Microwave-assisted exploration of the electron configuration-dependent electrocatalytic urea oxidation activity of 2D porous NiCo_(2)O_(4) spinel

Urea holds promise as an alternative water-oxidation substrate in electrolytic cells.High-valence nickelbased spinel,especially after heteroatom doping,excels in urea oxidation reactions(UOR).However,traditional spinel synthesis methods with prolonged high-temperature reactions lack kinetic precision,hindering the balance between controlled doping and highly active two-dimensional(2D)porous structures design.This significantly impedes the identification of electron configuration-dependent active sites in doped 2D nickel-based spinels.Herein,we present a microwave shock method for the preparation of 2D porous NiCo_(2)O_(4)spinel.Utilizing the transient on-off property of microwave pulses for precise heteroatom doping and 2D porous structural design,non-metal doping(boron,phosphorus,and sulfur)with distinct extranuclear electron disparities serves as straightforward examples for investigation.Precise tuning of lattice parameter reveals the impact of covalent bond strength on NiCo_(2)O_(4)structural stability.The introduced defect levels induce unpaired d-electrons in transition metals,enhancing the adsorption of electron-donating amino groups in urea molecules.Simultaneously,Bode plots confirm the impact mechanism of rapid electron migration caused by reduced band gaps on UOR activity.The prepared phosphorus-doped 2D porous NiCo_(2)O_(4),with optimal electron configuration control,outperforms most reported spinels.This controlled modification strategy advances understanding theoretical structure-activity mechanisms of high-performance 2D spinels in UOR.

Microwave shock motivating the Sr substitution of 2D porous GdFeO_(3) perovskite for highly active oxygen evolution

The incorporation of partial A-site substitution in perovskite oxides represents a promising strategy for precisely controlling the electronic configuration and enhancing its intrinsic catalytic activity.Conventional methods for A-site substitution typically involve prolonged high-temperature processes.While these processes promote the development of unique nanostructures with highly exposed active sites,they often result in the uncontrolled configuration of introduced elements.Herein,we present a novel approach for synthesizing two-dimensional(2D)porous GdFeO_(3) perovskite with A-site strontium(Sr)substitution utilizing microwave shock method.This technique enables precise control of the Sr content and simultaneous construction of 2D porous structures in one step,capitalizing on the advantages of rapid heating and cooling(temperature~1100 K,rate~70 K s^(-1)).The active sites of this oxygen-rich defect structure can be clearly revealed through the simulation of the electronic configuration and the comprehensive analysis of the crystal structure.For electrocatalytic oxygen evolution reaction application,the synthesized 2D porous Gd_(0.8)Sr_(0.2)FeO_(3) electrocatalyst exhibits an exceptional overpotential of 294 mV at a current density of 10 mA cm^(-2)and a small Tafel slope of 55.85 mV dec^(-1)in alkaline electrolytes.This study offers a fresh perspective on designing crystal configurations and the construction of nanostructures in perovskite.

微波热冲快速制备二维多孔La_(0.2)Sr_(0.8)CoO_(3)钙钛矿用于高效电催化析氧反应

析氧反应(OER)被认为是电解水的关键限制步骤,已被广泛作为清洁能源方式用于解决能源和环境问题。钙钛矿氧化物(ABO_(3))具有可调的电子结构、高灵活性的元素组成,能在OER中表现出良好的催化活性。然而,钙钛矿氧化物的合成通常需要经历长时间的高温,极易导致金属的聚集和影响材料的本征活性。气相微波技术可以显著缩短热处理时间,从而减少相关的碳排放。这项技术不仅解决了对碳中性过程日益增长的需求,而且还增加了对合成的控制,以避免产品的不良团聚。本文采用微波热冲法快速制备了二维(2D)多孔La_(0.2)Sr_(0.8)CoO_(3)钙钛矿。伴随微波过程的快速熵增可以有效地暴露La_(0.2)Sr_(0.8)CoO_(3)结构中丰富的活性位点。此外,高能微波冲击过程可以精准地将Sr2+引入到LaCoO_(3)的晶格中,通过增加Co的氧化态来增加氧空位量。这种锶元素取代镧引入的氧空位能极大提高催化剂的本征催化活性。对于碱性电解液中的OER应用,制备的La_(0.2)Sr_(0.8)CoO_(3)在10 m A·cm^(-2)下展现出了360 m V的过电位,Tafel斜率为76.6 mV·dec^(-1)。且在经历30000秒的长时间循环测试后仍能维持初始电流密度的97%。这项研究为高活性二维钙钛矿的合成提供了一种简便、快速的策略。

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.

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.