Energy Conversion Efficiency Of System Research Articles

Suppressing Structure Delamination for Enhanced Electrochemical Performance of Solid Oxide Cells.

Reversible solid oxide cells (rSOCs) have significant potential as efficient energy conversion and storage systems. Nevertheless, the practical application of their conventional air electrodes, such as La0.8Sr0.2MnO3-δ (LSM), Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF), and PrBa0.8Ca0.2Co2O5+δ (PBCC), remains unsatisfactory due to interface delamination during prolonged electrochemical operation. Using micro-focusing X-ray absorption spectroscopy (µ-XAS), a decrease (increase) in the co-valence state from the electrode surface to the electrode/electrolyte interface is observed, leading to the above delamination. Utilizing the one-pot method to incorporate an oxygen-vacancy-enriched CeO2 electrode into these air electrodes, the uniform distribution of the Co valence state is observed, alleviating the structural delamination. PBCC-CeO2 electrodes exhibited a degradation rate of 0.095mVh-1 at 650°C during a nearly 500-h test as compared with 0.907mVh-1 observed during the 135-h test for PBCC. Additionally, a remarkable increase in electrolysis current density from 636 to 934mAcm-2 under 1.3V and a maximum power density from 912 to 989mWcm-2 upon incorporating CeO2 into PBCC is also observed. BSCF-CeO2 and LSM-CeO2 also show enhanced electrochemical performance and prolonged stability as compared to BSCF and LSM. This work offers a strategy to mitigate the structural delamination of conventional electrodes to boost the performance of rSOCs.

Synergetic effect of spontaneous Fe diffusion for enabling immediately switchable operations in NiFe-supported solid oxide cells

Solid oxide cells (SOCs) are highly efficient energy conversion systems, offering switchable capabilities for power and fuel production. NiFe metal-supported structures in SOCs show promising advantages in structural stability and scalability. This study explores the synergistic effect of spontaneous Fe diffusion in NiFe-supported SOCs, enhancing alloy catalyst formation in the electrode and improving the sinterability of the zirconia-based electrolyte. This results in increased activity for carbon fuel reactions, resistance to coking, and a remarkably low ohmic resistance of 0.06 Ω cm2 at 800 °C. The NiFe support also enhances structural stability, enabling reversible and multifuel operation. The single cell achieves exceptional maximum power densities of 2.6 and 2.0 W cm−2 in fuel cell mode (3 % H2O/H2 and dry CO) and current densities of − 1.51 and − 1.38 A cm−2 in electrolysis cell mode (1.3 V, 20 % H2O/H2 and 20 % CO2/CO) at 800 °C, respectively.

Multi-Objective Optimization of Vortex Magnetohydrodynamics (MHD) Generator using Response Surface Methodology

The introduction of electromagnetic fields in fluid dynamics in magnetohydrodynamics (MHD), particularly when those fields are vector and non-uniform, complicates its application in vortex geometry. The imperative to optimize MHD generators arises from the inherent trade-off between voltage and pressure drop in energy conversion systems, to maximize voltage output while minimizing associated pressure drop. This study focuses on optimizing vortex MHD generators by applying Response Surface Methodology (RSM), which is based on mathematical models that capture the complex relationships between factor and response variables. This method offers a comprehensive approach to obtaining the optimum solution to the objectives, voltage and pressure drop, based on fluid velocity and magnetic field strength input parameters. Numerical optimization RSM generates 11 solutions. The optimum solutions obtained are a velocity of 1.415 m/s, and magnetic field strength of 0.43 T, and the corresponding optimum output voltage and pressure drop will be 4.264 mV and 4.254 psi, respectively, with a desirability level of the selected solution is 0.770. This study suggests the RSM method shows a good measurement of R2 and RSME. Our findings contribute to the understanding of optimizing vortex MHD generators and offer insights into achieving efficient energy conversion systems of a set of optimum generator operating parameters.

Trivalent Nickel-Catalyzing Electroconversion of Alcohols to Carboxylic Acids.

The comprehension of activity and selectivity origins of the electrooxidation of organics is a crucial knot for the development of a highly efficient energy conversion system that can produce value-added chemicals on both the anode and cathode. Here, we find that the potential-retaining trivalent nickel in NiOOH (Fermi level, -7.4 eV) is capable of selectively oxidizing various primary alcohols to carboxylic acids through a nucleophilic attack and nonredox electron transfer process. This nonredox trivalent nickel is highly efficient in oxidizing primary alcohols (methanol, ethanol, propanol, butanol, and benzyl alcohol) that are equipped with the appropriate highest occupied molecular orbital (HOMO) levels (-7.1 to -6.5 eV vs vacuum level) and the negative dual local softness values (Δsk, -0.50 to -0.19) of nucleophilic atoms in nucleophilic hydroxyl functional groups. However, the carboxylic acid products exhibit a deeper HOMO level (<-7.4 eV) or a positive Δsk, suggesting that they are highly stable and weakly nucleophilic on NiOOH. The combination (HOMO, Δsk) is useful in explaining the activity and selectivity origins of electrochemically oxidizing alcohols to carboxylic acid. Our findings are valuable in creating efficient energy conversions to generate value-added chemicals on dual electrodes.

The Sustainable Technology Research on High-Efficiency Conversion and Utilization of Biomass-Based Energy

This study delves into the sustainability of biomass-based energy as an alternative energy source, its technical conversion methods, and its environmental and economic impacts. Biomass resources, including plants, agricultural residues, and forestry residues, are not only widely distributed and renewable but also exhibit significant potential in reducing greenhouse gas emissions and combating climate change. The research focuses on three primary conversion technologies for biomass energy: physical conversion, chemical conversion, and biological conversion. It further explores key technologies for enhancing the sustainability of biomass-based energy, including biomass pretreatment, optimization techniques, and the integration of efficient energy conversion systems. The results indicate that, despite challenges, with continuous technological innovation and improvement, biomass energy can become a more sustainable energy option.

An Innovative Tubular Thermoelectric Generator (TTEG) for Enhanced Waste Heat Recovery in Industrial and Automotive Applications

In response to the growing need for efficient energy conversion technologies, this paper introduces an innovative Tubular Thermoelectric Generator (TTEG), specifically designed for the high-efficiency conversion of waste heat into electrical energy. Unlike conventional flat-plate thermoelectric generators (FTEGs), the TTEG incorporates full-ring thermoelectric elements within a tubular layout, offering a novel approach to thermal energy recovery from fluid-based systems. This design significantly enhances the heat transfer capabilities, thereby improving the efficiency of energy conversion. Moreover, it is optimally tailored for integration into any cylindrical pipe to recapture and repurpose waste heat. Comprehensive simulations and analyses form the core of this study, where the performance of the TTEG is rigorously compared with traditional FTEGs. Under identical conditions of heat exposure, volume, and properties of thermoelectric materials, the TTEG demonstrates a 62.5% increase in output power compared to the TGM1-127-1.0-0.8 thermoelectric module (FTEG). These comparisons highlight the advantages of the tubular design in terms of energy conversion efficiency and practical applicability in various scenarios. The findings reveal that the TTEG not only outperforms its flat-plate counterparts but also presents a scalable and adaptable solution for waste heat recovery in a wide range of industrial and automotive applications. This research contributes to the field of energy science and technology by presenting a detailed experimental setup, complete with reproducible procedures and results. It opens new pathways for the development of more sustainable and efficient energy conversion systems, aligning with the goal of harnessing renewable and sustainable energy sources. The potential applications of this technology in enhancing energy efficiency and reducing environmental impact are vast, making it a significant step forward in the quest for clean and sustainable energy solutions.

Single Idiosyncratic Ionic Generator Working in Iso-Osmotic Solutions Via Ligand Confined Assembled in Gaps Between Nanosheets.

Numerous reported bioinspired osmotic energy conversion systems employing cation-/anion-selective membranes and solutions with different salinity are actually far from the biological counterpart. The iso-osmotic power generator with the specific ionic permselective channels (e.g., K+ or Na+ channels) which just allow specific ions to get across and iso-osmotic solutions still remain challenges. Inspired by nature, we report a bioinspired K+ -channel by employing a K+ selective ligand, 1,1,1-tris{[(2'-benzylaminoformyl)phenoxy]methyl}ethane (BMP) and graphene oxide membrane. Specifically, the K+ and Na+ selectivity of the prepared system could reach up to ≈17.8, and the molecular dynamics simulation revealed that the excellent permselectivity of K+ mainly stemmed from the formed suitable channel size. Thus, we assembled the K+ -selective iso-osmotic power generator (KSIPG) with the power density up to ≈15.1 mW/m2 between equal concentration solutions, which is higher than traditional charge-selective osmotic power generator (CSOPG). The proposed strategy has well shown the realizable approach to construct single-ion selective channels-based highly efficient iso-osmotic energy conversion systems and would surely inspire new applications in other fields, including self-powered systems and medical materials, etc.

Experimental and neural network prediction of the cyclic stability and light absorption characteristics of supercritical CO2 based CNTs nanofluids

Traditional working fluids face challenges including constrained heat transfer efficiency and inadequate thermal stability, which are detrimental to the thermal efficiency of energy conversion systems. To overcome these limitations and achieve a profound breakthrough in the field of energy conversion, it is imperative to develop innovative working fluids. Consequently, this study builds a nanofluid circulation flow experimental platform and prepares a supercritical carbon dioxide/hydroxylated multi-walled carbon nanotubes nanofluid. The study conducts a series of meaningful experimental tests and performance predictions, including stability analysis, deposition characterization research, light absorption potential investigation, and artificial neural network prediction. Remarkably, the artificial neural network model exhibits excellent learning capacity in training, validation, and testing, with root mean square error of only 9.069 W/m2, 8.9996 W/m2, and 13.0143 W/m2, respectively. Test results indicate that the nanofluid reaches a steady state after 4 min, with a fluctuation amplitude of only 2.13 %. Furthermore, the deposition density of the nanofluid on nickel sheet saturates after 4 h, confirming its considerable potential for promotion and application. The light absorption capacity and power decay rate of the nanofluid are enhanced by 606–881 W/m2 and 32.3–46.99 %, compared to other typical substances. The transmittance is reduced by 8.51–22.96 % compared to other nanofluids. The nanofluid proves to be an effective alternative to conventional working fluids, providing a practical reference solution for researchers aiming to improve working fluids in the field of energy conversion.

Optimization DC-DC boost converter of BLDC motor drive by solar panel using PID and firefly algorithm

The use of solar photovoltaic panels as source of power for Brushless Direct Current (BLDC) motors requires a DC-DC Converter circuit. One application of solar energy is as a power source for Brushless Direct Current (BLDC) motors. The main problem is the voltage fluctuation and low DC voltage generated by the solar panel. This research aims to improve the performance of the DC-DC Boost Converter circuit and minimize voltage fluctuations. The methodology encompasses mathematical modeling of the circuit in the form of transfer functions and optimizing the DC-DC Boost Converter circuit using the Proportional Integral Derivative (PID) controller and the Firefly algorithm. Simulation testing results indicate an improvement in transient response performance of the DC-DC Converter circuit as a driver for the BLDC motor. This is evidenced by an increase in rise time from 499 s to 820 s, a decrease in settling time from 3.33 e+03 s to 2.07e+03 s, and a reduction in overshoot to 0 % from previously 11.4 %. The utilization of the firefly algorithm in optimization significantly enhances system efficiency, as demonstrated by faster achievement of stability without excessive oscillation and a reduction in the time required for the system to settle. Overall, this study shows that the firefly algorithm is effective in developing DC-DC Boost Converter circuits, improving system efficiency by reducing settling time and eliminating overshoot. These findings provide empirical evidence of the effectiveness of using artificial intelligence algorithms in enhancing the operational efficiency of energy conversion systems.

Molecular Engineering of Perylene Diimide Polymers with a Robust Built-in Electric Field for Enhanced Solar-Driven Water Splitting.

The built-in electric field of the polymer semiconductors could be regulated by the dipole moment of its building blocks, thereby promoting the separation of photogenerated carriers and achieving efficient solar-driven water splitting. Herein, three perylene diimide (PDI) polymers, namely oPDI, mPDI and pPDI, are synthesized with different phenylenediamine linkers. Notably, the energy level structure, light-harvesting efficiency, and photogenerated carrier separation and migration of polymers are regulated by the orientation of PDI unit. Among them, oPDI enables a large dipole moment and robust built-in electric field, resulting in enhanced solar-driven water splitting performance. Under simulated sunlight irradiation, oPDI exhibits the highest photocurrent of 115.1 μA cm-2 for photoelectrochemical oxygen evolution, which is 11.5 times that of mPDI, 26.8 times that of pPDI and 104.6 times that of its counterparts PDI monomer at the same conditions. This work provides a strategy for designing polymers by regulating the orientation of structural units to construct efficient solar energy conversion systems.

Molecular Engineering of Perylene Diimide Polymers with a Robust Built‐in Electric Field for Enhanced Solar‐Driven Water Splitting

AbstractThe built‐in electric field of the polymer semiconductors could be regulated by the dipole moment of its building blocks, thereby promoting the separation of photogenerated carriers and achieving efficient solar‐driven water splitting. Herein, three perylene diimide (PDI) polymers, namely oPDI, mPDI and pPDI, are synthesized with different phenylenediamine linkers. Notably, the energy level structure, light‐harvesting efficiency, and photogenerated carrier separation and migration of polymers are regulated by the orientation of PDI unit. Among them, oPDI enables a large dipole moment and robust built‐in electric field, resulting in enhanced solar‐driven water splitting performance. Under simulated sunlight irradiation, oPDI exhibits the highest photocurrent of 115.1 μA cm−2 for photoelectrochemical oxygen evolution, which is 11.5 times that of mPDI, 26.8 times that of pPDI and 104.6 times that of its counterparts PDI monomer at the same conditions. This work provides a strategy for designing polymers by regulating the orientation of structural units to construct efficient solar energy conversion systems.

Optimizing Induction Wind Energy System with EDLC and PMSG for Efficient Power Control

This paper represents a comprehensive study on the optimization of an Induction Wind Energy System (IWEC) integrated with Electric Double Layer Capacitors (EDLCs) and a Permanent Magnet Synchronous Generator (PMSG) to enhance power control in the quest for sustainable and efficient energy conversion systems. As wind energy plays a pivotal role in the renewable energy landscape, maximizing its conversion efficiency is crucial for a sustainable future. Advanced control strategies and optimization techniques are applied to delve into the intricate details of the IWEC-EDLC-PMSG system, resulting in improved power quality, enhanced transient response, and superior grid integration capabilities. The research demonstrates that this integrated configuration outperforms conventional wind energy systems in terms of efficiency, grid compatibility, and dynamic response. Moreover, the study addresses key aspects like system stability, fault tolerance, and reliability, ensuring the robustness of this innovative solution. In addition to advancing wind energy technology, this research offers valuable insights into integrating energy storage systems and advanced control techniques for efficient power control in renewable energy applications, contributing to a sustainable energy future.

Oxygen vacancies and tailored redox activity encountered with NiCo2O4 nanostructures for promising applications in supercapacitor and water oxidation

It is well known that transition metal oxides play a significant role in the development of efficient electrochemical energy storage and conversion systems. However, their application is limited by low electrical conductivity, a limited number of electroactive sites, and limited stability. In this study, nickel‑cobalt bimetallic oxide (NiCo2O4) nanostructures were prepared using orange peel extract and its fruit juice during hydrothermal method. The use of green chemical components from orange peel extract and its fruit juice was to demonstrate their ability to manipulate NiCo2O4's structural and functional properties. For this reason, the optimized 1 mL of orange peel extract and its fruit juice was found highly active for improving the electrochemical properties of NiCo2O4 nanostructures. The electrochemical supercapacitor performance of optimized NiCo2O4 nanostructures showed a specific capacitance of 997.50 Fg−1 with a cycling stability of more than thirty thousand cycles, resulting in a capacitance retention rate of almost 100 % at 1.5 Ag−1. In addition, during the oxygen evolution reaction (OER), the overpotential was 120 mV at 20 mA/cm2 and the Tafel slope was 110 mVdec−1, with a prolonged stability exceeding 45 h were observed for optimized NiCo2O4 nanostructures. With an electrode material comprising NiCo2O4 nanostructures and an orange peel extract, outstanding electrochemical performance was obtained. This could be explained by several factors, including high electroactive site exposure, rapid charge transfer kinetics, high hydroxide adsorption, oxygen vacancies on the surface, and abundance of Co(III). The approach described here can be used for the facile synthesis of a wide range of nanostructured functional materials that exhibit impressive electrochemical properties, particularly for energy storage and conversion applications.

Optimization Design and Simulation Approach of an Axial Inward Flow Reaction Turbine Incorporating with Organic Rankine Cycle

The demand for sustainable and efficient energy conversion systems has led to the exploration of various turbines design and working fluids. This study focuses on the design and simulation investigation of an axial inward flow reaction turbine utilizing organic fluids as the working medium. Organic fluids have gained attention due to their favourable themodynamic properties and low environmental impact. The selection process for the working fluid takes into consideration factors such as temperature limitations fluids availability and efficiency. The design process begins with a thorough analysis of the fundamental principles govering inward flow reaction turbines. Fluids flow path, blade profiles, the interaction between the fluid and these blades are carefully studied. Design parameters such as specific spedd, specific diameter and specific speed coefficient are determind to ensure optimal turbine performance

Modified Efficient Energy Conversion System Based on PMSG with Magnetic Flux Modulation

The article presents the solution of a power rectifier system dedicated to cooperating with an electric generator based on a special synchronous generator, which can be used in wind or water energy systems. In this generator, a pair of three-phase windings in a stator is utilized. One of the windings is connected in a star, and the second one is connected in a delta configuration. Two six-pulse uncontrolled (diode) rectifiers are included at the outputs of the windings. The rectifiers are coupled by a pulse transformer. The primary windings of this transformer are supplied by a power-electronics current source called a current modulator. With the help of this current modulator, the quasi-sinusoidal magnetomotive force (mmf) in the stator of the machine can be obtained. Additionally, to improve the efficiency of the described system, the low-power transistor rectifier, which is connected to the DC bus of the current modulator, has been used. With the help of this converter, it is possible to control and stabilize the voltage level in a DC circuit. It works, in this case, in inverter mode. The principle of working and elaborated control methods of the current modulator and the additional rectifier are presented. Selected results of simulation and experimental tests are also presented.

Phytic acid-derivative Co2B-CoPOx coralloidal structure with delicate boron vacancy for enhanced hydrogen generation from sodium borohydride

Application of transition metal boride (TMB) catalysts towards hydrolysis of NaBH4 holds great significance to help relieve the energy crisis. Herein, we present a facile and versatile metal-organic framework (MOF) assisted strategy to prepare Co2B-CoPOx with massive boron vacancies by introducing phytic acid (PA) cross-linked Co complexes that are acquired from reaction of PA and ZIF-67 into cobalt boride. The PA etching effectively breaks down the structure of ZIF-67 to create more vacancies, favoring the maximal exposure of active sites and elevation of catalytic activity. Experimental results demonstrate a drastic electronic interaction between Co and the dopant phosphorous (P), thereby the robustly electronegative P induces electron redistribution around the metal species, which facilitates the dissociation of B-H bond and the adsorption of H2O molecules. The vacancy-rich Co2B-CoPOx catalyst exhibits scalable performance, characterized by a high hydrogen generation rate (HGR) of 7716.7 mL min−1 g−1 and a low activation energy (Ea) of 44.9 kJ/mol, rivaling state-of-the-art catalysts. This work provides valuable insights for the development of advanced catalysts through P doping and boron vacancy engineering and the design of efficient and sustainable energy conversion systems.

Directional surface hydroxylation on 6H-SiC induces surface electron polarization and proton activation promoting photocatalytic water splitting for hydrogen

Photocatalytic water splitting for hydrogen production is a promising solution to converse solar energy to green fuel. A high-performance photocatalyst system always requires fast surface reaction rate and efficient charge separation. Herein, a novel strategy that photo-assisted silanizing-hydrolyzing method is used to trigger in situ surface hydroxylation selectively on Si atoms of micro-sized 6H-SiC particles. Due to this functionalization, the results show that the silanizing-hydrolyzing process occurs at the Si sites while the C is passivated, leading the Si atoms with electron deficiency property by XPS characterization. It also drives the SiC surface from native hydrophobicity to hydrophilicity, which is benefit to proton absorption and desorption of generated H2 by FT-IR and contact angle (CA) result. Furthermore, the photo-electron-chemical characterization demonstrate the charge migration and separation of SiC are promoted. The DFT calculation further indicates these surface properties changes are mainly attribute to the surface electron polarization through the hydroxylation, inducing the Si-O spatial charge separation. More importantly, the positive Si atoms exhibit an appropriate proton absorption energy, resulting in easily H2 desorption from SiC surface. The hydrogen evolution is significantly enhanced by 33 times compared to pristine SiC without any cocatalysts introduced. Our method provides an efficient route to design an environmental-friendly photocatalytic material SiC and construct highly efficient solar energy conversion systems, which can simultaneously facilitate carrier generation, transportation and surface reduction reaction rate.

Highly active Mo-modified NiCoP/NiCoN flower-like sphere: Controlled phase engineering for efficient water splitting

Reasonable design and preparation of a versatile catalyst for the ultra-high efficiency energy conversion system has remarkable practical significance. Herein, a facile phase engineering strategy is employed to synthesize molybdenum modified nickel cobalt nitride and nickel cobalt phosphide flower-like sphere heterostructure (labeled as Mo-NiCoP/NiCoN FS) to improve the performance of Mo-NiCoN FS. The significant geometric structure advantages, the exposure to abundant active centers and the interfacial effect of heterostructure of the target product is evaluated in detail. When the as-obtained Mo-NiCoP/NiCoN FS is applied to the electrochemical bifunctional hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), it demonstrates remarkable electrocatalytic activity, high-conductivity and excellent corrosion resistance compared with Mo-NiCoN FS with a single phase. As a result, Mo-NiCoP/NiCoN FS indicates a low overpotential towards HER (204 mV at 10 mA/cm2) and OER (262 mV at 10 mA/cm2) compared with Mo-NiCoN (234 mV for HER and 357 mV for OER at 10 mA/cm2) in an alkaline medium and it exhibits excellent activity and stability during the dual-electrode full water-splitting. Therefore, the advanced nano-catalyst with superior activity developed through the controllable phase engineering method illustrates a potential application prospect in high efficiency energy equipment water-splitting and fuel-cells.

NEW DESIGN OPTIONS FOR THE IMPROVEMENT OF THE MUTRIKU POWER PLANT

The research based on the development of OWC devices continues growing and nowadays there are endless options that have already been studied. From the type of turbine and its control, to the most efficient energy conversion system or design, the OWC technology needs to be further developed in order to be economically attractive.&#x0D; &#x0D; This research studies several possibilities to improve the efficiency of the Mutriku breakwater wave plant. On the one hand, the L-shape configuration of this plant allows studying a new configuration based on the coupling of the well-known U-shape [1], to create a new L+U-shape breakwater. In addition, the installation of harbor-walls has been proven as a promising option to enhance the interior damping of the camera [2], and this option seems to be very promising because of the design of the Mutriku plant allows its performance. Finally, a design based on the sharp-edges round off its being studied in order to reduce the energy losses and therefore enhance the energy harnessing of the plant.&#x0D; &#x0D; The experimental work has been carried out in the 12.5 m long wave flume located at the laboratory of Fluid Mechanics of the Energy Engineering Department (UPV/EHU). The physically constructed OWC device corresponds to one of the cameras installed at the Mutriku breakwater wave plant, an isolated camera, according to the construction plan and applying a 1:36 scale. All the experiments were carried out at two tides that correspond to the medium and maximum equinoctial live tides of Mutriku location. According to the information of the Basque Coast sea states [3], a constant incident regular waves of 30 mm were generated at several periods: 0.7&lt;T[s]&lt;1.7 for the medium tide and 0.7&lt;T[s]&lt;2.1 for the maximum tide.&#x0D; &#x0D; The L+U-shape was created with two lateral walls joined by frontal walls of different heights (W), as shown in Figure 1-left, that were positioned at several distances from the physical model. However, another L+U-shape was considered using a transversal wall of different heights and without lateral walls (TW, Figure 1-right), and placing at several distances form the plant.&#x0D; The obtained results reveals that the promising configuration corresponds to the one containing lateral walls, so that the influence of harbor walls will be further studied.&#x0D; &#x0D;

Photoluminescence Property of Cu(In,Ga)S2 Quantum Dots Depending on Their Composition and Nanostructure

Multinary quantum dots (QDs) composed of less toxic elements, such as CuInS2 and AgInS2, have been intensively investigated for the application to highly efficient solar energy conversion systems and novel luminescent devices, because their electronic energy structure and optical properties can be controlled by the size and chemical composition of QDs. Recently we have successfully prepared alloy QDs composed of Ag–In–Ga–S and Ag–In–Ga–Se semiconductors, the Eg of which was tunable in the visible and near-IR wavelength regions, respectively [1, 2]. These QDs exhibited a narrow PL peak assignable to the band-edge emission and their peak wavelengths were widely tunable by changing their Eg. However, there have been few investigations to prepare Cu-based multinary QDs with a narrow PL peak. Thus, in this study, we prepare spherical QDs composed of less-toxic Cu–In–Ga–S (CIGS) alloy semiconductor and investigate their composition-dependent optical properties.The synthesis of CIGS QDs was carried out by our previous heating-up method with a slight modification [1]. Powders of Cu(OAc)2, In(acac)3, Ga(acac)3, elemental sulfur were dispersed in a mixture solution of oleylamine and dodecanethiol, followed by the heat treatment at 300 oC. The resulting solution was subjected to centrifugation to remove large precipitates, and QDs were isolated from the supernatant by adding methanol as a non-solvent. Thus-obtained QDs were used as a core to prepare cores-shell-structured particles, in which the surface of CIGS core was coated by thin shell composed of ZnS or GaSx.The chemical composition of obtained QDs was controlled by the fractions of individual metal salts used as precursors. The Cu/(In+Ga) and In/(In+Ga) of obtained QDs roughly agreed with those used in preparation. The obtained QDs were spherical and their average diameter decreased from 5.4 nm to 3.4 nm with an increase in the In fraction. The absorption spectra of CIGS QDs were varied depending on both the fractions of Cu and In. The onset wavelength of QDs was blue-shifted from 840 nm to 540 nm with a decrease in the Cu/(In+Ga) in preparation from 0.7 to 0.1 when the QDs were prepared with the fixed ratio of In/(In+Ga)= 0.7. On the other hand, the QDs exhibited a blue shift of absorption onset from ca. 750 nm to 480 nm with a decrease in In/(In+Ga) ratio from 1.0 to 0 under the fixed Cu fraction in preparation, Cu/(In+Ga)= 0.3. The obtained Eg monotonously decreased from 2.77 eV to 1.74 eV with an increase in In/(In+Ga) ratio from 0 to 1.0, and these values were larger than those of corresponding bulk semiconductors due to the quantum size effect. From the ionization energy of the QDs evaluated from the onset energy of the photoelectron yield spectra in air, we determined the electronic energy structure of CIGS QDs. With a decrease in the Eg of QDs, the conduction band minimum level shifted to a lower level from ca. –2.3 eV to –3.4 eV, while the valence band maximum level was almost constant to ca. 5.1–5.2 eV.Surface coating of CIGS QDs with other semiconductor shells increased the photoluminescence (PL) intensity. The ZnS shell coating to form CIGS@ZnS core-shell QDs produced a PL peak at 649 nm (FWHM: 0.47 eV), being much broader than that of CIGS cores (FWHM: 0.23 eV) because of alloying at the interface between ZnS shell and CIGS core, though the PL quantum yield (QY) increased to 30% from 8%. In contrast, the GaSx coating on CIGS QD surface enlarged the intensity of PL peak without changing its peak width: CIGS@GaSx QDs exhibited a narrow PL peak (FWHM: 0.20 eV) at 671 nm, being comparable to the PL peak of CIGS QDs (the peak wavelength of 675 nm and the FWHM of 0.23 eV). The PL QY was also increased to 27% from 8% by the GaSx coating on CIGS QDs. The tunabilities of electronic energy structure and PL property of CIGS QDs are useful for constructing efficient light energy conversion systems and luminescent devices.[1] T. Kameyama, et al., ACS Applied. Mater. Interfaces 2018, 10, 42844-42855.[2] T. Kameyama, et al., ACS Appl. Nano Mater. 2020, 3, 3275-3287.