Molten metal-organic complex to synthesize versatile ultrathin nonlayered oxides

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.

All-Day Thermogalvanic Cells for Environmental Thermal Energy Harvesting

Direct conversion of the tremendous and ubiquitous low-grade thermal energy into electricity by thermogalvanic cells is a promising strategy for energy harvesting.The environment is one of the richest and renewable low-grade thermal source.However,critical challenges remain for all-day electricity generation from environmental thermal energy due to the low frequency and small amplitude of temperature fluctuations in the environment.In this work,we report a tandem device consisting of a polypyrrole(PPy)broadband absorber/radiator,thermogalvanic cell,and thermal storage material(Cu foam/PEG1000)that integrates multiple functions of heating,cooling,and recycling of thermal energy.The thermogalvanic cell enables continuous utilization of environmental thermal energy at both daytime and nighttime,yielding maximum outputs as high as 0.6 W m^(-2) and 53 mW m^(-2),respectively.As demonstrated outdoors by a large-scale prototype module,this design offers a feasible and promising approach to all-day electricity generation from environmental thermal energy.

Cobalt doping boosted electrocatalytic activity of CaMn3O6 for hydrogen evolution reaction

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 CaMn_(3)O_(6)(CMO)nanowires(NWs)as effective electrocatalyst for HER.The as-obtained CaMn_(3-x)Co_(x)O_(6)(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 HClO_(4),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).

Assembly of two-dimensional nanofluidic channel with high proton conductivity using single-layer MnO_(2) nanosheets

Two-dimensional(2D)single-layer δ-MnO_(2)(SLMO)with cations intercalated in the interlayers demonstrates specific structural characteristics,possessing superiority in the fields such as energy storage,catalysis,and sensor.However,the synthesis technology of large-lateral-size SLMO nanosheets with high uniformity is rare,which hinders their correlated research.Herein,we report an intercalation-assisted exfoliation approach to produce large-sized SLMO nanosheets with high dispersity in aqueous solution.Few-layer K^(+)-intercalated δ-MnO_(2)(KMnO)nanosheets were used as a precursor to ensure complete exfoliation.On account of high dispersion and ultrathin 2D morphology,SLMO nanosheets self-assembled into a flexible and free-standing film to construct ordered nanochannels.A high surface charge density of 1.71 mC m^(-2) and proton mobility of 2.59×10^(-3) cm^(2) V^(-1) s_(-1) were achieved in the free-standing SLMO film.With the extraordinary properties and easily scaled fabrication of the 2D SLMO film,this approach will pave the way for the study of confined ion transportation and enable the easy construction of nanofluidic devices.

Li_(x)Na_(2-x)W_(4)O_(13) nanosheet for scalable electrochromic device

The printed electronics technology can be used to efficiently construct smart devices and is dependent on functional inks containing well-dispersed active materials.Two-dimensional(2D)materials are promising functional ink candidates due to their superior properties.However,the majority 2D materials can disperse well only in organic solvents or in surfactant-assisted water solutions,which limits their applications.Herein,we report a lithium(Li)-ion exchange method to improve the dispersity of the Na_(2)W_(4)O_(13) nanosheets in pure water.The Li-ion-exchanged Na_(2)W_(4)0_(13)(Li_(x)Na_(2-x)W_(4)O_(13))nanosheets show highly stable dispersity in water with a zeta potential of-55 mV.Moreover,this aqueous ink can be sprayed on various substrates to obtain a uniform LixNa2_xW4O13 nanosheet film,exhibiting an excellent electrochromic performance.A complementary electrochromic device containing a Li_(x)Na_(2-x)W_(4)O_(13) nanosheet film as an electrochromic layer and Prussian white(PW)as an ion storage layer exhibits a large optical modulation of 75% at 700 nm,a fast switching response of less than 2 s,and outstanding cyclic stability.This Na2W4Oi3-based aqueous ink exhibits considerable potential for fabricating large-scale and flexible electrochromic devices,which would meet the practical application requirements.