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Despite the development of quinone as the potential cathode material for Zn-organic batteries, there are undesired behaviors for the rate and cycling performances. To achieve high-performance Zn-organic batteries, intentional organic molecular design and a deep understanding of the mechanism of Zn-organic batteries are highly essential. Herein, strong electron-withdrawing and conjugating groups (-CN) were introduced to lower the highest occupied molecular orbital (HOMO)/lowest unoccupied molecular orbital (LUMO) energy on an aromatic Schiff base (Hexaazatrinnphthalene, denoted as HATN). With such a decoration, HATN-3CN exhibits an outstanding rate capacity with retention of 60.7% of the initial capacity at 400 times the initial current density and long cycle life of over 5800 cycles. Besides, the charge storage mechanism was systematically investigated through experiments and density functional theory calculation, showing that C N moieties are the active site for the storage of H+/Zn2+. This strategy and insight provided by molecular orbital theory and kinetics-controlled process offer a feasible pathway of molecular-level design for constructing high-performance Zn-organic batteries.

It has long been of interest to explore cathode materials for achieving high-performance rechargeable zinc ion batteries through rational design and highly efficient synthesis. Based on the combination of reversible Zn2+ insertion/-extraction and electrolyte anion doping/dedoping mechanisms, a polymer/graphene composite cathode, named poly-quinol-phenylenediamine/graphene (POLA/G), is obtained via a hydrothermal synthesis method. The hydroquinone and p-phenylenediamine building blocks of POLA/G can not only provide a reversible redox reaction associated with Zn2+, but they can also interact with the anions in the aqueous electrolyte. As a result, Zn//POLA/G batteries deliver extremely good electrochemical performance, with a high-rate capability of 225 mA h g−1 at 0.1 A g−1 and 152 mA h g−1 at 20 A g−1. Moreover, the composite cathode presents exceptional long-term cycling performance, retaining 90% of its initial capacity after 5000 cycles at a current of 10 A g−1. Hence, this work develops a new direction for the use of polymers to increase zinc ion storage.

With distinct advantages like high gravimetric and volumetric capacity, low redox potential, a natural abundance of zinc, and compatibility with water, Zn-ion batteries have become a potential alternative to Li-ion batteries. However, several challenges still need to be addressed prior to the practical applications of Zn-ion batteries, such as their narrow electrochemical window, irreversibility, unstable anode, sluggish kinetics and difficulties regarding the insertion of Zn2+ into the host material for the cathode. Such issues can be addressed by regulating the components and structures of the electrolyte which connects the cathode and anode parts. In this mini review, we systematically describe the compositions and structures of the electrolyte and then discuss the core issues faced by the batteries, particularly their mechanism and affected factors. Furthermore, a relatively comprehensive overview is presented of the strategies being utilized to improve Zn-ion batteries via regulating liquid electrolyte, mainly including the optimization of solvents and salts, adjustment of electrolyte concentration, introduction of additives into the electrolyte, and the fabrication of a hybrid-ion battery. In the final section, we offer insights into the development of liquid electrolytes for Zn-ion batteries.

Introducing and adjusting the oxygen vacancies (VO) of transition metal oxides has been proposed as a significant and effective way to tackle the sluggish nitrogen reduction reaction (NRR) in the electrocatalysis process. In this work, we present the synthesis of an In2O3−x/CeO2−y nanotube with abundant VOvia the electrospinning technique, followed by the controlled post-treatment calcination process. It is demonstrated that the electrochemical properties of In2O3−x/CeO2−y are successfully optimized through VO engineering and the reaction mechanism of the NRR is the dissociative pathway, which remarkably enhanced electronic conduction and the NRR reaction kinetics simultaneously. The optimized In2O3−x/CeO2−y nanotube exhibits excellent NRR catalytic activity and durability, with an outstanding average yield of 26.1 μg h−1 mgcat−1 while the faradaic current efficiency of 16.1% at −0.3 V is ultrahigh versus the reversible hydrogen electrode. This study offers insights into designing excellent catalysts for the NRR through a combination of the nanotube structure and the adjustment of the VO strategy.

Without fabricating intermediate tunnel junctions or wafer bonding schemes for interconnecting the subcells, heterojunction bipolar transistor solar cells offer a promising new route in solar energy conversion. In this work, an improved theory for the three-terminal heterojunction bipolar transistor solar cell is presented with inclusion of non-ideal effects missing from the previous treatment, namely the non-radiative recombination and the thermal conduction losses that are inevitably present in realistic devices. Following detailed balance theory, the revised analytical formula for the cell conversion efficiency is derived, and the maximum efficiencies under different conditions are further calculated. Under the condition of 100 sun irradiance and 50% injection efficiency, a Gallium arsenide/Gallium antimonide-based solar cell operating at 465 K yields a maximum efficiency of 46.4%. Moreover, the effects of solar concentration, injection efficiency, and other key parameters on the cell performance are analyzed, and, consequently, optimal operating conditions and limiting factors on the conversion efficiency are determined. Simulation results show that such a solar cell operating with low injection efficiency under moderate concentration factor and low cell temperature can significantly boost its conversion performance. This work provides new physical insights for optimal designs, thus paving a route towards the development of low-cost high-performance solar cells.

Manganese-based compounds have emerged as attractive cathode materials for zinc-ion batteries owing to their high operating voltage, large specific capacity, and no pollution. However, the structural collapse and sluggish kinetics of manganese-based compounds are major obstacles that hinder their practical applications. Here, a kind of novel layered Ca

As a key part of the mechanical automation system, the gear coupling rotor system often occurs faults, and more than 60% of faults are caused by misalignment. In order to further explore the impact of misalignment on the dynamic performance of the rotor system and reduce the occurrence of faults. A signal processing method combining EEMD, median filter as well as FFT is introduced to denoise the original signal, and finite element model is built. A gear coupling-multi-span rotor system test platform is established and results of the finite element analysis is used to verify the experiment. Finally, the parallel misalignment of the gear coupling is simulated by adjusting the distribution of bearing seat gasket. The dynamic response results of the rotor system under different parallel misalignments and different speeds are studied and the impact of parallel misalignment on rotor system is obtained, which has guiding significance for reducing rotor faults.

We characterize finite-time thermodynamic processes of multidimensional quadratic overdamped systems. Analytic expressions are provided for heat, work, and dissipation for any evolution of the system covariance matrix. The Bures-Wasserstein metric between covariance matrices naturally emerges as the local quantifier of dissipation. General principles of how to apply these geometric tools to identify optimal protocols are discussed. Focusing on the relevant slow-driving limit, we show how these results can be used to analyze cases in which the experimental control over the system is partial., Comment: Comments are welcome!

We derive an analytical expression for maximum efficiency at fixed power of heat pumps operating along a finite-time reverse Carnot cycle under the low-dissipation assumption. The result is cumbersome, but it implies simple formulas for tight upper and lower bounds on the maximum efficiency and various analytically tractable approximations. In general, our results qualitatively agree with those obtained earlier for endoreversible heat pumps. In fact, we identify a special parameter regime when the performance of the low-dissipation and endoreversible devices is the same. At maximum power, heat pumps operate as work to heat converters with efficiency 1. Expressions for maximum efficiency at given power can be helpful in the identification of more practical operation regimes.

The aim of this study is to deeply search and understand the performance of the coupling system composed of an alkali metal thermoelectric converter and a thermoelectric generator. The main methods are to update the model of the coupling system, which includes the main irreversible losses existing in subsystems and coupling system, and obtain the analytical expressions of the power outputs and efficiencies of two subsystems and coupling system. The main novelties are to discuss the influences of the thickness of the β ″ -alumina solid electrolyte on the whole performance of the system and solve the matching problem between two subsystems. The main contents of this study include that the influences of the thickness of the electrolyte membrane, current density of the alkali metal thermoelectric converter, and electric current of the thermoelectric generator on the power output density and efficiency are discussed and the maximum power output density and efficiency of the system are calculated and compared with those of the single alkali metal thermoelectric converter and the existing coupling models. The results obtained reveal the advantages of the present model. The whole performance of the coupling system can be optimized and the parametric selection criteria of several key parameters of the coupling system operating at optimum states can be provided, When the thickness of the electrolyte membrane is optimally selected, the maximum efficiency of the present model attain 34.6% and increase about 10.4%, compared with those of the existing best coupling system. The waste heat released by the alkali metal thermoelectric converter can be efficiently utilized by the thermoelectric generator.

We analytically derive maximum efficiency at given cooling power for Carnot-type low-dissipation refrigerators. The corresponding optimal cycle duration depends on a single parameter, which is a specific combination of irreversibility parameters and bath temperatures. For a slight decrease in power with respect to its maximum value, the maximum efficiency exhibits an infinitely-fast nonlinear increase, which is standard in heat engines, only for a limited range of parameters. Otherwise, it increases only linearly with the slope given by ratio of irreversibility parameters. This behavior can be traced to the fact that maximum power is attained for vanishing duration of the hot isotherm. Due to the lengthiness of the full solution for the maximum efficiency, we discuss and demonstrate these results using simple approximations valid for parameters yielding the two different qualitative behaviors. We also discuss relation of our findings to those obtained for minimally nonlinear irreversible refrigerators., Comment: 10 pages, 4 figures, updated references

A new model of the intermediate band thermoradiative cell (IBTRC) is put forward. Expressions for the power output density (POD) and efficiency of the IBTRC are derived. The current densities and PODs arising from the normal transitions and interband transitions of electrons are compared. It is found that when the IBTRC with a bandgap of 0.2 eV is operated between the heat source at 1000 K and the surroundings at 300 K, the maximum POD and efficiency of the cell are approximately $1.583\times $ and $1.096\times $ of those of the thermoradiative cell without intermediate bands (IBs) under the same operating temperature and bandgap, respectively. This shows that the performance of the IBTRC can be largely improved by the insert of the IB. Moreover, the optimal selection criteria of some key parameters are provided, and then the optimum operating conditions of the IBTRC are determined. Finally, several issues that will influence the performances of the IBTRC are pointed out. These results may help engineers to fabricate high-performance IBTRCs.

A coupling system composed of a high temperature fuel cell such as a molten carbonate fuel cell (MCFC), a regenerator, and a thermoradiative cell (TRC) is established. The efficiency and power output of the coupling system are analytically derived. The performances of the system are evaluated. The optimum operation states of the system are determined. The optimal selection criteria of some key parameters are provided. It is found that when the MCFC is operated at the temperature of 923 K and the band gap of the TRC equals 0.2 eV, the maximum power output density (MPOD) of the coupling system is approximately 2.020 times of that of a single MCFC and the corresponding efficiency of the coupling system is approximately 1.304 times of that of the MCFC. The percentage improvements of the MPODs of the coupling system and other MCFC-based coupling systems in the existing literatures are compared. The results show that the MCFC-TRC coupling system can exhibit better performance and make use of the waste heat released by the MCFC more effectively in comparison with other MCFC-based coupling systems. Moreover, it is expounded that the TRC is an efficient device which can recycle and utilize the waste heat produced by other high temperature fuel cells such as solid oxide fuel cells and direct carbon fuel cells.

A thermionic-thermoradiative converter (TITRC) is established by combining the concepts of the thermionic emission and thermoluminescence, where the main irreversible losses are considered. The TITRC utilizes simultaneously electron and photon fluxes and converts directly a part of them into electricity, which enables a significant enhancement on the heat transfer and performance of the TITRC. Compared with either the thermionic energy generator or the thermoradiative device, the TITRC possesses advantages of higher power output and conversion efficiency in an extended temperature range. When the emitter in the TITRC is operated at 1500 K and Ag-O-Cs is used as the collector, the maximum power density and efficiency of the proposed TITRC can reach up to 0.301 Wcm $^{-2}$ and 22.5%, respectively. This letter can benefit the optimal design of the TITRC, and shed light on developing the ongoing research of the alternative energy harvesting devices.

The cycle model of an alkali metal thermal electric converter (AMTEC) is updated, where the relation between the thickness of the electrolyte and the other parameters of the AMTEC is established. The effects of thickness of the electrolyte on the performance of the AMTEC are discussed. The operation states of the AMTEC are optimized. The maximum efficiency and power output density of the AMTEC are calculated. The selective criteria of the thickness of the electrolyte and other parameters are optimally provided. Moreover, it is expounded that the proportional coefficient related to the thickness of the electrolyte is closely dependent on electrolyte materials. The effects of this coefficient on the efficiency and power output density of the AMTEC are further discussed, and consequently, the rational range of the coefficient is determined.

A new model of the energy selective electron (ESE) device composed of four electron reservoirs and four energy filters is proposed. The device can work as a thermal amplifier, which may be equivalent to a coupling system consisting of two three-electron-reservoir heat pumps. Expressions for the heat-pumping rate (HPR) and coefficient of performance (COP) of the device are analytically derived through the heat flows of two-terminal ESE devices. The maximum HPR and COP are calculated. It is found that the maximum HPR of the coupling system can attain 2 times of that of a three-electron-reservoir heat pump while its COP is still equal to that of a three-electron-reservoir heat pump. Moreover, the effects of the chemical potentials of electron reservoirs, central levels of energy filters, half width at half maximum of energy filters on the HPR and COP of the device are discussed in detail. The optimal configuration of the device is determined. The cut-off value of the half width at half maximum of energy filters is calculated. The optimum selection criteria of main parameters are provided.

Aqueous zinc-ion batteries are a low-cost and safe energy storage system, but suffer from detrimental side reactions and Zn dendrites due to the strong interactions between Zn2+ and water molecules in the electrolytes, and random Zn2+ deposition on the anode surface. Here, an electrolyte involving a dual-functional additive of polyethylene glycol (PEG) to bypass these issues is reported. The electrolyte can not only tailor the solvation sheath of Zn2+ but also enable favorably oriented deposition of Zn2+ on the anode surface. The dendrite-free Zn anode in Zn//Zn cells is obtained with high Columbic efficiency (98.8%) and long cycling lifespan (1500 h), six times longer than that of electrolyte without PEG at 0.25 mA cm-2 . What is more, the excellent cycling stability of the prepared batteries (Zn//V2 O5 ·1.6 H2 O) suggests that the developed tailoring strategy may propel a promising pathway for stabilizing Zn metal anodes.

The conceptual designs of two nanoscale spin-Seebeck temperature sensors are proposed based on the longitudinal spin-Seebeck effect (LSSE) in bilayers made of a ferromagnetic insulator Y3Fe5O12 and a Pt, and the transverse spin-Seebeck effect) in Ni81Fe19/Pt structure. The working principles of two sensors are presented. The direct conversion of the temperature information into the electric voltage is described in detail. Moreover, the effect of the spin Hall angle on the performance of sensors is discussed. The results obtained here reveal that the LSSE and TSSE have the potential to realize practical temperature sensors.

We consider absorption refrigerators consisting of simultaneously operating Carnot-type heat engine and refrigerator. Their maximum efficiency at given power (MEGP) is given by the product of MEGPs for the internal engine and refrigerator. The only subtlety of the derivation lies in the fact that the maximum cooling power of the absorption refrigerator is not limited just by the maximum power of the internal refrigerator, but, due to the first law, also by that of the internal engine. As a specific example, we consider the simultaneous absorption refrigerators composed of low-dissipation (LD) heat engines and refrigerators, for which the expressions for MEGPs are known. The derived expression for maximum efficiency implies bounds on the MEGP of LD absorption refrigerators. It also implies that a slight decrease in power of the absorption refrigerator from its maximum value results in a large nonlinear increase in efficiency, observed in heat engines, whenever the ratio of maximum powers of the internal engine and the refrigerator does not diverge. Otherwise, the increase in efficiency is linear as observed in LD refrigerators. Thus, in all practical situations, the efficiency of LD absorption refrigerators significantly increases when their cooling power is slightly decreased from its maximum.

A model of the graphene-based thermionic solar cell (TSC) consisting of a concentrator, an absorber, and a thermionic emission device configured with graphene-based cathode is proposed, where the radiation and reflection losses from the absorber to the environment, the thermal radiation between the cathode and the anode electrodes, and the heat losses from the anode to the environment are considered. The performance characteristics of the TSC are analyzed by numerical calculations. It is found that the maximum efficiency can reach 21% when the area ratio is 0.24 and the voltage output is 2.01 V. In addition, the maximum efficiencies of the TSC under different concentrations and the optimal values of some key parameters are determined, and consequently, the corresponding optimally operating conditions are obtained. The results obtained here may provide guidance for the appropriate selection of electrode materials and the optimum design of practical TSC devices.

Organic materials typically present low rate performance and limited cycling durability due to the structural destruction and dissolution during electrochemical processes, which greatly hinders their application as promising cathodes for aqueous rechargeable zinc-ion batteries (ZIBs). Here, a strategy of in situ electrochemical oxidation with π-π interaction coupling between graphene and 2,3,6,7,10,11-Hexahydroxytriphenylene (HHTP) stabilizes the composite structure, rendering it a very promising organic composite cathode (named as GH) for ZIBs. More explicitly, the hydroxyl groups of HHTP are in-situ electrochemically transformed into carbonyl groups to form the redox-active sites, in which π-π interactions with graphene urges the highly reversible coordination/incoordination between zinc ions and the GH cathode. Further, such a GH cathode shows a specific capacity of 225 mAh g−1 at 0.05 A g−1 with a high capacity retention of 90% at 10 A g−1 after 7000 cycles, demonstrating high rate and cycle stability are achieved during the discharge/charge process. Thereby, this work provides a novel strategy for engineering an organic composite cathode which corrects the low rate and unstable cycling property for effective use in ZIBs.

We propose a quantum-mechanical Brayton engine model that works between two superposed states, employing a single particle confined in an arbitrary power-law trap as the working substance. Applying the superposition principle, we obtain the explicit expressions of the power and efficiency, and find that the efficiency at maximum power is bounded from above by the function: η+ = θ/(θ + 1), with θ being a potential-dependent exponent.

We propose and theoretically investigate a system of two coupled harmonic oscillators as a heat engine. We show how these two coupled oscillators within undamped regime can be controlled to realize an Otto cycle that consists of two adiabatic and two isochoric processes. During the two isochores the harmonic system is embedded in two heat reservoirs at constant temperatures T(h) and T(c)(

We propose a quantum absorption refrigerator driven by photons. The model uses a four-level system as its working substance and couples simultaneously to hot, cold, and solar heat reservoirs. Explicit expressions for the cooling power ${\stackrel{\ifmmode \dot{}\else \.{}\fi{}}{Q}}_{c}$ and coefficient of performance (COP) ${\ensuremath{\eta}}_{\text{COP}}$ are derived, with the purpose of revealing and optimizing the performance of the device. Our model runs most efficiently under the tight coupling condition, and it is consistent with the third law of thermodynamics in the limit $T\ensuremath{\rightarrow}0$.