Xiaobin Xu

Ultrathin Pt-Cu nanosheets and nanocones.

In this work, we have successfully synthesized free-standing ultrathin Pt-Cu alloy nanosheets of 4-6 atom thickness with tunable lateral size from 10 to 50 nm. The nanosheets with diameters >20 nm can be converted into nanocones in a controllable way. These nanosheets and nanocones exhibit excellent electrocatalytic activities for the oxidation of ethanol in comparison to commercial Pt black and Pt/C catalysts.

Well-Defined Metal–Organic Framework Hollow Nanocages†

Metal-organic frameworks (MOFs) have demonstrated great potentials in a variety of important applications. To enhance the inherent properties and endow materials with multifunctionality, the rational design and synthesis of MOFs with nanoscale porosity and hollow feature is highly desired and remains a great challenge. In this work, the formation of a series of well-defined MOF (MOF-5, Fe(II) -MOF-5, Fe(III) -MOF-5) hollow nanocages by a facile solvothermal method, without any additional supporting template is reported. A surface-energy-driven mechanism may be responsible for the formation of hollow nanocages. The addition of pre-synthesized poly(vinylpyrrolidone)- (PVP) capped noble-metal nanoparticles into the synthetic system of MOF hollow nanocages yields the yolk-shell noble metal@MOF nanostructures. The present strategy to fabricate hollow and yolk-shell nanostructures is expected to open up exciting opportunities for developing a novel class of inorganic-organic hybrid functional nanomaterials.

Hierarchical Zn/Ni‐MOF‐2 Nanosheet‐Assembled Hollow Nanocubes for Multicomponent Catalytic Reactions

Metal-organic frameworks (MOFs) are potentially useful molecular materials that can exhibit structure flexibilities induced by some external stimuli. Such structure transformations can furnish MOFs with improved properties. The shape-controlled growth of MOFs combined with crystal-structure transformation is rarely achieved. Herein, we demonstrate the synthesis of hierarchical Zn/Ni-MOF-2 nanosheet-assembled hollow nanocubes (NAHNs) by a facile surfactant-free solvothermal approach. The unique nanostructures undergo crystal-structure transformation from Zn/Ni-MOF-5 nanocubes to Zn/Ni-MOF-2 nanosheets, which is analogous to the dissolution and recrystallization of inorganic nanocrystals. The present synthetic strategy to fabricate isostructural MOFs with hierarchical, hollow, and bimetallic nanostructures is expected to expand the diversity and range of potential applications of MOFs.

Well‐Defined Metal–Organic‐Framework Hollow Nanostructures for Catalytic Reactions Involving Gases

The miniaturization of metal-organic-framework (MOF) crystals to the nanoscale brings enhanced or novel properties and fulfils specific application needs. The focus here is on a kind of nanoMOF with special configurations and outstanding properties - the hollow structure. Firstly recent advances on the synthesis of MOF hollow nanostructures are introduced. Then, a novel approach based on a heterometallic system is highlighted, by which the facile synthesis of well-defined hollow MOF structures with high complexity is achieved. Moreover, MOF hollow nanostructures are emphasized as hosts/shell materials to incorporate functional catalysts that show dramatically enhanced performances in gas-involved reactions due to their inherent gas-absorption/storage properties.

Three dimensional hierarchical Pt-Cu superstructures

Three-dimensional (3D) hierarchical Pt-Cu tetragonal, highly branched, and dendritic superstructures have been synthesized by a facile template-free hydrothermal approach, showing growth patterns along (111, 110), (111), and (100) planes, respectively. These structures have been characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDX), inductively coupled plasma optical emission spectrometry (ICP-OES) and a detailed formation mechanism has been developed, which shows that the in situ formed I2 and the galvanic replacement reaction between Cu and Pt4+ may guide the formation of these superstructures. The comparative electrocatalytic properties have been investigated for methanol and ethanol oxidation. Due to their interconnected arms, sufficient absorption sites, and exposed surfaces, these superstructures exhibit enhanced electrocatalytic performance for electro-oxidation of methanol and ethanol when compared with commercial Pt/C and Pt black.

Rapid synthesis of mesoporous NixCo3−x(PO4)2 hollow shells showing enhanced electrocatalytic and supercapacitor performance

The design of cost-effective electrocatalysts and supercapacitor electrode materials with delicate hierarchical morphologies and enhanced functionalities has great potential in energy conversion and storage processes. Here, a fast and efficient microwave-assisted oil-in-water microemulsion template hydrothermal method is applied for the synthesis of multiple components and functional mesoporous hollow NixCo3−x(PO4)2 shells. Due to the high surface area and correspondingly increased electroactive sites derived from the mesoporous and hollow characteristics, the obtained NixCo3−x(PO4)2 shells exhibit excellent performance as a non-enzymatic glucose sensor, non-precious metal electrocatalyst for the oxygen evolution reaction (OER), and electrode material for energy storage.

Tuning the growth of metal-organic framework nanocrystals by using polyoxometalates as coordination modulators

Host-guest supramolecular interactions, which exist widely between diverse metal cations and polyoxometalate (POM) anions, have always been utilized to construct metal-organic frameworks (MOF) /POMs bulk composites. Actually, the interactions can also be found application in realizing shape-controlled synthesis of MOF nanocrystals (NCs). In this context, simply by introducing Keggin-type POMs into MOF precursors, various uniform [Cu3(BTC)2]n (BTC = benzene-1,3,5-tricarboxylate) NCs, including (truncated) octahedrons, hollow hierarchical spheres and octahedrons, are fabricated. Besides, such reaction system can be applied to construct noble metal@MOF nanocomposite, which significantly enhances the catalytic performance of the noble metal.摘要在金属阳离子和多酸阴离子之间广泛存在着一种超分子相互作用, 它经常被用来合成多酸基金属-有机骨架晶态材料. 这种相互作用还可以用来调控金属-有机骨架材料的成核生长过程, 从而实现其纳米晶体的可控制备. 本文将Keggin型多酸阴离子引入到金属-有机骨架材料的前驱体溶液中作为调节剂, 得到一系列形貌规则、尺寸均一的[Cu3(BTC)2]n (BTC = 1,3,5-苯三甲酸)纳米晶, 包括八面体、截角八面体、多级空心球、空心八面体等. 此外, 这种体系可以用于构建贵金属纳米晶@金属-有机骨架复合材料, 其催化性质相对于单纯的贵金属纳米晶有较大提高.

Modifying Commercial Carbon with Trace Amounts of ZIF to Prepare Derivatives with Superior ORR Activities

Reducing costs while maintaining high activities and stabilities of oxygen reduction reaction (ORR) catalysts has long been pursued for applications to membrane fuel cells. Here, an absorption-reaction method is used to prepare a zeolitic imidazolate framework coated commercial carbon, and the pyrolysis of such material brings about impressive ORR activities and stabilities with large diffusion-limited current density, half-wave potential, and no obvious decay after 10 000 cyclic voltammetry cycles, which is even better than that of the commercial Pt/C catalysts. The absorption-reaction method is realized by simply soaking the commercial carbon black sequentially in Co(NO3 )2 and 2-methylimidazole solutions at ambient conditions. The detailed analysis on such carbon materials reveals that both Co and N are essential to activities, even the amount of N and Co species is very low. The reduction of raw materials and simplified handling procedures result in well-controlled costs in applications.

Synthesis of Mo-based nanostructures from organic-inorganic hybrid with enhanced electrochemical for water splitting

A simple method to fabricate Mo-based nanostructures were developed by the thermal decomposition of MoOx-based organic–inorganic hybrid nanowires. Well-defined Mo-based nanostructures, including MoO2 and MoO3 nanowires, can be prepared by changing the hybrid precursor. More importantly, Mo2C/MoO2 heterostructures with porous structure were successfully synthesized under an inert atmosphere. The resultant Mo2C/MoO2 heterostructures show enhanced electrocatalytic activity and superior stability for electrochemical hydrogen evolution from water. The enhanced performance might be ascribed to the high electrical conductivity and porous structures with one-dimensional structure. Indeed, our result described here provides a new way to synthesize other Mo-based nanostructures for various applications.中文摘要钼基纳米材料因其特殊的结 构和良好的化学性质被广泛应用于传感器和催化领域. 其中, 碳化钼 具有类似贵金属的电子结 构和催化特性, 受到了越来越多的关注. 在本研究工作中, 通过对有机-无机复合材料在惰性气氛下进行热处理, 制备了不同的一维钼氧 化物纳米材料以及碳化钼/氧化钼多孔异质纳米材 料. 析氢电催化性能表明碳化钼/氧化钼多孔异质材料显示出优异的氢析出性能和循 环稳定性. 此方法制备过程简单有效且适合大量制备, 同时为制备新型钼基纳米材料提供了新的思路.

Nickel Diselenide Ultrathin Nanowires Decorated with Amorphous Nickel Oxide Nanoparticles for Enhanced Water Splitting Electrocatalysis

Well-designed hybrid materials based on noble metal-free elements have great potential to generate hydrogen (H2 ) and oxygen (O2 ) sustainably via overall water splitting for developing practical energy-related technologies. Herein, an accessible method is presented to synthesize nickel diselenide (NiSe2 ) ultrathin nanowires decorated with amorphous nickel oxide nanoparticles (NiOx NPs) as multifunctional electrocatalysts (NSWANs) for hydrogen and oxygen evolution reaction (HER and OER). The NSWANs exhibit quite low HER and OER overpotentials of 174 and 295 mV, respectively, holding the current density of 20 mA cm-2 for 24 h continuous operations in alkaline media. Meanwhile, a cell voltage of 1.547 V at the current density of 10 mA cm-2 for overall water splitting has been achieved by the NSWANs for the practical application, which could maintain fascinating activity of 20 mA cm-2 for 72 h without degradation. The decorated NiOx NPs not only prevent the NiSe2 from further oxidation but also expose requisite active sites for electrocatalytic process. It is believed that this study may provide a valuable strategy to design high-efficiency electrocatalysts and expand the applications of selenide-based materials.