Two-dimensional (2D) materials have attracted a great deal of research interest because of their unique electrical, magnetic, optical, mechanical, and catalytic properties for various applications. To date, however, it is still difficult to fabricate most functional oxides as 2D materials unless they have a layered structure. Herein, we report a one-step universal strategy for preparing versatile non-layered oxide nanosheets by directly annealing the mixture of metal nitrate and dimethyl imidazole (2-MI). The 2-MI plays the key role for 2D oxides since 2-MI owns a very low molten point and sublimation temperature, in which its molten liquid can coordinate with metal ions, forming a metal-organic framework, and easily puffing by its gas molecules. A total of 17 materials were prepared by this strategy, including non-layered metal oxide nanosheets as well as metal/metal oxide loaded nitrogen-doped carbon nanosheets. The as-prepared cobalt particle-loaded nitrogen-doped carbon nanosheets (Co@N/C) exhibit remarkable bifunctional oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) electrocatalytic activity and durability. Besides, the Zn-air battery utilizing a Co@N/C catalyst exhibits high power density of 174.3 mW·cm⁻². This facile strategy opens up a new way for large-scale synthesis of 2D oxides that holds great potential to push 2D oxides for practical applications.

The development of earth-abundant-metal-based electrocatalysts with high efficiency and long-term stability for hydrogen evolution reaction (HER) is crucial for the clean and renewable energy application. Herein, we report a molten-salt method to synthesize Co-doped CaMn₃O₆ (CMO) nanowires (NWs) as effective electrocatalyst for HER. The as-obtained CaMn_3−xCo_xO₆ (CMCO) exhibits a small onset overpotential of 70 mV, a required overpotential of 140 mV at a current density of 10 mA·cm⁻², a Tafel slope of 39 mV·dec⁻¹ in 0.1 M HClO₄, and a satisfying long-term stability. Experimental characterizations combined with density functional theory (DFT) calculations demonstrate that the obtained HER performance can be attributed to the Co-doping which altered CMO’s surface electronic structures and properties. Considering the simplicity of synthesis route and the abundance of the pertinent elements, the synthesized CMCO shows a promising prospect as a candidate for the development of earth-abundant, metal-based, and cost-effective electrocatalyst with superior HER activity. Our results also establish a strategy of rational design and construction of novel electrocatalyst toward HER by tailoring band structures of transition metal oxides (TMOs).

MXenes have shown record-breaking redox capacitance in aqueous electrolytes, but in a limited voltage window due to oxidation under anodic potential and hydrogen evolution under high cathodic potential. Coupling Ti₃C₂T_x MXene negative electrode with RuO₂ or carbon-based positive electrodes expanded the voltage window in sulfuric acid electrolyte to about 1.5 V. Here, we present an asymmetric pseudocapacitor using abundant and eco-friendly vanadium doped MnO₂ as the positive and Ti₃C₂T_x MXene as the negative electrode in a neutral 1 M Li₂SO₄ electrolyte. This all-pseudocapacitive asymmetric device not only uses a safer electrolyte and is a much less expensive counter-electrode than RuO₂, but also can operate within a 2.1 V voltage window, leading to a maximum energy density of 46 Wh/kg. This study also demonstrates the possibility of using MXene electrodes to expand the working voltage window of traditional redox-capable materials.

Two-dimensional molybdenum disulfide (2D MoS₂) is considered as a promising candidate for many applications due to its unique structure and properties. However, the controllable synthesis of large-scale and high-quality 2D 1T-phase MoS₂ is still a challenge. Herein, we present the scalable and controllable synthesis of 2D MoS₂ from 2H to 1T@2H phase by using K₂SO₄ salt as a simultaneous high-temperature sulfur source and template. The as-synthesized 1T@2H-2D MoS₂ exhibits a high yield and can be easily assembled into freestanding electrode with high specific capacitance of 434 F/g at a scan rate of 1 mV/s in LiClO₄ ethylene carbonate/dimethyl carbonate (EC/DMC). Moreover, various single-crystal 2D transition metal sulfides (WS₂, PbS, MnS and Ni₉S₈) and 2D S-doped carbon can be synthesized using this method. We believe that this study may provide a new sight for scalable and controllable synthesis of other 2D materials beyond 2D MoS₂.

Two-dimensional (2D) carbon nanomaterials with hierarchical porous structure and heteroatoms doping are highly desirable in the fields of energy storage because of their rich active surface and open ion diffusion channels. However, the scalable preparation of carbon materials simultaneously possessing ultrathin 2D feature and hierarchical pores remains a considerable challenge. Herein, a facile one-step method to massively fabricate 2D porous chitin nanosheets (coded as PCNs) via a phytic acid assisted top-down exfoliation of bulk chitin under hydrothermal treatment was presented. Subsequently, 2D carbon nanosheets with extra-thin thickness (3.6 nm), well-defined hierarchical porosity, high specific surface area (855 m²·g^-1), as well as abundant self-doped heteroatoms (N, O, P) were fabricated by carbonizing the PCNs, and was named as HPCNs. The as-obtained HPCNs demonstrated remarkable electrochemical performance as electrode material for supercapacitors. The symmetric supercapacitors (SSCs) based on HPCNs exhibited a high specific capacitance of 79 F·g^-1 (316 F·g^-1 for single electrode) in 6 M KOH aqueous electrolyte solution, as well as a remarkable energy density of 23.8 W·h·kg^-1 by using 1 M Li₂SO₄ as electrolyte. It is also demonstrated that HPCNs/PCNs hybrid dispersions can be used as inks to fabricate conductive films and energy devices with high strength and superior flexibility. This work paves a new avenue for the economical and large-scale synthesis of 2D hierarchically porous carbon materials for energy storage related applications.