adjustment on the stroke and overlap between the stator and translator are demonstrated. Moreover, a comparison is made between this novel WEC and conventional fixed draft WEC, and both regular and irregular wave states are considered. The results show that the adjustable draft system could increase not only the absorbed power but also the generator conversion efficiency. In specific conditions, the delivered electrical power of the adjustable draft WEC was over 20 % and 10 % higher than a traditional fixed draft system for regular and irregular waves respectively.

Consistent emission correction factors applicable to novel energy carriers and conversion concepts

Volume correction factors have been an important aspect when reporting pollutant emissions from gaseous combustion for many years. Their application has become standard procedure in such a way that their applicability is seldom questioned. However, their emergence dates back to a time when power generation primarily relied on conventional fuels such as coal and gas. The advent of alternative fuels and new combustion concepts reveals the classical correction formula prescribed by many current legal regulations to produce results that can be misleading when comparing different mixtures with regard to their emission behavior. For this reason, this work derives a more generalized correction formula that extends the applicability to any fuel–oxidizer combination and is based on the same principles as conventional volume correction. The impact of the choice of correction formula is then exemplified by comparing results for various fuels for a selection of numerical and experimental examples. They consist of a simple equilibrium calculation, as well as experimental data from a premixed swirl combustor and a pulse detonation combustor. The results show that conventional correction terms can lead to misleading perceptions of emission performance when comparing fuels. In contrast, the extended correction terms derived in this work allow for a comparison of emission behavior on a common basis that is independent of effects introduced by fuel and oxidizer stoichiometry, in a manner similar to alternative fuel-mass based metrics such as emission index. This is not restricted to the investigated examples but can be applied to all areas where oxygen correction is common. It is suggested that future emission regulations should incorporate the issues discussed in this work to ensure unbiased comparison of emission values across a wide range of combustion applications.

Experimental Proof-of-Concept of a Hybrid Wave Energy Converter Based on Oscillating Water Column and Overtopping Mechanisms

This paper presents the results of laboratory tests on a hybrid wave energy converter concept, the O2WC (Oscillating-Overtopping Water Column) device. The proposed device aims at providing an alternative to the classical OWC concept, storing part of the wave energy of the highly energetic sea states in a second chamber at atmospheric pressure, through overtopping phenomena. In this way, the maximum airflow rate and air pressure in the OWC chamber are reduced, possibly aiding the safe functioning of the air turbine, and allowing to exploit the excess of energy instead of dissipating it through by-pass valves. The performance of the device is investigated under different incident wave conditions, for different design parameters. The height of the overtopping threshold from the second chamber of the device which allows to maximize the performance has been selected. Results show that the decrease of the primary conversion efficiency of the OWC component of the device caused by the decreased air pressure in the OWC chamber can be partially compensated by the additional energy stored in the overtopping chamber of the O2WC device. Overall, the studied O2WC device has capture width ratio values ranging between 0.3 and 0.7.

A Review of Point Absorber Wave Energy Converters

There are more than thousands of concepts for harvesting wave energy, and wave energy converters (WECs) are diverse in operating principles, design geometries and deployment manners, leading to misconvergence in WEC technologies. Among numerous WEC devices, the point absorber wave energy converter (PAWEC) concept is one of the simplest, most broad-based and most promising concepts that has been investigated intensively all over the world. However, there are only a few reviews focusing on PAWECs, and the dynamical advancement of PAWECs merits an up-to-date review. This review aims to provide a critical overview of the state of the art in PAWEC development, comparing and contrasting various PAWEC devices and discussing recent research and development efforts and perspectives of PAWECs in terms of prototyping, hydrodynamic modelling, power take-off mechanism and control.

Electronic-Level Insight into Interfacial Effects and Their Induced Anisotropic Ion Diffusion and Ion Selectivity in Nanochannels.

Osmotic energy conversion features directional ion migration in selective nanochannels, dominated by interfacial effects, temperature, and concentration. Current efforts emphasize membrane modification for superior reliability and durability, whereas the origin and implication of interfacial effects are unclear. This work performs ab initio molecular dynamics simulations for hydrated ion-graphene oxide interfaces by regulating the temperature and concentration. The interfacial effects associated with their induced anisotropic ion diffusion and ion selectivity are revealed. The scientific essence of the interfacial effects is an electron transfer triggered by hydrated ion-functional group interactions. The interfacial effects are clarified to include dynamic solvation structures, interfacial H-bonds, and chemical reactions. Ions possess incomplete hydration shells, and their arrangements vary from ordered to disordered to overlapped. Interfacial H-bonds restrict hydrated ions by constraining water molecules, whereas continuous reactions provide lateral pathways to generate anisotropy. Cation selectivity is further clarified by negative surface charges from hydroxyl deprotonation. Besides, temperature rise induces disordered hydrated ions as well as frequent and violent reactions, enhancing ion diffusion, selectivity, and anisotropy; excessive concentrations produce overlapped hydrated ions, more H-bonds, and inferior reactions, weakening ion diffusion, selectivity, and anisotropy. Finally, the bottom-up concept for osmotic energy conversion is summarized, and elevated temperature combined with low concentration is found to boost ion diffusion and ion selectivity synergistically. This work provides an in-depth understanding of interfacial phenomena and ion behaviors in nanochannels.

A wave energy converter based on a zero-pressure-angle mechanism for self-powered applications in near-zero energy sea-crossing bridges

The concept of near-zero energy conversion from ocean waves is an emerging topic that can be applied to supply power to self-powered applications in sea-crossing bridges. In this paper, a point-absorbing wave energy converter (WEC) with a novel zero-pressure-angle mechanism structure was proposed and investigated. The system includes a wave energy capture module, power take-off module (PTO), generator module, and energy storage module. The proposed PTO structure consists of a pair of guide rods, zero-pressure-angle rockers, gearbox, and flywheel, which convert the oscillation of the buoy into unidirectional continuous rotation of the generator, and electricity is stored in the supercapacitor. For accurate prediction, kinematic and dynamic approaches were employed for the non-constant damping PTO. The mechanical test and sensing system experiments achieved the highest mechanical efficiency of 81.87%, the maximum output power of 5.49 W, and the 53.44% average efficiency. It was found that the PTO with a flywheel can effectively improve the output performance compared to without a flywheel. In addition, the experiments of the actual WEC were performed and recorded an output power ranging from 0.964 W to 3.218 W, proving that the proposed structure meets the power requirements for self-powered sea-crossing bridge applications.

Controlled Growth of the Interface of CdWOx/GDY for Hydrogen Energy Conversion

AbstractDirectly extracting hydrogen energy from water in one device to achieve sustainable hydrogen energy generation‐conversion‐electricity storage system is an ideal major step forward for enabling a zero‐pollution, hydrogen‐fueled economy. The new concept of hydrogen energy conversion can be enabled by spontaneous reduction of nitrate to ammonia driven by potential differences between the well‐matched anode and cathode, leading to the full use of the electrochemical redox reactions to generate electric energy. The hydrogen energy in the acidic electrolyte can be transformed to electric energy with the rationally assembled primary battery, which can simultaneously power the electric devices and produce high value‐added ammonia. The new concept of hydrogen conversion device shows a record‐high specific capacity of 15 500 mA h g–1 and achieves the highest ammonia production rate (149 mmol gcat–1 h–1) and Faradaic Efficiency (99.2%) in acidic electrolytes. This work opens a new direction for hydrogen conversion and utilization which has obvious advantages over lithium and battery solutions.