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One essential element of redox flow batteries (RFBs) is the flow field. Certain dead zones that cause local overpotentials and side effects are present in all conventional designs. To lessen the detrimental effects, a dead-zone-compensated design of flow field optimization is proposed. The proposed architecture allows for the detection of dead zones and their compensation on existing flow fields. Higher reactant concentrations and uniformity factors can be revealed in the 3D multiphysical simulation. The experiments also demonstrate that at an energy efficiency (EE) of 80%, the maximum current density of the novel flow field is 205 mA cm-2, which is much higher than the values for the previous ones (165 mA cm-2) and typical serpentine flow field (153 mA cm-2). Extensions of the design have successfully increased system EE (2.7 to 4.3%) for a variety of flow patterns. As a result, the proposed design is demonstrated to be a general method to support the functionality and application of RFBs.

Lately, utilizing a novel electrically rechargeable liquid fuel (e-fuel), a fuel cell has been designed and fabricated, which is demonstrated to achieve a much better performance than alcoholic liquid fuel cells do. However, its current performance, which thus hampers its wide application, demands further improvement to meet up with industrial requirement. Therefore, to attain a better performance for this system, an in-depth understanding of the complex physical and chemical processes within this fuel cell is essential. To this end, in this work, a two-dimensional transient model has been developed to gain an extensive knowledge of a passive e-fuel cell and analyze the major factors limiting its performance. The effects of various structural parameters and operating conditions are studied to identify the underlying performance-limiting factors, where deficient mass transport is found to be one of the major causes. The increment of anode porosity and thickness are found to be effective methods of improving the cell performance. This study therefore provides insights on achieving further performance advancement of the fuel cell in the future. © 2023 The Author(s)

The application of micrometer-sized silicon (mSi) ischallengingdue to the severe volume change during cycling, resulting in seriouspulverization of the mSi and detachment of active materials from thecurrent collector and consequently causing a capacity loss. Here,a new LiPF6-compatible ether electrolyte is developed toenhance the cycling performance of the mSi anode. Ethylene glycoldibutyl ether (EGDE) with large steric hindrance renders PF6 (-)-rich solvation complexes in the electrolyte,which are favorable for rapidly passivating the mSi anode surfaceand forming a LiF-rich, thin, and stratified solid electrolyte interphase(SEI). As a result, the mSi anode displays a high capacity retentionof 1901 mAh g(-1) after 500 cycles and a high CE of99.92% in a medium-concentration EGDE-LiPF6-based electrolyte.This work provides an effective strategy for extending the cyclinglife of the mSi anode by designing a new LiPF6-ether electrolytesystem.

Designing flow fields that can uniformly distribute electrolytes while maintain a low pumping work is challenging for high-performance redox flow batteries, especially for scaled-up battery stacks. In this work, we propose a bifurcate interdigitated flow field, which hierarchically splits the electrolyte and transports it into branch channels, thereby lowering the pumping loss and enhancing the uniformity of electrolyte distribution. The application of the flow field to a vanadium redox flow battery reduces the pressure drop by 45%, thereby increasing the pump-based voltage efficiency from 69.95% to 73.10% compared to that with conventional interdigitated flow field at a flow rate of 2.4 mL min−1 cm−2 and current density of 250 mA cm−2. Furthermore, three-dimensional modeling reveals that the superiority of reducing the pumping loss becomes more extraordinary with the enlargement of active area, indicating that the bifurcate interdigitated flow field shows great potential for the scale-up of high-performance flow batteries with a low pumping work.

Designing flow fields that can lead to uniform distributions of reactants at a minimum pump work is critical to enhancing the performance of redox flow batteries. This paper reports on an improved design of conventional serpentine flow fields, in which the channel depth is linearly reduced from the inlet to the outlet, speeding up the flow speed along the flow path and enhancing the under-rid convection downstream toward the outlet. Three-dimensional numerical simulations reveal that the optimized gradient at 25% (the channel-depth ratio between the outlet and inlet) can lead to the highest pump-based voltage efficiency. Experimental validations demonstrate that the application of the optimized flow field to a vanadium redox flow battery leads to significant improvements in both energy efficiency and electrolyte utilization, which is 5.0% and 27.7%, respectively, higher than that with the conventional serpentine flow field at a relatively high current density and low flow rate (400 mA cm−2, 12 mL min−1 cm−2). The effectiveness of the flow field design in boosting the uniform reactant distribution provides a feasible approach for scaling up high-performance redox flow batteries. © 2023 Elsevier B.V.

The operating temperature of vanadium redox flow batteries (VRFBs) affects their performance and reliability. However, previous studies focused on evaluating the effects on the performance of lab-scale single cells, in which electrolyte flow rates and current densities are different from those in stack-scale VRFBs, leading to the lack of guidance for the design of stacks. In this work, we investigate thermal effects on the performance of stack-scale VRFBs. It is found that as the operating temperature increases from 25 to 50 °C, the discharge capacity increases by 42%, whereas the energy efficiency increases by 10%, implying that the temperature has greater effects on the discharge capacity than that on the energy efficiency. Additionally, the enhancement effect of temperature on the energy efficiency is gradually weakened with increasing flow rate, while that on the discharge capacity is almost unchanged. Furthermore, the enhancement effect of temperature on energy efficiency increases with the operating current density. Notably, an optimum operating condition of the stack-scale VRFBs is identified with a critical flow rate (2.88 ml min−1 cm−2) at 40 °C to achieve a high system efficiency. This work provides guidance for the design of stack-scale VRFBs with high performance and safety. © 2023 The Electrochemical Society (“ECS”). Published on behalf of ECS by IOP Publishing Limited.

Nafion series membranes are widely used in vanadium redox flow batteries (VRFBs). However, the poor ion selectivity of the membranes to vanadium ions, especially for V2+, results in a rapid capacity decay during cycling. Although tremendous efforts have been made to improve the membrane's ion selectivity, increasing the ion selectivity without sacrificing the proton conductivity is still a challenging issue. In this work, instead of focusing on enhancing the membranes' ion selectivity, we develop an efficient valence regulation strategy to suppress the capacity decay caused by the crossover of V2+ in VRFBs. Despite the discharge capacity of the VRFB with the elevated average valence electrolytes (V3.68+) being slightly lower than that with commercial electrolytes (V3.50+) in the first 35 cycles, the accumulated discharge capacity in 400 cycles is improved by 52.33%. Moreover, this method is efficient, is easy to scale up, and provides deep insights into the capacity decay mechanism of VRFBs.

The promising features and capabilities of liquid fuel cells for power generation and further application in electric vehicles have drawn more research attention in recent times. Notably is the recently proposed and demonstrated fuel cell which employs an electrically rechargeable liquid fuel (e-fuel) along with a catalyst-free material at its anode. The smooth and successful functioning of the e-fuel cell generally requires the supply of oxidant at its cathode. However, the space and storage requirement with the use of pure oxygen as oxidant not only limits the energy density of the fuel cell, but as well results in higher cost. Herein, the operation and performance of this e-fuel cell is examined with the use of air as oxidant, in lieu of the commonly used pure oxygen, at the cell cathode. A peak power density of 168.3 mW cm−2 was obtained when the cathode is fed with air. Such performance when air is employed as oxidant in the e-fuel cell outperforms most conventional direct liquid fuel cells that are even fed with oxygen and thereby demonstrates the use of air as a promising alternative for future application. The performance of the cell when operated with air at various flow rates and operating temperatures, and during a constant current discharge test were also examined. This study therefore provides basis and useful insights for future investigations towards utilizing and catalyzing air as oxidant in the e-fuel cell for improved cell performance. © 2022 Elsevier Ltd

Efficient thermal management is crucial for ensuring the safety and performance of lithium-ion batteries powering electric vehicles. Here, we develop a passive battery thermal management system with thermally enhanced water adsorbents by evenly loading MIL-101(Cr) particles onto a copper foam. MIL-101(Cr) particles can absorb water from the ambient and release water at an elevated temperature to dissipate heat, while the copper foam acts as a thermal conductive network to transfer the heat among the particles. The cooling performance of the system is tested under various battery working conditions. Results show that the thermal conductivity of the composite water adsorbent is increased to 1.9 W m−1 K−1, nearly 10 times of the pure MIL-101(Cr). Compared with natural cooling, air cooling and solid–liquid phase change material cooling, the proposed passive cooling method reduces the battery temperature by 7.5, 2.6, and 2.1 °C, respectively, at 3 C discharge. Additionally, the battery temperature and the temperature difference are confined below 37.6 and 1.5 °C in the dynamic discharge–charge cycling test. All these encouraging results indicate that the developed passive thermal management system achieves high cooling capability, good temperature uniformity, and zero energy consumption, which possesses a broad application prospect in electric vehicles. © 2022 Elsevier Ltd

The addition of an oxygen evolution electrocatalyst to an anode catalyst layer is demonstrated as a practical approach to address the voltage reversal of proton exchange membrane fuel cells (PEMFCs). In this work, IrOXnanoparticles uniformly deposited on niobium-doped TiO2(IrOX/Nb0.1Ti0.9O2) by a sol-gel method are employed as reversal tolerant anodes (RTAs) for PEMFCs. The membrane electrode assembly (MEA) with this RTA possesses a reversal tolerance time of 29.1 min, which is the best result among all the as-prepared MEAs. Meanwhile, the decrease in the cell voltage of this MEA after reversal testing is only 61 mV at a current density of 1.2 A cm-2with a degradation rate of 11.1%. The improved reversal tolerance is attributed, in part, to the uniformly distributed IrOXnanoparticles, boosting the oxygen evolution reaction and, in part, to avoid the carbon oxidation reaction by the application of a noncarbon support. This result can lay a fundamental basis for the application of RTA based on a noncarbon support to improve the anode reversal tolerance for PEMFCs. © 2022 American Chemical Society. All rights reserved.

High-performance vanadium redox flow batteries (VRFBs) necessitate robust carbon electrodes, whose rational design demands quantitative relationships between the electrode properties and performance. Here, we decipher the exceptional kinetics of VO2+/VO2+ on a hierarchical nitrogen-doped carbon (HNC) electrode. Diffusion-less cyclic voltammetry, a method developed to evade the complex influence of diffusion in three-dimensional porosity, quantifies a rate constant of similar to 5 x 10(-7) cm s(-1) on the electrode, substantially higher than that of un-doped porous carbons, in line with the calculated adsorption energies of solvated vanadium cations. The hierarchy is further linked to the high specific area via a comparison with graphite felt with and without carbon nanotube-decoration. The HNC electrode enables a VRFB of an exceptional energy efficiency of 76.8% over 2000 cycles at 400 mA cm(-2), among the best reported. The work offers deep insights into the relationship of heteroatom doping, structural hierarchy, and kinetics for porous carbon electrodes for developing next-generation flow batteries.

The electrochemical performance of carbon nanofiber (CNF) electrodes in vanadium redox flow batteries (VRFBs) is enhanced by optimizing the morphological and physical properties of low-cost electrospun CNFs. The surface area, porosity and electrical conductivity of CNFs are tailored by modifying the precursor composition, especially the sacrificing agent, Fe(acac)3, in the polymer precursor and carbonization temperature. A highly porous structure with a large surface area is generated by the catalytic growth of graphitic carbon spheres surrounding the iron nanoparticles which are removed by an acid etching process. The graphitic carbon layers formed at a high carbonization temperature improve the electrical conductivity of CNFs. The large surface area of 349 m2 g−1 together with the abundant mesopore-dominant structure leads to high wettability and high activity for redox reactions of the electrode, giving rise to enhanced electrochemical performance in VRFBs. It delivers an energy efficiency (EE) of 91.4% at a current density of 20 mA cm−2 and 79.3% at 100 mA cm−2, and maintains an average EE of 72.5% after 500 charge/discharge cycles at 100 mA cm−2 © 2022 The Royal Society of Chemistry

The liquid fuel cell, with its high energy density and ease of fuel handling, has attracted great attention worldwide. However, its real application is still being greatly hindered by its limited power density. Hence, the recently proposed and demonstrated fuel cell, using an electrically rechargeable liquid fuel (e-fuel), is believed to be a candidate with great potential due to its significant performance advancement. Unlike the conventional alcoholic liquid fuels, the e-fuel possesses excellent reactivity, even on carbon-based materials, which therefore allows the e-fuel cell to achieve superior performance without any noble metal catalysts. However, it is found that, during the cell operation, the water generated at the cathode following the oxygen reduction reaction could lead to a water flooding problem and further limit the cell performance. To address this issue, in this work, by manipulating the cathode composition, a blended binder cathode using both Nafion and polytetrafluoroethylene as binding agents is fabricated and demonstrated its superiority in the fuel cell to achieve an enhanced water management and cell performance. Furthermore, using the developed cathode, a fuel cell stack is designed and fabricated to power a 3D-printed toy car, presenting this system as a promising device feasible for future study and real applications. © 2022 American Chemical Society. All rights reserved.

An efficient pack-level battery thermal management system is essential to ensure the safe driving experience of electric vehicles. In this work, we perform three-dimensional modeling of a liquid thermal management system for a real-world battery pack powering electrical vehicles. The effects of system structures, coolant flow direction layout, coolant flow rates, and inlet temperatures on the thermal performance are investigated. Under 2.0 C discharge, the system structure with interspersed cooling plates reduces the maximum temperature of the battery pack to 36.3 °C, which is 15% lower than that of the conventional design with bottom-mounted cooling plates. With the present system structure, around 62.2% of the heat produced by the batteries is dissipated. Moreover, the temperature difference is decreased by 10.5% with appropriately arranging coolant flow directions in different liquid cooling plates. In addition, increasing the coolant flow rate and lowering the inlet coolant temperature can greatly reduce the maximum battery temperature, while the latter parameter shows little influence on the pack temperature difference, which only changes 0.3 °C when the inlet temperature is decreased by 6 °C. This work provides valuable guidance for the development of pack-level liquid battery thermal management systems in electric vehicles.

Due to the much higher electronic conductivity of selenium (Se) than sulfur (S), selenium doping has shown as an effective strategy to enhance the electrochemical performance of the sulfur cathodes in lithium (Li) metal-sulfur batteries. As a result, the Se-doped S cathode (SexSy) has received increasing interest for next-generation battery systems with high energy density. Since the electrolytes play a critical role in determining the chemistries of both the cathode and the anode, this chapter mainly focuses on the fundamental insights of the SexSy athodes during charge/discharge in various liquid electrolytes and solid-state electrolytes. In addition, recent progress based on cathode structures design for Li-SexSy batteries and suggestions for future development are presented in this chapter. © 2022 Elsevier Inc. All rights reserved.

Polybenzimidazole (PBI)-based membranes are one of the most promising proton exchange membranes for vanadium redox flow batteries (VRFBs) due to their excellent ion selectivity. However, the relatively lower proton conductivity limits their application. Herein, a PBI membrane with both high proton conductivity and ion selectivity is prepared through a secondary phosphoric acid-doping method. The secondary-doped PBI membrane has a lower doping level in the surface layer while a higher doping level at the inner layer, forming a significant gradient-doped structure. In this structure, the former ensures an excellent ion selectivity while the latter enables a preferable proton conductivity. As a result, the VRFB with the secondary-doped PBI membrane exhibits an ultrahigh coulombic efficiency (CE) of 99.2% at the operating current density of 200 mA cm−2, which is significantly higher than that of the Nafion 212 membrane (97.7%), signifying an excellent ion selectivity. Meanwhile, the corresponding voltage efficiency (VE) is high up to 87.1%, which is also better than that of the Nafion 212 membrane (84.8%), indicating a high proton conductivity. Therefore, the secondary-doped PBI membrane might be a promising candidate for the highly efficient membrane for VRFB, and the secondary-doping method is simple and facile to realize engineering applications.

Given the high energy density and eco-friendly characteristics, lithium-carbon dioxide (Li-CO2) batteries have been considered to be a next-generation energy technology to promote carbon neutral and space exploration. However, Li-CO2 batteries suffer from sluggish reaction kinetics, causing large overpotential and poor energy efficiency. Here, we observe enhanced reaction kinetics in aprotic Li-CO2 batteries with unconventional phase 4H/face-centered cubic (fcc) iridium (Ir) nanostructures grown on gold template. Significantly, 4H/fcc Ir exhibits superior electrochemical performance over fcc Ir in facilitating the round-trip reaction kinetics of Li+-mediated CO2 reduction and evolution, achieving a low charge plateau below 3.61 V and high energy efficiency of 83.8%. Ex situ/in situ studies and theoretical calculations reveal that the boosted reaction kinetics arises from the highly reversible generation of amorphous/low-crystalline discharge products on 4H/fcc Ir via the Ir-O coupling. The demonstration of flexible Li-CO2 pouch cells with 4H/fcc Ir suggests the feasibility of using unconventional phase nanomaterials in practical scenarios.