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The oxygen reduction reaction (ORR) is a critical, but sluggish reaction used for various applications, including fuel cells and metal-oxygen batteries. Currently, the benchmark catalysts for ORR are Pt-based catalysts. However, due to these catalysts being scarce and very expensive, alternative catalysts that are more abundant and less expensive are urgently in demand. MXenes, a new two-dimensional (2D) material based on transition metal carbides and nitrides, have advanced the performance of many existing technologies, including batteries, supercapacitors, sensors, etc. Owing to their unique electronic structure, physical and chemical properties, and tunable morphology, MXenes are expected to thrive in the ORR electro- and photo-catalytic systems. Recent studies reported better-performing ORR catalysts with MXenes as supports, which holds promise in the significant reduction of Pt loading for efficient catalysts. Furthermore, MXenes exhibit wide applicability and stability in a range of pH values, from acidic to basic. In this work, we carefully review the most pertinent works on ORR using MXenes. We first discuss the catalytic performance of MXenes in alkaline and acidic environments, followed by their application in metal-air batteries. We investigate the gaps and challenges in the field, identify key areas that need further attention, and provide directions for future research. [ABSTRACT FROM AUTHOR]

One of the key impediments to aluminum (Al) as an anode in alkaline Al-air batteries is self-corrosion, which limits the battery's efficiency due to the capacity loss and lifespan reduction. Thus, it is vital to find an efficient electrolyte additive that reduces selfcorrosion in Al anodes. In this study, the effect of adding 0.5 to 1.5 wt% of cerium chloride to 4 mol l-1 KOH electrolyte on the self-corrosion of pure Al anode was investigated using electrochemical experiments. The results show that the addition of cerium chloride to the electrolyte reduces self-corrosion of the Al anode with a negligible effect on the anode activity. Cerium chloride forms cerium hydroxide (Ce (OH)3) in the alkaline electrolyte, which is adsorbed on the Al surface. Therefore, the corrosion potential increased, and self-corrosion current density decreased. As the cerium chloride concentration increased, the Al anode efficiency increased from 43.8% to 76.1%, and the capacity density increased from 1294 to 2244 mAh g-1. Furthermore, increasing the immersion time of the Al anode in the electrolyte containing cerium chloride increased the self-corrosion resistance and provided the self-healing properties for the anode. [ABSTRACT FROM AUTHOR]

This work reports the use of collard greens extract as a potent inhibitor for self-corrosion of the aluminum electrode in an alkaline aluminum-air battery via galvanostatic discharge tests, weight loss measurements, and electrochemical measurements. Scanning electron microscopy (SEM), atomic force microscopy (AFM), and fourier transform infrared (FT-IR) spectroscopy were performed to explore the morphology of aluminum. The obtained results show that the utilization efficiency and capacity density of the battery were significantly enhanced by the presence of the extract. The inhibition efficiency attained the maximum values at 2.0 g l-1, about 89.61% and 87.90% from potentiodynamic polarization and electrochemical impedance spectroscopy measurements, respectively. Collard greens extract served as a cathodic inhibitor, and the adsorption mechanism of the extract adhered to the Freundlich adsorption isotherm. In particular, the physical absorption of the extract inhibitor on the aluminum surface was elucidated through nuclear magnetic resonance spectroscopy. Moreover, the phenolic compounds in the extract correspond to the corrosion inhibition effect on aluminum. [ABSTRACT FROM AUTHOR]

Rechargeable alkaline zinc batteries (RAZBs) have attracted great attention due to their inexpensive use of electrode materials and high safety features. However, the development of RAZBs is restricted by their low capacity and volumetric energy density, mainly suffering from poor electric conductivity of the cathode. Aluminium-doped SrTiO3 (1.0% Al-STO) has successfully enhanced the capacity of pristine STO from 387 to 646 mAh cm-3 at a current density of 2 mA cm-2. This may be attributed to the fact that Al doping improves electrical conductivity as well as promoting the transportation of ions/electrons. Based on the Nyquist plot, the charge-transfer resistance of Al-STO was reduced from 7.8 to 1.2 Ω, indicating the enhancement of electrical conductivity after Al doping. This outstanding electrochemical performance of Al-STO as cathode provide valuable insights for designing high-performance electrode for RAZBs. [ABSTRACT FROM AUTHOR]

The mechanisms of charge storage in four typical electrochemical capacitor systems are compared and contrasted. These systems are based on activated carbon, ruthenium dioxide, manganese dioxide and nickel hydroxide. Charge storage is discussed in terms of charge delocalization either on the surface or throughout the electrode material. Electrical double layer formation, such as on activated carbon, is considered an example of charge delocalization, with charge distributed over the electrolyte accessible surface irrespective of the applied potential. Ruthenium dioxide also stores delocalized charge, in this case through the reversible Ru(IV)/Ru(III) redox couple. Manganese dioxide is unique in that in alkaline (battery) electrolytes charge is localized in specific structural domains, while in neutral (capacitor) electrolytes charge is delocalized over the material structure. Nickel hydroxide in an alkaline electrolyte is an example of charge localization when redox cycling due to its two-phase redox mechanism. The impact of these differing charge storage mechanisms on electrochemical performance is discussed. [ABSTRACT FROM AUTHOR]

Redistribution of zinc over the electrode surface, also known as shape change, is a major problem and a cause of failure in alkaline zinc anode batteries. To mitigate this phenomenon, we propose a scalable approach based on an in situ formed, highly porous electrochemically synthesized ZnO matrix with uniformly electrodeposited zinc particles. This results in ~70% improvement in cycle life performance at a rate of 10 mA cm−2 compared to control Zn anodes, which have not gone through the formation process. A quantitative electrolyte analysis revealed under-saturated zincate ion concentration in the electrochemically synthesized ZnO/Zn cells indicating reduced zincate movement. Post mortem analysis of the anodes indicated higher retention of both Zn and ZnO on the electrochemically synthesized ZnO anodes signifying reduced redistribution of active material. Image analysis of the cycled anodes revealed a narrower Zn particle size distribution (62−79 μm) in contrast to a wider particle size distribution of 51–96 μm observed in the control anodes. The formation approach results in electrochemically synthesized ZnO/Zn anodes providing a stable ZnO matrix in which Zn particles retain their localized distribution on cycling better than control electrodes conventionally made by pasting zinc particles together with a binder. [ABSTRACT FROM AUTHOR]

Ni-rich cathode materials have attracted much attention due to the high energy density and low cost. However, the poor cycling performance and low rate capacity have produced a serious impact on the practical commercial application. In this work, the B3+ incorporation and polypyrrole coating were both applied to enhance the electrochemical properties of LiNi0.85Co0.05Mn0.10O2 by using the co-precipitation process followed by a chemical vapor phase polymerization way. Herein, the B3+ incorporation into crystal structure could enlarge the lattice spacing, contributing to accelerating the Li+ insertion/extraction speed and enhancing the structural stability during cycling. The polypyrrole surface coating played a great effect on preventing cathode surface from the electrolyte erosion owing to a shield of polypyrrole. As a result, a maximum discharge capacity of 129.8 mAh g−1 at 5 C high rate and prominently enhanced cycling performance with capacity retention of 90.1% after 300 cycles were acquired for the Polypyrrole coated LiNi0.835Co0.05Mn0.10B0.015O2. By comparison, the pristine LNCMO cathode demonstrated a fast decaying capacity and delivered a capacity retention of only 81.9%. [ABSTRACT FROM AUTHOR]

Herein, we report a binder-free, low-cost and high performance cathode for lithium-oxygen batteries based on carbon black BP2000 decorated Ni(OH)2 nanoflakes array on Ni foam. The Ni(OH)2 nanoflakes array is fabricated by hydrothermal treatment of Ni foam in acidic medium without nickel salt. The highly organized structure of Ni(OH)2 nanoflakes array provides a more uniform distribution of catalysts and discharge products, resulting in high capacity with a relatively stable cycling voltage profile. The cathode outputs a discharge capacity as high as 12400 mAh gcarbon−1 at 160 mA gcarbon−1, which is 244% higher than that of BP2000 decorated Ni foam electrode without Ni(OH)2 nanoflakes array. The cathode can sustain 100 cycles under a capacity limitation of 320 mAh gcarbon−1 with high energy efficiency (~67%). Our work points out the key issues and suggests an effective method for the surface modification technology. [ABSTRACT FROM AUTHOR]

Electrochemical behavior and discharge performance of pure Al and Al-0.55Mg-0.028Sn-0.015Ga alloy anodes for Al-air battery were investigated. Solution heat treatment of the alloy was performed at different temperatures and the relationship between microstructural characteristics and properties was analyzed. The results indicated that the secondary phases dissolve into the Al matrix after solution treatment, and a more homogeneous distribution of the alloy elements is obtained. The solution treatment of the Al alloy anodes at 600 °C exhibits a superior performance in both the self-corrosion tests and the Al-air alkaline battery discharge. The energy density of the Al-air battery using this anode is comparable with that of other Al-air battery in the literatures. The anode utilization at 80 mA cm−2 obtains 87.3% in the battery discharge, which is a desirable performance for the Al-air battery anode. Furthermore, the discharge mechanism of the Al alloy anode is also illuminate based on the microstructural characteristics and electrochemical evaluation. [ABSTRACT FROM AUTHOR]

Lithium bis(fluorosulfonyl)amide (LiFSI)-based electrolytes not only deliver improved ionic conductivity, but also provide high thermal stability and water tolerance. However, the notorious corrosion of sulfonamide anions against aluminum (Al) current collector restricts their application. High concentration electrolytes (HCEs) have been proposed as alternative electrolytes for lithium batteries owning to their merits of good electrochemical performance and less flammability. Although HCEs have been proved stable to many alkaline cathodes and anodes in the past reports, their compatibility with other battery components, such as the current collector, has not been clearly reported. Herein, electrochemical stabilities of various metals in LiFSI/dimethyl carbonate (DMC) electrolytes were characterized by linear sweep voltammetry and cyclic voltammogram. According to results, when the concentration of the LiFSI/DMC electrolyte is higher than 1:3 (salt/solvent) by molar for Al, and 1:1.2 for titanium (Ti) and stainless steel (SS304), the three materials can be used as the cathode current collector or the other battery components. Moreover, Al that exhibits the best electrochemical stability is still the most ideal current collector compared to other metals. Notably, in the LiFSI:DMC (1:1.5) electrolyte with an Al current collector, stable battery performance with a remaining capacity of 98.8% after 50 cycles can be obtained. [ABSTRACT FROM AUTHOR]

Zinc continues to garner immense interest due to its versatility as an anode material in several configurations utilizing either alkaline or mild-pH electrolytes. Current research on using mild-pH electrolytes has improved the rechargeability aspect of Znbased batteries since Zn2+ is solely utilized for plating/stripping of Zn. Several studies have incorporated Zn metal foils, yet, dramatic improvements can be achieved by expressing Zn as a porous structure. Herein, we use a quasi-pulsed electrodeposition process to prepare a conformal Zn coating onto 3D porous copper foam. By tuning the electrodeposition parameters, we achieved an optimal Zn coating that undergoes reversible plating/stripping when tested in symmetric Zn cells, which supported a low overpotential of ∼60 mV for up to 100 cycles. We further investigated changes in the surface morphology by studying the Zn surface of both foil and 3D structure using scanning electron microscopy and X-ray micro-computed tomography. Both techniques showed that the Zn foil undergoes dramatic alterations at the surface, which results in inhomogeneous deposition of Zn, whereas the 3D form exhibited minimal changes. Lastly, we paired both Zn foil and 3D Zn with vanadium oxide and demonstrated that the porous structure supports high rate capability and high specific capacity. [ABSTRACT FROM AUTHOR]

Al-0.5 wt.% MgO, Al-1 wt.% MgO, Al-1.5 wt.% MgO and pure Al anodes were prepared to investigate the effect of MgO particles addition on the electrochemical performance of aluminum anode for Al-air batteries in alkaline electrolyte. The electrochemical performance of these battery devices, including anodic polarization, corrosion characteristics, hydrogen evolution rate, AC impedance, and discharge behavior was examined and analyzed comparatively in 4 M KOH solution. The results show that Al-0.5 wt.% MgO, Al-1 wt.% MgO composite anodes exhibit a negative shift in the open-circuit potential compared with pure Al anode. Appropriate amount of MgO addition obviously improves the electrochemical activity, corrosion resistance and anode utilization of pure Al anode. These behaviors should be related to the interface characteristic of MgO particles with Al matrix which helps to destroy the integrity and compactness of the oxide layer on anode surface. The influence of MgO addition on the corrosion resistance of composite Al anode is well explained by the energy band and state density calculation based on density functional theory. [ABSTRACT FROM AUTHOR]

Zn–Ni battery is an attractive aqueous alkaline secondary battery due to its low cost, safety, and environmental friendliness. However, the problems of hydrogen evolution reaction, zinc dendrites growth and deformation of zinc anodes hampering the commercial application of Zn–Ni battery. In this work, the dynamic imbalance behavior of capacity of the Zn–Ni battery which caused by low coulombic efficiency of the anode is studied. Results reveal that due to the hydrogen evolution effect of the anode, the sintered Ni(OH)2 cathode which commonly used in the research of anode of Zn–Ni batteries cannot be fully discharged. Residual capacity will increase the potential of the cathode continuously, shorten the constant current charging time, and cause the battery cycle capacity decay rapidly. This phenomenon is confirmed by adding nano Bi powders to suppresse the hydrogen evolution of the zinc anode. This work reveals that the decline in the cycle life of Zn–Ni batteries is not only due to irreversible changes in the electrode structure but also due to the coulombic efficiency mismatch of the cathode and anode. [ABSTRACT FROM AUTHOR]

The construction of the air electrode structure is critical in the rechargeable zinc-air batteries. So far, the majority of previous articles have been reported on the process in boosting electrocatalytic bifunctional oxygen reaction activity. Nevertheless, the reason that caused the deterioration of air electrodes has been rarely investigated, which dramatically influences cell performance. Herein, self-supported MnO2 bifunctional electrocatalysts on nickel foam are integrated with the gas diffusion layer to form air electrodes. The charge voltage of the as-prepared electrode used in rechargeable zinc-air battery is reduced by 1.82% and the discharge voltage is decreased by 5.25% after 1000 cycles at the current density of 20 mA cm−2 under the mode of 5 min charge and 5 min discharge, which demonstrate the feasibility of the novel electrode structure design. Besides, The X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and electrochemical impedance spectroscopy (EIS) were conducted to analyze the change of composition, structure, and performance. The origin of the decrease of the discharge profile was analyzed. Experimental studies revealed that the main cause of voltage loss is mainly attributed to the destroyed gas diffusion structure (at large current densities) and the activation loss of MnO2 caused by the (oxy)hydroxide film (at small current densities). The destroyed gas diffusion structure gives rise to the poor oxygen transfer and further water flooding due to the formation of large pore caused by oxygen evolution in the charging process and increased hydrophilicity by the carbon oxidation. Meanwhile, the film growing overtop of the electrocatalysts would result in mass transfer and activation losses. [ABSTRACT FROM AUTHOR]

Herein, a high performance Ni–Fe composite nanowires array based supercapacitor anode was fabricated via electrochemical deposition using polycarbonate membrane. The synthesized nanowires demonstrate outstanding electrochemical performance with good specific capacitance of 1255.17 Fg−1 at 3 Ag−1 and 80% capacitive retention at the end of 5000 charge-discharge cycles. In addition, an asymmetrical supercapacitor (Ni–Zn//Ni–Fe) was also fabricated that demonstrates 95.23% of capacitive retention after 2000 cycles. The fabricated supercapacitor device showed energy density of 63.62 Wh kg−1 at a power density of 0.64 KW kg−1. Further, the practical performance of a single asymmetrical supercapacitor device was demonstrated by lighting up a 2.2 V green LED. These results reveal the potential of the synthesized nanowires in potable energy storage gadgets. [ABSTRACT FROM AUTHOR]

Rechargeable Zinc-air batteries are considered as the promising power source for energy storage. Air electrodes integrated with bifunctional electrocatalysts play a vital role in improving performance and reducing cost of zinc-air batteries. Recently, the selfsupported bifunctional electrocatalysts synthesized by in situ growth of active materials on conductive substrates have gained increasing popularity, because they often provide high performance of both electrocatalytic activity and stability. In this work, we review the state-of-the-art development of self-supported non-precious-metal electrocatalysts, including carbon-based metal-free materials, transition metal materials, and metal-based hybrid materials, especially the efficient strategies (e.g., heteroatom doping, defect engineering and structures design, etc.) for preparation of self-supported electrocatalysts, as well as the understandings of fabrication mechanism. This review highlights the future development of excellent self-supported electrocatalysts for electrochemical devices. [ABSTRACT FROM AUTHOR]

Recent advances in rechargeable Zn/MnO2 alkaline batteries have shown promise for scalable energy storage systems which provide a safe, low-cost alternative with a demonstrated lifetime over thousands of cycles. This cathode technology is based on a 2-electron Mn redox process where a layered birnessite-type phase has been shown to form after the first cycle with excellent reversibility between the discharge product, Mn(OH)2. Herein, we investigate the reversible reaction between birnessite and Mn(OH)2 with and without a Bi2O3 additive using multimodal structural characterization techniques during active battery cycling. Diffraction results provide evidence of Bi3+ residing in the interlayer of birnessite which prevents irreversible Mn3O4 formation by limiting Mn3+ diffusion within the crystal lattice. Also, upon charge no MnOOH intermediate phases are observed. Instead, X-ray absorption and Raman spectroscopy indicate a disordered, non-crystalline birnessite-type phase consisting of mostly neutral H2O within the interlayer. Birnessite phases will reform without Bi2O3 present, but Mn3O4 formation severely polarizes the potential they are formed at, leading to capacity fade. Also, we discuss the reversible Bi2O3 conversion to Bi0 and its contribution to the observed capacity. We expect the results will provide crucial insight into the development of aqueous, rechargeable battery systems utilizing MnO2. [ABSTRACT FROM AUTHOR]

The rechargeable Zn2+ ion batteries are promising for the sustainable energy storage device applications. Recently they have been extensively evaluated for finding new cathode material and prevention of dendrite growth at Zn plate anode. Herein we have evaluated redox active organic molecule 7,7,8,8Tetracyanoquino dimethane (TCNQ) as a cathode material for aqueous zinc battery with zinc plates as anode in 1 M ZnSO4. The charging/discharging of the battery was associated with formation and deformation of Zn-TCNQ complex, which was confirmed by XRD and FTIR. The specific capacity of cathode was found to be 123.2 mAh g-1 at 100 mA current density with 96% coulombic efficiency. Whereas specific capacity at 1 A current density was found to be 60 mAh g-1 with 94% coulombic efficiency. In a cycling experiments we observed the fading of capacity with time by partial dissolution of Zn-TCNQ complex. The fading of capacity was prevented by confining TCNQ molecules inside the nano structures of newly prepared covalent organic polymers. The confinement remarkably increased the capacitance to 171 mAh g-1 at 1 A current density. As the material is readily available and the absence of toxic inflammable volatile organic electrolytes in our battery this material offers a very good choice as cathode material for zinc battery. [ABSTRACT FROM AUTHOR]

In this study, an Al-0.08Sn-0.08Ga-0.5Mg alloy was annealed at 200 °C-400 °C for 10 h. The microstructure and corrosion morphology of the Al anode were observed by scanning electron microscopy (SEM), and the effects of different annealing temperatures on the electrochemical properties of the Al anodes were studied by the hydrogen evolution rate, open circuit potential, Tafel curves, EIS and constant current discharge. The results show that the annealing treatment had a certain effect on the number and size of precipitates on the alloy surface, which improved the electrochemical activity and corrosion resistance of the Al alloy. Additionally, the Al-Sn-Ga-Mg alloy anode material has an excellent discharge performance in the actual use process when the annealing temperature is 350 °C, the related performance parameters were greatly improved compared with other annealing temperature conditions. The capacity density is 2670.99 mAh·g-1, and the energy density is 3379.15 mWh·g-1. [ABSTRACT FROM AUTHOR]

Three quinone-based organic electrodes were tested in nonaqueous Zn-batteries using different salts and solvents. The Zn(TFSI)2/acetonitrile system exhibited the best performance due to its excellent transport and electrochemical properties. The mechanistic studies on the electrode kinetics were also carried out. While 2,5-dimethoxybenzoquinone (DMBQ) displayed a typical faradaic battery behavior, its polymeric derivatives showed a slow charge transfer inside the polymeric film as depicted by cyclic voltammograms. [ABSTRACT FROM AUTHOR]

Graphene is commonly used as a performance enhancer for batteries. Other than increasing the electronic conductivity, however, additional performance beneficial mechanisms remain unclear. Herein, we report a combined experimental and theoretical study on the role of graphene nanoplate (GN) in a high-capacity aqueous-ZIB cathode hydrated Ca0.67V8O20 (CaVO). The experimental results reveal that the GN does improve the interfacial charge transfer kinetics and affect the stability and capacity of the cathode without changing the bulk property of the cathode. The theoretical results suggest that GN helps enhance Zn-adsorption on the interface, which increases the Zn-coverage and thus promotes faster kinetics. [ABSTRACT FROM AUTHOR]

Rechargeable alkaline batteries containing zinc anodes suffer from redistribution of active material due to the high solubility of ZnO in the electrolyte, limiting achievable capacity and lifetime. Here, we investigate pre-saturating the KOH electrolyte with ZnO as a strategy to mitigate this issue, utilizing rechargeable Ni–Zn cells. In contrast to previous reports featuring this approach, we use more practical limited-electrolyte cells and systematically study ZnO saturation at different levels of zinc depth-of-discharge (DODZn), where the pre-dissolved ZnO is included in the total system capacity. Starting with 32 wt. % KOH, cells tested at 14%, 21%, and 35% DODZn with ZnO-saturated electrolyte exhibit 191%, 235%, and 110% longer cycle life respectively over identically tested cells with ZnO-free electrolyte, with similar energy efficiency and no voltage-related energy losses. Furthermore, anodes cycled in ZnO-saturated electrolyte develop more favorable compact zinc deposits with less overall mass loss. The effect of initial KOH concentration was also studied, with ZnO saturation enhancing cycle life for 32 wt % and 45 wt % KOH but not for 25 wt % KOH, likely due to cell failure by passivation rather than shorting. The simplicity of ZnO addition and its beneficial effect at high zinc utilization make it a promising means to make secondary alkaline zinc batteries more commercially viable. [ABSTRACT FROM AUTHOR]

In the synthesis of 5,5′-azotetrazolate energetic salts, the key reaction is the oxidative-coupling of 5-amino-1H-tetrazole (5AT). But in the conventional KMnO4 oxidation method for 5AT coupling, it suffers from several issues in high energy consumption, insufficient security and inconvenient purification. Here, an electrochemical approach for the oxidative-coupling of 5AT into 5,5′-azotetrazolate under mild conditions is reported. The electrochemical oxidative-coupling of 5AT can be achieved on several precious-metal (Pt, Au, Ag) and transition-metal (Fe, Co, Ni, Cu, Mo, W) electrodes in alkaline electrolyte. The oxidative-coupling of 5AT on Pt electrode was mainly initiated by hydroxyl radical intermediates that formed during the electrocatalytic oxidation of water on Pt, whereas on Ni electrode the oxidative-coupling of 5AT was initiated via direct electrooxidation on the Ni surface without mediation by intermediate species. Due to the convenience of this electrochemical method, yields of up to 10 g of 5,5′-azotetrazolate salt could be easily afforded. [ABSTRACT FROM AUTHOR]

Carbonaceous air cathodes in zinc-air batteries have attracted attention due to their high electron conductivity and low cost; however, the increment in the catalytic activity for the oxygen reduction and evolution in addition to the durability are demanded. Based on a fundamental study about the substantial effect of a three-dimensional active site at a step on a highly-oriented pyrolytic graphite basal plane on the electrode reactions, we attempted to extend the idea to a graphitic carbon fiber surface as a more applied form for the air electrode. Coating of a carbonaceous thin film derived from iron phthalocyanine on finely-etched graphitic carbon fibers produced a highly step-enriched surface demonstrated by the field-emission scanning electron microscope image and Raman spectra with a developed defect peak. The iron K-edge X-ray absorption fine structure showed a step-oriented iron atom coordinated by two nitrogen atoms and a basal plane oriented iron atom coordinated by 4 nitrogen atoms. The step-enrichment enhanced the oxygen reduction and evolution; in particular, the low overpotential phenomenon observed for the fundamental graphite system was reproduced in the carbon fiber paper, both in a half cell and a full cell of the zinc-air battery, which also showed a favorable cycling performance. [ABSTRACT FROM AUTHOR]

The penetration of renewable sources (solar and wind power) into the power system network has been increasing in the recent years. As a result of this, there have been serious concerns over reliable and satisfactory operation of the power systems. One of the solutions being proposed to improve the reliability and performance of these systems is to integrate energy storage devices into the power system network. Zinc-bromine batteries systems among other energy storage technologies has appeared as one of the best options. This paper presents the performance of three different electrodes feedermaterials (carbon, nickel and a titanium) coupled and investigated within a fabricated ZnBr2 cell system via numerical modelling, DDPM+DEM model in ANSYS Fluent to simulate an incorporated anode zinc-electrode and COMSOL Multiphysics for the electrochemical behavior of the cell. After introducing briefly other alternatives to store energy, ZnBr2 cell systems, and its mode of operation were then discussed, before focusing on the numerical modelling and simulation and the laboratory experiments. Several extensive electrochemical experiments were implemented on the cell to achieve fast deposition of zinc onto the electrode surface during charge and fast dissolution during discharge for high performance. The mechanical action of the fluidised design of electrode is intended to improve deposit morphology, obviate the risk of dendrite growth and provide high transport rates of reactant to and from the active electrode surface. In conclusion, this paper has analyzed electrochemical techniques like chronopotentiometry, cyclic voltammetry (CV), and electrochemical impedance spectroscopy that were used to understand the behavior of the zinc bromide cells at a particular flow rate of 166.7cm³ min-1 required to give good fluidization of the anode. [ABSTRACT FROM AUTHOR]

Zinc-air batteries (ZABs) have been considered as promising next-generation batteries due to their natural abundance, flat discharge voltage and high theoretical specific energy density. However, the wide application of these ZABs is seriously hindered by the high cost and poor electrochemical stability of noble electrocatalysts. In this paper, we develop a facile method to prepare ultra-small iron-based nitride and nitrogen doped carbon nanotubes (Fe2N/N-CNTs) hybrid materials as bifunctional electrocatalysts for ZABs. In the presence of CNTs with large surface areas, ultra-small Fe2N nanoparticles with the diameter of around 5 nm are successfully prepared. The oxygen reduction reaction (ORR) activity of Fe2N/N-CNTs is comparable to the Pt/C, while the oxygen evolution reaction (OER) activity is much better than the Pt/C. At last, the home-made ZABs with Fe2N/N-CNTs have significant rechargeable activities and cyclic stability. [ABSTRACT FROM AUTHOR]

Rechargeable alkaline Zn/MnO2 batteries are an attractive solution for large-scale energy storage applications. Recently, Bi and Cu additives have been used to increase the cycle life and capacity of rechargeable Zn/MnO2 batteries, with an equivalent of the full two-electron capacity realized for many cycles, in the absence of zinc. However, the mechanism of the effect of Bi and Cu on the performance of rechargeable Zn/MnO2 batteries has not been investigated in detail. We apply first-principles density functional computational methods to study the discharge mechanisms of the unmodified and Bi/Cu-modified γ-MnO2 electrodes in rechargeable alkaline Zn/MnO2 batteries. Using the results of our calculations, we analyze the possible redox reaction pathways in the γ-MnO2 electrode and identify the electrochemical processes leading to the formation of irreversible discharge reaction products, such as hausmannite and hetaerolite. Our study demonstrates the possibility of formation of intermediate Bi-Mn and Cu- Mn oxides in deep-cycled Bi/Cu-modified MnO2 electrodes. The formation of intermediate Bi-Mn and Cu-Mn oxides could reduce the rate of accumulation of irreversible reaction products in the MnO2 electrode and improve the rechargeability and cyclability of Zn/MnO2 batteries. [ABSTRACT FROM AUTHOR]

Aqueous chargeable batteries always suffer from narrow voltage window due to water electrolysis. In this paper, a high-voltage aqueous lead dioxide-zinc battery is constructed by designing negative and positive materials in alkaline and acidic electrolytes, respectively. It not only exhibits an open circuit voltage of 2.8 V and a discharge voltage of 2.75 V, which is the highest among PbO2-based aqueous batteries, but also provides a promising strategy to obtain high operating voltage without using expensive organic electrolytes or solid electrolyte separator. [ABSTRACT FROM AUTHOR]

The use of three-dimensional porous nickel foam as the current collector of the nickel hydroxide electrode adds significantly to the cost of the nickel-based alkaline rechargeable batteries. Although iron is considerably less expensive than nickel, iron corrodes at the operating potential of the nickel hydroxide electrode. We have found that a 70-100 nm thick thermal coating of cobalt ferrite spinel protects the iron from corrosion. Such a coated iron substrate was found to be stable against corrosion even when polarized anodically at 10 mA cm-2 in 30% potassium hydroxide electrolyte for 1000 h. While the thermal coating of cobalt ferrite protected iron against corrosion, incorporation of lithium ions into the coating was found to enhance the electrical conductivity of the coating. XPS and EXAFS studies confirmed that the enhanced conductivity resulted from an increase in the population of Co3+ in the ferrite spinel lattice. An inexpensive iron (steel) substrate protected by such a coating when used as a nickel hydroxide battery electrode exhibited a specific capacity of 0.25 Ah g-1 at C/5 discharge rate, comparable to a nickel hydroxide electrode based on a relatively expensive nickel foam substrate. The steel-based electrode also exhibited no noticeable degradation over 150 cycles at C/2 rate. This demonstration of a robust and economical steel substrate presents a unique opportunity for reducing the cost of the nickel hydroxide battery electrode in alkaline batteries. [ABSTRACT FROM AUTHOR]

Submicron spherical zinc powders with high surface area, activity and low cost were prepared by DC arc plasma evaporation method. Based on the characterization of morphology, particle size and composition of ultrafine zinc powder, the effects of addition amount of PTFE and compounding of PTFE with PAAs and CMCs, electrolyte addition amount, compound mass ratio of flake and spherical zinc powder on the discharge performance of zinc electrode had been systematically studied. The results showed that ultrafine zinc powder was polycrystalline, spherical and its purity reached 99.96wt%. Under 0.2C, the discharge capacity reached 577.5mAh when addition of PTFE was 10wt.%. When 2.5wt.% PTFE was compound with 6.5wt.%(PAAs: CMCs = 2:1), the discharge capacity improved which reached 613.4 mAh. The discharge capacity was 580.3mAh when the electrolyte content was 38wt.%. When the mass ratio of special flake zinc powder to spherical zinc powder was 3:7, the discharge capacity reached 664.1 mAh, it was 13.5% higher than 584.9 mAh of pure spherical zinc powder and 22.6% higher than 541.5 mAh of pure flake zinc powder. Under 1.8C, compared with alkaline manganese battery prepared using flake zinc powders, the mass specific capacity increased by 57.12% and the volume specific capacity increased by 187.79%. [ABSTRACT FROM AUTHOR]

The spinel cobalt oxide (Co3O4) nanoplate exposed with hexagonal {111} facets is demonstrated to be a highly active catalyst, while the effect of cation substitution on the oxygen electrocatalysis is still unclear. Herein, the electrocatalytic activity of cation-substituted spinel cobaltite MCo2O4 (M = Fe, Co, and Ni) nanoplates with the {111} facets is investigated systematically by experiments and theoretical calculations. For both oxygen reduction and evolution reactions, Ni-substituted Co3O4 hexagonal nanoplates show the best activity. It is mainly attributed to the increased surface energy per unit area and the enhanced oxygen species absorption ability, which are also evidenced by density functional theory calculations. Moreover, the three kinds of MCo2O4 nanoplates are applied in Zn-air batteries and the corresponding electrochemical performance is tested. Among the three batteries, NiCo2O4 hexagonal nanoplates also enable the highest peak power density of 110.3 mW cm-2 and the most stable discharge-charge voltage profiles for 50 cycles, indicating that NiCo2O4 nanoplates are the promising catalyst for further Zn-air battery applications. Besides, this work illustrates that the substitution of Co byNi or Fe can remarkably change the electronic structural states, thus tuning the electrochemical properties of the hexagonal Co3O4 nanoplates. [ABSTRACT FROM AUTHOR]

Rechargeable zinc-air batteries (ZABs) are considered as some of the most promising electrochemical storage systems owing to their high energy density and low-cost. However, the low energy efficiency and poor cycle-life impede the further development of rechargeable ZABs. It is desirable to improve the performance of ZABs by developing highly efficient, long-life time bifunctional air electrodes. We propose a Janus-typed integrated bifunctional air electrode, which consists of MnOx and NiFe layered double hydroxide (LDH) by means of electrodeposition on Ni foam. The Janus-typed integrated bifunctional air electrode can avoid positive oxidation ofMnOx owing to the spatial separation of the oxygen reduction and evolution reactions (ORR and OER). Moreover, based on the unique structure, the resulting air electrode exhibits better catalytic activity due to the combination of the unique advantages of MnOx and FeNi LDH, and the enhancement of active species transportation. This Janus-typed air electrode for rechargeable ZAB achieved an energy efficiency of 65.7% at 10 mA cm-2, excellent stability over 110 h, and peak power density of 120 mW cm-2. The Janus structure for the bifunctional electrode provides a valuable approach to develop high-performance rechargeable ZABs. [ABSTRACT FROM AUTHOR]

A mathematical model was developed to study the voltage behavior of LixNi0.5Mn1.5O4(LNMO) electrode at particle scale. The phase transition process of Li1 → Li0.5 → Li1 in spinel LNMO was modeled by Avrami equation, which was incorporated into lithium transport process in the particle. By simulating the charge and discharge process, numerical results indicated that phase distributions in the LNMO particle are different between charge and discharge at the same SOC condition, which can lead to different capacity utilization in practical battery operation. Results of average phase fractions also qualitatively demonstrated the existence of path dependent behavior of phase transformation inside LNMO electrode, which can be attributed to the competition between diffusion and phase transformation. The path-dependent behavior at different SOC conditions were then studied. Results show that longer phase change time can result in more capacity utilization. The relaxation impact was investigated at last. Numerical results showed that the path-dependence behavior can be reduced by long relaxation, and this is because phase transformation reactions take place during the relaxation period and eventually can reduce the path-dependence effect. [ABSTRACT FROM AUTHOR]

The voltage behavior of the LixNi0.5Mn1.5O4 (LNMO) electrode was studied in this work. A thin-layer LNMO electrode was prepared for testing in a coin cell format where lithium metal was used as the counter electrode. A series of charge and discharge cycling experiment was designed to investigate LNMO rate performance and voltage behavior. Our results indicated that a phase transformation process in the LNMO electrode has significant influence on its voltage behavior. Results also showed that the LNMO electrode has path-dependent behavior on both discharge and charge, which is due to the lithium transport inside theLNMOelectrode. Experiments revealed that this path-dependent behavior depends on the state of charge (SOC), and may result from limited phase transformation rates. Relaxation experiments were also conducted at different SOC conditions. Results showed that the voltage behavior of the LNMO electrode is time-dependent, where long relaxation can lead to the vanishing of the electrode path-dependent behavior. [ABSTRACT FROM AUTHOR]

Nanoscale Ca(OH)2 particles as a novel cathode additive for nickel-based secondary batteries are synthesized by a homogeneous precipitation method. The influence of Ca(OH)2 additive on the electrochemical performance of two types of nickel electrode (using spherical Ni(OH)2 and γ-CoOOH@Ni(OH)2) were evaluated. It is interestingly discovered that nano-Ca(OH)2 additives can efficiently improve the charge acceptance of both nickel electrodes. Especially, the charge acceptance of the 1.0 wt% nano- Ca(OH)2@γ-CoOOH@Ni(OH)2 electrode at 70°C at 5C is over 90% and the discharge capacity can reach about 218 mAh g-1. These performance enhancements of nickel electrode mainly result from the combined coating with Ca(OH)2 and γ-CoOOH. The modification of oxygen evolution reaction on the nickel electrode is primarily resulting from the use of Ca(OH)2 by increasing its potential and suppressing its rate. The observably lower charge transfer resistance of nickel electrode is mainly due to the high conductivity coating of γ-CoOOH. Consequently, the proposed cathode additive is promising for the high-temperature property enhancement of nickel-based rechargeable batteries. [ABSTRACT FROM AUTHOR]

This study aims to discuss the effect of stannum ion (potassium stannate) in alkaline zincate solution on the deposition/dissolution behavior of zinc anode for single-flow zinc-nickel battery (SFZNB). Physical analysis is conducted using scanning electron microscopy and energy dispersive X-ray spectroscopy (EDS) technologies. The electrochemical performance of the battery is tested using cyclic voltammetry and galvanostatic techniques. Results show that adding potassium stannate in alkaline solution promotes crystal seed formation and grain growth and substantially improves the charge retention of the battery. The battery is charged to 18.75 mAh·cm-2 (based on the area of the electrode) at current density of 10 mA·cm-2 and set aside for 12 h. Then, the battery using electrolyte with 0.1 mol·L-1 potassium stannate has a discharge capacity of 15.20 mAh·cm-2 (coulomb efficiency of 81.1%). Moreover, the control sample has a discharge capacity of 11.25 mAh·cm-2 (coulomb efficiency of 60.0%). Thus, the present work provides a simple approach to restrain the SFZNB from self-discharge. [ABSTRACT FROM AUTHOR]

In this work, the leaching of the active material electrodes of spent alkaline batteries was carried out using a deep eutectic solvent formed by acetylcholine chloride-urea as leaching medium. From the leaching liquors of the cathode or the cathode/anode mix, the electrochemical formation of Mn or Mn-Zn alloy, onto a glassy carbon electrode, was respectively performed by means of cyclic voltammetry and chronoamperometry techniques. The analysis of the potentiostatic current density transients was done using of models that involve the three-dimensional nucleation and diffusion controlled growth of a) bimetallic phases [Díaz-Morales et al. J. Solid. State Electrochem. 17 (2013) 345-351], in the case of the Mn-Zn alloy and b) metallic nuclei, for Mn electrodeposition [Scharifker and Mostany, J. Electroanal. Chem., 177 (1984) 13-23]. From scanning electron microscopy and EDX, it was verified that the nuclei formed were composed of Mn, or the Mn-Zn alloy depending on the leaching liquors used. [ABSTRACT FROM AUTHOR]

Metal selenides, as a new class of alkaline aqueous battery materials, have attracted more researchers' attention in recent years. In this work, the M0.85Se (M=Ni, Co) materials with different morphologies are successfully synthesized via a two-step hydrothermal method by using different solvents. The effects of solvents and transition metals on structure, morphology, specific surface area and pore structure and electrochemical properties of the products are systematically explored. The electrochemical measurements reveal that the Ni0.85Se products prepared by H2O and ethanol exhibit higher specific capacity (83.8 and 65.3 mAh g-1 at 1 A g-1), whereas the Co0.85Se products prepared by H2O and ethanol display better rate capability (75.1 and 69.0% of capacity retention rate at 50 A g-1) and cycling stability (97.6 and 94.5% of capacity retention at 5 A g-1 after 2000 cycles), respectively. The different electrochemical properties can be ascribed to the fact that theNi0.85Se electrodes showdiffusion-controlled faradaic chracteristic while the Co0.85Se electrodes present mixed behavior of diffusion-controlled faradaic and capacitive feature. Such work is of fundamental importance and it provides a valuable reference for the tailoring of these different properties by the use of various solvents and transition metals. [ABSTRACT FROM AUTHOR]

At a low depth of discharge, the performance of rechargeable alkaline Zn/MnO2 batteries is determined by the concomitant processes of hydrogen ion insertion and electro-reduction in the solid phase of γ-MnO2. Ab initio computational methods based on density functional theory (DFT) were applied to study the mechanism of hydrogen ion insertion into the pyrolusite (β), ramsdellite (R), and nsutite (γ)MnO2 polymorphs. Itwas found that hydrogen ion insertion induced significant distortion in the crystal structures ofMnO2 polymorphs. Calculations demonstrated that the hydrogen ions inserted into γ-MnO2 initially occupied the larger 2×1 ramsdellite tunnels. The protonated form of γ-MnO2 was found to be stable over the discharge range during which up to two hydrogen ions were inserted into each 2×1 tunnel. At the same time, the study showed that the insertion of hydrogen ions into the 1×1 pyrolusite tunnels of γ-MnO2 created instability leading to the structural breakdown of γ-MnO2. The results of this study explain the presence of groutite (α-MnOOH) and the absence of manganite (γ-MnOOH) among the reaction products of partially reduced γ-MnO2. [ABSTRACT FROM AUTHOR]

Bipolar membrane fuel cells, which features a hybrid acid-alkaline membrane architecture, show great potential for practical applications because of their ability for self-humidification during operation. The principle of self-humidification behavior and associated transport mechanisms are reported in previous studies with reduced-dimension models. This paper reports on a three-dimensional model and new experimental data that further elucidate the mechanism of self-humidification, provide detailed characterization of the effects of design parameters on flow field and cell performance. The multidimensional-multiphysics model accounts for interface reaction kinetics, as well as transport of gas species, charged species and momentum. Simulations and quantitative analysis are performed for the cathode catalyst layer where water transport is critical for the electrochemical reaction therein. Three-dimensional model fully captures geometric features and gradients, and offers more comprehensive resolution of mass transport inside the cell. Based on the three-dimensional model, effects of channel width on cell performance are investigated both numerically and experimentally. [ABSTRACT FROM AUTHOR]

The leading cause for safety vent rupture in alkaline batteries is the intrinsic instability of Zn in the highly alkaline reacting environment. Zn and aqueous KOH react in a parasitic process to generate hydrogen gas, which can rupture the seal and vent the hydrogen along with small amounts of electrolyte, and thus, damage consumer devices. Abusive conditions, particularly deep discharge, are known to accelerate this "gassing" phenomena. In order to understand the fundamental drivers and mechanisms for such gassing behavior, the results from multiphysics modeling, ex-situ microscopy and operando measurements of cell potential, pressure and visualization have been combined. Operando measurements were enabled by the development a new research platform that enables a cross-sectional view of a cylindrical Zn-MnO2 primary alkaline battery throughout its discharge and recovery. A second version of this cell can actively measure the in-cell pressure during the discharge. It is shown that steep concentration gradients emerge during the cell discharge through a redox electrolyte mechanism, leading to the formation of high surface area Zn deposits that experience rapid corrosion when the cell rests to its open circuit voltage. Such corrosion is paired with the release of hydrogen and high cell pressure - eventually leading to cell rupture. [ABSTRACT FROM AUTHOR]

Severe self-corrosion is the main barrier preventing the application of aluminum as an anode material in alkaline air battery. In this work, a hybrid organic/inorganic inhibitor based on L-Cysteine/zinc oxide was tested to see if its addition to alkaline electrolyte can reduce self-corrosion of a commercial 1060 pure aluminum. Results obtained have shown that self-corrosion of pure aluminum is significantly restrained by the L-Cysteine/ZnO hybrid inhibitor without affecting its discharge performance. An interaction between ZnO and L-Cysteine leads to formation of a dense layer on pure aluminum surface. In both NaOH + ZnO and NaOH + LCysteine + ZnO solutions, the reaction mechanism is mainly controlled by diffusion of zincate ions. By using the L-Cysteine/ZnO hybrid inhibitor, cheap commercial 1060 pure aluminum can replace expensive 5N5 super-pure aluminum to achieve a comparable performance. This has been demonstrated in this study by comparing the battery based on commercial 1060 pure aluminum with the L-Cysteine/ZnO inhibitor and the battery made of 5N5 super-pure aluminum with 4 M NaOH solution. [ABSTRACT FROM AUTHOR]

A new ageing mode for positive electrode, associated to Ni2O3H formation, was observed for the first time in alkaline batteries (Ni-Cd, Ni-MH) during harsh shallow cycling operations. The study of Ni2O3H synthesis conditions outlined that γ-NiOOH and βIII-NiOOH phases display instability versus electrolyte at elevated temperature, leading to the irreversible formation of Ni2O3H through a reduction, followed by a dissolution / precipitation mechanism. It was shown also that Ni2O3H is a rather moderate electronic conductor and is almost electrochemically inactive, in good correlation with the loss of cell capacity. Highlighting NiOOH / Ni2O3H transformation provides a new understanding of nickel hydroxide and oxyhydroxide phase transformations diagram. [ABSTRACT FROM AUTHOR]

Rechargeable alkaline Zn/MnO2 batteries are being developed for use as cost-effective grid-scale energy storage devices. Previous studies have shown that limiting the depth of discharge (DOD) of the MnO2 cathode extends cell lifetime while still providing a cost-effective battery system. Herein, a comprehensive study of triethanolamine (TEA) as an additive in Zn/MnO2 limited DOD batteries is provided by examining the effect of TEA in full cells as well as independently on the cathode, anode, separator, and electrolyte. Improvement in cycle-ability of the cathode (on average, 80% of cycled capacity remains after 191 cycles without TEA, 568 cycles with TEA) and a decrease in ionic zinc mobility across Celgard 3501 (7.91 x 10-5 cm²/min without TEA, 3.56 x 10-5 cm²/min with TEA) and Cellophane 350P00 (3.26 x 10-5 cm²/min without TEA, 4.74 x 10-6 cm²/min with TEA) separators upon the addition of TEA are demonstrated. However, TEA increased both the reduction potential of Zn (-0.68 V vs. Hg/HgO without TEA, -0.76 V with TEA) and the solubility of Zn2+ (0.813 M without TEA, 1.023 M with TEA). Overall, the addition of TEA extended the lifetime of limited DOD cells on average by 297%. [ABSTRACT FROM AUTHOR]

Sheet-like, well crystalline carbon-coated Zn-Al-Bi layered double oxides (Zn-Al-Bi-LDOs/C) nanocomposites with a ~2 nmthick amorphous carbon layers have been synthesized via hydrothermal reaction and carbonization of precursor. The structural analysis and morphology characterization of as-prepared Zn-Al-Bi-LDOs/C are characterized by transmission electron microscope (TEM), X-ray diffraction (XRD), energy dispersive spectrometer (EDS) and scanning electron microscope (SEM). Applying a thin surface-anchoring carbon layer is an effective way in prohibiting the Zn-Al-Bi-LDOs in electrode from disintegrating in the alkaline electrolyte, which could accelerate the activation of active substance because of higher anti-corrosion and superior electrical conductivity. The elementary results prove that the Zn-Al-Bi-LDOs/C nanocomposites show better Zn-Ni rechargeable battery performance with brilliant reversible capacity, remarkable cyclic performance (475 mA h g-1 after 900 cycles at 1 C), giving credence to the practicability of Zn-Al-Bi-LDOs/C for high-efficiency reaction of active materials for power storage for Zn-Ni secondary battery. [ABSTRACT FROM AUTHOR]

Iron-based alkaline rechargeable batteries such as iron-air and nickel-iron batteries are particularly attractive for large-scale energy storage because these batteries can be relatively inexpensive, environment-friendly, and also safe. Therefore, our study has focused on achieving the essential electrical performance and cycling properties needed for the widespread use of iron-based alkaline batteries in stationary and distributed energy storage applications. We have demonstrated for the first time, an advanced sintered iron electrode capable of 3500 cycles of repeated charge and discharge at the 1-hour rate and 100% depth of discharge in each cycle, and an average Coulombic efficiency of over 97%. Such a robust and efficient rechargeable iron electrode is also capable of continuous discharge at rates as high as 3C with no noticeable loss in utilization. We have shown that the porosity, pore size and thickness of the sintered electrode can be selected rationally to optimize specific capacity, rate capability and robustness. These advances in the electrical performance and durability of the iron electrode enables iron-based alkaline batteries to be a viable technology solution for meeting the dire need for large-scale electrical energy storage. [ABSTRACT FROM AUTHOR]

The influence of C45 carbon black modified with H3PMo12O40 (C45-MPA) on the electrocatalytic activity of a composite hydride electrode containing LaNi5 hydrogen storage alloy was analyzed. There was a reduction in the overpotential and an increase of the exchange current density for the hydrogen evolution reaction on hydride electrodes containing C45-MPAin comparison to unmodified electrodes. A significant increase in both the discharge capacity and kinetic parameters of composite hydride electrodes, which is associated with the addition of C45-MPA to the electrode, is a promising result indicating the catalytic activity of heteropolyacid in a strongly alkaline environment. [ABSTRACT FROM AUTHOR]

The commonly observed irreversibility of the passive state on carbon steel in alkaline solutions was examined in simulated concrete pore solution under anoxic conditions replicated by applying relatively negative film formation potentials, at which the cathodic process dominates the passive system. The fundamental source of this irreversibility was investigated by describing the kinetics of the passive system via a previously developed mixed potential model that combines the point defect model accounting for the anodic process and the Butler-Volmer equation accounting for the cathodic process. Electrochemical impedance spectroscopy, Mott-Schottky analysis and model optimization were performed at each potential when the potential was first stepped in the anodic direction and then in the cathodic direction. The experiment and optimization results demonstrate that the irreversibility of the passive state is closely associated with the discrepancy in the defect structure of the passive film upon opposite stepping directions of the film formation potential, and is essentially caused by the slower film formation and slower film dissolution during the cathodic potential stepping than those during the anodic potential stepping. [ABSTRACT FROM AUTHOR]

In this investigation, there was deduced from experiments that an exothermic reaction in the thermal runaway process in alkaline batteries is the electrochemical reaction of atomic hydrogen recombination Hadscd + HadsNi→ H2↑ (H2O+Hads + e- → H2 ↑ + OH- on a cathode and Hads + OH- → H2O + e- on an anode), A rate-limiting step for this reaction on both a cathode and an anode is found to be a step of metal-hydrides disintegration. This electrochemical reaction proceeds at voltage 0.5-0.6 V on battery terminals according to experimental data on the thermal runaway. The possible thermal runaway mechanism has been proposed corresponding to all the experimental results obtained. [ABSTRACT FROM AUTHOR]

Iron-based alkaline rechargeable batteries such as nickel-iron and iron-air batteries are promising candidates for large-scale energy storage applications because of their relatively low cost, inherent robustness to cycling, and eco-friendliness. In the present study, we demonstrate iron electrodes containing iron (II) sulfide and bismuth oxide additives that do not exhibit any noticeable capacity loss even after 1200 cycles at 100% depth of discharge in each cycle. In iron electrodes prepared with bismuth sulfide additive, capacity loss occurred during cycling, accompanied by a decrease in discharge rate capability and rapid passivation. The recovery of capacity by adding sulfide ions to the electrolyte confirmed that the electrode that suffered capacity fade did not have an adequate supply of sulfide ions. We also found that the loss of cycleability was accompanied by the steady accumulation of magnetite and loss of iron sulfides at the iron electrode. The use of sparingly soluble iron (II) sulfide as an electrode additive ensured a sustained and steady supply of sulfide preventing the accumulation of magnetite during cycling. Thus, we have gained understanding of the critical role of sulfide additives in achieving long cycle life in rechargeable alkaline iron electrodes. [ABSTRACT FROM AUTHOR]