Enhanced Energy Conversion Research Articles

Dynamical modeling and parametric analysis of an electret-based wave energy converter

Carbon neutrality and the Internet of Underwater Things have injected new impetus into the development of wave energy converters (WECs) albeit most of WEC projects have ended in failure due to low cost-effectiveness. Hereupon we present the dynamical modeling and parametric analysis of a novel electret-based WEC that has a distinct power take-off system compared to the conventional ones and has exhibited high power density in our previous study. Linear wave theory and Morison equation are applied for wave field and forces, respectively. WEC motions parallel with incident waves are modeled, and the electrical subsystem of the generator is treated as a current source and a capacitor. With these simplifications, the governing equations of the nonlinear and non-smooth electromechanical system are obtained and then numerically solved using an event-driven algorithm. The new power take-off system is experimentally validated. We find that the power output varies nonlinearly with wave parameters under regular wave excitation but linearly under irregular ones, and that superharmonic resonance can significantly enhance energy conversion performance at relatively low frequencies, based on which the optimum parameters are obtained. A peak average power of around 2 mW (at a matched load resistance) is generated from each generator encapsulated in the WEC of a diameter of 15 cm. The findings shed light on the characteristics of electret-based WECs and provide support for the development of wave energy farm; moreover, the methodologies of modeling and analysis can be extended to the design and optimization of the scaleups of the proposed electret-based WEC.

Trace Mn-doped on highly dispersed Fe/Mn-SNC ultrathin carbon nanosheets for efficient oxygen reduction reaction

The design and development of non-noble metal carbon-based catalysts with efficient oxygen reduction activity remains a difficult problem. Here, Ultrathin two-dimensional carbon nano sheet catalyst Fe/Mn-SNC with rich pore structure doped with trace manganese was synthesized by simple sodium chloride template cracking method and freeze-drying method. Citric acid containing a large number of OH and COOH groups can provide multiple coordination sites for metal ions. In 0.1 M KOH solution, the Fe/Mn-SNC catalyst performed better than Pt/C in terms of ORR performance (E1/2 was 0.920 V vs RHE) and endurance (E1/2 fell roughly 5 mV after 10,000 cycles). The reaction path of the Fe/Mn-SNC was calculated through DFT calculation. It was found that a small amount of Mn doping would reduce the adsorption energy of OH*, the last step in ORR reaction, which was conducive to OH* falling off from the catalyst surface, reducing the potential barrier required for the reaction, and improving its ORR activity. This research offers fresh perspectives on the development of enhanced energy conversion as well as the design and synthesis of high-performance ORR catalysts.

Insights into interfacial thermal conductance in Bi2Te3-based systems for thermoelectrics

The thermal resistance at the interface between thermoelectric materials and metallic electrodes plays an important role in the energy conversion efficiency of thermoelectric devices. This is especially prevalent in the Bi2Te3-based flexible thermoelectric generators for wearable electronics, where the temperature difference between the human skin and the ambient environment is small. In this work, we study the phonon interfacial thermal conductance (ITC) in Bi2Te3/Au and Bi2Te3/Cu, by using non-equilibrium molecular dynamics simulations. It is found that the ITC in Bi2Te3/Cu is 3-fold higher than that in Bi2Te3/Au. We explore the underlying mechanism and find that both the stronger interfacial van der Waals interaction and phonon coupling contribute to the higher ITC in Bi2Te3/Cu. We further show that the ITC of Bi2Te3/Au and Bi2Te3/Cu can be tuned effectively by mechanical strain. Remarkably, a 0.04 compressive strain leads to the increase in ITC of Bi2Te3/Au and Bi2Te3/Cu by 120% and 62%, respectively. Our work not only provides physical insights into the ITC in thermoelectric devices, but is also useful in designing the Bi2Te3-based thermoelectric generators with enhanced energy conversion efficiency.

Energy and exergy analysis of combined power, methanol, and light olefin generation system fed with shale gas

Environmental problems and limitations of fossil fuel resources, especially crude oil, have intensified the importance of using cleaner and cheaper fuels besides enhancing energy conversion processes. Therefore, a novel power, methanol, and light olefin multi-generation system is designed and modeled in this paper. Chemical looping reforming, chemical looping combustion cycles, and Rankine power system are combined with methanol and light olefin production processes. The input fuel of the system is shale gas. The mass, energy, and exergy balance equations are applied for each system unit as a steady-state control volume to assess its thermodynamic operation. Then, the effects on the system performance of critical parameters are studied comprehensively. The results show that the necessary syngas can be supplied when 71.5% of the inlet shale gas is used in the steam reforming reactor of the chemical looping reforming cycle, and the steam to fuel ratio and carbon dioxide to fuel ratio are 0.61. Furthermore, if 31% of the produced methanol is consumed in the olefin production unit, the system energy and exergy efficiencies are achieved at 67.3% and 71.5%, respectively. In this case, the carbon dioxide flow rate is 800 kmol/hr, separated and stored in the chemical looping combustion cycle, leading to a clean thermodynamic system.

Photoinduced Cu+/Cu2+ interconversion for enhancing energy conversion and storage performances of CuO based Li-ion battery

Pursuing appropriate photo-active Li-ion storage materials and understanding their basic energy storage/conversion principle are pretty crucial for the rapidly developing photoassisted Li-ion batteries (PA-LIBs). Copper oxide (CuO) is one of the most popular candidates in both LIBs and photocatalysis. While CuO based PA-LIBs have never been reported yet. Herein, one-dimensional (1D) CuO nanowire arrays in situ grown on a three-dimensional (3D) copper foam support were employed as dual-functional photoanode for both ‘solar-to-electricity’ and ‘electricity-to-chemical’ energy conversion in the PA-LIBs. It is found that light energy can be indeed stored and converted into electrical energy through the assembled CuO based PA-LIBs. Without external power source, the photo conversion efficiency of CuO based photocell reaches about 0.34%. Impressively, at a high current density of 4000 mA g−1, photoassisted discharge and charge specific capacity of CuO based PA-LIBs respectively receive 64.01% and 60.35% enhancement compared with the net electric charging and discharging process. Mechanism investigation reveals that photogenerated charges from CuO promote the interconversion between Cu2+ and Cu+ during the discharging/charging process, thus forcing the lithium storage reaction more completely and increasing the specific capacity of the PA-LIBs. This work can provide a general principle for the development of other high-efficient semiconductor-based PA-LIBs.

Enhanced energy conversion efficiency promoted by cavitation in gasoline direct injection

High-pressure direct fuel injection plays the most crucial role in energy conversion and improving engine combustion efficiency and emission. The optimization of turbulent and multiphase fuel injection has focused on controlling hydrodynamic parameters such as injection pressure. While the thermodynamic influence is often considered in the flash boiling situation, we inquire into how gasoline-type fuel's hydro- and thermodynamic properties impact the injection dynamics by fuel-temperature-induced cavitation. The turbulent and cavitating flows emanating from the direct-injection nozzle are visualized by ultrafast x-ray imaging with an unprecedented spatiotemporal resolution. The ultrafast liquid-fuel dynamics are dominated by injection pressure as well as fuel temperature through cavitation, an important thermodynamic parameter but often difficult to control in engine combustion. With the most direct and quantitative measurement, we discovered that the near-nozzle fuel-jet dynamics could be perfectly scaled by a single dimensionless parameter, cavitation number, particularly sensitive to the fuel temperature, in a wide operation range. This universal scaling shows that cavitation can be harnessed to elevate the pneumatic-hydraulic to kinetic energy conversion efficiency, which is critical for promoting fuel atomization and engine combustion performance. This enhancement effect will have even more impact on engine combustion using alternative low-emission fuels with higher saturated vapor pressure.

Experimental investigation and validation of solar PV cooling for enhanced energy conversion efficiency for Indian climatic conditions

Solar Photovoltaic (PV) cells convert an average of 10 to 15% of the incident solar radiation into electricity and remaining energy is wasted as unused heat energy. The p erformance of solar PV is largely dependent on its operating temperature, which is again dependent on solar irradiation. The efficiency of solar PV reduces the higher PV temperature due to charge carrier recombination. The solar PV efficiency drops considerably wit h increasing temperature. Dust deposition on the surface of solar PV cells reduce incident energy and no technology is commercially available to mitigate the problem. The objective of the present work is to enhance the energy conversion efficiency of solar PV by adopting Front Water (FW) cooling technique. The FW cooling technique maintains the cell temperature at Standard Test Conditions (STC) irrespective of ambient air conditions and also washes away dust deposits, thereby providing maximum energy conversion efficiency specified by the cell manufacturer during the operation with increased lifecycle of solar cells. The experiment was carried out on a 100 W solar panel for a period of 2 weeks and data acquisition system with Arduino controller was used to analyze and maintain STC of the panel to obtain maximum power. The mathematical model of the system was analyzed and obtained results were in good agreement with the experimental measurements. The solar PV panel with FW cooling yielded an efficiency improvement of 9% with 17 W of increased power output at Maximum Power Point (MPP). MATLAB Simulink software is used to model t he FW cooling technique. The model is able to predict the power generated by the solar PV cells for the given irradiance with and without cooling. The developed model can now be utilized to design cooling systems for larger installation of solar PV systems.

Development of large-scale electret fabrication system for triboelectric nanogenerator electrical output amplification

The triboelectric nanogenerator (TENG), which converts mechanical energy to electrical output, is garnering attention owing to their application in low-energy electronic devices as a power source. To utilize the TENG as a power source, amplifying the electrical output and enhancing energy conversion efficiency are necessary. As the TENG generates electrical output through contact electrification and electrostatic charge induction, the electrical output can be amplified by enhancing the two mechanisms through the enlargement of the TENG area and the adoption of the pre-charge injected film (electret). In this regard, the fabrication of the large-scale electret is significant for amplifying the electrical output of the TENG. In this study, a corona charging system is proposed for the fabrication of the large-scale electret with a uniform charge-distributed area. Corona charging injects O2 ions into a dielectric film with an electric field generated between the pin electrode and ground electrode (GE). Through the utilization of a multi-PE (MPE) and conveyor belt-shaped GE (CBsGE) in the corona charging system, the O2 molecules near the pins can be ionized simultaneously while the CBsGE is rotating. Thus, the O2 ions can be injected uniformly into a wide area. About a voltage of 400 V and current of 45 μA can be generated by applying the fabricated electret to the TENG. As several electrets with various sizes can be fabricated simultaneously, the TENG with high electrical output can be batch fabricated to enhance its practicality significantly.

Stepwise dispersion of nickel species for efficient coupling of electrocatalytic redox reactions

Advanced electrocatalysts are highly desirable to enhance energy conversion efficiency for properly coupling electrocatalytic redox reactions, but the fabrication of efficient bifunctional catalysts is still highly challenging. Herein, a self-feeding deposition strategy was demonstrated to disperse nickel species into single nickel atoms along with the growth of nitrogen-doped carbon nanotubes, thus inhibiting the thermal aggregation of nickel nanoparticles. The residual nickel nanoparticles are encapsulated among the bamboo-like carbon nanotubes and porous carbon matrix, which promotes the efficient electron transfer via the formation of heterojunctions. With the regulation of electronic and geometric structures between the single atom active sites and the isolated nickel nanoparticles, the unique nucleo- and electro-philic interfaces facilitate the targeted adsorption and activation of carbon dioxide and benzylamine molecules, respectively, thus narrowing the energy barriers to enhance electrocatalytic performances. The improved bifunctional electrocatalysis enables the carbon dioxide reduction into CO with an impressive Faraday efficiency (FE) up to 99.3 % and the highly efficient oxidation of benzylamine into benzonitrile (FE ∼ 98 %). This work not only reveals the fundamental understanding of the underlying structure–activity relationship, but also provides a new method for value-added chemicals production.

Visible Light-Driven Photoelectrochemical Platform Based Biosensor

The characterization of the photoinduced carriers' production, separation, and interfacial reaction processes is critical in developing effective photoelectrochemical (PEC) detection. The design and fabrication of a visible-light-driven PEC device based on CdSe-Co3O4@TiO2 nanoflower are presented in this report. In addition, an application for the ultrasensitive detection of viruses, including hepatitis E virus (HEV), HEV-like particles (HEV-LPs), and SARS-CoV-2 spike protein in complex lysate solution. The photocurrent response output of a CdSe-Co3O4@TiO2 based PEC device is improved compared to the individual components, TiO2 and CdSe-Co3O4. This can be ascribed to forming a heterojunction structure obtained by the hybridization of TiO2 and CdSe-Co3O4. CdSe QDs sensitization effect and strong visible light absorption can extend interfacial carrier lifetime and enhance energy conversion efficiency coupling with a robust oxygen-evolving catalyst (Co3O4) at the hole trapping site (CdSe) to improve overall system stability. The developed PEC-based biosensing device has been effectively used for quantitative virus detection through effective hybridization among antibody and viral specimens. The effective capture of the virus resulted in a linear relationship of change in photocurrent output versus the HEV concentration ranging from 10 fg mL–1 to 100 ng mL–1 with a detection limit of 3.5 fg mL–1. This CdSe-Co3O4@TiO2-based PEC device shows a significant ability to develop an improved device with affordable and portable biosensing capabilities.

Enhanced energy conversion performance of silicon solar cells by quantum-confinement effect of polysilicon oxide

We propose a highly transparent polysilicon oxide (poly-SiOx)/crystalline silicon (c-Si) front passivation contact (poly-SiOx/c-Si) to overcome the parasitic current drawback and enhance the stability of silicon heterojunction (SHJ) solar cells. Poly-SiOx has a mixed-phase crystalline structure with large crystalline grains embedded in a wide-gap amorphous silicon oxide (a-SiOx) matrix, resulting in a quantum confinement effect. While the large crystalline phase facilitates dopant activation toward high conductivity (elevated Fermi level), resulting in substantial band bending at the c-Si/poly-SiOx interface for additional field-effect passivation, the a-SiOx matrix allows additional chemical surface passivation. Thus, passivation quality with an implied open-circuit voltage of 732 mV and a recombination current density of 4.3 fA/cm2 was achieved. Owing to the interaction between the quantum confinement effect and the wide-gap a-SiOx phase, the mixed-phase structure had a wide bandgap (1.98 eV), significantly increasing the absorption of the device in the short-wavelength region (≤500 nm). A hybrid rear-emitter SHJ solar cell using poly-SiOx/c-Si achieved an efficiency of 23.95% with Voc = 723 mV, a short-circuit current density of 40.9 mA/cm2, and a fill factor of 81%.

AIEgens in Solar Energy Utilization: Advances and Opportunities.

Solar energy is the most abundant energy resource on earth. Unfortunately, only a very small portion of the solar radiation can be utilized by current light-harvesting materials, thus leading to the poor utilization efficiency of solar energy. In this regard, aggregation-induced emission luminogens (AIEgens) have demonstrated versatile properties that can enhance energy conversion and potentially revolutionize solar utilization systems. AIEgens with great processability can selectively absorb radiation across multiple spectral regions and transform solar energy into longer-wavelength light, heat, or alternative forms of energy. These processes can considerably enhance the solar energy utilization performance by either developing light-harvesting systems based on AIEgens or hybridizing modern light-harvesting systems with AIE technology. In this Perspective, based on material properties, we highlight different functions of AIEgens related to solar light utilization, including sunlight transformation, chemical conversion, and thermal conversion.

Pt Single Atom Electrocatalysts at Graphene Edges for Efficient Alkaline Hydrogen Evolution

AbstractGraphene edges exhibit a highly localized density of states that result in increased reactivity compared to its basal plane. However, exploiting this increased reactivity to anchor and tune the electronic states of single atom catalysts (SACs) remains elusive. To investigate this, a method to anchor Pt SACs with ultra‐low mass loadings at the edges of edge‐rich vertically aligned graphene (as low as 0.71 µg Pt cm–2) is developed. Angle‐dependent X‐ray absorption spectroscopy and density‐functional theory calculations reveal that edge‐anchored Pt SACs has a robust coupling with the π‐electrons of graphene. This interaction results in a higher occupancy of the Pt 5d orbital, shifting the d‐band center toward the Fermi level, improving the adsorption of *H for the hydrogen evolution reaction (HER). Pt primarily coordinated to the graphene edge shows improved alkaline HER performance compared to Pt coordinated in mixed environments (turnover frequencies of 22.6 and 10.9 s–1 at an overpotential of 150 mV, respectively). This work demonstrates an effective route to engineering the coordination environment of Pt SACs by using the graphene edge for enhanced energy conversion reactions.

A miniaturized low frequency direct-current magnetic-bias-integrated magnetoelectric wireless power transfer system with enhanced energy conversion efficiency

Wireless power transfer (WPT), which transfers energy without a physical link, has recently received significant research interest. Due to the advantages of small dimension, low operation frequency, and low transmission loss, magnetoelectric WPT (ME-WPT) has been shown to be a promising technology for internet of things (IoT) and implantable medical device (IMD) applications. However, ME-WPT requires a direct-current (DC) magnetic bias for optimal performance and prior arts have implemented large electromagnets, Helmholtz coils, or externally positioned magnet bias systems, which increase the system dimension. Furthermore, the highest energy conversion efficiency (ECE) reported by prior ME-WPT studies is 0.62%, which needs to be improved. In this paper, we present an ME-WPT system with a novel miniaturized ME-WPT receiver and a spiral coil based transmitter. Four DC magnets are integrated onto the ME-WPT receiver to significantly reduce its dimension while providing a DC magnetic bias of 190 Oe for optimal performance. Electrochemical polarization characterizations are introduced to analyze the performance of the WPT receiver, which reveal that a maximum output power of 4.096 mW is obtained. A record ECE of 2.64% is reported, the highest among all ME-WPTs to date. The output power is improved by at least 49.3 times compared with the ME-WPT without integrated DC magnets. The influence of the input voltage and the distance between transmitter/receiver on the performance of the ME-WPT system is studied, which shows that the output power increases as the distance decreases and the input voltage increases. The proposed ME-WPT system with integrated DC magnets has potential applications in IoT and IMDs.

Topology Optimization of Piezoelectric Energy Harvesters for Enhanced Open-Circuit Voltage Subjected to Harmonic Excitations.

Energy harvesting devices made of piezoelectric material are highly anticipated energy sources for power wireless sensors. Tremendous efforts have been made to improve the performance of piezoelectric energy harvesters (PEHs). Noticeably, topology optimization has shown an attractive potential to design PEHs with enhanced energy conversion efficiency. In this work, an alternative yet more practical design objective was considered, where the open-circuit voltage of PEHs is enhanced by topologically optimizing the through-thickness piezoelectric material distribution of plate-type PEHs subjected to harmonic excitations. Compared to the conventional efficiency-enhanced designs, the open-circuit voltage of PEHs can be evidently enhanced by the proposed method while with negligible sacrifice on the energy conversion efficiency. Numerical investigations show that the voltage cancellation effect due to inconsistent voltage phases can be effectively ameliorated by optimally distributed piezoelectric materials.

Atomic Bridging of Metal‐Nitrogen‐Carbon toward Efficient Integrated Electrocatalysis

AbstractThe rational design of robust electrocatalysts for efficient integrated devices is crucial to enhance energy conversion performance. The coordination of organic ligands with metal ions provides high flexibility to anchor metal atoms among carbon materials. Herein, the atomic anchoring of Zn and Ni atoms into N‐doped carbon networks with adjustable atomic structure is developed by the facile pyrolysis of metal‐organic framework nanoplates in the presence of dicyandiamide. Theoretical calculations reveal the descriptor‐based design principles to adjust the bridging structures of metal‐nitrogen‐carbon moieties with changing d‐band centers, thereby improving electrocatalytic performance. The resulting electrocatalyst displays good multiple electrocatalytic activities for carbon dioxide reduction, oxygen reduction, and evolution reactions, enabling the fabrication of integrated energy devices. Importantly, the CO2‐H2O overall splitting with the as‐prepared electrocatalysts has been driven by the commercial solar cell and the zinc‐air battery assembled with the same catalyst respectively, showing high CO faradaic efficiency up to 90%. Especially, the overall solar‐to‐CO conversion efficiency is up to 13% and the corresponding utilization efficiency of solar‐to‐electricity can reach 54.4%, demonstrating the large promising space to chase the limit that solar cells can possibly achieve. This work provides new opportunities to modulate the atomic bridging structure of metal‐nitrogen‐carbon for integrated electrolysis.

Design of bimetallic 3D-printed electrocatalysts via galvanic replacement to enhance energy conversion systems

3D-printing (also known as additive manufacturing) has recently emerged as an appealing technology to fight against the mainstream use of carbon-based fossil fuels by the large-scale, decentralized, and sustainable manufacturing of 3D-printed electrodes for energy conversion devices. Although promising strides have been made in this area, the tunability and implementation of cost-effective metal-based 3D-printed electrodes is a challenge. Herein, a straightforward method is reported to produce bimetallic 3D-printed electrodes with built-in noble metal catalysts via galvanic replacement. For this goal, a commercially available copper/polylactic acid composite filament has been exploited for the fabrication of Cu-based 3D-printed electrodes (3D-Cu) using fused filament fabrication (FFF) technology. The subsequent electroless deposition of an active noble metal catalyst (viz. Pd) onto the 3D-Cu surface has been carried out via galvanic exchange. A detailed electrochemical study run by scanning electrochemical microscopy (SECM) has revealed that the resulting bimetallic 3D-PdCu electrode exhibits enhanced capabilities by energy conversion related reactions —hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR)— when compared with the monometallic 3D-Cu counterpart. Thus, this simple functionalization approach provides a custom way for manufacturing functional metal-based 3D-printed electronics harboring noble metal catalysts to improve energy-converting applications on-demand and beyond.

GaAs-based near-field thermophotonic devices: Approaching the idealized case with one-dimensional PN junctions

Thermophotonics (TPX) is a technology close to thermophotovoltaics (TPV), where a heated light-emitting diode (LED) is used as the active thermal emitter of the system. It allows to tune the heat flux, by means of electroluminescence, to a spectral range matching better the gap of a photovoltaic cell. The concept is extended to near-field thermophotonics (NF-TPX), where enhanced energy conversion is due to both electric control and wave tunnelling. We perform a thorough numerical analysis of a GaAs-based NF-TPX device, by coupling a near-field radiative heat transfer solver based on fluctuational electrodynamics with an algorithm based on a simplified version of the drift–diffusion equations in 1D. This allows for the investigation of the emission and absorption profiles in the LED and the photovoltaic (PV) cell, and for the scrutiny of the impact of key parameters. We also demonstrate that the performance obtained with this algorithm can approach idealized cases for improved devices. For the considered simplified architecture and 300 K temperature difference, we find a power density output of 1 W cm − 2 , underlining the potential for waste heat harvesting close to ambient temperature. • Near-field thermophotonics allows waste-heat harvesting of moderate temperatures. • GaAs is a promising material for the thermophotonic elements: LED and photovoltaic cell. • Thorough modelling of the 1D pn junction architecture is performed. • About 35 W m −2 K −1 can be produced if radiative recombinations are limited.

Transparent spin thermoelectricity with enhanced energy conversion

Spin-thermoelectrics (STE) allows energy harvesting from the waste heat through the orthogonal relationship between the charge and heat flow, which offers large area scalability. Moreover, STE devices can be well adapted for transparent energy harvesting when a transparent magnetic insulator is exploited as a spin current source. Nevertheless, the transparent characteristics of STE devices have not been studied extensively so far. In this study, we show transparent characteristics of STE device based on thin films of Yttrium Iron Garnet (YIG)/Pt bilayers. Decreasing thickness of the Pt layer not only improves transmittance of visible light but simultaneously enhances the STE performance. The fabricated STE device of YIG (20 nm)/Pt (0.8 nm) exhibits a longitudinal spin Seebeck coefficient, SLSSE ≈ 7.04 μV/K, while sustaining over 80% transparency at λ = 700 nm. Our study shows the potential usage of STE as an alternative transparent energy harvesting, which could be adapted in various multi-purpose coatings.

Enhanced Energy Conversion and Storage Properties of Sn-Doped BaTiO3 Bulk Ceramics Using Compressive Stresses

Enhanced Energy Conversion and Storage Properties of Sn-Doped BaTiO3 Bulk Ceramics Using Compressive Stresses