Compared with organic electrolytes, aqueous electrolytes are safer (no risk of burning) and can achieve an ionic conductivity several orders of magnitude higher than organic electrolytes. [1][2][3][4] This makes aqueous rechargeable batteries cheap, nonpolluting and safe, with potentially high power density capability (although the cell voltage is limited). [1] However, the widely studied aqueous lithium-ion batteries and sodium-ion batteries have low specific capacities (<150 mAh g −1 ). [2] Among potential alternatives, the aqueous Zn-ion battery (AZIB) is currently attracting significant attention due to key features of Zn metal, including abundance (low cost) and high theoretical specific capacity (820 mAh g −1 ). [5][6][7][8][9] The main challenges for the development of aqueous Zn-ion batteries are to achieve dendrite-free Zn deposit at the anode [10,11] and find suitable cathode materials. MnO 2 (theoretical capacity is 308 mAh g −1 ) is one of the most attractive cathode materials for aqueous zinc ion batteries due to their high energy density and high power density. [5,6,8,[11][12][13][14][15] Among various crystallographic polymorphs (α-, β-, γ-, δ-, λ-, and εtype), birnessite-type δ-MnO 2 with layered structure owns a large interlayer spacing (≈0.7 nm), which is more suitable for rapid and reversible (de-)insertion of Zn ions. [16] However, δ-MnO 2 was reported to show poor rate capability and cycling stability. [15] According to the literature, δ-MnO 2 -based cathodes are limited by the serious structural degradation with phase transformation, which is mainly attributed to the cointercalation of water molecules and dissolution of Mn during cycling processes. [17,18] It has been reported that the preintercalation of large cations (such as, K + , Ce 3+ , and Ca 2+ ) in MnO 2 during synthetic process can stabilize the structure through coordination of guest-ions with adjacent host atoms. [16,[19][20][21][22][23][24][25] Moreover, the preintercalation of alkaline ion strategy in MnO 2 has also attracted much attention as an effective approach to enhance the electronic conductivity, activating more active sites, and promoting diffusion kinetics. [25] To date, various types of reaction mechanisms have been reported for Mn oxide-based positive electrode of Zn-MnO 2 battery in Zn-containing aqueous electrolyte. [15,[26][27][28] Pan et al. [26] proposed a chemical-assisted conversion reaction mechanism Recently, rechargeable zinc-ion batteries in mild acidic electrolytes have attracted considerable research interest as a result of their high sustainability, safety, and low cost. However, the use of conventional Zn-ion storage materials is hindered by insufficient specific capacity, sluggish reaction kinetics, or poor cycle life. Here, these limitations are addressed by preintercalating alkali ions and water crystals into layered δ-MnO 2 (birnessite) to prepare K 0.27 MnO 2 •0.54H 2 O (KMO) and Na 0.55 Mn 2 O 4 •1.5H 2 O with ultrathin nanosheet morphology via a rapid molten salt method. In these materials, alk...

2D materials have demonstrated good chemical, optical, electrical, and magnetic characteristics, and offer great potential in numerous applications. Corresponding synthesis technologies of 2D materials that are highquality, high-yield, low-cost, and time-saving are highly desired. Salt-assisted methods are emerging technologies that can meet these requirements for the fabrication of 2D materials. Herein, the recent process for the salt-assisted synthesis of 2D materials and their typical applications are summarized. First, the properties of salt crystals and molten salts are briefly introduced, and then some examples of 2D materials synthesis with the assistance of salt as well as their representative applications are presented. The underlying mechanisms of salts with different states on the formation of 2D morphology are discussed to aid in the rational design of synthetic route of 2D materials. At last, the challenges and future perspectives for salt-assisted methods are briefly described. This review provides guidance for the controllable synthesis of 2D materials based on the salt-assisted approaches.The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/adfm.201908486.MoO 3 , and LaNb 2 O 7 ), [14][15][16] layered double hydroxides (LDHs, e.g., Mg 6 Al 2 (OH) 16 CO 3 •4H 2 O), [17] hexagonal-boron nitride (h-BN), [2,18] transition metal halides (such as MoCl 2 and CrCl 3 ), [19] black phosphorus, [20] graphitic carbon nitride (g-C 3 N 4 ), [5] MXene (such as Ti 2 C and Ti 3 CN), [21][22][23][24][25] and clays (for instance, [(Mg 3 )(Si 2 O 5 ) 2 (OH) 2 ] and [(Al 2 )(Si 3 Al) O 10 (OH) 2 ]K). [19] Notably, many nonlayered structure species can also form 2D morphology with specific synthetic methods, largely expanding the 2D family (such as hexagonal-MoO 3 (h-MoO 3 ), hexagonal-WO 3 (h-WO 3 ), [15] transition metal nitrides (TMNs), [26,27] and transition metal phosphides (TMPs)). [28] To exploit the applications of 2D materials, the development of a synthetic method should be prioritized. Currently, synthesis processes of 2D materials could be divided into two categories, naming the top-down and bottom-up approaches. [29][30][31] Generally, exfoliation is the most common top-down method to produce monolayer or few-layer 2D materials. [19,32] Graphene was first prepared by mechanical exfoliation of highly oriented pyrolytic graphite with sellotape in 2004. [33] The exfoliation can weaken the interlayer Van der Waals force for bulk materials with layered crystal structures while maintain the covalent bonding in plane to produce monolayer or few-layer nanosheets. Although the productivity based on this method is limited due to the low efficiency, the exfoliation approach provides a new synthesis methodology for 2D materials. A series of studies on liquid exfoliation have been conducted by Coleman and co-workers. [19,34,35] By sonicating the bulk material in an appropriate solvent with similar interface energy, 2D material ink can be prepared. After the liq...

layered MnO 2 materials, composed of exotic electronic properties and accessible active sites with alkali metal ions, provide a comprehensive platform for developing catalysts with chemical modification. Significantly, K + -contained layered MnO 2 catalysts have been verified as strong candidates toward catalytic oxidation of formaldehyde (HCHO). Unveiling the effects of alkali metal ions on active sites is critical to understand the interaction between reactants and active centers. Through a combination of analytical tools with periodic computational density functional theory modeling, the surface structures and the exposing specific defects of alkali metal ions affiliated to oxygen vacancies (Vo) are figured out by comparing three typical alkali metal ionintercalated (Na + , K + , and Cs + ) layered MnO 2 materials. These materials have been synthesized via a molten salt method, with high yield, large lateral size, and nanometer thickness in a few moments. We demonstrate that the alkali metal ions could remarkably alter the formation energy of Vo by the sequence of CsMnO (1.94 eV) < KMnO (1.97 eV) < NaMnO (2.07 eV) < ideal MnO 2 surface without the intercalated ion (2.23 eV). As a result, CsMnO with the most surface Vo sites could achieve efficient HCHO oxidation to CO 2 , with a HCHO consumption rate of about 0.149 mmol/(g•h) at 40 °C in 200 ppm HCHO/humid air [gas hourly space velocity = 80,000 mL/(g•h)]. Different from the Mars−van-Krevelen process, quantum chemical calculations and in situ diffuse reflectance infrared Fourier transform spectroscopy revealed that the main reaction pathway might be HCHO(ad) + [O](ad) → DOM → [HCOO − ] s → CO 2 via a Langmuir−Hinshelwood (L−H) mechanism. Alkali metals remarkably promoted the HCHO conversion by trapping oxygen through Vo sites and accelerating the facile reaction among adsorbed oxygen with adsorbed HCHO to deep degradation products (CO 2 and H 2 O).

Vanadium oxides are a promising class of cathode materials for rechargeable aqueous zinc-ion batteries (ZIBs). However, the intrinsically low electrical conductivity and unstable structure of vanadium materials often lead to fast performance degradation. In this work, we report on potassium-rich preintercalated vanadium oxide (K 1.1 V 3 O 8 ) as a high-performance cathode material for ZIBs. The K 1.1 V 3 O 8 cathode exhibits a high specific capacity of 386 mAh g −1 at 0.1 A g −1 and good long-term cycling stability with a capacity retention of 114.9% (180.7 mAh g −1 ) after 10 000 cycles at 10 A g −1 . The DFT calculations reveal a low Zn diffusion barrier and low Bader charge of K in K 1.1 V 3 O 8 , which are responsible for its good rate capability and high storage performance. The demonstration approach of maximizing ZIB performance proves to be an effective way to design promising cathode materials for ZIBs by regulating the appropriate preintercalation metal ions.

Rechargeable aqueous zinc ion batteries (ZIBs) represent a promising technology for large‐scale energy storage due to their high capacity, intrinsic safety and low cost. However, Zn anodes suffer from poor reversibility and cycling stability caused by the side‐reactions and dendrite issues, which limit the Zn utilization in the ZIBs. Herein, to improve the durability of Zn under high utilization, an aluminum‐doped zinc oxide (AZO) interphase is presented. The AZO interphase inhibits side reactions by isolating active Zn from the bulk electrolyte, and enables facile and uniform Zn deposition kinetics by accelerating the desolvation of hydrated Zn2+ and homogenizing the electric field distribution. Accordingly, the AZO‐coated Zn (AZO@Zn) anode exhibits a long lifespan of 600 h with Zn utilization of 34.1% at the current density of 10 mA cm−2. Notably, even under ultrahigh Zn utilization of 80%, the AZO@Zn remains stable cycling over 200 h. Meanwhile, the V2O5/AZO@Zn full cell with limited Zn excess displays high capacity retention of 86.8% over 500 cycles at 2 A g−1. This work provides a simple and efficient strategy to ensure the reversibility and durability of Zn anodes under high utilization conditions, holding a great promise for commercially available ZIBs with competitive energy density.

Two-dimensional (2D) oxides have unique electrical, optical, magnetic, and catalytic properties, which are promising for a wide range of applications in different fields. However, it is difficult to fabricate most oxides as 2D materials unless they have a layered structure. Here, we present a facile strategy for the synthesis of ultrathin oxide nanosheets using a self-formed sacrificial template of carbon layers by taking advantage of the Maillard reaction and violent redox reaction between glucose and ammonium nitrate. To date, 36 large-area ultrathin oxides (with thickness ranging from ~1.5 to ~4 nm) have been fabricated using this method, including rare-earth oxides, transition metal oxides, III-main group oxides, II-main group oxides, complex perovskite oxides, and high-entropy oxides. In particular, the as-obtained perovskite oxides exhibit great electrocatalytic activity for oxygen evolution reaction in an alkaline solution. This facile, universal, and scalable strategy provides opportunities to study the properties and applications of atomically thin oxide nanomaterials.

Electrochromic (EC) smart windows are considered one promising energy-conservation and emission-reduction device for green construction. However, conventional EC devices need external power to switch colors, which causes additional energy consumption. Herein, we propose a potential gradient strategy to attain a fast self-chargeable and -dischargeable EC system. In this strategy, the potential difference between Prussian blue (PB) and zinc (Zn) is established to reduce PB to Prussian white (PW) in 1.0 s, while etched carbon paper (ECP) could oxidize PW to its original state in 2.2 s. Moreover, this strategy is shown to be applicable for other highperformance EC systems, including Zn||WO 3 ||ECP, Zn|| PEDOT||ECP, Al||PB||ECP, and Zn||PB||ZnHCF. The potential application of large-scale windows is discussed in terms of a prototype 25 cm 2 EC window. Thus, the unique potential gradient strategy provides new insights for developing a fast self-switching EC device, which exhibits great application prospects in both energy conservation and energy storage.

Large-scale conducting polymer nanosheets (PPy, PANi and PEDOT) with tunable thicknesses and sizes have been successfully fabricated using CuCl2·2H2O salt as the oxidant and template via the vapor phase polymerization method.