Chun-Hua Cui

Octahedral PtNi Nanoparticle Catalysts: Exceptional Oxygen Reduction Activity by Tuning the Alloy Particle Surface Composition

We demonstrate how shape selectivity and optimized surface composition result in exceptional oxygen reduction activity of octahedral PtNi nanoparticles (NPs). The alloy octahedra were obtained by utilizing a facile, completely surfactant-free solvothermal synthesis. We show that the choice of precursor ligands controls the shape, while the reaction time tunes the surface Pt:Ni composition. The 9.5 nm sized PtNi octahedra reached a 10-fold surface area-specific (~3.14 mA/cm(Pt)(2)) as well as an unprecedented 10-fold Pt mass based (~1.45 A/mg(Pt)) activity gain over the state-of-art Pt electrocatalyst, approaching the theoretically predicted limits.

A Free‐Standing Pt‐Nanowire Membrane as a Highly Stable Electrocatalyst for the Oxygen Reduction Reaction

Proton exchange membrane fuel cells (PEMFCs) have attracted a great deal of attention because of their high energy conversion effi ciency, low operation temperature, and low pollution emission. [ 1 ] However, there are still some challenges, such as sluggish kinetics and poor electrocatalyst durability of the oxygen reduction reaction (ORR) at the cathode, that limit the effi ciency and commercial viability of PEMFCs. [ 2,3 ] Therefore, it is necessary to develop a highly active and durable catalyst to improve the ORR performance of PEMFCs. [ 4,5 ]

Synthesis of an Attapulgite Clay@Carbon Nanocomposite Adsorbent by a Hydrothermal Carbonization Process and Their Application in the Removal of Toxic Metal Ions from Water

A new kind of attapulgite clay@carbon (ATP@C) nanocomposite adsorbent has been synthesized by a one-pot hydrothermal carbonization process under mild conditions using two cheap, ecofriendly materials (i.e., attapulgite clay (ATP), which is a magnesium aluminum silicate that is abundant in nature, and glucose, which is a green chemical obtained from biomass). Compared to carbon-based materials, this new ATP@C nanocomposite exhibits a high adsorption ability for Cr(VI) and Pb(II) ions with maximum adsorption capacities of 177.74 and 263.83 mg·g(-1), respectively. The results demonstrate that this nanocomposite is an exceptionally promising candidate as a low-cost, sustainable, and effective adsorbent for the removal of toxic ions from water.

Engineering interface and surface of noble metal nanoparticle nanotubes toward enhanced catalytic activity for fuel cell applications.

In order for fuel cells to have commercial viability as alternative fuel sources, researchers need to develop highly active and robust fuel cell electrocatalysts. In recent years, the focus has been on the design and synthesis of novel catalytic materials with controlled interface and surface structures. Another goal is to uncover potential catalytic activity and selectivity, as well as understand their fundamental catalytic mechanisms. Scientists have achieved great progress in the experimental and theoretical investigation due to the urgent demand for broad commercialization of fuel cells in automotive applications. However, there are still three main problems: cost, performance, and stability. To meet these targets, the catalyst needs to have multisynergic functions. In addition, the composition and structure changes of the catalysts during the reactions still need to be explored. Activity in catalytic nanomaterials is generally controlled by the size, shape, composition, and interface and surface engineering. As such, one-dimensional nanostructures such as nanowires and nanotubes are of special interest. However, these structures tend to lose the nanoparticle morphology and inhibit the use of catalysts in both fuel cell anodes and cathodes. In 2003, Rubinstein and co-workers proposed the idea of nanoparticle nanotubes (NNs), which combine the geometry of nanotubes and the morphology of nanoparticles. This concept gives both the high surface-to-volume ratio and the size effect, which are both appealing in electrocatalyst design. In this Account, we describe our developments in the construction of highly active NNs with unique surface and heterogeneous interface structures. We try to clarify enhanced activity and stability in catalytic systems by taking into account the activity impact factors. We briefly introduce material structural effects on the electrocatalytic reactivity including metal oxide/metal and metal/metal interfaces, dealloyed pure Pt, and mixed Pt/Pd surfaces. In addition, we discuss the geometric structure and surface composition changes and evolutions on the activity, selectivity, and stability under fuel cell operation conditions. We expect that these nanostructured materials with particular nanostructured characteristics, physical and chemical properties, and remarkable structure changes will offer new opportunities for wide scientific communities.

Element-specific anisotropic growth of shaped platinum alloy nanocrystals

Morphological shape in chemistry and biology owes its existence to anisotropic growth and is closely coupled to distinct functionality. Although much is known about the principal growth mechanisms of monometallic shaped nanocrystals, the anisotropic growth of shaped alloy nanocrystals is still poorly understood. Using aberration-corrected scanning transmission electron microscopy, we reveal an element-specific anisotropic growth mechanism of platinum (Pt) bimetallic nano-octahedra where compositional anisotropy couples to geometric anisotropy. A Pt-rich phase evolves into precursor nanohexapods, followed by a slower step-induced deposition of an M-rich (M = Ni, Co, etc.) phase at the concave hexapod surface forming the octahedral facets. Our finding explains earlier reports on unusual compositional segregations and chemical degradation pathways of bimetallic polyhedral catalysts and may aid rational synthesis of shaped alloy catalysts with desired compositional patterns and properties. Platinum-rich phases that initially form create the edges and corners of octahedral nanoparticle alloys. Nanoparticle growth starts at the edges The high activity of precious metals such as platinum for reactions that occur in fuel cells can be enhanced by alloying with metals such as nickel and cobalt to form shaped nanoparticles, where platinum is concentrated at the corner and edge sites. Gan et al. used a combination of high-resolution imaging and modeling to follow the formation of octadedral nanoparticles of these alloys with increasing growth times. A platinum-rich phase with an extended morphology forms initially and becomes the edges and corners for the particles, and the alloying metals deposit to fill in the facets. Science, this issue p. 1502

Ultrathin PtPdTe Nanowires as Superior Catalysts for Methanol Electrooxidation

Ultrathin and ultralong: Highly uniform, ultrathin (diameter 5-7 nm), and ultralong (aspect ratio >10(4)) PtPdTe nanowires (NWs) were synthesized by using a facile method employing Te NWs as both sacrificial templates and reducing agents. Fine-tuning of the molar ratios of Pt and Pd precursors afforded PtPdTe NWs with different compositions and enhanced electroactivity in the methanol oxidation reaction in comparison with a commercial Pt/C catalyst.

A Methanol‐Tolerant Pt/CoSe2 Nanobelt Cathode Catalyst for Direct Methanol Fuel Cells

Direct methanol fuel cells (DMFCs) have received considerable and persistent attention, because methanol is an abundant, inexpensive liquid fuel that is easier to store and transport than hydrogen. Despite the great advances made in this field, two main issues affecting efficiency and power density must still be considered, that is, sluggish kinetics of the fuel-cell anode reaction and so-called methanol crossover. The small methanol molecule can easily cross over from the anode to the cathode side through the polymer membranes of DMFCs, and then reacts directly with the cathode catalyst and O2 to decrease the cathode potential and thus reduce fuel efficiency. One approach to addressing this problem is the development of methanol-tolerant cathode catalysts for the oxygen reduction reaction (ORR). Recent research on methanol-tolerant catalysts has shown that transition metal macrocycles, Ru-based chalcogenides, and some platinumbased alloys all show methanol tolerance while retaining catalytic activity for the ORR. Nevertheless, disadvantages still exist. For instance, Pt-free electrocatalysts often show much lower activity and inferior long-term stability under fuel-cell conditions; Pt-based alloy cathode electrocatalysts are available only with low metal loading and thus are not quite suitable for DMFCs. Therefore, development of novel methanol-tolerant electrocatalysts with considerable stability and high ORR activity is important. Currently, cobalt chalcogenides are attracting enormous interest as new ORR electrocatalysts. Cobalt sulfides such as Co3S4 and Co9S8 are rather active for four-electron ORR in acidic electrolytes. In addition, cobalt selenides and tellurides show electrocatalytic ORR activity in nanocrystal form. In particular, the CoSe2/C nanoparticles fabricated by Alonso-Vante et al. exhibit good methanol tolerance. However, the ORR activity of these materials is still low, and they are far from DMFC application. Recently, we described a synthetic strategy that allows large-scale fabrication of ultrathin lamellar mesostructured CoSe2/diethylenetriamine (DETA) nanobelts in a binary solution. The lamellar nanobelts have several advantages over previous cobalt chalcogenides: homogeneously distributed, copious surface amino groups that allow loading of highly dispersed metal nanoparticles, and exceptional stability under strongly acidic conditions. With these merits, we expect that methanoltolerant electrocatalysts with high performance can be designed on the basis of this material. Here we report that a new methanol-tolerant Pt/CoSe2 nanobelt electrocatalyst for DMFC applications can be synthesized by in situ loading of Pt nanoparticles on CoSe2/ DETA nanobelts through a polyol reduction approach. The Pt/CoSe2 electrocatalysts display relatively high ORR catalytic activity in acidic medium. More importantly, the nanohybrid structures are highly resistant to methanol, even at concentrations of up to 5m. Mesostructured CoSe2/DETA nanobelts were first synthesized in high yield by a simple solvothermal strategy reported previously. Then, Pt NPs were synthesized in situ on the surface of CoSe2/DETA nanobelts through a facile polyol reduction approach. The multilayered CoSe2/DETA nanobelts are highly acid resistant, although selenides are generally vulnerable to attack by acids. The H2SO4 treatment process is followed the recent report by Kanatzidis et al. on treatment of mesostructured c-C20PyPtSnSe materials with strong acids. The H2SO4-treated sample retains the singlecrystalline nature and growth direction of the original CoSe2/ DETA nanobelts (see Supporting Information Figure S1). High-resolution (HR) TEM studies along the lateral thickness direction of H2SO4-treated CoSe2/DETA nanobelts showed that interlayer distance decreased from 1.08 to 0.67 nm (see Supporting Information Figure S1d). In fact, acid treatment is a simple ion-exchange process. Only protonated DETA molecules between two neighboring CoSe2 slabs are replaced by protons, and then the flexible inorganic skeleton contracts accordingly. The results suggest that the nanobelts have exceptional stability under strongly acidic conditions and retain their shape, composition, structural integrity, and single-crystalline nature. Moreover, they have a high BET surface area of 77 m g 1 (see Supporting Information Figure S2). Loading of Pt NPs on the surface of CoSe2/DETA nanobelts was confirmed by XRD patterns (see Supporting Information Figure S3c, left). The TEM images in Figure 1a and b show that Pt NPs are homogeneously decorated on the backbone of CoSe2/DETA nanobelts. The average size of the Pt NPs is about 8.3 nm (inset in Figure 1a), which corresponds [*] Dr. M.-R. Gao, Q. Gao, J. Jiang, C.-H. Cui, W.-T. Yao, Prof. Dr. S. H. Yu Division of Nanomaterials & Chemistry Hefei National Laboratory for Physical Sciences at Microscale Department of Chemistry, University of Science and Technology of China Hefei 230026 (P. R. China) Fax: (+ 86)551-360-3040 E-mail: shyu@ustc.edu.cn Homepage: http://staff.ustc.edu.cn/~ yulab/

Remarkable enhancement of electrocatalytic activity by tuning the interface of Pd-Au bimetallic nanoparticle tubes.

The interface, which formed in a bimetallic system, is a critical issue to investigate the fundamental mechanism of enhanced catalytic activity. Here, we designed unsupported Pd-Au bimetallic nanoparticle tubes with a tunable interface, which was qualitatively controlled by the proportion of Pd and Au nanoparticles (NPs), to demonstrate the remarkably enhanced effect of Pd and Au NPs in electro-oxidation of ethanol. The results demonstrated that the electrocatalytic activity is highly relative to the interface and has no direct relation with individual metal component in the Pd-Au system. This effect helps us in achieving a fundamental understanding of the relationship between their activity and the interface structure and chemical properties and, consequently, is helpful in designing new catalysts with high performances.

Large scale restructuring of porous Pt-Ni nanoparticle tubes for methanol oxidation: A highly reactive, stable, and restorable fuel cell catalyst

We report a large scale restructuring of porous Pt-Ni nanoparticle tubes for electrocatalytic oxidation of methanol, showing high catalytic activity, stability and resistance to poisoning. The surface restructuring highly improved the electrochemical active surface area (ECSA) by potential cycling in a strong acid electrolyte at room temperature. After a long-time stability test, the ECSA can be restored to its initial value after another potential cycling, thus this kind of electrocatalyst shows the potential possibility for next-generation highly restorable catalysts in direct methanol fuel cells.

Direct fabrication of photoconductive patterns on LBL assembled graphene oxide/PDDA/titania hybrid films by photothermal and photocatalytic reduction

A photo-thermal/catalytic reduction lithography (PRL) approach for the fabrication of photoconductive patterns by 300 W Xe lamp illumination of the (PDDA/GO/PDDA/TiO)20 hybrid films formed through layer by layer (LBL) assembly technique has been reported. High quality (PDDA/GO/PDDA/TiO)20 hybrid films were fabricated on the glass substrate through alternative LBL self-assembly with graphene oxide (GO), titania (TiO) nanosheets, and poly(diallyldimethylammonium) (PDDA). Then, the photoconductive pattern was fabricated by illuminating the hybrid film equipped with a pre-designed aluminium foil as the shadow mask. The “on-off” photoconductive response of the fabricated pattern was directly tested due to the photo-electro conversion role of TiO nanosheets and electronic transportation of reduced GO (RGO) nanosheets, which shows a high photocurrent generation and good reversibility.