Energy Storage Capability Research Articles

Local spin-state tuning enables high-efficiency nickel sulfide cathode for stable alkaline Zn batteries

Nickel sulfide (Ni3S2) has shown great promise as advanced cathode in alkaline nickel-zinc batteries (ANZBs) for its good electrochemical reversibility and electronic conductivity. However, due to the unfavorable OH− adsorption capability and low intrinsic activity of Ni sites originated from the unsuitable d-electron spin state, the overall performances of Ni3S2 are yet unsatisfactory for practical ANZBs. Herein, we demonstrate the engineering of local spit state of Ni sites via a facile electrochemical activation in Ni3S2 to significantly boost its comprehensive energy storage capability. After electrochemical treatment, the spit state of fractional Ni2+ (eg4t2g4) sites of Ni3S2 is successfully transformed into high-valence Ni3+ (eg4t2g3), which considerably enhances the OH− adsorption capability and redox reactivity. The optimal Ni3S2 electrode exhibits a high capacity of 1.11 mAh cm−2 at 1 mA cm−2 and no capacity decay after 3000 cycles, which are far greater than the pristine Ni3S2 (0.39 mAh cm−2) electrode and also comparable to the best ever-reported alkaline cathodes. Furthermore, the assembled full ANZB can afford a peak energy density of 1.59 mWh cm−2 and power density of 33.92 mW cm−2. This work affords valuable insights into local electronic structure modulation of electrode materials for aqueous energy storage devices.

Synthesis and characterization of ZnCo2O4 nanocomposites with enhanced electrochemical features for supercapacitor applications

Supercapacitors have recently emerged as a promising alternative to conventional batteries due to their improved energy storage capabilities. The optical, electrochemical, and structural properties of ZnCo2O4 nanocomposites produced by hydrothermal synthesis are detailed in this study. In order to study the physicochemical properties of the synthesized goods, the created nanocomposite samples were analyzed using XRD, FT-IR, UV–Vis, SEM with EDAX, HR-TEM, BET, XPS, and charge storage potential. Crystallite size was found to be inversely proportional to increasing range of 5.01 nm to 10.62 nm in the XRD data, which compared the cubic structure. Electron microscopy and high-resolution transmission electron microscopy (HR-TEM) indicated a morphological shift indicative of improved electrochemical capabilities. The absorption research showed that different molar ratios were successful in increasing the optical bandgap from zero to 1.93 eV, whereas functional component adsorption lowered it from 2.35 eV. A maximum specific capacitance of 383.3 Fg−1 was determined by the electrochemical research, which indicated an inherent pseudo capacitance. Experimental results show that the ZnCo2O4 nanocomposite can effectively store charges, which is in line with expectations given its high capacitance and very inexpensive production.

High-energy and durable aqueous Zn batteries enabled by multi-electron transfer reactions

Aqueous Zn batteries (AZBs) have emerged as a highly promising technology for large-scale energy storage systems due to their eco-friendly, safe, and cost-effective characteristics. The current requirements for high-energy AZBs attract extensive attention to reasonably designed cathode materials with multi-electron transfer mechanisms. This review systematically overviews the development and challenges of typical cathode hosts capable of multiple electron transfer reactions for high-performance Zn batteries. Moreover, we also summarize how to trigger the multi-electron transfer chemistry of cathodes, including transition metal oxides, halogens, and organics, to further boost the energy storage capability of AZBs. Finally, perspectives on critical issues and future directions of the multi-electron transfer battery systems offer novel insights for advanced Zn batteries.

Recent Advances in Catalyst Design and Performance Optimization of Nanostructured Cathode Materials in Zinc-Air Batteries.

This review focuses on the advanced design and optimization of nanostructured zinc-air batteries (ZABs), with the aim of boosting their energy storage and conversion capabilities. The findings show that ZABs favor porous nanostructures owing to their large surface area, and this enhances the battery capacity, catalytic activity, and life cycle. In addition, the nanomaterials improve the electrical conductivity, ion transport, and overall battery stability, which crucially reduces dendrite growth on the zinc anodes and improves cycle life and energy efficiency. To obtain a superior performance, the importance of controlling the operational conditions and using custom nanostructural designs, optimal electrode materials, and carefully adjusted electrolytes is highlighted. In conclusion, porous nanostructures and nanoscale materials significantly boost the energy density, longevity, and efficiency of Zn-air batteries. It is suggested that future research should focus on the fundamental design principles of these materials to further enhance the battery performance and drive sustainable energy solutions.

Synthesis and high-temperature energy storage performances of fluorinated polyimides

In light of the increasingly stringent requirements for the applications of light-weight flexible high-temperature-resistant dielectric materials in the fields of aerospace, electronics, and electric vehicles, the imperative lies in the development of dielectric materials with high discharged energy density, enduring temperature resistance and high reliability. This work introduced side-chain trifluoromethyl (–CF3) groups into high-temperature engineering polymer polyimides and conducted comprehensive studies on the breakdown and energy storage capabilities. The introduction of bulky –CF3 substituents reduces the intermolecular interactions, increases the free volume, and suppresses the high-temperature leakage conductance loss by decreasing the formation of intermolecular charge transfer complexes between polymer chains. As a result, the fluorinated polyimides (PFI) with lower dielectric constant exhibit enhanced breakdown strengths (730 MV m−1 at 25 °C; 630 MV m−1 at 150 °C), leading to a high discharged energy density of 3.6 J cm−3 (∼1.7 times of pristine polyimides), alongside a charge-discharge energy efficiency of ∼80% at 150 °C. These findings underscore the great potential of PFI for applications in the field of high-temperature energy storage.

Surface plasma treatment boosting antiferroelectricity and energy storage performance of AgNbO3 film

The utilization of AgNbO3 film in dielectric energy storage poses challenges due to its susceptibility to impurity phase formation, which compromises its antiferroelectric properties and breakdown electric field. In this study, we successfully fabricated an AgNbO3 film with outstanding antiferroelectric properties and energy storage capabilities by employing oxygen ion surface plasma technology in conjunction with the sol-gel method. Our results demonstrate that the surface of the AgNbO3 film undergoes a layer-by-layer treatment using oxygen ion plasma, effectively suppressing impurity phases and oxygen vacancies formation while reducing grain size and enhancing insulation performance. The AgNbO3 film, which has undergone surface plasma treatment with oxygen ion, exhibits exceptional characteristics as an antiferroelectric material by demonstrating an impressive energy storage density of 13.13J/cm3 and a high energy storage efficiency of 56%. Overall, we present a straightforward and viable approach for fabricating high-performance AgNbO3 films for efficient dielectric energy storage.

Partial-Power Conversion for Increased Energy Storage Capability of Li-Ion Battery Energy Storage System

Full-power converters are used in battery energy storage systems (BESS) because of their simple structure, high efficiency and relatively low cost. However, cell-to-cell variation, including capacity, state of charge (SOC), and internal resistance, will decrease the available capacity of serially connected battery packs, thereby negatively affecting the energy utilization rate (EUTR) of BESS. This article proposes a novel BESS scheme that combines a modular converter with partial power conversion architecture to make a modular partial power converter (MPPC) that addresses the issue. The MPPC consists of input-serial and output-paralleled (ISOP) isolated phase-shift full-bridge (PSFB) sub-modules. It processes only the serial compensation power, about 1/3 of the full power. Consequently, the MPPC shrinks the converter capacity, which can reduce the cost and power loss. Furthermore, this article develops a BESS model considering cell-to-cell variations to analyze the energy storage capability of the MPPC-BESS compared with the existing full-power BESS. To test the model, we run a simulation using parameter values from 100 real retired batteries. Our simulation results show that the MPPC can significantly alleviate the reduction of EUTR as the voltage level increase. Finally, we construct a 36V/720W MPPC-BESS prototype with two battery packs and PSFB sub-modules to verify the bidirectional operating stability and energy storage capability.

Assessing the impact of copper wools on a phase change material-based TES tank prototype

Phase Change Materials (PCMs) stand out as a promising solution within the current array of Thermal Energy Storage (TES) technologies, thanks to their superior energy storage capacities (compared to sensible solutions) and technological readiness. Nonetheless, the limited thermal conductivity of these materials may lead to incomplete phase transitions during use, resulting in a decrease in their effective energy storage capabilities. The major solutions to mitigate this issue that are present in literature either require a significant modification in the heat exchanger design (e.g. by fins) or are costly and still lack robustness and reliability (e.g. by additivities). In this study, the use of copper wools is proposed as fillers within a PCM-based heat exchanger prototype, and the assessment of its impact on the heat transfer behaviour of the material is evaluated by performing charging and discharging processes. This type of inclusion was chosen as it is relatively cheap, it can be implemented within an already existing heat exchanger, and it does not suffer from segregation. Two different wools were tested in two configurations, thus resulting in five test cases (four containing the wools and one containing solely PCM). The promising results, especially the remarkable decrease in the time needed for the complete solidification of the PCM within the tank (up to 67%), open the opportunity to additional numerical analyses regarding different configurations and/or materials, thus possibly targeting further optimizations in terms of the specific energy density and the specific power density.

Green ammonia production: Process technologies and challenges

Ammonia, a vital player in the global economy, propels economic growth through its key role in fertilizer production, boosting agricultural output significantly. While traditional methods dominate its production, recent efforts focus on sustainable pathways like green ammonia, produced using renewable energy. This colourless gas, beyond agriculture, becomes a versatile input in chemical manufacturing, finding applications in solvents and fertilizers. Industries are increasingly adopting green pathways to reduce carbon footprints, exploring methods using green hydrogen and CO2 by-products. Green ammonia, a beacon for decarbonization, surpasses hydrogen in volumetric energy density, making it a preferred energy carrier. Power-to-Ammonia technology supports energy storage and transfer capabilities, aiding renewable energy integration. Despite challenges like low reactivity, NOx emissions, and toxicity, ammonia's global demand is projected to rise to 350 million tonnes/year by 2050. This review article emphasizing the need for sustainable ammonia production to achieve economic competitiveness, environmental sustainability, and a carbon–neutral future.

Designing intimately interconnected neuron-shaped nickel-copper(I) sulfide nanocomposites as cathode material for supercapacitors

Nanostructured transition metal sulfides have attracted significant attention as pseudocapacitance materials owing to their high specific capacitance and improved conductivity compared to oxides. Bimetallic nickel‑copper(I) (NiCu) sulfides are promising candidates for use in asymmetric supercapacitors because of their high specific capacitance, wide voltage range, and high conductivity. In this study, we synthesize neuron-shaped Ni-Cu(I) sulfide nanocomposites with intimate interconnectivity via the sulfidation and ion exchange of Ni-Cu(I) carbonate hydroxide, prepared by a straightforward hydrothermal process. The product's unique structure, featuring a neuronal network, exhibits a high specific capacitance of 1226.5 F g−1 at 1 A g−1 and an excellent cycling stability (88.97 % capacitance retention after 5000 cycles), which is attributed to the coexistence of bimetallic components and an inherently interconnected neuron-shaped configuration that prevents structural collapse and self-aggregation, while providing easy electrolyte accessibility. Furthermore, an asymmetric supercapacitor with a Ni-Cu(I) sulfide cathode material demonstrates a maximum power and energy densities of 9000 W kg−1 and 23.99 Wh kg−1, respectively, with an initial capacity retention rate of 83.69 % after 5000 cycles. The distinctive structural features of Ni-Cu(I) sulfides enhance the energy storage capabilities of the nanomaterials, enabling the development of portable electronic devices.

Bio-extract mediated green synthesis of bi-functional ammonium cobalt phosphate nanoflakes electrode/catalyst for supercapattery and ethanol oxidation

The present study proposes a low-cost, green technique to the synthesis of bi-functional ammonium cobalt phosphate for energy storage and conversion applications. The comprehensive physiochemical investigations are carried out using various spectral-analytical techniques. The results of phase and surface morphology confirm the formation of an orthorhombic crystal structure with flakes-like microstructure. With a maximal specific capacity of 448.3 mAhg−1 at 2 mAcm−2, bio-solvent driven NH4CoPO4·H2O with graphene oxide (GO) nanoflakes demonstrates exceptional battery-type energy storage capabilities. As constructed supercapattery device exhibits a high specific energy of 85.4 Wh kg−1 at power output of 1283 W kg−1 and 81 % stability after 5000 cycles. Further exploration as a non-precious metal-based catalyst for ethanol oxidation reaction (EOR), NH4CoPO4·H2O /GO showed a high peak current density of 83.4 mAcm−2 at 20 mVs−1. Coupled oxygen/hydrogen evolution processes are investigated in 1 M KOH in order to acquire a better understanding of the catalyst's EOR activity. The NH4CoPO4·H2O/GO sample exhibited the lowest overpotentials of |ηOER@10| = 420 mV, and |ηHER@10| = 112 mV, with Tafel slopes of 169.8 mV dec−1 for OER and 132.8 mV dec-1 for HER, respectively. This is due to the catalyst's slow OH adsorption during OER and the limited H*recombination during HER. Therefore, this approach provides a green and cost-effective method to synthesis efficient bi-functional electrode/catalysts for supercapattery and alkaline fuel cells.

Porous carbon-MnO2 heterostructures for high energy density aqueous ammonium-ion asymmetric supercapacitors

Aqueous ammonium-ion (NH4+) is gaining attention as a viable energy storage option due to the use of NH4+ as the charge carrier, offering advantages of resource abundance, safety, fast diffusion, and a unique storage mechanism. Despite these benefits, the development of storage devices with NH4+ as the charge carrier are still in the early stages, highlighting the crucial need to explore suitable electrode materials for the production of high-performance devices. In this study, broken porous carbon nanocages (BPCs) serve as the support structure to form a heterostructure with δ-MnO2 nanosheets (MnO2-BPCs) grown onto them, building aqueous NH4+ asymmetric supercapacitors (ASCs). Both MnO2-BPCs and BPCs act as host materials for storing aqueous NH4+, exhibiting high specific capacitance and long cycling durability. The assembled NH4+ ASCs present good capacitive performance, with a large specific capacitance of 223 F g−1 and capacitance preservation of 91.4 % over 10,000 cycles. The high energy density achieved by NH4+ ASCs is crucial for advanced energy storage thanks to their elevated specific capacitance and broad operating voltage. The balanced capacitive performance of the positive and negative electrodes is essential in enhancing the energy storage capabilities of NH4+ ASCs. This work provides a straightforward method for creating porous carbon-MnO2 heterostructures for NH4+ storage and paves the way for designing aqueous NH4+-based sustainable energy storage systems (SESSs) for capacitive energy storage.

Enhancing reliability and efficiency of solar chimney by phase change material Integration: An Experimental study

The Solar Chimney Power Plant (SCPP) presents an eco-friendly and straightforward technique for converting solar radiation into electricity. However, the performance limitations and reliability challenges of SCPPs are inherently linked to the variability and intermittency of solar radiation. To tackle this issue, using phase change materials (PCMs) can enhance the thermal energy storage and release capabilities of SCPPs. This study aims to explore the impact of PCM on the exergy efficiency and performance of a solar chimney. Two pilot solar chimneys with identical dimensions were constructed, each featuring a 4 m height chimney and a 5 m diameter collector. One solar chimney was equipped with hydrated salt PCM as an energy storage layer, while the other operated without PCM. Both systems' power production and ventilation potential were evaluated using theoretical turbines, and subsequent exergy analysis discerned the operational behavior and efficiency of the systems. Results indicate that PCM increased the average air mass flow rate through the solar system during the day. The average daily air mass flow rate was 0.045 kg/s with PCM and 0.033 kg/s without PCM. Notably, mean pressure drops resulting from the airflow through the turbine were 2.44 and 1.83 Pa in the presence and absence of PCM, respectively, over a complete day. Additionally, PCM improved exergy efficiency by about 19 % due to enhanced thermal energy storage.

Transparent supercapacitors with networked MXene on NiCo-layered double hydroxide

This study investigates the growth mechanisms of NiCo-layered double hydroxide (LDH) electrodeposition on indium tin oxide (ITO) substrates, aiming to optimize thickness control for transparent supercapacitor applications. Despite the promising energy storage capabilities of NiCo-LDH, long-term cycle stability and transparency degradation due to irreversible redox reactions limit its applicability. To address these challenges, we introduced networked MXene nanosheets into the NiCo-LDH matrix, significantly enhancing electrochemical properties and cycle resilience while maintaining excellent transparency. Under optimized conditions, NiCo-LDH and MXene composites achieved an impressive areal capacitance of 136.9F cm−2 and retained 74.2 % capacitance even after 7000 charge–discharge cycles. Notably, the transparency of the composite remained strong at 80.1 %, outperforming NiCo-LDH without the networked MXene, which retained only 51.4 % transparency after the same cycles, thus indicating that the well-networked MXene nanosheets played a crucial role in improving electrical conductivity and charge-transfer efficiency across the electrode surface. The transparent symmetric supercapacitor developed, utilizing MXene-coated NiCo-LDH, demonstrated outstanding performance with an energy density of 2.23 µWh cm−2 at a power density of 120.00 µW cm−2. Moreover, it showcased an admirable capacitance retention of 85.9 % following 9000 charge–discharge cycles, underlining the robustness of the composites and efficiency for transparent supercapacitor applications. In conclusion, this research highlights the potential of NiCo-LDH/MXene composites for transparent supercapacitors. By carefully controlling thickness and optimizing MXene concentration, we effectively addressed durability and transparency challenges during extended charge–discharge cycles.

How pressure affects costs of power conversion machinery in compressed air energy storage; Part I: Compressors and expanders

This study addresses a critical economic aspect in compressed air energy storage that has not been discussed much in existing literature: the impact of operating pressure on machinery capital cots. It aims to answer whether the cost per unit of power for power conversion systems changes with the maximum storage pressure. Considering that higher storage pressures are associated with greater energy density, enhanced energy storage capabilities and improved system efficiency. This paper helps clarify uncertainties in initial cost estimations for power-generation plants. Effects of operating pressure on the components and overall sizes and consequently costs of power conversion machinery are individually investigated in two parts. Part I encompasses the compressor and expanders, and part II comprehensively discusses the effects of the operating pressure on the costs of heat exchangers. The analysis employs a conceptual engineering approach, revealing that higher intake pressure reduces overall compressor/expander size, leading to cost savings. Additionally, increasing the number of compression stages for higher storage pressures enhances exergy storage cost-effectiveness. To establish an advanced adiabatic CAES plant with a storage pressure of 200 bar instead of 50 bar, there is potential for a 6 % reduction in $/kW expenditure.

Boosting High‐Performance Aqueous Zinc‐Ion Hybrid Capacitors via Organic Redox Species on Laser‐Induced Graphene Network

AbstractHybrid zinc‐ion capacitors combine the energy storage capabilities of zinc‐ion batteries with the high‐power output of supercapacitors. However, the limited cycle life and narrow electrochemical window of hybrid zinc‐ion capacitors currently restrict their potential applications. Herein, a hybrid zinc‐ion capacitor is fabricated on laser‐induced graphene (LIG) based on in situ electropolymerization of organic compound poly(8‐amino‐2‐naphthol). The electropolymerized long‐conjugated chain polymers on the 3D conductive framework of LIG can enhance reaction kinetics, suppress the dissolution of organic compounds, and boost capacity. Simultaneously, hydrogen bonds form between polymer chains, aiding in proton transport. The assembled Zn//carbon cloth/LIG/poly(8‐amino‐2‐naphthol) hybrid zinc‐ion capacitors possess a high specific capacity of 308 mAh g−1 at 0.1 mA cm−2, which is twice as much as that of the batteries without LIG. Additionally, these hybrid capacitors can stably endure 10 000 cycles at a current density of 5 mA cm−2.

Stable and reliable PEG/TiO2 phase change composite with enhanced thermal conductivity based on a facile sol-gel method without deionized water

Some shortcomings exist in organic phase change materials, including leakage susceptibility, low thermal conductivity, and preparation complexity. Herein, polyethylene glycol/titanium dioxide shape-stabilized composite phase change material (PEG/TiO2 ss-CPCM) was fabricated by facile sol-gel method without deionized water using tetrabutyl titanate (TBOT) as precursor. In this composite, not adding deionized water prolonged the gelation time, allowing PEG to bind as much TiO2 as possible and enhancing energy storage capability; TiO2 acted as the supporting framework to maintain the material's shape stability and enhance thermal conductivity. The melting and crystallization phase change enthalpies of prepared PEG/TiO2 ss-CPCM were 128.3 J/g and 113.1 J/g with an encapsulation efficiency of 74.14 % when PEG: TBOT = 1.5: 1. After repeating 300 thermal cycles, the phase change enthalpy remained almost constant. Besides, the thermal conductivity of PEG/TiO2 ss-CPCM was 1.22 times that of PEG, and the potential for thermal management applications. The advantages (energy storage capability, shape stability in thermal environments, thermal reliability, and thermal management) of the PEG/TiO2 ss-CPCM prepared by facile synthesis, not only propose a phase change material with excellent thermal properties and shape stabilization but provide a green and feasible strategy for the fabrication of PEG/TiO2 composite phase change materials utilizing the sol-gel method.

Hydroxylation strategy enhances the energy storage performance of Co2CuMn Prussian blue analogues for zinc-ion capacitors

Prussian blue analogues (PBAs) are renowned for their distinctive structural characteristics and cost-effectiveness; however, they encounter challenges due to limited active sites and structural defects, which resulting in low capacity. In this study, we introduce a hydroxylation method to enhance the energy storage capabilities of Co2CuMn-PBAs in aqueous zinc-ion capacitors. The modified Co2CuMn-PBA electrode exhibits enhanced capacitance and rate performance, demonstrating an remarkable reversible capacitance of 232.2F/g at 0.1A/g and a rate capacitance of 85.6F/g at 2 A/g, thus positioning it as a promising cathode material for supercapacitors.

Silver nanoparticle−decorated MnO2 for promoted Mn4+/Mn2+ redox reaction in aqueous Zn−MnO2 batteries

Rechargeable aqueous Zn−MnO2 batteries have garnered increasing attention recently due to intrinsic safety, high theoretical capacity, appealing output voltage, and low material cost. However, challenges still exist in exploring for high−performance manganese oxides capable of delivering comparable capacity to the Zn anode. Herein, a composite material made of layered MnO2 decorated with Ag nanoparticles (Ag NPs) can be prepared by a one−step hydrothermal reaction. The silver decoration strategy can provide facile electron transport of the composite cathode and induce structural vacancies via forming Ag−O−Mn bond. These features enable the AgMO cathode to exhibit smaller charge−transfer resistance (23.0 vs 41.3 Ω) and accelerated ion transport kinetics (1.25×10−10 vs 3.90×10−11 cm2 s−1). More importantly, the presence of Ag NPs is found to promote the reaction kinetics of Mn4+/Mn2+ redox. By taking these advantages, the AgMO sample exhibits a higher attainable capacity of 333 mAh g–1 at 0.3 A g–1 compared with the Ag−free counterpart (MO, 268 mAh g–1). Moreover, AgMO demonstrates better rate performance with the discharge capacity of 109 mAh g–1 at 8 A g–1 (90 mAh g–1 for MO), and a specific capacity of 93 mAh g–1 can still be achieved for AgMO after 2000 cycles at 4 A g–1 (55 mAh g–1 for MO). This work presents a holistic approach to enhance the energy storage capability of MnO2 cathode in rechargeable aqueous Zn−ion batteries.

Utilizing Ragone framework for optimized phase change material-based heat sink design in electronic cooling applications

This study explores the latent thermal energy storage potential of an organic phase change material with porous copper foam and its applicability in electronic cooling under varying heat load conditions. The organic phase change material, n-eicosane, is known for its inherently low thermal conductivity of 0.15 W/mK, rendering it vulnerable during power spikes despite its abundant latent heat energy for phase transition from solid to liquid. Porous copper foams are often integrated into n-eicosane to enhance the composite's thermal conductivity. However, the volume fraction of the phase change material in the porous foam that optimally improves the thermal performance can be dependent on the boundary condition, the cut-off temperature, and the thickness. A finite difference numerical model was developed and utilized to ascertain the energy consumption for the composite of n-eicosane with two kinds of porous copper foam with varying porosity under different heat rates, cut-off temperatures, and thickness. In addition, the results are compared with a metallic phase change material (gallium), a material chosen with a similar melting point but significantly high thermal conductivity and volumetric latent heat. For validation of the numerical model and to experimentally verify the effect of boundary condition (heat rate), experimental investigation was performed for n-eicosane and high porosity copper foam composite at varying heat rates to observe its melting and solidification behaviors during continuous operation until a cut-off temperature of 70 °C is reached. Experiments reveal that heat rate influences the amount of latent energy storage capability until a cutoff temperature is reached. For broad comparison, the numerical model was used to obtain the accessed energy and power density and generate thermal Ragone plots to compare and characterize pure gallium and n-eicosane - porous foam composite with varying volume fractions, cutoff temperature, and thickness under volumetric and gravimetric constraints. Overall, the proposed framework in the form of thermal Ragone plots effectively delineates the optimal points for various combinations of heat rate, cut-off point, and aspect ratio, affirming its utility for comprehensive design guidelines for PCM-based composites for electronic cooling applications