Activated carbon derived from melaleuca barks for outstanding high-rate supercapacitors.

Activated carbon (AC) was prepared via carbonizing melaleuca bark in an argon atmosphere at 600 °C followed with KOH activation for high-rate supercapacitors. This AC electrode has a high capacitance of 233 F g(-1) at a scan rate of 2 mV s(-1) and an excellent rate capability of ∼80% when increasing the sweep rate from 2 to 500 mV s(-1). The symmetric supercapacitor assembled by the above electrode can deliver a high energy density of 4.2 Wh kg(-1) with a power density of 1500 W kg(-1) when operated in the voltage range of 0-1 V in 1 M H2SO4 aqueous electrolyte while maintaining great cycling stability (less than 5% capacitance loss after 10 000 cycles at sweep rate of 100 mV s(-1)). All the outstanding electrochemical performances make this AC electrode a promising candidate for potential energy storage application.

Synthesis of single crystalline two-dimensional transition-metal phosphides via a salt-templating method.

Transition-metal phosphides (TMPs) are considered as promising non-noble electrochemical catalysts for hydrogen evolution reaction (HER). Their highly active sites are located on certain facets, and single crystalline two-dimensional (2D) structures enable them to expose the most active facets for HER. However, the synthesis of single crystalline 2D TMPs is still a challenge owing to their intrinsically non-layered structures. Herein, we demonstrate the synthesis of various single crystalline 2D TMPs (Co2P, MoP2, Ni12P5 and WP2) by a salt-templating method. The as-synthesized 2D Co2P exhibited efficient electrocatalytic ability for HER with an overpotential of 41 mV at 10 mA cm-2 and a Tafel slope of 35 mV dec-1 in 0.5 M H2SO4 solution. We expect that the synthesis of 2D TMPs reported here will open the way to expand the family of 2D materials for electrocatalysis and beyond.

Energy Harvest from Organics Degradation by Two-Dimensional K+-Intercalated Manganese Oxide.

Pollution treatment, a problem our world is being deeply puzzled by, has required large amounts of energy during enrichment and degradation. However, some pollutants, for instance organics in wastewater, could offer an energy supply but instead are wasted. Here we report an energy harvesting galvanic cell, built by using a Pt foil as an anode and 2D K+-intercalated MnO2 as a cathode, which combines both dye degradation in wastewater and energy harvesting during the degradation process. Owing to the galvanic effect, this cell could accelerate the degradation rate and indicate the progress of degradation. Different kinds of organics could be degraded and produce energy in this cell with a stable open-circuit voltage (0.45 V). Magnification and imitation of this strategy offer a new chance to harvest waste energy in other exothermic reactions.

Salt-Templated Synthesis of 2D Metallic MoN and Other Nitrides.

Two-dimensional (2D) transition-metal nitrides just recently entered the research arena, but already offer a potential for high-rate energy storage, which is needed for portable/wearable electronics and many other applications. However, a lack of efficient and high-yield synthesis methods for 2D metal nitrides has been a major bottleneck for the manufacturing of those potentially very important materials, and only MoN, Ti4N3, and GaN have been reported so far. Here we report a scalable method that uses reduction of 2D hexagonal oxides in ammonia to produce 2D nitrides, such as MoN. MoN nanosheets with subnanometer thickness have been studied in depth. Both theoretical calculation and experiments demonstrate the metallic nature of 2D MoN. The hydrophilic restacked 2D MoN film exhibits a very high volumetric capacitance of 928 F cm-3 in sulfuric acid electrolyte with an excellent rate performance. We expect that the synthesis of metallic 2D MoN and two other nitrides (W2N and V2N) demonstrated here will provide an efficient way to expand the family of 2D materials and add many members with attractive properties.

Rapid mass production of two-dimensional metal oxides and hydroxides via the molten salts method.

Because of their exotic electronic properties and abundant active sites, two-dimensional (2D) materials have potential in various fields. Pursuing a general synthesis methodology of 2D materials and advancing it from the laboratory to industry is of great importance. This type of method should be low cost, rapid and highly efficient. Here, we report the high-yield synthesis of 2D metal oxides and hydroxides via a molten salts method. We obtained a high-yield of 2D ion-intercalated metal oxides and hydroxides, such as cation-intercalated manganese oxides (Na0.55Mn2O4·1.5H2O and K0.27MnO2·0.54H2O), cation-intercalated tungsten oxides (Li2WO4 and Na2W4O13), and anion-intercalated metal hydroxides (Zn5(OH)8(NO3)2·2H2O and Cu2(OH)3NO3), with a large lateral size and nanometre thickness in a short time. Using 2D Na2W4O13 as an electrode, a high performance electrochemical supercapacitor is achieved. We anticipate that our method will enable new path to the high-yield synthesis of 2D materials for applications in energy-related fields and beyond.

Natural Materials Assembled, Biodegradable, and Transparent Paper-Based Electret Nanogenerator.

Developing eco-friendly and low-cost electronics is an effective strategy to address the electronic waste issue. In this study, transparent cellulose nanopaper (T-paper) and polylactic acid (PLA) electret were used to construct a biodegradable and transparent paper-based electret nanogenerator. The nanogenerator could be assembled with paper products to form a self-powered smart packaging system without impairing the appearance, due to the high transparency and desirable output performance. Furthermore, the self-degradation property in the natural soil of the nanogenerator is demonstrated, indicating that the nanogenerator is recycled and will not pollute the environment. We anticipate that this study will provide new insights to develop eco-friendly power source and paper-based electronics.

Scalable salt-templated synthesis of two-dimensional transition metal oxides.

Two-dimensional atomic crystals, such as two-dimensional oxides, have attracted much attention in energy storage because nearly all of the atoms can be exposed to the electrolyte and involved in redox reactions. However, current strategies are largely limited to intrinsically layered compounds. Here we report a general strategy that uses the surfaces of water-soluble salt crystals as growth templates and is applicable to not only layered compounds but also various transition metal oxides, such as hexagonal-MoO3, MoO2, MnO and hexagonal-WO3. The planar growth is hypothesized to occur via a match between the crystal lattices of the salt and the growing oxide. Restacked two-dimensional hexagonal-MoO3 exhibits high pseudocapacitive performances (for example, 300 F cm(-3) in an Al2(SO4)3 electrolyte). The synthesis of various two-dimensional transition metal oxides and the demonstration of high capacitance are expected to enable fundamental studies of dimensionality effects on their properties and facilitate their use in energy storage and other applications.

2D vanadium doped manganese dioxides nanosheets for pseudocapacitive energy storage.

Ultrathin two-dimensional (2D) crystals have been predicted to have high electrochemical activity because nearly all active atoms are exposed to the electrolytes, which offers great potential for energy storage. However, to construct layered structure metal oxides, simplifying the synthetic methods and improving the electronic conductivity remain a challenge. Herein, we synthesized 2D vanadium doped manganese oxides through a facile hydrothermal method. Vanadium dopant is also used as a template agent for the formation of nanosheet-shaped MnO2, further leading to high specific surface area as well as significant enhancement of the electronic conductivity, as confirmed by the first-principle calculations and four-point probe method. For the sake of a shortened ion transport distance and enhanced electronic conductivity, V-doped MnO2 nanosheets display an excellent electrochemical performance as a supercapacitor electrode.