Yujie Han

Simple and Sensitive Fluorescent and Electrochemical Trinitrotoluene Sensors Based on Aqueous Carbon Dots

Aqueous N-rich carbon dots (CDs), prepared by the microwave-assisted pyrolysis method, are applied as a dual sensing platform for both the fluorescent and electrochemical detection of 2,4,6-trinitrotoluene (TNT). The fluorescent sensing platform is established on the strong TNT-amino interaction which can quench the photoluminescence of amino functionalized CDs through charge transfer. The resultant linear detection ranges from 10 nM to 1.5 μM with a fast response time of 30 s. Glassy carbon electrode modified with CDs exhibits a fine capability for TNT reduction with the linear range from 5 nM to 30 μM, better than that obtained by the fluorescent method. Moreover, the minimum distinguishable response concentration with respect to these two methods is down to the nanomolar level with a high specificity and sensitivity.

Porous CoP concave polyhedron electrocatalysts synthesized from metal–organic frameworks with enhanced electrochemical properties for hydrogen evolution

Developing highly efficient and low-cost noble metal-free catalysts toward hydrogen evolution from water splitting is an attractive alternative strategy to solve the ever-increasing environmental contamination and energy demand. Herein, a porous CoP electrocatalyst with a concave polyhedron (CPH) structure was facilely prepared by a topological conversion strategy using Co-MOF (ZIF-67) polyhedrons as the precursor. The morphology of Co-MOFs is well inherited by the as-prepared CoP sample due to the multi-step calcination process at low temperature, which results in the formation of a porous structure. Compared with the contrastive CoP nanoparticles (NPs), the obtained porous CoP CPH electrocatalyst exhibits a remarkably enhanced electrocatalytic performance with a current density of 10 mA cm−2 at an overpotential of 133 mV and a superior durability for the hydrogen evolution reaction (HER) in acid media. A small Tafel slope of ca. 51 mV dec−1 reveals a Volmer–Heyrovsky mechanism during the HER. This work provided a new insight to fabricate morphology-controlled transition metal phosphides with a porous structure via topological conversion, which have importantly potential applications, such as electrocatalysis, photocatalysis and sensors, thanks to their porosity and controllability.

Ultrasonic synthesis of highly dispersed Au nanoparticles supported on Ti-based metal–organic frameworks for electrocatalytic oxidation of hydrazine

In this work, Au nanoparticles supported on amino-functionalized Ti-benzenedicarboxylate metal–organic frameworks (Au/NH2-MIL-125(Ti)) were prepared by a facile ultrasonic method. The complex was characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), UV-Vis absorption spectroscopy and electrochemical methods. The obtained nanocomposites exhibit excellent electrocatalytic activity toward hydrazine oxidation, which is attributed to their large specific surface area and good conductivity. In addition, we found that solution pH has an obvious effect on the electrocatalytic activity of Au/NH2-MIL-125(Ti) toward hydrazine oxidation. On this basis, we constructed a simple, sensitive, selective and inexpensive electrochemical method to detect hydrazine. A linear dynamic range of 10 nM to 100 μM with a detection limit of 0.5 nM was obtained. It was demonstrated that the fabrication of Au NPs on amino-functionalized Ti-based MOFs could be promising for the sensing of hydrazine. Our results imply the potential application of metal nanoparticle/MOF nanocomposites in the field of electroanalytical chemistry.

3D Graphene Aerogels Decorated with Cobalt Phosphide Nanoparticles as Electrocatalysts for the Hydrogen Evolution Reaction.

The development of non-precious-metal hydrogen evolution reaction (HER) electrocatalysts with high activity and excellent durability in acidic media is of significant importance for renewable energy research. We report a novel electrocatalyst based on a three-dimensional (3D) graphene aerogel decorated with cobalt phosphide nanoparticles (CoP/GA). The material has a unique hierarchical porous structure with CoP nanoparticles encapsulated uniformly within the graphene sheets. The optimized catalyst shows superior activity, with an overpotential of only 121 mV at 10 mA cm-2 , a Tafel slope of 50 mV dec-1 , and an exchange current density of 0.105 mA cm-2 , and it maintains its catalytic activity for at least 13 h. More importantly, this work provides a versatile way for the rational design and fabrication of 3D graphene-based multifunctional composite materials.

In situ synthesis of ultrathin metal–organic framework nanosheets: a new method for 2D metal-based nanoporous carbon electrocatalysts

Two-dimensional (2D) metal–organic framework (MOF) nanosheets, which possess the advantages of both 2D layered nanomaterials and MOFs, are considered as promising nanomaterials. However, it is still difficult to directly synthesize MOF nanosheets. Here we for the first time report a new bottom-up strategy for in situ synthesis of high-quality ZIF-67 nanosheets with the salt-template assistance. The as-prepared ZIF-67 nanosheets exhibit a uniform morphology and ultrathin structure with a thickness of 4.5 nm. Furthermore, because of the highly open structure, larger surface area, more accessible active sites and smaller diffusion barrier compared with bulk-sized MOFs, the directly carbonized Co,N-doped nanoporous carbon nanosheets also greatly boost the oxygen reduction reaction (ORR). More importantly, the general synthesis process indicates that this effective salt-template confined bottom-up strategy can be expanded to synthesize other ultrathin 2D MOF nanosheets with extensive applications in gas separation, catalysis, sensors, and energy storage and conversion.

Core–Shell‐Structured Tungsten Carbide Encapsulated within Nitrogen‐Doped Carbon Spheres for Enhanced Hydrogen Evolution

It is highly desirable and remains a great challenge to develop alternative hydrogen evolution reaction (HER) electrocatalysts that are low-cost, highly efficient, and exhibit excellent stability. In this work, we report the synthesis of tungsten carbide nanocrystallites encapsulated within nitrogen-doped carbon (TCNC) spheres through in situ polymerization of dopamine with metatungstate followed by carburization under an inert atmosphere. During the in situ and confined carburization process, very small tungsten carbide nanocrystallites are obtained and uniformly dispersed in the simultaneously generated carbon matrix. Benefited from the unique structure and morphology, the resultant TCNC spheres exhibit high electrocatalytic activity and excellent stability toward HER in both acidic and alkaline solutions.

RGO/Au NPs/N-doped CNTs supported on nickel foam as an anode for enzymatic biofuel cells

In this study, three-dimensional reduced graphene oxide/Au NPs/nitrogen-doped carbon nanotubes (RGO/Au NPs/N-doped CNTs) assembly supported on nickel foam was utilized as an anode for enzymatic biofuel cells (EBFCs). 3D RGO/Au NPs was obtained by electrodepositing reduced graphene oxide on nickel foam (Ni foam), while Au NPs were co-deposited during the process. Afterwards, nitrogen doped CNTs (N-CNTs) were allowed to grow seamlessly on the surfaces of 3D RGO/Au NPs via a simple chemical vapor deposition (CVD) process. In this nanostructure, Au NPs co-deposition and nitrogen doping offer more active sites for bioelectrocatalysis. Additionally, N-CNTs were demonstrated providing high specific surface area for enzyme immobilization and facilitating the electron transfer between glucose oxidase (GOx) and electrode. The resulting bioanode achieved efficient glucose oxidation with high current densities of 7.02mAcm-2 (0.3V vs. Ag/AgCl). Coupling with a Pt cathode, the fabricated glucose/air biofuel cell exhibited an open-circuit potential of 0.32V and generated a maximum power density 235µWcm-2 at 0.15V. This novel electrode substrate achieved high performance in current density at bioelectrochemical systems and could be useful for further exploiting the application of three dimensional carbon-based nanomaterials in EBFCs.

Shape-Control of Pt–Ru Nanocrystals: Tuning Surface Structure for Enhanced Electrocatalytic Methanol Oxidation

Despite the fact that both electrochemical experiments and density functional theory calculations have testified to the superior electrocatalytic activity and CO-poisoning tolerance of platinum-ruthenium (PtRu) alloy nanoparticles toward the methanol oxidation reaction (MOR), the facet-dependent electrocatalytic properties of PtRu nanoparticles are scarcely revealed because it is extremely difficult to synthesize well-defined facets-enclosed PtRu nanocrystals. Herein, we for the first time report a general synthesis of ultrathin PtRu nanocrystals with tunable morphologies (nanowires, nanorods, and nanocubes) through a one-step solvothermal approach and a systematic investigation of the structure-directing effects of different surfactants and the formation mechanism by control experiments and time-dependent studies. In addition, we utilize these {100} and {111} facets-enclosed PtRu nanocrystals as model catalysts to evaluate the electrocatalytic characteristics of the MOR on different facets. Remarkably, {111}-terminated PtRu nanowires exhibit much higher stability and electrocatalytic mass activity toward MOR, which are 2.28 and 4.32 times higher than those of {100}-terminated PtRu nanocubes and commercial Pt/C, respectively, indicating that PtRu {111} facets possess superior methanol oxidation activity and CO-poisoning resistance relative to {100} facets. Our present work provides a series of well-defined PtRu nanocrystals with tunable facets which would be ideal model electrocatalysts for fundamental research in fuel cell electrocatalysis.

A miniature origami biofuel cell based on a consumed cathode

Considerable interest has been focused on miniature biofuel cells (BFCs) because of their portability and possibility to be implantable. Origami devices with hollow channels will provide novel insight into the assembly methods of miniature BFCs. Herein a miniature origami BFC has been fabricated from a MnO2-graphite flake consumed solid-state cathode. For further practical applications, miniature origami BFCs can directly generate energy from soft drinks.

Facile synthesis of Ni based metal-organic frameworks wrapped MnO 2 nanowires with high performance toward electrochemical oxygen evolution reaction

The transition metal oxides based catalysts have drawn great attention for their application in the electrolysis of water for renewable energy generation. Although manganese oxides were rarely used as oxygen evolution reaction (OER) catalysts, they were still considered as active and efficient OER catalysts due to the earth-abundant and low toxic nature of manganese. In this work, we proposed a facile method for the synthesis of high-performance electrochemical OER catalyst by magnetically stirring the mixture of 1,3,4-thiadiazole-2,5-dithiol (DMTD), Ni2+ and MnO2 nanowires (NWs) in ethanol at room temperature, noted as Ni/DMTD/MnO2. The Ni/DMTD complex and MnO2 NWs showed synergistically enhanced OER activity and excellent durability in alkaline solution. The introducing of MnO2 and the presence of Ni3+ after the oxidation of Ni2+ were the key factors which improve the OER performance. The potential at 10 mA cm-2 was 1.492 V (vs RHE) with a Tafel slope of 69.46 mV dec-1 in 1 M KOH aqueous solution, comparable to the state-of-art RuO2. The results indicated that MnO2 was found to have the capability to enhance not only the catalytic activity but also operation stability of Ni/DMTD/MnO2 towards OER.