High-performance Power Sources Research Articles

Internally connected porous PVA/PAA membrane with cross-aligned nanofiber network for facile and long-lasting ion transport in zinc–air batteries

In response to the growing interest in next-generation wearable devices, the demand for high-performance, safe, and flexible power sources has increased. Flexible zinc–air batteries (ZABs) based on gel polymer electrolytes (GPEs) have emerged as promising candidates for wearable power sources owing to their high energy density, safety, and cost efficiency. However, persistent electrolyte evaporation through the air cathode poses a significant challenge, resulting in poor lifespan characteristics that impede practical applications. In this study, we developed a polymer composite-type GPE composed of cross-aligned nanofibers (NFs) of a polyacrylic acid (PAA)-based framework embedded in a polyvinyl alcohol (PVA) matrix. Upon immersion in a liquid electrolyte (6 M KOH), the superabsorbent PAA spontaneously generated an internally connected porous (IP) structure adjacent to the aligned PAA NFs. These pores served as directional water channels, facilitating rapid hydroxide ion conduction and yielding a remarkable ionic conductivity of 235.7 mS cm−1. The PVA matrix acts as both a packaging material and the main body of the GPE, providing good dimensional stability and mitigating the swelling of PAA, even under conditions of high electrolyte uptake, while also ensuring high flexibility. The IP-PVA/PAA composite GPE demonstrated a high power output, rate performance, and excellent lifespan in flexible ZABs. Furthermore, successful operation at various bending angles provides empirical evidence supporting the viable application of flexible ZABs.

Cultivating High-Performance Flexible All-in-One Supercapacitors With 3D Network Through Continuous Biosynthesis.

Flexible supercapacitors can potentially power next-generation flexible electronics. However, the mechanical and electrochemical stability of flexible supercapacitors under different flexible conditions is limited by the weak bonding between adjacent layers, posing a significant hindrance to their practical applicability. Herein, based on the uninterrupted 3D network during the growth of bacterial cellulose (BC), a flexible all-in-one supercapacitor is cultivated through a continuous biosynthesis process. This strategy ensures the continuity of the 3D network of BC throughout the material, thereby forming a continuous electrode-separator-electrode structure. Benefitting from this bioinspired structure, the all-in-one supercapacitor not only achieves a high areal capacitance (3.79 F cm-2) of electrodes but also demonstrates the integration of high tensile strength (2.15MPa), high shear strength (more than 54.6kPa), and high bending resistance, indicating a novel pathway toward high-performance flexible power sources.

Penerapan Sistem Akuntansi Sumber Daya Manusia Terhadap Kinerja Karyawan Pada Bengkel Daniyah Lubis Motor

The company's problems still revolve around human resources surviving in the era of globalization. This research aims to analyze accounting systems, human resources on employee performance. One of the key elements for the successful implementation of an efficient organization is human resources. Facilities, abundant infrastructure and resources all support this, but without the help of human resources, company operations cannot be handled effectively. A reliable, high-performance power source is required. The increasing complexity of the legal system, the awareness that humans are a very useful instrument for increasing productivity and understanding the negative impacts of ineffective human resource management are the main causes of the increasing importance of human resources. The analytical method that the author uses in this research is comparative and qualitative descriptive methodology. The results of the research show that: the implementation of the human resources employee accounting system for the performance of the Daniyah Lubis Motor Workshop is in accordance with the study theory. In implementing the Human Resources Accounting system, Daniyah Lubis Motor Workshop is still less effective, this can be seen from the contribution of employee performance.

Graphene/SiC composite porous electrodes for high-performance micro-supercapacitors

Micro-supercapacitor (MSC) electrodes prepared by chemical vapor deposition (CVD) possess high potential as on-chip integrated micro-power sources for future microdevices. In this study, porous graphene/SiC composite films are grown using laser CVD. A double-layer specific capacitance up to 219.3 mF/cm2 is achieved at 10 mV/s, which is 26 times higher than those of the electrodes prepared by CVD with the same energy storage mechanism reported in literatures. After 20000 charge-discharge cycles at room temperature (20 °C) and variable temperatures (0–60 °C), the electrode exhibits robust cycling stability with 99.9% and 109.6% capacitance retention, respectively. Subsequently, it is revealed that the abundance of graphene on the SiC porous skeleton plays a key role in promoting the capacitance enhancement. The strong structure of SiC as well as the strong adhesion between graphene and SiC guarantee the excellent cycling stability. Evidently, the preparation of graphene/SiC porous composite films as MSC electrodes is a highly promising route for fabricating high-performance and reliable on-chip power sources for future miniaturized devices.

A high-energy/power and ultra-stable aqueous ammonium ion microbattery based on amorphous/crystalline dual-phase layered metal oxides

The prosperity of microelectronic systems stimulates fast development of high-performance power sources with micro/nano sizes. Considering the defects of conventional lithium-ion microbatteries, i.e. high cost, severe safety concerns as well as the unsatisfactory power delivery due to the sluggish ion transport of the organic electrolytes, novel energy storage microdevices are worth looking forward to. Here, we assemble an aqueous ammonium-ion microbattery using 2D (NH4)xV2O5 with amorphous/crystalline dual-phase nanostructure deposits on 3D nanoporous Au as anode while nanoporous Au/δ-MnO2 composite as cathode. As a result of the superb electronic/ionic conductivities as well as the large voltage window, the resultant NP Au/ac-(NH4)xV2O5//NP Au/δ-MnO2 aqueous ammonium-ion microbattery exhibits ultrahigh energy density of 0.126 Wh cm−3 with electrical powers ∼280-fold higher than commercial lithium thin-film batteries, in addition to excellent rate capability (∼84.2% capacity retention at 5–50 mV s−1 scan rates) and cycling stability (retains ∼93.3% of the initial value after 10,000 cycles at 500 mV s−1). The superb performance endows it to be promising candidate as monolithic micropower source for micro/nano portable/wearable electronics with high energy storage and power delivery demands.

Inkjet Printing of MnO2 Nanoflowers on Surface-Modified A4 Paper for Flexible All-Solid-State Microsupercapacitors

Printing technologies are gaining growing attention as a sustainable route for the fabrication of high-performance and flexible power sources such as microsupercapacitors (MSCs). Here, the inkjet printing method is utilized for the fabrication of manganese dioxide (MnO2)-based, flexible all-solid-state MSCs on surface-modified A4 paper substrate. The appropriate rheology of the formulated ethanol-based ink (Fromm number <10) and the proper dimensions of MnO2 nanoflowers (average size ∼600 nm) ensure a reliable inkjet printing process. Moreover, the underlying graphene/Ag nanowire pattern serves as a primer and highly conductive (Rs < 2 Ω sq-1) layer on top of the paper to facilitate the anchoring of MnO2 nanoflowers and rapid electron transportation. The resulting all-solid-state MSCs deliver a maximum areal capacitance of 0.68 mF cm-2 at a current density of 25 μA cm-2, reasonable durability (>80% of capacity remained after 3000 cycles), and remarkable foldability. Additionally, the inkjet-printed MSC devices deliver a superior areal energy density of 0.01 μWh cm-2 and also a power density of 1.19 μW cm-2. This study demonstrates the power of the inkjet printing method to produce MSCs on flexible substrates, which have great potential for flexible/wearable electronics.

2D bimetallic organic framework nanosheets for high-performance wearable power source and real-time monitoring of glucose.

Diabetics often prick their fingertips to measure the glucose levels in their blood. However, this traditional method not only causes prolonged pain but also increases the risk of infection. Hence, in this study, a non-invasive flexible glucose biosensor with high sensitivity was fabricated. Specifically, NiCo metal-organic frameworks (NiCo-MOFs) served as the electrode material of a micro-supercapacitor and sensing material of a glucose sensor. The electrochemical tests verified that the prominent sensitivity of the NiCo bimetal product is 1422.2 μA mM-1 cm-2. The micro-supercapacitor based on the as-fabricated NiCo-MOFs showed a high energy density of 11.5 mW h cm-2 at the power density 0.26 mW cm-2. In addition, the as-designed glucose device exhibited an excellent sensitivity of 0.31 μA μM-1. Furthermore, a flexible energy storage and glucose detection system was successfully prepared by further integrating the micro-supercapacitor and glucose sensor. The smart detector could accurately and conveniently measure the glucose concentration in sweat in real-time. Therefore, the wearable real-time sensing device displays feasible application for non-invasive glucose monitoring and health management.

Experimental study on the influence of environment conditions on the performance of paper-based microfluidic fuel cell

• The effects of temperature and relative humidity on PMFC were investigated experimentally. • The temperature of 45 °C achieves a shortest starting time and highest output performance. • The relative humidity is insensitive to the PMFC performance under a constant temperature. • The maximum power density of 22.27 mW/cm 2 is obtained by using 0.3 M CHCOOK at 45 °C. Since new requirements of portability, sustainability and cleanliness have been implemented for electronic biomedical diagnosis devices, the development of high-performance power sources has attracted great attention. Paper-based microfluidic fuel cells (PMFCs) use the capillary force from cellulose paper to drive the fuel and oxidant solutions and maintain the co-laminar flowing behavior in the paper channel, which are candidates for portable electronic devices due to their advanced features of small structure, low cost, and pollution-free nature. However, the promotion of PMFCs has been restricted by unstable performance under various environmental conditions. No researchers have put their attentions and efforts on understand the potential influences of temperature and humidity conditions on PMFC performance. Therefore, the current study elaborates the use of a temperature-humidity control and test chamber to investigate the influences of environmental conditions on PMFC performance. We found that with a constant relative humidity, increasing the temperature from 5 °C to 45 °C can accelerate the redox reaction rates, achieve a quick start and obtain higher output performance. However, when the ambient temperature is 65°C, the output performance of the fuel cell will not continue to improve with the increase of the ambient temperature. The regularity of the effect of relative humidity on PMFC performance is not obvious under different temperatures. With increasing fuel concentration to 0.3 M, the maximum peak power density of PMFC increases to 22.27 mW·cm −2 at 45 °C. We envision that the current work could guide the design and utilization of an integrated PMFC-biosensor device under various environmental conditions.

High-Performance flexible Quasi-Solid-State aqueous Nickel-Iron battery enabled by MOF-Derived N-Doped carbon hollow nanowall arrays

The development of portable, flexible and wearable electronic devices has accelerated ever-growing demand for high-performance power sources with high specific energy/power density, high-level safety, low cost, and highly flexible features. Herein, a flexible quasi-solid-state aqueous nickel–iron (QSSA Ni-Fe) battery with high energy and power densities is rationally developed using ultrathin Ni(OH)2 nanoflakes and porous ɑ-Fe2O3 nanorods conformally deposited on vertically aligned MOF-derived N-doped carbon hollow nanowalls supported by carbon textiles (NC/CTs) as the cathode (Ni(OH)2@NC/CTs) and anode (ɑ-Fe2O3@NC/CTs), respectively. The obtained flexible QSSA Ni-Fe battery delivers optimal electrochemical performance, including high energy density (155.4 Wh Kg−1), high power density (14.0 KW Kg−1) and excellent cycling stability (∼86.1 % retention after 10,000 cycles). Impressively, the flexible QSSA Ni-Fe battery delivers stable electrochemical performance even under different bending conditions. The excellent electrochemical properties may be attributed to the following reasons: (i) The ultrathin Ni(OH)2 nanoflakes and porous ɑ-Fe2O3 nanorods deposited on 2D hollow NC arrays possess a high porosity and large specific surface area; (ii) The 2D hollow NC arrays on flexible CTs not only increase the electrical conductivity, but also function as a scaffold to hold the active materials (such as Ni(OH)2 or ɑ-Fe2O3) and thus maintain the structural integrity of the composites. This work provides a novel approach to design and develop QSSA batteries with satisfactory electrochemical properties and excellent flexibility, and have greater potential for future flexible and wearable electronic devices.

Low-Temperature Calcination of Metal-Organic Frameworks(MOFs) to Derive the High Entropy Stabilized Oxide for High Performance Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) battery owing to high energy density and theoretical capacity is anticipated as a high-performance rechargeable power source for flexible electronic devices and electric vehicles. However, the rapid capacity fade, low Coulombic efficiency, and significant self-discharge capacity loss due to the polysulfides shuttling are the major constraints of its real-world applications. To conquer these challenges, despite the physical encapsulation of polysulfides, chemical interactions between shuttle effect-suppressive sulfur host materials and soluble lithium polysulfides have recently been emphasized. Herein, a novel approach to synthesize the high entropic stabilized oxide (HEO) at low temperature is developed from the self-sacrificing template of metal-organic frameworks (MOFs) to chemically anchor the lithium polysulfides. As-synthesized HEO850 at 850 ºC (transition temperature) exhibited a single-phase rocksalt crystalline structure with homogenous dispersion of Ni, Mg, Cu, Co, and Zn and reversible entropic phase stabilization in the certain temperature range (750-850 ºC). When employed as a chemical anchor to lithium polysulfides (LIPSs) and compared the electrochemical performance of Li-S cells with medium configurational entropic oxide (MEOs) (HEOs-one metal cation), low entropy oxide (LEOs) (HEOs-three metal cations), and routine sulfur ketjen black (S/KB) cells, it revealed a competitive reversible capacity, excellent cycling stability and a low capacity decay rate by immobilizing the LIPSs and facilitating the redox reaction in the cathode. The cells with HEO850/KB/S cathode delivered a higher initial specific discharge capacity of 1244.1 mAh g-1 than those of MEO850/S/KB (979.625 mAh g-1), LEO850/S/KB (908 mAh g-1), and S/KB (966 mAh g-1). After 800 cycles of continuous charging and discharging at 0.5 C, the capacity of 784.1 mAh g-1 with outstanding Coulombic efficiency of 99.66 % is still retained demonstrating excellent cycling stability with a negligible capacity fade rate of 0.04% per cycle. This outstanding performance could be attributed to the synergistic contribution and exposure of numerous active sites of randomly dispersed elements in the HEO850. This study not only highlights the extraordinary electrochemical performance of Li-S battery with efficient immobilization of LIPSs but also provide a novel strategy for the synthesis of HEOs at lower calcination temperature for various energy conversion and storage applications. After getting confidence with these prilimary results, Ti-based HEOs owing to both high ionic and electric conductivities will be investigated at coin and pouch cell level as future research direction.

Synthesis and plasma treatment of nitrogen-doped graphene fibers for high-performance supercapacitors

Graphene fiber-based supercapacitor has aroused great interest as a flexible power source in future wearable electronics. However, the low electrochemical performance of graphene fibers (GFs) usually causes the serious limitation of use in practical applications due to the material stacking, hydrophobicity and fabrication process complexity. In this work, a facile and effective plasma-assisted strategy is put forward to increase specific surface area, tune hierarchically porous structure and promote wettability of nitrogen-doped graphene fibers (NGFs), resulting in the improvement of electrochemical performance. The supercapacitor assembled from plasma-treated NGFs shows superior capacitance (878 mF/cm 2 at 0.1 mA/cm 2 current density) and high energy density (19.5 μW h/cm 2 at 40 mW/cm 2 power density), which is 23.7% and 131.4% higher than that of NGFs and GFs, respectively. Additionally, the fiber-based supercapacitor based on plasma-treated NGFs exhibits high rate capability of 59.8% and excellent cyclic performance (95.8% retention over 10,000 cycles). These plasma-treated NGFs can be promising candidates for high-performance and flexible power sources in future wearable electronics.

Heterostructured hollow fibers stitched together from nickel sulfides capped S, N-codoped carbon nanotubes as a trifunctional electrode for flexible hybrid Zn batteries

The explorations of highly performance cathodes are the key concerns of hybrid Zn batteries (HZBs) that combine the Zn-ion (ZIBs) and Zn-air (ZABs) batteries. Herein, a freestanding hollow fiber stitched by the heterostructures of S, N-codoped carbon nanotubes (SNCNT) confined nickel sulfides (Ni3S2) nanoparticles are designed as a trifunctional electrode for HZB. The nickel sulfide nanoparticles are encapsulated by in-situ grown S, N-codoped carbon nanotubes, which stitch together to assemble the hollow fibers. Their highly porous and conductive frame gives fast electron/ion pathways and abundant active sites. The interaction between Ni3S2 and SNCNT favors the OER catalytic properties and the S, N-codopant in SNCNT endows ORR activities in the heterostructured unit. Both experimental and theoretical results demonstrate the Ni3S2@SNCNT hollow fiber is a trifunctional and flexible electrode with high OER/ORR electrocatalytic activities and superior electrochemical properties. The hybrid Zn battery based on Ni3S2@SNCNT hollow fiber cathode manifests two-set charge/discharge characteristics, high energy/power densities and good long-term durability. Additionally, the flexible HZB devices based on the Ni3S2@SNCNT flexible cathode achieve the high performance, unique “self-breathing” abilities and high adaptation in multfarious working conditions. More impressively, they exhibit good uninterrupted working ability even in the sudden transitions on working conditions. Therefore, this work not only provides a highly reliable, trifunctional and flexible electrode, but also promotes the development of the high-performance power sources for the electronics in multifarious conditions.

Progress in Piezoelectric Nanogenerators Based on PVDF Composite Films.

In recent years, great progress has been made in the field of energy harvesting to satisfy increasing needs for portable, sustainable, and renewable energy. Among piezoelectric materials, poly(vinylidene fluoride) (PVDF) and its copolymers are the most promising materials for piezoelectric nanogenerators (PENGs) due to their unique electroactivity, high flexibility, good machinability, and long–term stability. So far, PVDF–based PENGs have made remarkable progress. In this paper, the effects of the existence of various nanofillers, including organic–inorganic lead halide perovskites, inorganic lead halide perovskites, perovskite–type oxides, semiconductor piezoelectric materials, two–dimensional layered materials, and ions, in PVDF and its copolymer structure on their piezoelectric response and energy–harvesting properties are reviewed. This review will enable researchers to understand the piezoelectric mechanisms of the PVDF–based composite–film PENGs, so as to effectively convert environmental mechanical stimulus into electrical energy, and finally realize self–powered sensors or high–performance power sources for electronic devices.

Highly efficient flexible perovskite solar cells with vacuum-assisted low-temperature annealed SnO2 electron transport layer

The demand for lightweight, flexible, and high-performance portable power sources urgently requires high-efficiency and stable flexible solar cells. In the case of perovskite solar cells (PSCs), most of the common electron transport layer (ETL) needs to be annealed for improving the optoelectronic properties, while conventional flexible substrates could barely stand the high temperature. Herein, a vacuum-assisted annealing SnO2 ETL at low temperature (100 °C) is utilized in flexible PSCs and achieved high efficiency of 20.14%. Meanwhile, the open-circuit voltage (Voc) increases from 1.07 V to 1.14 V. The flexible PSCs also show robust bending stability with 86.8% of the initial efficiency is retained after 1000 bending cycles at a bending radius of 5 mm. X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and contact angle measurements show that the density of oxygen vacancies, the surface roughness of the SnO2 layer, and film hydrophobicity are significantly increased, respectively. These improvements could be due to the oxygen-deficient environment in a vacuum chamber, and the rapid evaporation of solvents. The proposed vacuum-assisted low-temperature annealing method not only improves the efficiency of flexible PSCs but is also compatible and promising in the large-scale commercialization of flexible PSCs.

Nanostructuring of Iron Disulfide Cathode Materials for Enhanced Thermal Batteries

For the U.S. Department of Defense, high-performance power sources are a critical technology for current and future gun-fired munitions. Molten salt thermal batteries are the reserve power source of choice for many weapon systems due to their high power density, proven long shelf life, and capability to function across a wide range of operating environments. The incorporation of nanomaterials into thermal battery components offers the potential to produce batteries with performance improvements, such as higher voltages at increased current densities. In this study, nanoscale iron disulfide (FeS2) was synthesized using a fully scalable, high energy milling method, and characterized utilizing SEM, XRD, ICP-OES, BET surface area analysis, TGA-DSC, and other techniques. Nanostructured cathode mixtures containing the nanoscale FeS2 and LiCl-KCl eutectic salt electrolyte were pressed into electrode pellets. Their electrochemical performance was then characterized as compared to standard FeS2 cathode electrode pellets currently used in industry. Single cell thermal battery discharge testing, polarization type scans, and pulse load capability were used to compare cell performance for better understanding of best-use applications for these materials. Compared to control cells, the cells utilizing nanostructured cathodes provided higher power response, with respect to both voltage and runtime.

A novel redox capacitor with a natural rubber-based solid polymer electrolyte for energy applications

The development of high-performance power sources such as super capacitors (EDLCs and redox capacitors) has become an urgent requirement in recent years due to the unprecedented growth of portable technology. The present study was carried out to fabricate a redox capacitor using a natural rubber-based solid polymer electrolyte (SPE). Zinc trifluoromethanesulfonate (ZnTf), propylene carbonate (PC), and pyrrole were used as electrode materials whereas ZnTf and methyl-grafted natural rubber (MGNR) were used to prepare the SPE. Warburg type diffusion as well as capacitive behavior was observed from the EIS test. Single electrode specific capacitance (Csc) from cyclic voltammetry (CV) was 27.5 Fg−1 at the scan rate of 10 mVs−1. Retention of the Csc value was 92% over 500 cycles. Single electrode specific discharge capacitance (Csd) found from galvanostatic charge discharge test was 6 Fg−1.

(Invited) Printed Built-in Power Sources with Dimensional Conformability

The ongoing surge in demand for flexible/wearable electronics, self-powered systems, soft robotics, and Internet of Things (IoT) has inspired the relentless pursuit of form factor-free, high-performance power sources that can be monolithically and seamlessly integrated with various electronics. To reach this challenging goal, a new class of advanced power sources with various form factors that are different from existing commercial ones are needed. From the viewpoint of power source design and architecture, traditional cell materials and fabrication have resulted in power sources that feature a lack of variety in form factors and flexibility. In specific, most of the current power sources are manufactured by winding or stacking of slurry-casted electrode sheets and separator membranes, followed by the injection of liquid electrolytes inside a fixed form of canisters or pouch packaging substances; these methods impose stringent restrictions on the unitization of power sources with electronic devices. Printed power sources have recently garnered considerable attention as a fresh and game-changing approach due to their design diversity, shape/performance compatibility with electronic devices, and scalable/low-cost processability. Printed power sources based on high-fidelity printing techniques and rationally designed material chemistry are fabricated directly on complex-shaped objects, thereby enabling monolithic integration and electrochemical coupling with target devices that lie far beyond those achievable with conventional power source technologies.Here, this talk introduces form factor-free, printed built-in power sources, with particular attention to their dimensional conformability and performance compatibility with newly emerging complex-structured electronic devices. A key-enabling technology for the printed power sources is the design of battery inks (specifically, electrode and electrolyte inks), with a focus on their rheology and electrochemistry. Our research interests are directed to discussing effects of the battery inks on printing processability, microstructure (focusing on bicontinuous ion/electron transport channels) and electrochemical performance of the resultant printed power sources. We envision that the printed power sources open a new avenue towards form factor-free/monolithic integrated power sources with object-tailored design versatility and dimensional conformability.

Pyrolysis of ammonium perfluorooctanoate (APFO) and its interaction with nano-aluminum

Application of ammonium perfluorooctanoate (APFO) in nano-aluminum (nAl) based energetic nanocomposites is proposed in this work. By fixating fluorine in AlF3, combustion as oxidizer introduces both an efficient defluorination strategy and a high performance power source for APFO. The laser ignition temperature build-up of nAl/APFO is about 2300 °C/s, and the combustion temperature approaches 1240 °C with an energy density of 12.6 kJ/g. The combustion residue of nAl/APFO contains AlF3 as primary condensed product with graphite, tar and Al2O3. And the gaseous fluorinated product is CF4 with low abundance. With the higher heat release obtained from oxygen bomb comparing to the stoichiometric value, results exhibit a high defluorination efficiency. The pyrolysis mechanism of APFO and its interaction with nAl were investigated by DSC-TG-PyMS-FTIR, T-jump-PyGC-MS coupling analysis and in-situ XRD. It shows that APFO undergoes multi-stage pyrolysis including proton transfer, skeletal chain breakage succeeded by a distinct polymerization before C-F bond cleavage. Al2O3 on the surface of nAl adsorbs the evolved fluorides after the initial pyrolysis of APFO in nAl/APFO, which also decreases the apparent activation energies of the last two stages of pyrolysis. The passivation layer on the surface of Al corroded by HF and perfluorocarboxylic acid before the violent fluorination of active Al core.

Optimum sub-megawatt electric-hybrid power source selection

PurposeThe limited energy density of batteries generates the need for high-performance power sources for emerging eVTOL applications with radical operational improvement potential over traditional aircraft. This paper aims to evaluate on-design and off-design recuperated turbogenerator performances based on newly developed compression loaded ceramic turbines, the Inside-out Ceramic Turbine (ICT), in order to select the optimum engine configuration for sub-megawatt systems.Design/methodology/approachSystem-level thermal engine modeling is combined with electric generators and power electronics performance predictions to obtain the Pareto front between efficiency and power density for a variety of engine designs, both for recuperated and simple cycle turbines. Part load efficiency for those engines are evaluated, and the results are used for an engine selection based on a simplified eVTOL mission capability.FindingsBy operating with high turbine inlet temperature, variable output speed and adequately sized recuperator, a turbogenerator provides exceptional efficiency at both nominal power and part load operation for a turbomachine, while maintaining the high power density required for aircraft. In application with a high peak-to-cruise power ratio, such power source would provide eight times the range of battery-electric power pack and an 80% improvement over the state-of-the-art simple cycle turbogenerator.Practical implicationsThe implementation of a recuperator would provide additional gains especially important for military and on-demand mobility applications, notably reducing the heat signature and noise of the system. The engine low-pressure ratio reduces its complexity and combined with the fuel savings, the system could significantly reduce operational cost.Originality/valueImplementation of radically new ICT architecture provides the key element to make a sub-megawatt recuperated turbogenerator viable in terms of power density. The synergetic combination of a recuperator, high temperature turbine and variable speed electric generator provides drastic improvement over simple-cycle turbines, making such a system highly relevant as the power source for future eVTOL applications.

Ti3C2Tx MXene-Reduced Graphene Oxide Composite Electrodes for Stretchable Supercapacitors.

The development of stretchable electronics requires the invention of compatible high-performance power sources, such as stretchable supercapacitors and batteries. In this work, two-dimensional (2D) titanium carbide (Ti3C2Tx) MXene is being explored for flexible and printed energy storage devices by fabrication of a robust, stretchable high-performance supercapacitor with reduced graphene oxide (RGO) to create a composite electrode. The Ti3C2Tx/RGO composite electrode combines the superior electrochemical and mechanical properties of Ti3C2Tx and the mechanical robustness of RGO resulting from strong nanosheet interactions, larger nanoflake size, and mechanical flexibility. It is found that the Ti3C2Tx/RGO composite electrodes with 50 wt % RGO incorporated prove to mitigate cracks generated under large strains. The composite electrodes exhibit a large capacitance of 49 mF/cm2 (∼490 F/cm3 and ∼140 F/g) and good electrochemical and mechanical stability when subjected to cyclic uniaxial (300%) or biaxial (200% × 200%) strains. The as-assembled symmetric supercapacitor demonstrates a specific capacitance of 18.6 mF/cm2 (∼90 F/cm3 and ∼29 F/g) and a stretchability of up to 300%. The developed approach offers an alternative strategy to fabricate stretchable MXene-based energy storage devices and can be extended to other members of the large MXene family.