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In this work, a density functional theory (DFT) based first-principles study is carried out to investigate the potential of phosphorene-like SiS and SiSe monolayers as anode materials for sodium-ion (Na-ion) batteries. Results show that both SiS and SiSe have large adsorption energies towards single Na atom of −0.94 and −0.43 eV, owing to the charge transfers from Na to SiS or SiSe. In addition, it is found that the highest Na concentration for both SiS and SiSe is x = 1 with the chemical formulas of NaSiS and NaSiSe, corresponding to the high theoretical specific capacities for Na storages of 445.6 and 250.4 mAh g−1, respectively. Moreover, Na diffusions are very fast and show strong directional behaviors on SiS and SiSe monolayers, with the energy barriers of only 0.135 and 0.158 eV, lower than those of conventional anode materials for Na-ion batteries such as Na2Ti3O7 (0.19 eV) and Na3Sb (0.21 eV). Finally, although SiS and SiSe show semiconducting behaviors, they transform to metallic states after adsorbing Na atoms, indicating enhanced electrical conductivity during battery cycling. Given these advantages, it is expected that both SiS and SiSe monolayers are promising anode materials for Na-ion batteries, and in principle, other Na-based batteries as well.

It is widely recognized that the oxygenated carbonaceous materials improve the performance of vanadium redox flow batteries (VRFBs). However, whether the enhanced vanadium redox reactions are due to the existence of grafted oxygen‐containing functional groups (OCFGs) or the enlarged specific surface areas (SSAs) during the course of surface treatments is still under dispute. To determine which factor is indeed responsible for the enhanced redox reactions, a set amount of OCFGs is intentionally grafted on the model carbon electrode without modifying the surface area using an alkaline‐mediated hydrothermal treatment. Experimental results, using the peak potential separation and the activation energy as electroactivity descriptors in the three‐electrode cell, demonstrate that OCFGs promote the V(II)/V(III) redox reaction, while exhibiting a minute catalytic effect on the V(IV)/V(V) redox reaction. The superior electroactivity is also testified by a flow battery test, in which the energy efficiency as well as the charge/discharge capacity of VRFBs with hydrothermally treated samples is significantly higher than those of VRFBs with the pristine one. Through these experiments, it is verified that OCFGs contribute to the electroactivity promotion for carbon electrodes rather than the enhanced SSA. The findings can guide the effort to design high‐performing carbonaceous electrodes for VRFBs.

In this work, we conceived and fabricated a three-electrode electrochemical cell and transparent vanadium redox flow battery to in-situ investigate the hydrogen evolution reaction during battery operation. Experimental results show that operating temperature has a strong influence on the HER rate. In particular, compared with V3+ reduction reaction, HER is more sensitive to temperature variation. It is also found that, contrary to the conventional wisdom that side reactions occur at the late stage of the charge process, H2 evolves at a relatively low SOC. About 0.26 and 1.94 mL H2 were collected at an early (SOC lower than 20%) and end of the charge process, respectively, suggesting that attention to the hydrogen formation at the negative electrode in the early charge process should also be paid to during long-term battery operations. Moreover, the produced hydrogen gas at the negative side prefers to form macroscopically observable bubbles onto the electrode surface, covering the active sites for vanadium redox reactions, while oxygen evolution (including CO2 production) at the positive side corrodes electrode surface and introduces certain oxygen-containing functional groups. © 2017

Alkaline direct ethanol fuel cells (DEFC), which convert the chemical energy stored in ethanol directly into electricity, are one of the most promising energy-conversion devices for portable, mobile and stationary power applications, primarily because this type of fuel cell runs on a carbon-neutral, sustainable fuel and the electrocatalytic and membrane materials that constitute the cell are relatively inexpensive. As a result, the alkaline DEFC technology has undergone a rapid progress over the last decade. This article provides a comprehensive review of transport phenomena of various species in this fuel cell system. The past investigations into how the design and structural parameters of membrane electrode assemblies and the operating parameters affect the fuel cell performance are discussed. In addition, future perspectives and challenges with regard to transport phenomena in this fuel cell system are also highlighted. (C) 2016 Elsevier B.V. All rights reserved.

We assess the performance of the combined Open Accelerator (OpenACC) programming standard and graphics processing unit (GPU) accelerator for lattice Boltzmann (LB) simulations of fluid flow, heat and mass transfer. By optimizing the data layout, minimizing the memory access frequency, and adjusting the number of gangs and vector length, we show that the enhanced parallel computations can result in orders of magnitudes of speedup relative to the serial implementation of the LB algorithm. Based on such implementations, benchmark quality results are obtained with fine grid of 20492 for both two-dimensional lid driven cavity flow with Reynolds number up to 7500, and double diffusive cavity flow with solute Rayleigh number up to 108. © 2017 Elsevier Ltd

Li-polyiodide batteries are attractive because of their high energy density and excellent rate performance. Nevertheless, the polyiodide shuttle effect and Li dendrite growth over cycling result in fast degradation of the Li anode and a short cycle life. Here we report a facile yet efficient design of high-energy membrane-free Li-polyiodide battery, in which the Li anode is shielded by a pre-deposited indium (In) layer and a graphene paper layer. The proof-of-concept semi-liquid battery with such a dual-protection strategy demonstrates a remarkably enhanced cycling stability for the reasons: (i) the In layer is capable of mitigating the Li dendrite growth and resisting the polyiodide shuttle attack; and (ii) the graphene paper physically suppresses the anode surface evolution and enables the formation of a separated passivation layer. Consequently, the battery can operate with a concentrated catholyte of 6 M I− and achieves a volumetric energy density as high as 165.3 Wh L−1 (1.5 C) for 100 cycles. The high performances achieved suggest the aprotic Li-polyiodide battery with a compact and robust architecture shows the potential for various energy storage applications. © 2017 Elsevier B.V.

The redox flow battery (RFB) is one of the most promising large-scale energy storage technologies for the massive utilization of intermittent renewables especially wind and solar energy. This work presents a novel redox flow battery that utilizes inexpensive and abundant Fe(II)/Fe(III) and Pb/Pb(II) redox couples as redox materials. Experimental results show that both the Fe(II)/Fe(III) and Pb/Pb(II) redox couples have fast electrochemical kinetics in methanesulfonic acid, and that the coulombic efficiency and energy efficiency of the battery are, respectively, as high as 96.2% and 86.2% at 40 mA cm−2. Furthermore, the battery exhibits stable performance in terms of efficiencies and discharge capacities during the cycle test. The inexpensive redox materials, fast electrochemical kinetics and stable cycle performance make the present battery a promising candidate for large-scale energy storage applications. © 2017 Elsevier B.V.

In this paper, we report a high-energy-density lithium/polyiodide (Li/PI) semi-liquid battery with soluble polyiodide in ether-based solvents as the catholyte. The challenge of shuttle effect is addressed by adopting a hybrid membrane coated with negatively charged sulfonate-ended perfluoroalkyl polymer, which allows for inhibition of polyiodide shuttles due to the electrostatic repulsion. The assembled Li/PI battery demonstrates a superior volumetric energy density (170.5 Wh L−1), a stable cycling performance (>100 cycles, averaged decay < 0.16% at 0.2 C), a high energy efficiency (>84%, 100 cycles at 2 C), and a high coulombic efficiency (>95%, 100 cycles at 2 C). These high performances achieved suggest that the aprotic Li/polyiodide battery with a compact architecture has the potential for various energy storage applications. © 2016 Elsevier B.V.

A semi-liquid polysulfide cathode renders a higher sulfur loading for Li-S batteries. However, the aggravated polysulfide shuttle effect and the poor interaction between polysulfide and carbonaceous electrode lower the battery’s cycling stability and performance. Here we report a freestanding N-TiO2 nanowire (NW) decorated carbon cloth electrode for a Li-polysulfide battery, where the nitrogen doping in the formed nanowires allows for a higher electrical conductivity and stronger polysulfide binding ability. Meanwhile, with the facile adsorption of View the MathML source and more active sites provided by the nanowire structure, Li2S precipitation can be improved as well. With the rationally engineered nanostructured polysulfide binding electrode, the battery achieves a remarkably enhanced cycling stability and prolonged discharge capacity (1210 mAh g−1, 0.2C and 600 mAh g−1, 1C), in comparison with the pristine carbon cloth (890 mAh g−1, 0.2C and 210 mAh g−1, 1C). The facile strategy of fabricating conductive and polysulfide binding nanostructure in this work is thus expected to facilitate the design of high-energy sulfur cathode.

Fuel cells and flow batteries are promising technologies to address climate change and air pollution problems. An understanding of the complex multiscale and multiphysics transport phenomena occurring in these electrochemical systems requires powerful numerical tools. Over the past decades, the lattice Boltzmann (LB) method has attracted broad interest in the computational fluid dynamics and the numerical heat transfer communities, primarily due to its kinetic nature making it appropriate for modeling complex multiphase transport phenomena. More importantly, the LB method fits well with parallel computing due to its locality feature, which is required for large-scale engineering applications. In this article, we review the LB method for gas-liquid two-phase flows, coupled fluid flow and mass transport in porous media, and particulate flows. Examples of applications are provided in fuel cells and flow batteries. Further developments of the LB method are also outlined.

This paper reports on a one-dimensional lithium-oxygen (Li-O2) battery model incorporating the competitive uptake of discharge intermediate between the electrode surface and the aprotic electrolyte. Unlike previous models, in which a single-step reaction is assumed for aprotic Li-O2 batteries (2Li+ + 2e− + O2 → Li2O2), the present model more realistically depicts the electrochemical process in a battery system by taking account of multiple-step reactions, including the surface reduction reactions of adsorbed oxygen (Li++O2 ∗+e-→LiO2 ∗) and adsorbed superoxide (LiO2 ∗+Li++e-→Li2O2) along with the dissolution of superoxide into electrolyte. Transient and spatial analyses are performed to identify the limiting steps for the battery's performance, including oxygen transport and final discharge product precipitation. The effects of the kinetics of oxygen reduction reaction and superoxide dissolution are also investigated. In addition, the impact of cathode microstructures on the battery's performance is studied. It is found that the electrolyte's ability to dissolve the discharge intermediate (LiO2) is critically important to improve the discharge capacity. © 2016 Elsevier Ltd

The zinc bromine flow battery (ZBFB) is regarded as one of the most promising candidates for large-scale energy storage attributed to its high energy density and low cost. However, it suffers from low power density, primarily due to large internal resistances caused by the low conductivity of electrolyte and high polarization in the positive electrode. In this work, chloride based salts including KCl and NH4Cl are investigated as supporting electrolyte to enhance electrolyte conductivity, while graphite-felt electrodes are thermally treated to improve electrocatalytic activity. It is found that the use of 4 M NH4Cl as a supporting electrolyte enables the battery to be operated at a current density of 40 mA cm−2 with an energy efficiency of 74.3%, whereas without the addition of a supporting electrolyte the battery only outputs an energy efficiency of 60.4%. In combination with a thermally treated graphite-felt electrode, efficiency further reaches up to 81.8% at the same current density. More impressively, we demonstrate that even at a high current density of up to 80 mA cm−2, the battery is capable of delivering an energy efficiency of 70%, representing one of the highest performances of ZBFBs in the open literature.

Rechargeable lithium-air batteries have ultra-high theoretical capacities and energy densities, allowing them to be considered as one of the most promising power sources for next-generation electric vehicles. The technology has been honed in various ways over the years, but it still experiences critical issues that need to be addressed in order to make it commercially viable. For instance, its practical capacity, round-trip efficiency, and cycling life are among the factors that need to be improved. In this review, the developments of this type of battery are presented. In particular, the system levels of design that encompass the optimization of the battery's electrolyte and electrodes are discussed. More importantly, this report provides perspectives on achieving the desired battery performance to meet the demands of commercial viability. © 2017 Elsevier Ltd

In this work, we prepare a highly catalytic and stabilized titanium nitride (TiN) nanowire array-decorated graphite felt electrode for all vanadium redox flow batteries (VRFBs). Free-standing TiN nanowires are synthesized by a two-step process, in which TiO2 nanowires are first grown onto the surface of graphite felt via a seed-assisted hydrothermal method and then converted to TiN through nitridation reaction. When applied to VRFBs, the prepared electrode enables the electrolyte utilization and energy efficiency to be 73.9% and 77.4% at a high current density of 300 mA cm−2, which are correspondingly 43.3% and 15.4% higher than that of battery assembled with a pristine electrode. More impressively, the present battery exhibits good stability and high capacity retention during the cycle test. The superior performance is ascribed to the significant improvement in the electrochemical kinetics and enlarged active sites toward V3+/V2+ redox reaction. © 2016 Elsevier B.V.

The low density associated with low sulfur areal loading in the solid-state sulfur cathode of current Li S batteries is an issue hindering the development of this type of battery. Polysulfide catholyte as a recyclable liquid fuel was proven to enhance both the energy density and power density of the battery. However, a critical barrier with this lithium (LO/polysulfide battery is that the shuttle effect, which is the crossover of polysulfides and side deposition on the Li anode, becomes much more severe than that in conventional Li S batteries with a solidstate sulfur cathode. In this work, we successfully applied an acrylatebased gel polymer electrolyte (GPE) to the Li/polysulfide system. The GPE layer can effectively block the detrimental diffusion of polysulfides and protect the Li metal from the side passivation reaction. Cathode static batteries utilizing 2 M catholyte (areal sulfur loading of 6.4 mg cm(-2)) present superior cycling stability (727.4 mAh g(-1) after 500 cycles at 0.2 C) and high rate capability (814 mAh g(-1) at 2 C) and power density (similar to 10 mW cm(-2)), which also possess replaceable and encapsulated merits for mobile devices. In the cathode-flow mode, the Li/polysulfide system with catholyte supplied from an external tank demonstrates further improved power density (similar to 59 mW cm(-2)) and stable cycling performance. This novel and simple Li/polysulfide system represents a significant advancement of high energy density sulfur-based batteries for future power sources.

Ultrafast ion transport in carbon nanotubes (CNTs) has been experimentally observed, but the underlying mechanism is unknown. In this work, we investigate ion transport in CNTs through molecular dynamics (MD) simulations. It is found that the flow in CNTs undergoes a transition from the passage of a continuous liquid chain to the transport of isolated ion-water clusters as the CNT length or the external electric filed strength is increased. The breakup of the liquid chain in CNTs greatly reduces the resistance caused by the hydrogen bonds of water and significantly enhances the ionic mobility, which explains the two-order-magnitude enhancement of ionic conductance in CNTs reported in the literature. A theoretical criterion for fluid breakup is proposed, which agrees well with MD results. The fluid breakup phenomenon provides new insights into enhancing ion transport in nanoconfinements.

To eliminate the adverse impacts of hydrogen evolution on the capacity of iron-chromium redox flow batteries (ICRFBs) during the long-term operation and ensure the safe operation of the battery, a rebalance cell that reduces the excessive Fe(III) ions at the positive electrolyte by using the hydrogen evolved from the negative electrolyte is designed, fabricated and tested. The effects of the flow field, hydrogen concentration and H2/N2 mixture gas flow rate on the performance of the hydrogen-ferric ion rebalance cell have been investigated. Results show that: i) an interdigitated flow field based rebalance cell delivers higher limiting current densities than serpentine flow field based one does; ii) the hydrogen utilization can approach 100% at low hydrogen concentrations (≤5%); iii) the apparent exchange current density of hydrogen oxidation reaction in the rebalance cell is proportional to the square root of the hydrogen concentration at the hydrogen concentration from 1.3% to 50%; iv) a continuous rebalance process is demonstrated at the current density of 60 mA cm−2 and hydrogen concentration of 2.5%. Moreover, the cost analysis shows that the rebalance cell is just approximately 1% of an ICRFB system cost. © 2017 Elsevier B.V.

As the fraction of electricity generated from intermittent renewable sources (such as solar and wind) grows, developing reliable energy storage technologies to store electrical energy in large scale is of increasing importance. Redox flow batteries are now enjoying a renaissance and regarded as a leading technology in providing a well-balanced solution for current daunting challenges. In this article, state-of-the-art studies of the complex multicomponent transport phenomena in aqueous redox flow batteries, with a special emphasis on all-vanadium redox flow batteries, are reviewed and summarized. Rather than elaborating on the details of previous experimental and numerical investigations, this article highlights: i) the key transport issues in each battery's component that need to be tackled so that the rate capability and cycling stability of flow batteries can be significantly improved, ii) the basic mechanisms that control the active species/ion/electron transport behaviors in each battery's component, and iii) the key experimental and numerical findings regarding the correlations between the multicomponent transport processes and battery performance. (C) 2016 Elsevier B.V. All rights reserved.

To investigate the impact of pore size of ordered mesoporous carbon (OMC) FDU-15-supported Platinum (Pt) catalysts on oxygen reduction reaction (ORR), OMC FDU-15 with various pore sizes ranging from 4.0 nm to 8.1 nm are synthesized through a soft-template method, and then FDU-15-supported Pt catalysts are prepared by chemical impregnation method. Characterizations show that increase in pore size enlarges the specific surface area and the pore volume of FDU-15, but decreases the electrical conductivity. Particle size of FDU-15-supported Pt catalyst is also influenced in a decreasing trend with the increase of pore size. Electrochemical measurement demonstrates that FDU-15-supported Pt catalyst with a pore size of 6.5 nm yields the highest electrocatalytic activity for ORR, which is further confirmed by single cell test on DMFC, as the catalyst for cathode.

The polysulfide shuttle effect and lithium dendrite growth in lithium-sulfur (Li-S) batteries can repeatedly breach the anodic solid electrolyte interphase (SEI) over cycling. As a result, irreversible short-chain sulfide side products (Li2Sx, x = 1, 2) keep depositing on the Li anode, leading to the active material loss, increasing the Li+ transport resistance, and thereby reducing the cycle life. In this work, indium iodide (InI3) is investigated as a bifunctional electrolyte additive for Li-S batteries to protect the Li anode and decompose the side products spontaneously. On the one hand, Indium (In) is electrodeposited onto the Li anode prior to Li plating during the initial charging process, forming a chemically and mechanically stable SEI to prevent the Li anode from reacting with soluble polysulfide species to form Li2Sx (x = 1, 2) side products. On the other hand, by adequately overcharging the battery, the triiodide/iodide redox mediator is capable of chemically transforming side products deposited on the Li anode and separator into soluble polysulfides, which can be recycled by the cathode. It is shown that the battery with the InI3 additive exhibits a prolonged cycle life, and is capable of retrieving its capacity by a facile overcharging process. © 2017 Elsevier B.V.

In this work, we adopt a first-principles study to evaluate the potential of boron phosphide (BP) monolayer as an anode material for alkali metal-based (e.g., Li, Na and K) batteries. It is found that the BP monolayer shows negative adsorption energies of −0.202, −0.160 and −0.681 eV, respectively, for Li, Na and K. During loading, when any of the three alkali metal atoms reaches a critical position (∼6 Å), the adsorption energy increases dramatically with no energy barrier. It is also shown that after adsorbing Li, Na or K, the semiconducting BP monolayer is transformed to a metallic state, becoming an electrical conductor. More importantly, the alkali metal atoms show high diffusivities on the BP monolayer, with low energy barriers of 0.364, 0.217 and 0.155 eV for Li, Na and K, respectively. Finally, the BP monolayer has high theoretical specific capacities of 1283 and 570 mA h g−1 for Li and K storages, which are among the highest values of the anode materials reported in the literature, and multiple times higher than that of graphite anode materials in use. The above-mentioned results suggest that the BP monolayer is a promising anode material not only for Li-ion and K-ion batteries, but also for other lithium-based and potassium-based batteries. © The Royal Society of Chemistry.

Two-dimensional inorganic materials, such as exfoliated graphene, have been under much research attention as of late, for their high surface-to-mass ratio and unique physical and chemical properties. Many of these properties are highly sought after in Li/Na-based batteries. In this paper, we review recent advances in inorganic 2D materials and summarize their applications as: (i) the electrode materials or additives for Li/Na-ion batteries; (ii) the scaffold or interfacial layer for lithium-metal anodes; (iii) the cathode for Li/Na-O-2 batteries; and (iv) the anchoring material for lithium polysulfides for Li-S batteries. The challenges of employing 2D materials in these Li/Na-based batteries to improve performance are discussed and possible solutions are proposed.

An issue with the use Of Metallic lithium as an anode material for lithium-based batteries is,dendrite growth, causing a periodic breaking and repair of the solid electrolyte interphase (SEI) layer. Adding 2D atomic crystals, such as h-BN; as an interfacial layer between the lithium metal anode and liquid electrolyte has been demonstrated to be effective to mitigate dendrite growth, thereby enhancing the Columbic efficiency of lithium metal batteries. But the underlying mechanism leading to the reduced dendrite growth remains unknown. In this work, with the aid of first-principle calculations, we find that the interaction between the h-BN and lithium metal layers is a weak van der Waals force, and two atomic layers of h-BN are thick enough to block the electron tunneling from lithium metal to electrolyte, thus prohibiting the decomposition of electrolyte. The interlayer spacing between the h-BN and lithium metal layers can provide larger adsorption energies toward lithium atoms than that provided by bare lithium or h-BN, making lithium atoms prefer to intercalate under the cover of h-BN during the plating process. The combined high stiffness of h-BN and the low diffusion energy barriers of lithium at the Li/h-BN interfaces induce a uniform distribution of lithium, under h-BN, therefore effectively suppressing dendrite growth. © 2016 American Chemical Society.

Fuel cells and flow batteries are promising technologies to address climate change and air pollution problems. An understanding of the complex multiscale and multiphysics transport phenomena occurring in these electrochemical systems requires powerful numerical tools. Over the past decades, the lattice Boltzmann (LB) method has attracted broad interest in the computational fluid dynamics and the numerical heat transfer communities, primarily due to its kinetic nature making it appropriate for modeling complex multiphase transport phenomena. More importantly, the LB method fits well with parallel computing due to its locality feature, which is required for large-scale engineering applications. In this article, we review the LB method for gas-liquid two-phase flows, coupled fluid flow and mass transport in porous media, and particulate flows. Examples of applications are provided in fuel cells and flow batteries. Further developments of the LB method are also outlined.

In this work, we adopt a first-principles study to evaluate the potential of boron phosphide (BP) monolayer as an anode material for alkali metal-based (e.g., Li, Na and K) batteries. It is found that the BP monolayer shows negative adsorption energies of −0.202, −0.160 and −0.681 eV, respectively, for Li, Na and K. During loading, when any of the three alkali metal atoms reaches a critical position (∼6 Å), the adsorption energy increases dramatically with no energy barrier. It is also shown that after adsorbing Li, Na or K, the semiconducting BP monolayer is transformed to a metallic state, becoming an electrical conductor. More importantly, the alkali metal atoms show high diffusivities on the BP monolayer, with low energy barriers of 0.364, 0.217 and 0.155 eV for Li, Na and K, respectively. Finally, the BP monolayer has high theoretical specific capacities of 1283 and 570 mA h g−1 for Li and K storages, which are among the highest values of the anode materials reported in the literature, and multiple times higher than that of graphite anode materials in use. The above-mentioned results suggest that the BP monolayer is a promising anode material not only for Li-ion and K-ion batteries, but also for other lithium-based and potassium-based batteries. © The Royal Society of Chemistry.

Ultrafast ion transport in carbon nanotubes (CNTs) has been experimentally observed, but the underlying mechanism is unknown. In this work, we investigate ion transport in CNTs through molecular dynamics (MD) simulations. It is found that the flow in CNTs undergoes a transition from the passage of a continuous liquid chain to the transport of isolated ion-water clusters as the CNT length or the external electric filed strength is increased. The breakup of the liquid chain in CNTs greatly reduces the resistance caused by the hydrogen bonds of water and significantly enhances the ionic mobility, which explains the two-order-magnitude enhancement of ionic conductance in CNTs reported in the literature. A theoretical criterion for fluid breakup is proposed, which agrees well with MD results. The fluid breakup phenomenon provides new insights into enhancing ion transport in nanoconfinements.