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Acidic tin–iron flow batteries (TIFBs) employing Sn/Sn2+ and Fe2+/Fe3+ as active materials are regarded as promising energy storage devices due to their superior low capital cost, long lifecycle, and high system reliability. In this paper, the performance of TIFBs is thoroughly investigated via a proposed dynamic model. Moreover, their design and operational parameters are comprehensively analyzed. The simulation results show that (i) a flow factor of two is favorable for practical TIFBs; (ii) about 20% of the system's efficiency is decreased as the current density increases from 40 mA cm−2 to 200 mA cm−2; (iii) the optimal electrode thickness and electrode aspect ratio are 6 mm and 1:1, respectively; and (iv) reducing the compression ratio and increasing porosity are effective ways of lowering pump loss. Such in-depth analysis can not only provide a cost-effective method for optimizing and predicting the behaviors and performance of TIFBs but can also be of great benefit to the design, management, and manufacture of tin–iron flow batteries. [ABSTRACT FROM AUTHOR]

Lithium, with its high theoretical capacity and low potential, has been widely investigated as the anode in energy storage/conversion devices. However, their commercial applications always suffer from undesired dendrite growth, which forms in the charging process and may puncture the separator, leading to short cycle lives and even security problems. Herein, by an in situ displacement reaction using SnF2 at room temperature, we constructed an artificial solid electrolyte interface (ASEI) of LiF/Li–Sn outside the Li anode. This hybrid strategy can induce a synergy between the high Li+ conductivity of the Li–Sn alloy and good electrical insulation of LiF. Moreover, extreme synergy can be achieved by moderating the thickness of the LiF/Li–Sn ASEI, guiding dendrite-free lithium plating and stripping. As a result, a Li//LiFePO4 battery that is assembled from the LiF/Li–Sn ASEI-engineered Li anode can obtain 1000 cycled lives with 86.3% capacity retention under a charge/discharge rate of 5 C. This work provides an alternative way to construct dendrite-free lithium metal anodes, which significantly benefit the cycle lives of LMBs. [ABSTRACT FROM AUTHOR]

Designing low-cost, highly active and stable electrocatalysts is important to various renewable energy storage and conversion devices. We fabricated a NiMoN nanosheet hybrid catalyst through a reduction reaction of NiMoO4 nanosphere and urea under high-temperature annealing. The effects of annealing temperature on the surface chemical compositions of the catalyst were investigated, and it was found that the relative contents of various N-type species, Ni and Mo changed with the temperature. The relative contents of metal–N, metallic Ni, Mo3+ and Mo4+cations were increasing with the temperature increment, and significantly improved the activity of electrocatalytic water splitting. To drive a current density of 10 mA cm−2, the bimetallic NiMoN requires an overpotential of 202 mV and 191 mV for the OER and HER, respectively. The two-electrode system using the NiMoN needs a very low cell potential of 1.58 V to reach a current density of 10 mA cm−2. The catalyst also shows high durability in the case of 40 hours, while the overpotential is only slightly attenuated. The superior activity and long-term stability demonstrate that the NiMoN catalyst has promising potential for application in large-scale water splitting. [ABSTRACT FROM AUTHOR]

Lithium‐sulfur (Li−S) battery is considered as a promising energy storage system because of its high theoretical energy density of 2600 Wh kg−1, whose practical performance is limited by the sluggish sulfur redox kinetics. Homogeneous redox mediators (RMs) are effective promotors to propel the sulfur redox kinetics. However, most of the RMs only focus on a single reaction process. Herein, a strategy of mixed redox mediators (mixed‐RM) is proposed for full‐range redox mediation on the sulfur redox kinetics in working Li−S batteries. Concretely, one of the mixed‐RM mainly mediates the liquid‐solid reduction from polysulfides (LiPSs) to Li2S during discharge, while the other aims to promote the solid‐liquid conversion from Li2S to LiPSs and the liquid‐solid conversion from LiPSs to S8 during charge. Consequently, 2.5 Ah Li−S pouch cells with the mixed‐RM achieve an actual initial energy density of 354 Wh kg−1 alongside stable 20 cycles. This work provides an effective strategy on promoting the sulfur redox kinetics for high‐energy‐density Li−S batteries and inspires rational combination of novel functional molecules for practical energy storage systems. [ABSTRACT FROM AUTHOR]

Designing low-cost, highly active and stable electrocatalysts is very important for various renewable energy storage and conversion devices. We fabricated a hierarchically porous Ni–Fe–S hollow hierarchical sphere through a solvothermal reaction of Ni2+, Fe3+ with a mixed solution of glycerol and isopropanol and a S2− ion-exchange process. The incorporation of hybrid metal atoms significantly improved the oxygen evolution reaction (OER) activity of the hollow hierarchical sphere. Typically, the Ni–Fe–S hollow hierarchical sphere exhibits superior OER and HER activities to the single-phase Ni–S and Fe–S hollow hierarchical spheres, as well as most of the bifunctional electrocatalysts when catalyzing full water splitting. To drive a current density of 10 mA cm−2, the Ni–Fe–S hollow hierarchical sphere requires an overpotential of only 223 and 115 mV for the OER and HER, respectively. Furthermore, the Ni–Fe–S hollow hierarchical sphere catalyst shows excellent durability after a long-term test. The superior activity and long-term stability demonstrate that the Ni–Fe–S hollow hierarchical sphere catalyst has promising potential for application in large-scale water splitting. [ABSTRACT FROM AUTHOR]

CoSe 2 /CoO-CNTs catalyst was rationally designed as separator modifier for Li-S battery to selectively catalyze the sulfur species conversion via Mott-Schottky effect. [Display omitted] • CoSe 2 /CoO Mott-Schottky catalyst has been rationally designed and blended with CNTs for using as a separator modifier in Li-S battery. • CoSe 2 /CoO-CNTs synergistically utilizes the high electrocatalytic activity of CoSe 2 /CoO heterostructure and high conductivity of CNTs to selectively catalyze the sulfur species conversion via Mott-Schottky effect. • The Li-S battery with a CoSe 2 /CoO-CNTs modified separator displays a high initial discharge capacity of 1236 mAh/g at 0.5C and a low decay rate of 0.070% per cycle over 500 cycles at 2C. The lithium sulfur (Li-S) battery is an active research area in the field of energy storage systems, but the shuttle effect is a serious obstacle hindering its application. Herein, a CoSe 2 /CoO Mott-Schottky catalyst is blended with carbon nanotubes (CNTs) and subsequently coated onto a commercial separator as a modifier, whereby the synergy between the high electrocatalytic activity of the CoSe 2 /CoO heterostructure and high conductivity of the CNTs selectively mediate the conversion of sulfur species. As a result, a cell with a CoSe 2 /CoO-CNTs modified separator displays a high initial discharge capacity of 1573 and 910 mAh/g at 0.1 and 2C, respectively. Furthermore, a low decay rate of 0.070% per cycle can be obtained over 500 cycles at 2C. The results of this study suggest that the as-prepared CoSe 2 /CoO-CNTs is an effective modifier that can improve the performance of Li-S batteries for use in next-generation energy storage systems. This study provides fundamental insights into the rational design of Mott-Schottky catalysts for practical high-performance Li-S batteries. [ABSTRACT FROM AUTHOR]

MnO 2 has the highest potential as a supercapacitor electrode; however, its disadvantage in electronic conductivity hinders its widespread use. This study reports the excellent electrochemical performance of MnMC/NF (MnO 2 and ZIF-derived nanoporous carbon on nickel foam) composites. MnMC/NF composites are produced when leaf-like Co-ZIF is annealed on nickel foam, followed by potassium permanganate treatment. When the annealing temperature reaches 700 °C, the maximum specific capacitance of 531 F/g is achieved at 1 A/g (456 F/g at 20 A/g) with a rate capability of 85.5%. MnMC/NF700 has a long cyclic stability, and the capacitance retention was 82% after 5000 cycles. The energy density of an assembled device using MnMC/NF700 composite as positive electrodes can reach 38.8 Wh/kg. This is due to the combined effect of nickel substrate's 3D porous structure and the excellent electronic conductivity of ZIF-derived nanoporous carbon. The unique configuration of MnMC/NF composites may provide a referable design for energy storage systems, including materials that have the highest potential for use as supercapacitor electrodes. [ABSTRACT FROM AUTHOR]

The iron-vanadium flow batteries (IVFBs) employing V2+/V3+ and Fe2+/Fe3+ as active couples are regarded as promising large-scale energy storage technologies, benefited from their outstanding combination of system reliability, long cycling life and capital cost. In this paper, to thoroughly investigate the performance of IVFB system and accordingly optimize its design and operation, an in-depth analysis is conducted by the development of a stack-level dynamic model. A 10 kW stack composed of 60 single cells is engaged for simulation, and the results demonstrate that: i) the optimal system efficiency is obtained at the flow factor of two; ii) the premature cut-off and additional system efficiency loss can arise at high current densities; iii) electrodes with medium-sized thickness, long side and low height, proper porosity and compression ratio are favoured in practice; iv) adopting high flow rates to enhance thermal behaviors is undesirable; v) outstanding thermal behaviors is potentially realized for systems of long discharge duration and operated at appropriate current density in surroundings of proper temperature. Such in-depth investigations can not only be of great significance for the design, manufacture and management of IVFBs, but also provide a cost-effective way to predict and optimize the behavior and performance for large-scale IVFBs. • Stack-level dynamic model for iron-vanadium flow batteries is proposed. • A 10 kW stack consisting of 60 individual cells is engaged for simulation. • Optimal system efficiency is obtained at the flow factor of two. • Electrodes with medium-sized thickness, long side and low height are preferred. • IVFBs with long discharge duration tend to behave superior thermal behaviors. [ABSTRACT FROM AUTHOR]

Lithium-sulfur (Li–S) batteries have attracted increasing attention as one of the most promising candidates for next-generation energy storage systems. However, the shuttle effect of soluble intermediates, lithium polysulfides, results in a loss of active materials and sluggish redox kinetics, hampering the cyclability and rate capability of Li–S batteries. Here, we apply the commercial polypropylene separators modified with a 3D Ti 3 C 2 T x aerogel to resolve the issues in Li–S batteries. This special structure of the Ti 3 C 2 T x aerogel not only effectively avoids the restacking phenomenon of 2D Ti 3 C 2 T x materials to expose more active surface and anchor lithium polysulfides but also increases the reaction kinetics of high-order lithium polysulfides to low-order lithium polysulfides, due to the high conductivity of Ti 3 C 2 T x surfaces. Due to the high specific surface area and the 3D structure, the Li–S batteries with 3D Ti 3 C 2 T x aerogel-functionalized separators exhibit superior performances, including a high discharge capacity of 1487 mAh g−1 at 0.1 C, a long cycling stability, and a low decay rate of 0.037% per cycle at 1 C for 1500 cycles. • Ti 3 C 2 T x aerogel is applied to modify separators of Li–S batteries to improve active material utilization and cycle stability. • Ti 3 C 2 T x aerogel reduces the restacking phenomenon of 2D Ti 3 C 2 T x nanosheets to expose more absorption site for anchor LiPSs. • Ti 3 C 2 T x aerogel with high conductivity enhances the converting kinetics from high-order LiPSs to low-order LiPSs. • The Li–S batteries with Ti 3 C 2 T x aerogel modified separators suppress the shuttle effect and exhibit superior performance. [ABSTRACT FROM AUTHOR]