The ever‐growing demands for electrical energy storage have stimulated the pursuit of alternative advanced batteries. Zn‐ion batteries (ZIBs) are receiving increased attentions due to the low cost, ...high safety, and high eco‐efficiency. However, it is still a big challenge to develop suitable cathode materials for intercalation of Zn ions. This review provides a timely access for researchers to the recent activities regarding ZIBs. First, cathode materials including various manganese oxides, vanadium compounds, and Prussian blue analogs are summarized with details in crystal structures and Zn ion storage mechanisms. Then, the electrolytes and their influences on the electrochemical processes are discussed. Finally, opinions on the current challenge of ZIBs and perspective to future research directions are provided.
Recent advances in zinc‐ion batteries, especially the cathode materials including Mn‐based, V‐based, and Prussian blue analogs based materials, are comprehensively summarized here. The relationships between crystal structure, reaction mechanism, and electrochemical performance are elaborated.
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Hybrid metal‐ion capacitors (MICs) (M stands for Li or Na) are designed to deliver high energy density, rapid energy delivery, and long lifespan. The devices are composed of a battery anode and a ...supercapacitor cathode, and thus become a tradeoff between batteries and supercapacitors. In the past two decades, tremendous efforts have been put into the search for suitable electrode materials to overcome the kinetic imbalance between the battery‐type anode and the capacitor‐type cathode. Recently, some transition‐metal compounds have been found to show pseudocapacitive characteristics in a nonaqueous electrolyte, which makes them interesting high‐rate candidates for hybrid MIC anodes. Here, the material design strategies in Li‐ion and Na‐ion capacitors are summarized, with a focus on pseudocapacitive oxide anodes (Nb2O5, MoO3, etc.), which provide a new opportunity to obtain a higher power density of the hybrid devices. The application of Mxene as an anode material of MICs is also discussed. A perspective to the future research of MICs toward practical applications is proposed to close.
Hybrid metal‐ion capacitors are found to deliver high energy density and rapid energy delivery. The material design strategies particularly in pseudocapacitive oxide anodes in Li‐ion and Na‐ion capacitors (LICs and NICs) are systematically discussed. A perspective on the challenges and opportunities of LIC and NIC devices is also presented.
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Exploring highly efficient and low‐cost electrocatalysts for electrochemical water splitting is of importance for the conversion of intermediate energy. Herein, the synthesis of dual‐cation (Fe, ...Co)‐incorporated NiSe2 nanosheets (Fe, Co‐NiSe2) and systematical investigation of their electrocatalytic performance for water splitting as a function of the composition are reported. The dual‐cation incorporation can distort the lattice and induce stronger electronic interaction, leading to increased active site exposure and optimized adsorption energy of reaction intermediates compared to single‐cation‐doped or pure NiSe2. As a result, the obtained Fe0.09Co0.13‐NiSe2 porous nanosheet electrode shows an optimized catalytic activity with a low overpotential of 251 mV for oxygen evolution reaction and 92 mV for hydrogen evolution reaction (both at 10 mA cm−2 in 1 m KOH). When used as bifunctional electrodes for overall water splitting, the current density of 10 mA cm−2 is achieved at a low cell voltage of 1.52 V. This work highlights the importance of dual‐cation doping in enhancing the electrocatalyst performance of transition metal dichalcogenides.
Dual‐cation incorporation makes NiSe2 nanosheet a more effective catalyst. Introducing both Fe and Co atoms with an optimal ratio into porous NiSe2 nanosheets causes evident lattice distortion and strong electronic interaction, leading to a more efficient bifunctionality in overall electrochemical water splitting.
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Organometal trihalide perovskites have recently emerged as promising materials for low‐cost, high‐efficiency solar cells. In less than five years, the efficiency of perovskite solar cells (PSC) has ...been updated rapidly as a result of new strategies adopted in their fabrication process, including device structure, interfacial engineering, chemical compositional tuning, and crystallization kinetics control. To date, the best PSC efficiency has reached 20.1%, which is close to that of single crystal silicon solar cells. However, the stability of PSC devices is still unsatisfactory and is the main bottleneck impeding their commercialization. Here, we summarize recent studies on the degradation mechanisms of organometal trihalide perovskites in PSC devices, and the strategies for stability improvement.
Organometal trihalide solar cells, despite their high efficiency and low cost, still have a serious air instability limitations. Recent studies of the degradation mechanisms of organometal trihalide perovskites in photovoltaics and various strategies for stability improvement are summarized.
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The slow kinetics of oxygen evolution reaction (OER) causes high power consumption for electrochemical water splitting. Various strategies have been attempted to accelerate the OER rate, but there ...are few studies on regulating the transport of reactants especially under large current densities when the mass transfer factor dominates the evolution reactions. Herein, NixFe1–x alloy nanocones arrays (with ≈2 nm surface NiO/NiFe(OH)2 layer) are adopted to boost the transport of reactants. Finite element analysis suggests that the high‐curvature tips can enhance the local electric field, which induces an order of magnitude higher concentration of hydroxide ions (OH−) at the active sites and promotes intrinsic OER activity by 67% at 1.5 V. Experimental results show that a fabricated NiFe nanocone array electrode, with optimized alloy composition, has a small overpotential of 190 mV at 10 mA cm−2 and 255 mV at 500 mA cm−2. When calibrated by electrochemical surface area, the nanocones electrode outperforms the state‐of‐the‐art OER electrocatalysts. The positive effect of the tip‐enhanced local electric field in promoting mass transfer is also confirmed by comparing samples with different tip curvature radii. It is suggested that this local field enhanced OER kinetics is a generic effect to other OER catalysts.
A new mechanistic understanding of the enhanced alkaline oxygen evolution reaction (OER) kinetics is achieved by employing dense arrays of nanocones with sharp tips. A local electric field promotes aggregation of hydroxide ions near the high‐curvature active sites, leading to lower overpotential and higher intrinsic OER activity compared to blunt cones.
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Electrochemical splitting of water to produce hydrogen and oxygen is an important process for many energy storage and conversion devices. Developing efficient, durable, low‐cost, and earth‐abundant ...electrocatalysts for the oxygen evolution reaction (OER) is of great urgency. To achieve the rapid synthesis of transition‐metal nitride nanostructures and improve their electrocatalytic performance, a new strategy has been developed to convert cobalt oxide precursors into cobalt nitride nanowires through N2 radio frequency plasma treatment. This method requires significantly shorter reaction times (about 1 min) at room temperature compared to conventional high‐temperature NH3 annealing which requires a few hours. The plasma treatment significantly enhances the OER activity, as evidenced by a low overpotential of 290 mV to reach a current density of 10 mA cm−2, a small Tafel slope, and long‐term durability in an alkaline electrolyte.
Down to the wire: CoN nanowire arrays were synthesized by means of a fast and efficient N2 plasma method that is both safe and environmentally friendly. Owing to better conductivity and a large surface area, the obtained CoN nanowire arrays on nickel foam exhibit outstanding performance in the oxygen evolution reaction.
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Achieving high‐performance Na‐ion capacitors (NICs) has the particular challenge of matching both capacity and kinetics between the anode and cathode. Here a high‐power NIC full device constructed ...from 2D metal–organic framework (MOFs) array is reported as the reactive template. The MOF array is converted to N‐doped mesoporous carbon nanosheets (mp‐CNSs), which are then uniformly encapsulated with VO2 and Na3V2(PO4)3 (NVP) nanoparticles as the electroactive materials. By this method, the high‐power performance of the battery materials is enabled to be enhanced significantly. It is discovered that such hybrid NVP@mp‐CNSs array can render ultrahigh rate capability (up to 200 C, equivalent to discharge within 18 s) and superior cycle performance, which outperforms all NVP‐based Na‐ion battery cathodes reported so far. A quasi‐solid‐state flexible NIC based on the NVP@mp‐CNSs cathode and the VO2@mp‐CNSs anode is further assembled. This hybrid NIC device delivers both high energy density and power density as well as a good cycle stability (78% retention after 2000 cycles at 1 A g−1). The results demonstrate the powerfulness of MOF arrays as the reactor for fabricating electrode materials.
Metal–organic framework (MOF)‐derived electrodes for a Na‐ion capacitor. Mesoporous carbon nanosheet arrays are fabricated from 2D Co/Zn‐MOF array, on which anode material VO2 and cathode Na3V2(PO4)3 thin films are deposited. The assembled solid‐state flexible Na‐ion capacitor shows high‐rate performance.
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Water electrolysis represents a promising sustainable hydrogen production technology. However, in practical application which requires extremely large current densities (>500 mA cm
−2
), the oxygen ...evolution reaction (OER) becomes unstable and kinetically sluggish, which is a major hurdle to large-scale hydrogen production. Herein, we report an exceptionally active and binder-free NiFe nanowire array based OER electrode that allows durable water splitting at current densities up to 1000 mA cm
−2
up to 120 hours. Specifically, NiFe oxyhydroxide (shell)-anchored NiFe alloy nanowire (core) arrays are prepared
via
a magnetic-field-assisted chemical deposition method. The ultrathin (1-5 nm) and amorphous NiFe oxyhydroxide is
in situ
formed on the NiFe alloy nanowire surface, which is identified as an intrinsically highly active phase for the OER. Additionally, the fine geometry of the hierarchical electrode can substantially improve charge and mass (reactants and oxygen bubbles) transfer. In an alkaline electrolyte, this OER electrode can yield current densities of 500 and 1000 mA cm
−2
stably over 120 hours at overpotentials of only 248 mV and 258 mV respectively, which are dramatically lower than any recently reported overpotentials. Notably, the integrated alkaline electrolyzer (with pure Ni nanowires as HER electrode) is demonstrated to reach the current density of 1000 mA cm
−2
with super low voltage of 1.76 V, outperforming the state-of-the-art industrial catalysts. Our result may represent a critical step towards an industrial electrolyzer for large-scale hydrogen production by water splitting.
Exceptionally high OER & HER performances were achieved by rationally designing the electrode structure of non-noble NiFe materials.
The practical application of the Zn‐metal anode for aqueous batteries is greatly restricted by catastrophic dendrite growth, intricate hydrogen evolution, and parasitic surface passivation. Herein, a ...polyanionic hydrogel film is introduced as a protective layer on the Zn anode with the assistance of a silane coupling agent (denoted as Zn–SHn). The hydrogel framework with zincophilic –SO3− functional groups uniformizes the zinc ions flux and transport. Furthermore, such a hydrogel layer chemically bonded on the Zn surface possesses an anti‐catalysis effect, which effectively suppresses both the hydrogen evolution reaction and formation of Zn dendrites. As a result, stable and reversible Zn stripping/plating at various currents and capacities is achieved. A full cell by pairing the Zn–SHn anode with a NaV3O8·1.5 H2O cathode shows a capacity of around 176 mAh g−1 with a retention around 67% over 4000 cycles at 10 A g−1. This polyanionic hydrogel film protection strategy paves a new way for future Zn‐anode design and safe aqueous batteries construction.
A unique polyanionic hydrogel is employed as an artificial protective layer for reversible Zn‐metal anodes. The polyanions in the hydrogel framework facilitate a homogeneous zinc‐ion flux, and the Zn–O bonding strengthens the interface and suppresses surface corrosion and irregular Zn dendrites growth. This strategy could apply also to other aqueous metal batteries.
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Efficient thermal protection is essential to battery safety. Here, a self‐adaptive strategy is demonstrated to circumvent the thermal runaway of aqueous zinc‐ion batteries, by using a zinc ...chloride‐enriched hygroscopic hydrogel electrolyte. At high temperatures, water inside the hydrogel can quickly evaporate to dissipate the heat generated. Concurrently, excessive water evaporation causes a sudden drop in the ion diffusion of the hydrogel electrolyte, thereby effectively restricting the migration of ions and shutting down the battery. When the temperature lowers, the hydrogel absorbs water from the air and the battery recovers its function. The evaporation and regeneration of water in the hydrogel electrolytes are highly reversible, thus realizing intelligent and efficient thermal self‐protection of zinc‐ion batteries. By properly designing and engineering the hygroscopic hydrogel electrolytes, it is believed that other thermal self‐protective aqueous batteries with faster response can be abricated, which shows promise for a safe power supply in both consumable electronics and electric vehicles.
A general self‐adaptive strategy to circumvent the thermal runaway of zinc‐ion batteries is presented by employing zinc chloride‐enriched hygroscopic hydrogel electrolytes. Temperature changes cause water evaporation or absorption in the hydrogel, and then reversibly regulate the migration of ions in the hydrogel electrolyte, enabling the intelligent thermal self‐protection of batteries.
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