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Employing high-rate ion-intercalation electrodes represents a feasible way to mitigate the inherent trade-off between energy density and power density for electrochemical energy storage devices, but efficient approaches to boost the charge-storage kinetics of electrodes are still needed. Here, we demonstrate a water-incorporation strategy to expand the interlayer gap of α-MoO 3 , in which water molecules take the place of lattice oxygen of α-MoO 3 . Accordingly, the modified α-MoO 3 electrode exhibits theoretical-value-close specific capacity (963 C g −1 at 0.1 mV s −1 ), greatly improved rate capability (from 4.4% to 40.2% at 100 mV s −1 ) and boosted cycling stability (from 21 to 71% over 600 cycles). A fast-kinetics dual-ion-intercalation energy storage device is further assembled by combining the modified α-MoO 3 anode with an anion-intercalation graphite cathode, operating well over a wide discharge rate range. Our study sheds light on a promising design strategy of layered materials for high-kinetics charge storage. The power/energy trade-off is a common feature seen in a Ragone plot for an electrochemical storage device. Here the authors approach this issue by showing water-incorporated α-MoO 3 anodes with expanded interlayer gaps, which allow for the assembling of dual-ion energy storage devices.

In the present study, a topology optimization method of thermal-fluid-structural problems is researched to design the three-dimensional heat sink with load-carrying capability. The optimization is formulated as a mean temperature minimization problem controlled by Navier-Stokes (N-S) equations as well as energy balance and linear elasticity equations. In order to prevent an unrealistic and low load-carrying design, the power dissipation of the fluid device and the normal displacement on the load-carrying surface are taken as constraints. A parallel solver of multi-physics topology optimization problems is built-in Open Field Operation And Manipulation (OpenFOAM) software. The continuous adjoint method is adopted for the sensitivity analysis to make the best use of built-in solvers. With the developed tool, the three-dimensional (3D) thermal-fluid topology optimization is studied. It is found that the Darcy number, which is suitable for fluid design, may cause severe problems in thermal-fluid optimization. The structural features of 3D thermal-fluid-structural problems are also investigated. The “2D extruded designs” are helpful to improve the structural stiffness, and channels with a larger aspect ratio in high-temperature areas improve the cooling performance.

The moving morphable components (MMC)-based approach has advantages in describing geometry explicitly, feature size controlling, etc., and it has been successfully used for the topology design of bearing structures. In this work, the MMC-based approach is extended to thermal-fluid design which is formulated as a heat transfer maximization and fluid power dissipation minimization problem controlled by Navier–Stokes (N–S) and energy balance equations. Aiming at describing the geometry of bend pipes which usually have a larger curvature than the bearing structures, a cubic order component with elliptic joints is proposed. In order to limit the minimum width of pipes according to the manufacturing capacity, a feature size control technique is developed. The algorithm is investigated on a two-dimensional numerical model by comparing with density-based method and MMC approach with quadratic components. In our tests, besides the advantage of feather size controlling, the developed MMC also achieves lower objective values than the other two methods.

MXenes are emerging layered materials that are promising for electrochemical energy storage and (opto-)electronic applications. A fundamental understanding of charge transport in MXenes is essential for such applications, but has remained under debate. While theoretical studies pointed to efficient band transport, device measurements have revealed thermally activated, hopping-type transport. Here we present a unifying picture of charge transport in two model MXenes by combining ultrafast terahertz and static electrical transport measurements to distinguish the short- and long-range transport characteristics. We find that band-like transport dominates short-range, intra-flake charge conduction in MXenes, whereas long-range, inter-flake transport occurs through thermally activated hopping, and limits charge percolation across the MXene flakes. Our analysis of the intra-flake charge carrier scattering rate shows that it is dominated by scattering from longitudinal optical phonons with a small coupling constant ( α  ≈ 1), for both semiconducting and metallic MXenes. This indicates the formation of large polarons in MXenes. Our work therefore provides insight into the polaronic nature of free charges in MXenes, and unveils intra- and inter-flake transport mechanisms in the MXene materials, which are relevant for both fundamental studies and applications. The charge transport mechanism in MXenes—an emerging class of layered materials—is not yet fully understood. A combination of terahertz spectroscopy and transport measurements shows that the formation of large polarons play a crucial role.

The innovation in thermal storage systems for solar thermal power generation is crucial for achieving efficient utilization of new energy sources. Molten salt has been extensively studied as a phase change material (PCM) for latent heat thermal energy storage systems. In this study, a two-dimensional model of a vertical shell-and-tube heat exchanger is developed, utilizing water-steam as the heat transfer fluid (HTF) and phase change material for heat transfer analysis. Through numerical simulations, we explore the interplay between PCM solidification and HTF boiling. The transient results show that tube length affects water boiling duration and PCM solidification thickness. Higher heat transfer fluid flow rates lower solidified PCM temperatures, while lower heat transfer fluid inlet temperatures delay boiling and shorten durations, forming thicker PCM solidification layers. Adding fins to the tube wall boosts heat transfer efficiency by increasing contact area with the phase change material. This extension of boiling time facilitates greater PCM solidification, although it may not always optimize the alignment of bundles within the thermal energy storage system.

The liquid-cooled heat sink is an effective and robust cooling device and has been widely used in the industry. The fluid-thermal topology optimization approaches have been adopted for the heat sink design by many researchers. However, none of these works considered the optimization of heat source distribution. This work focuses on the synergic design of the cooling channels and the layout of heat sources with diverse intensities. A hybrid topology optimization approach is adopted, in which the channels are implicitly described with pseudo-density while the heat sources are considered as moving components. The maximum temperature of the system is taken as the objective and constrained by the fluid power dissipation. In order to avoid unrealistic designs such as suspended structures, the stiffness of the structure is considered as a constraint. Considering when heat sources have diverse intensities, the initial locations of the heat sources could significantly affect the optimal result. Aiming at this problem, a heuristic algorithm that can redistribute the heat sources efficiently during the optimization process by exchanging their locations is developed. The topology optimization is performed with a parallel solver developed in Open Field Operation And Manipulation (OpenFOAM) framework. The numerical tests show that the influence of the heat source distribution on the cooling performance could be even higher than the cooling channel design, and the synergic topology optimization method is an effective way to design high-performance heat sink.

The pressing demand for sustainable energy storage solutions has spurred the burgeoning development of aqueous zinc batteries. However, kinetics-sluggish Zn 2+ as the dominant charge carriers in cathodes leads to suboptimal charge-storage capacity and durability of aqueous zinc batteries. Here, we discover that an ultrathin two-dimensional polyimine membrane, featured by dual ion-transport nanochannels and rich proton-conduction groups, facilitates rapid and selective proton passing. Subsequently, a distinctive electrochemistry transition shifting from sluggish Zn 2+ -dominated to fast-kinetics H + -dominated Faradic reactions is achieved for high-mass-loading cathodes by using the polyimine membrane as an interfacial coating. Notably, the NaV 3 O 8 ·1.5H 2 O cathode (10 mg cm −2 ) with this interfacial coating exhibits an ultrahigh areal capacity of 4.5 mAh cm −2 and a state-of-the-art energy density of 33.8 Wh m −2 , along with apparently enhanced cycling stability. Additionally, we showcase the applicability of the interfacial proton-selective coating to different cathodes and aqueous electrolytes, validating its universality for developing reliable aqueous batteries. Sluggish Zn 2+ -dominated Faradic reactions lead to suboptimal charge-storage capacity and durability of aqueous zinc battery cathodes. Here, the authors present a proton-selective interfacial coating strategy that enables high-performance cathodes with fast-kinetics proton-dominated Faradic reactions.

The anion-intercalation chemistries of graphite have the potential to construct batteries with promising energy and power breakthroughs. Here, we report the use of an ultrathin, positively charged two-dimensional poly(pyridinium salt) membrane (C2DP) as the graphite electrode skin to overcome the critical durability problem. Large-area C2DP enables the conformal coating on the graphite electrode, remarkably alleviating the electrolyte. Meanwhile, the dense face-on oriented single crystals with ultrathin thickness and cationic backbones allow C2DP with high anion-transport capability and selectivity. Such desirable anion-transport properties of C2DP prevent the cation/solvent co-intercalation into the graphite electrode and suppress the consequent structure collapse. An impressive PF 6 − -intercalation durability is demonstrated for the C2DP-covered graphite electrode, with capacity retention of 92.8% after 1000 cycles at 1 C and Coulombic efficiencies of > 99%. The feasibility of constructing artificial ion-regulating electrode skins with precisely customized two-dimensional polymers offers viable means to promote problematic battery chemistries. The application of graphite as anodes for anion-intercalation chemistry-based batteries suffers from durability issues. Here authors demonstrate that a positively charged two-dimensional poly(pyridinium salt) membrane can work as the artificial skin of the graphite electrode to enable long-term cycling stability.

This paper proposes an integrated two-step strategy for an optimal design of liquid-cooled channel layout based on the moving morphable component (MMC)-density approach. The proposed strategy intends to take the advantage of both the MMC approach for its high flexibility in searching a physically reasonable layout and the density approach for its better capacity of topology description. On the basis of the above-mentioned strategy, an intermediate layout is obtained through MMC approach and further optimized as initial solution of density approach step. Through density approach step, the final layout shows smoother boundary while retaining reasonable feature size. The original contributions of this paper are as follows: (i) An assembled quadratic Bézier curves component is proposed to describe the largely curved channel with limited numbers of optimization variables and computation order. (ii) Benefited from explicit geometric description, adaptive mesh refinement (AMR) is applied in MMC approach step for the first time. The application of AMR, from the numerical point of view, has two key ingredients to be highlighted: (i) the accuracy of solution in fluid–solid boundary region can be ensured with relatively limited computational cost. (ii) The contradiction that the difference step of MMC updating needs to be both as small as possible and integer multiple of the mesh size can be avoided. The performance of our methodology is demonstrated by numerical examples aiming for maximal heat exchange with power dissipation constraint. The main finding reveals that the proposed strategy can offer reasonable channel layout with better thermal performance, compared with conventional density approach. The whole numerical implementation relies on OpenFOAM and PETSc open-source software packages.

Aluminium-based aqueous batteries hold promises for next-generation sustainable and large-scale energy storage due to the favorable metrics of Al and water-based electrolytes. However, the performance of current aluminium-based aqueous batteries falls significantly below theoretical expectations, with a critical bottleneck of realizing cathodes with high areal capacities. Herein, we present a hydrate-melt electrolyte design utilizing cost-effective AlCl 3 and organic halide salts, which enables the demonstration of aqueous Al-Br batteries with enhanced energy-power characteristics. The optimal electrolyte features suppressed water activity and loosely bound halogen anions, attributed to its unique electrolyte structure, where the majority of water molecules engage in robust ion solvation (>98% as suggested by simulations) and halogen anions reside in the outer solvation sheath of cations. These distinctive features ensure good compatibility of the electrolyte with the reversible Br − /Br 0 /Br + conversion, enabling cathodes with a high areal capacity of 5 mAh cm −2 . Besides, the electrolyte allows for Zn-Al alloying/de-alloying with minimal polarization (around 100 mV at 5 mA cm −2 ) and a smooth alloy surface. The assembled Al-Br cell delivers an energy density (267 Wh L −1 , based on the volume of anode, cathode and separator) comparable to commercial Li-ion batteries and a substantial power density (1069 W L −1 ) approaching electrochemical capacitors. Achieving cathodes with large areal capacities is crucial for advancing aqueous aluminum-based batteries. Here, authors report a hydrate-melt electrolyte based on AlCl 3 and organic halide salts that enables reversible Br − /Br 0 /Br + chemistry with a high areal capacity of 5 mAh cm −2 .