2D carbon nanomaterials such as graphene and its derivatives, have gained tremendous research interests in energy storage because of their high capacitance and chemical stability. However, scalable synthesis of ultrathin carbon nanosheets with well-defined pore architectures remains a great challenge. Herein, the first synthesis of 2D hierarchical porous carbon nanosheets (2D-HPCs) with rich nitrogen dopants is reported, which is prepared with high scalability through a rapid polymerization of a nitrogen-containing thermoset and a subsequent one-step pyrolysis and activation into 2D porous nanosheets. 2D-HPCs, which are typically 1.5 nm thick and 1-3 µm wide, show a high surface area (2406 m g ) and with hierarchical micro-, meso-, and macropores. This 2D and hierarchical porous structure leads to robust flexibility and good energy-storage capability, being 139 Wh kg for a symmetric supercapacitor. Flexible supercapacitor devices fabricated by these 2D-HPCs also present an ultrahigh volumetric energy density of 8.4 mWh cm at a power density of 24.9 mW cm , which is retained at 80% even when the power density is increased by 20-fold. The devices show very high electrochemical life (96% retention after 10000 charge/discharge cycles) and excellent mechanical flexibility.

have also greatly aroused the positive exploration of alternative LIB technologies in recent years. [44] In contrast to the flammable organic electrolyte in LIBs, the aqueous one exhibits lower cost, higher safety, and especially the superior ionic conductivity, which is generally two orders of magnitude higher than that of the organic system. [9,10] All those unparalleled advantages would make the aqueous battery technologies to be the promising candidates in the future. [11] Rechargeable aqueous zinc-ion batteries (AZIBs), which is mainly composed of zinc metal anode, zinc salt-based aqueous electrolyte, and Zn 2+ host cathode, hold the great promise for energy storage applications in very recent years. [12,13] Compared with nonaqueous alkali-ion batteries, the use of cheap and high ambient stable zinc metal anode and inexpensive aqueous electrolyte with superior ionic conductivity (Figure 1a) would make such type of battery to be one of the most promising commercial candidates in the future market. [14-17] To date, extensive studies have been reported for AZIBs, and relating publications have dramatically increased especially in these two years, as shown in Figure 1b. However, the insufficient energy density seems to become the bottleneck that hinder their practical applications at current status. [4,5,18] Such issue could be ascribed to the narrow operating voltage of aqueous electrolyte, insufficient electrochemical performance of cathode materials, and Zn anode. [13,19,20] Besides, the influence of other components such as separator and collector also should be considered to some extent. [20,21] Among them, the studies of widening operating voltage of electrolyte and the optimization of other components only received less attention, which still remain at the early stage. [22,23] On the contrary, more attentions were paid to the electrochemical performance tuning of electrode materials. [24-26] Besides, considering the fixed operating voltage of Zn metal anode, the modification of cathode materials seems to provide more possibilities to effectively improve the energy density of AZIBs, owing to their rich material systems. [20,26,27] Under these considerations, the rational design of advanced cathodes is expected to be a preferential task to develop. Up to now, many types of materials have been exploited as cathode candidates and applied for AZIBs, however, those Rechargeable aqueous zinc-ion batteries (AZIBs) have attracted extensive attention and are considered to be promising energy storage devices, owing to their low cost, eco-friendliness, and high security. However, insufficient energy density has become the bottleneck for practical applications, which is greatly influenced by their cathodes and makes the exploration of high-performance cathodes still a great challenge. This review underscores the recent advances in the rational design of advanced cathodes for AZIBs. The review starts with a brief summary and evaluation of cathode material systems, as well as the introduction of proposed storage mechani...

The sluggish sodium reaction kinetics, unstable Sn/Na O interface, and large volume expansion are major obstacles that impede practical applications of SnO -based electrodes for sodium-ion batteries (SIBs). Herein, we report the crafting of homogeneously confined oxygen-vacancy-containing SnO nanoparticles with well-defined void space in porous carbon nanofibers (denoted SnO /C composites) that address the issues noted above for advanced SIBs. Notably, SnO /C composites can be readily exploited as the working electrode, without need for binders and conductive additives. In contrast to past work, SnO /C composites-based SIBs show remarkable electrochemical performance, offering high reversible capacity, ultralong cyclic stability, and excellent rate capability. A discharge capacity of 565 mAh g at 1 A g is retained after 2000 cycles.

The room temperature (RT) sodium–sulfur batteries (Na–S) hold great promise for practical applications including energy storage and conversion due to high energy density, long lifespan, and low cost, as well based on the abundant reserves of both sodium metal and sulfur. Herein, freestanding (C/S/BaTiO3)@TiO2 (CSB@TiO2) electrode with only ≈3 wt% of BaTiO3 additive and ≈4 nm thickness of amorphous TiO2 atomic layer deposition protective layer is rational designed, and first used for RT Na–S batteries. Results show that such cathode material exhibits high rate capability and excellent durability compared with pure C/S and C/S/BaTiO3 electrodes. Notably, this CSB@TiO2 electrode performs a discharge capacity of 524.8 and 382 mA h g−1 after 1400 cycles at 1 A g−1 and 3000 cycles at 2 A g−1, respectively. Such superior electrochemical performance is mainly attributed from the “BaTiO3‐C‐TiO2” synergetic structure within the matrix, which enables effectively inhibiting the shuttle effect, restraining the volumetric variation and stabilizing the ionic transport interface.

Dendrite growth and parasitic side reactions are thorny issues that seriously damage the anode-electrolyte interface during Zn plating/stripping process, leading to uncontrollable Zn deposition and restraining application of aqueous Zn-ion batteries (AZIBs). Here, a unique facile strategy to in situ build indium (In) metal interphase on the Zn anode is first proposed. The combination of experimental and theoretical investigations demonstrate that such metallic interphase prevents the hydrogen evolution reaction (HER) and Zn corrosion, and guides preferential growth along the Zn(002) plane to achieve smooth Zn deposition. As a result, the modified Zn anodes achieve the ultrahigh cumulative capacities of 5600 and 5000 mAh cm −2 at the high current densities of 2 and 5 mA cm −2 , respectively, demonstrating an ultrastable plating/stripping behavior. More encouragingly, the rate performance and cyclic stability of the Zn-V 2 O 5 battery with the electrolyte additive can still deliver a specific capacity of 383.6 mAh g −1 after 5000 cycles at the high current density of 5 A g −1 . The strategy presented here as well as the in-depth understanding of modified mechanism can not only provide an effective solution to address the Zn anode concerns, but also deepen the understanding of AZIBs.

No abstract

Here, taking layered polymeric carbon nitride (CN) as an example, the dominant role of in-plane charge transport is demonstrated both theoretically and experimentally. The in-plane “sewing” and interlayer “cutting” effects of three alkaline potassium salts on the CN polymerization process are enhanced with the increase of alkalinity. The in-plane crystallinity-dependent charge transfer and separation and photocatalytic activity are elucidated through the samples of three alkaline potassium salt series. Our findings provide guidance for improving the photoelectric conversion efficiency by optimizing in-plane charge transfer rather than interlayer charge transfer, targeting layered photoelectric conversion materials.

The sluggish exciton dissociation and charge transfer and separation due to weak driving force still restrict the further improvement of photocatalytic performance in crystalline carbon nitride (CCN). Here, a series of heptazine-based K+-implanted CCNs (KCCNs) were successfully prepared, while the K+ ion concentration was gradiently inserted by controlling its diffusion from the surface to the bulk in carbon nitride (CN). The built-in electric field (BIEF) induced by the K+ ion concentration gradient and cyano groups has powerful driving force to promote the dissociation of excitons into electrons and holes and accelerate the separation of photogenerated carriers and their transport from the bulk to the surface. Consequently, the KCCN with an optimized BIEF has increased 34 times compared with the original CN for visible light H2 evolution. Our proposed strategy to induce BIEF by constructing concentration gradients through a thermodynamically feasible diffusion-controlled solid-state reaction can be adopted to design other photocatalytic systems.