Ordered Porous Carbons with Tunable Pore Sizes as Catalyst Supports in Direct Methanol Fuel Cell

The comparative study on inhibitory effect of natural organic matters on the TiO2 and activated carbon/TiO2 composites for the removal of 17α-ethinylestradiol

To reduce or eliminate the inhibition effect of natural organic matters (NOMs) in water on TiO₂ photocatalysis for removal of emerging contaminants, four activated carbon/titanium dioxide (AC/TiO₂) composites with different pore structure were prepared by hydrothermal method. The results showed that anatase TiO₂ particles were uniformly distributed in the pores or onto the surface of activated carbons. The total removal rate of 6 mg L^-1 17α-ethinylestradiol (EE2) on the four AC/TiO₂ composites reached above 90%, 30% higher than that of EE2 on TiO₂. The degradation rate constants of EE2 on four kinds of AC/TiO₂ were much higher than that on TiO₂. Further study indicated that the adsorption removal ratio of EE2 on the composites was slightly reduced mainly because competitive adsorption between hydrophilic NOMs (HA and FA) and EE2 molecules when HA and FA coexisted with EE2 in water. But importantly, the obvious inhibitory effect of FA for TiO₂ photocatalysis was eliminated on four composites because the introduction of AC with excellent adsorption capacity can preferentially transfer hydrophobic EE2 molecules onto adsorption sites of TiO₂/AC composites.

Synergetic Structural Transformation of Pt Electrocatalyst into Advanced 3D Architectures for Hydrogen Fuel Cells

A new direction for developing electrocatalysts for hydrogen fuel cell systems has emerged, based on the fabrication of 3D architectures. These new architectures include extended Pt surface building blocks, the strategic use of void spaces, and deliberate network connectivity along with tortuosity, as design components. Various strategies for synthesis now enable the functional and structural engineering of these electrocatalysts with appropriate electronic, ionic, and electrochemical features. The new architectures provide efficient mass transport and large electrochemically active areas. To date, although there are few examples of fully functioning hydrogen fuel cell devices, these 3D electrocatalysts have the potential to achieve optimal cell performance and durability, exceeding conventional Pt powder (i.e., Pt/C) electrocatalysts. This progress report highlights the various 3D architectures proposed for Pt electrocatalysts, advances made in the fabrication of these structures, and the remaining technical challenges. Attempts to develop design rules for 3D architectures and modeling, provide insights into their achievable and potential performance. Perspectives on future developments of new multiscale designs are also discussed along with future study directions.

Preparation of a Graphitized-Carbon-Supported PtNi Octahedral Catalyst and Application in a Proton-Exchange Membrane Fuel Cell

In this work, PtNi/GC octahedral nanocrystal catalysts are prepared using graphitized carbon (GC) to solve the problems of cathode catalysts in catalytic performance and proton-exchange membrane fuel cell application. The as-prepared supported catalysts exhibit well-crystallized octahedral morphologies and graphite layer structures with high corrosion resistance. Their mass activities and specific activities are 5 and 7 times higher than those of the commercial Pt/C. The sample with the best performance shows the cell voltage at 1000 mA cm^-2 of 0.672 V and maximum power density of 817.6 mW cm^-2 in the single-cell test, which are increased by 23 mV and 13.2 mW cm^-2 compared to the control. Especially after a high potential test, the above two parameters of this sample are reduced by only 5.6 and 8.4%, which are significantly lower than the attenuation of the control fabricated using Vulcan XC-72 carbon black. The work reveals that the GC-supported PtNi octahedral catalysts can give better consideration to the improvement of electrochemical and single-cell performances.

Adsorptive removal of resorcinol on a novel ordered mesoporous carbon (OMC) employing COK-19 silica scaffold: Kinetics and equilibrium study

Phenolic compounds and their derivatives have been found in industrial wastewater, which pose threats to the natural environment. Ordered mesoporous carbon (OMC) has been identified as an ideal adsorbent possessing high specific surface area and large pore volume to alleviate these pollutants. A novel ordered mesoporous carbon was prepared using COK-19 template with the cubic Fm3m structure for the first time. Ordered mesoporous silica COK-19 was synthesized and reported in 2015. Sucrose as the carbon precursor was impregnated into the mesopores of silica and converted to carbon through carbonization process using sulfuric acid as a catalyst. Ordered mesoporous carbon was obtained after the removal of silica framework using hydrofluoric acid. Boric acid was employed for the preparation of OMCs with tunable pore sizes in the range of 6.9-16.6 nm. Several characterization techniques such as nitrogen adsorption-desorption isotherms, transmission electron microscope (TEM), Fourier transform infrared spectroscopy, Boehm titration and elemental analysis were employed to characterize the OMCs. The pore size analysis and TEM images confirmed that OMC has replicated the mesostructure of the COK-19. Results obtained from adsorption kinetics and isotherms suggest that the Pseudo-second-order model and Langmuir isotherm well described the experimental data.

Ultrafine Pt Nanoparticles and Amorphous Nickel Supported on 3D Mesoporous Carbon Derived from Cu-Metal-Organic Framework for Efficient Methanol Oxidation and Nitrophenol Reduction

The development of novel strategy to produce new porous carbon materials is extremely important because these materials have wide applications in energy storage/conversion, mixture separation, and catalysis. Herein, for the first time, a novel 3D carbon substrate with hierarchical pores derived from commercially available Cu-MOF (metal-organic framework) (HKUST-1) through carbonization and chemical etching has been employed as the catalysts' support. Highly dispersed Pt nanoparticles and amorphous nickel were evenly dispersed on the surface or embedded within carbon matrix. The corresponding optimal composite catalyst exhibits a high mass-specific peak current of 1195 mA mg^-1 Pt and excellent poison resistance capacity ( I_F/ I_B = 1.58) for methanol oxidation compared to commercial Pt/C (20%). Moreover, both composite catalysts manifest outstanding properties in the reduction of nitrophenol and demonstrate diverse selectivities for 2/3/4-nitrophenol, which can be attributed to different integrated forms between active species and carbon matrix. This attractive route offers broad prospects for the usage of a large number of available MOFs in fabricating functional carbon materials as well as highly active carbon-based electrocatalysts and heterogeneous organic catalysts.

Synthesis of N-Doped Mesoporous Carbon Nanorods through Nano-Confined Reaction: High-Performance Catalyst Support for Hydrogenation of Phenol Derivatives

Traditional hard-template methods for the preparation of mesoporous carbon structures have been well developed, but there are difficulties associated with complete filling of the organic precursors in ordered mesochannels and exact replication of the templates. Herein, mesoporous carbon nanorods (meso-CNRs) were synthesized through thermal condensation of furfuryl alcohol followed by the nano-confined decomposition of polyfurfuryl alcohol in silica nanotubes (SiO₂ NTs) with porous shells. Limited and slow release of gaseous water through the porous shells and finite polyfurfuryl precursor inside silica nanotubes are responsible for the formation of the mesoporous structures. Nitrogen can be doped into the meso-CNRs by adding guanidine hydrochloride to the precursors. The nitrogen dopant not only stabilizes the ultrasmall and active Pd nanocatalyst in the meso-CNRs but also increases the electron density of Pd and accelerates the dissociation of H₂ , both of which increase the catalytic activity of the Pd catalyst in hydrogenation reactions.

Three-Dimensional Nanoprinting via Direct Delivery

Direct writing methods are a generic and simple means to produce designed structures in three dimensions (3D). The printing is achieved by extruding printing materials through a nozzle, which provides a platform to deliver a wide range of materials. Although this method has been routinely used for 3D printing at macroscopic scales, miniaturization to micrometer and nanometer scales and building hierarchical structures at multidimensional scales represent new challenges in research and development. The current work addresses these challenges by combining the spatial precision of atomic force microscopy (AFM) and local delivery capability of microfluidics. Specialized AFM probes serve dual roles of a microscopy tip and a delivery tool, enabling the miniaturization of 3D printing via direct material delivery. Stacking grids of 20 μm periodicity were printed layer-by-layer covering 1 mm × 1 mm regions. The spatial fidelity was measured to be several nanometers, which is among the highest in 3D printing. The results clearly demonstrate the feasibility of achieving high precision 3D nanoprinting with nanometer feature size and accuracy with practical throughput and overall size. This work paves the way for advanced applications of 3D hierarchical nanostructures.

One-Pot Synthesis of Monodisperse Noble Metal @ Resorcinol-Formaldehyde (M@RF) and M@Carbon Core-Shell Nanostructure and Their Catalytic Applications

We demonstrate that noble metal @ RF core-shell nanostructures can be obtained through a facile one-pot synthesis approach in the absence of any additional surfactants. Monodisperse metal@RF core-shell nanostructures can be produced within 1 h on a large scale. Both the core size and shell thickness can be readily tuned by altering the reaction parameters. Systematic studies reveal that resorcinol could have several functions: it could act as a reactant to form RF resin, and it also could passivate the surface of metallic nanoparticles to prevent them from aggregating. Additionally, for the first time, our results suggest that resorcinol may act as a reducing agent that can reduce metal salts to form metal nanoparticles. The core-shell nanoparticles can be carbonized into M@carbon nanostructures, which have shown great performance in the catalytic hydrogenation of chlorobenzene. This work not only will help to achieve the controllable synthesis of noble metal@RF resin and M@carbon core-shell nanostructures but also will promote research into other RF-based nanostructures and their catalytic applications.

Human hair-derived graphene-like carbon nanosheets to support Pt nanoparticles for direct methanol fuel cell application

A novel graphene-like carbon nanosheet (HGCN) with high specific surface area and multimodal pore system was synthesized using human hair as a carbon source for the deposition of PtNPs.

Rotating disk slurry electrodeposition of platinum at Y-zeolite/carbon Vulcan XC-72R for methanol oxidation in alkaline media

Platinum was electrodeposited onto Y-zeolite and Y-zeolite (Y)/Vulcan XC-72R (V) to produce Pt/Y/V and Pt/Y catalysts using a rotating disk slurry electrode technique.

Cube-like α-Fe2O3 supported on ordered multimodal porous carbon as high performance electrode material for supercapacitors

Well-dispersed cube-like iron oxide (α-Fe2O3) nanoparticles (NPs) supported on ordered multimodal porous carbon (OMPC) are synthesized for the first time by a facile and efficient glycine-assisted hydrothermal route. The effect of OPMC support on growth and formation mechanism of the Fe2O3 NPs is discussed. OMPC as a supporting material plays a pivotal role of controlling the shape, size, and dispersion of the Fe2O3 NPs. As-synthesized α-Fe2O3/OMPC composites reveal significant improvement in the performance as electrode material for supercapacitors. Compared to the bare Fe2O3 and OMPC, the composite exhibits excellent cycling stability, rate capability, and enhanced specific capacitances of 294 F g(-1) at 1.5 A g(-1), which is twice that of OMPC (145 F g(-1)) and about four times higher than that of bare Fe2O3 (85 F g(-1)). The improved electrochemical performance of the composite can be attributed to the well-defined structure, high conductivity, and hierarchical porosity of OMPC as well as the unique α-Fe2O3 NPs with cube-like morphology well-anchored on the OMPC support, which makes the composite a promising candidate for supercapacitors.

The oriented growth of tungsten oxide in ordered mesoporous carbon and their electrochemical performance

Electrocatalysts for hydrogen oxidation and methanol oxidation are the heart of the proton exchange membrane fuel cell. In spite of tremendous efforts, developing low-cost anodic electrocatalysts with high catalytic activity and corrosion resistance is still a great challenge. Here, we report a nanocomposite consisting of oriented WO3 nanorods grown in ordered mesoporous carbon as a high-performance functional catalyst carrier for proton exchange membrane fuel cells. As a result of the catalytic graphitization effect of tungsten compounds, the degree of graphitization and conductivity of mesoporous carbon film were improved even at a low temperature. Furthermore, compared with ordered mesoporous carbon, ordered mesoporous C-WO3 nanocomposites possess favorable hydrophilicity, excellent corrosion resistance and notable electrocatalytic activities. The unusual electrocatalytic activities arise from the ideal physical properties of the carrier and synergetic catalysis between Pt and WO3.

Carbon nanocages: a new support material for Pt catalyst with remarkably high durability

Low durability is the major challenge hindering the large-scale implementation of proton exchange membrane fuel cell (PEMFC) technology, and corrosion of carbon support materials of current catalysts is the main cause. Here, we describe the finding of remarkably high durability with the use of a novel support material. This material is based on hollow carbon nanocages developed with a high degree of graphitization and concurrent nitrogen doping for oxidation resistance enhancement, uniform deposition of fine Pt particles, and strong Pt-support interaction. Accelerated degradation testing shows that such designed catalyst possesses a superior electrochemical activity and long-term stability for both hydrogen oxidation and oxygen reduction relative to industry benchmarks of current catalysts. Further testing under conditions of practical fuel cell operation reveals almost no degradation over long-term cycling. Such a catalyst of high activity, particularly, high durability, opens the door for the next-generation PEMFC for “real world” application.

Urchin-like TiO2@C core–shell microspheres: coupled synthesis and lithium-ion battery applications

Carbon coated urchin-like TiO₂ microspheres were prepared through coupled hydrolysis of titanium tetrachloride and catalyzed carbonization of glucose.