Shuni Li

Unexpected catalytic activity of rhodium nanodendrites with nanosheet subunits for methanol electrooxidation in an alkaline medium

Nanocrystals of Rh, an important member of the noble metal catalyst family, have wide applications in heterogeneous catalytic reactions. Controlling the morphology of these noble metal nanocrystals has become an effective strategy for improving their catalytic activity and durability. In this work, well-defined Rh nanodendrites with very thin triangular branches as subunits are synthesized using a facile diethylene glycol reduction method, assisted by polyethyleneimine as a complex-forming agent and surfactant. For the first time, the methanol oxidation reaction (MOR) on Rh nanocrystals with a well-defined morphology is investigated using various electrochemical techniques in an alkaline medium. Unexpectedly, the as-prepared Rh nanodendrites, with ultrathin nanosheet subunits, exhibit superior electrocatalytic activity and durability during the MOR in an alkaline medium, indicating that Rh nanocrystals with specific morphology may be highly promising alternatives to Pt electrocatalysts in the MOR in an alkaline medium.

Polyethyleneimine-assisted synthesis of high-quality platinum/graphene hybrids: the effect of molecular weight on electrochemical properties

Graphene-supported precious metal nanoparticle hybrids have received extensive attention in recent years because of the outstanding physical and chemical properties of graphene. In this work, we synthesize high-quality reduced graphene oxide (RGO) supported monodispersed Pt nanocrystal (Pt/RGO) hybrids with the assistance of polyethyleneimine (PEI), in which PEI serves as a multi-functional molecule for the coordination with K2PtCl4, anchorage of PtII precursors on the graphene oxide surface, and chemical functionalization of Pt nanocrystals. Then, we investigate in detail the effect of the molecular weight of PEI on the electrocatalytic activity of the resultant Pt/RGO hybrids for the formic acid oxidation reaction (FAOR). Electrochemical measurements show that PEI with high molecular weight (Mw = 10 000) between the two RGO sheets limits seriously the access of electrolytes to the Pt sites. In contrast, PEI with low molecular weight (Mw = 600) between the two RGO sheets allows electrolytes to access freely the Pt sites, and the resultant Pt/RGO hybrids show enhanced electrocatalytic activity and stability for the FAOR compared to the commercial Pt/C electrocatalyst due to the ensemble effect.

MnO2/MnCo2O4/Ni heterostructure with quadruple hierarchy: a bifunctional electrode architecture for overall urea oxidation

A three-dimensional MnO2/MnCo2O4/Ni core–shell heterostructured electrode has been fabricated through a facile method. This electrode architecture consists of four levels of interconnected hierarchy: a primary macroporous Ni foam scaffold (≥500 μm), an intermediate vertically-aligned MnCo2O4 core-nanoflake array (50–100 nm), topmost ultra-thin MnO2 nanosheets (∼10 nm) and short-range ordered mesopores (∼5 nm) on the MnO2 nanosheets. This freestanding, hierarchical porous electrode has advantages in enhancing electroactive surface area, enabling efficient mass transport through the porous structure. The heterostructured electrode exhibits a low onset potential (1.33 V vs. RHE), a high anodic peak current density (1000 mA cm−2 g−1 at 1.7 V vs. RHE) and long-term catalytic stability for urea oxidation, which surpasses previous reported electrode materials for urea electrolysis. Remarkably, the MnO2/MnCo2O4/Ni electrode possesses bifunctional catalytic activity for both urea oxidation and hydrogen evolution. A urea electrolytic cell with both anode and cathode using the heterostructured electrodes has been fabricated and a current density of 10 mA cm−2 has been achieved at a cell voltage of 1.55 V. This noble metal-free quadruple hierarchy electrode shows potential as a new platform for multi-purpose applications.

Sandwich-structured Au@polyallylamine@Pd nanostructures: tuning the electronic properties of the Pd shell for electrocatalysis

We report herein the synthesis of core–shell sandwich Au@polyallylamine@Pd nanostructures, in which the electronic structure of the Pd shell can be strongly tuned by the medial polyallylamine layers. The designed Au@polyallylamine@Pd nanostructures exhibit significantly improved electrocatalytic activity and stability for the formic acid oxidation reaction through the preferential dehydrogenation pathway.

Reduced graphene oxide supported platinum nanocubes composites: one-pot hydrothermal synthesis and enhanced catalytic activity

Reduced graphene oxide (rGO) supported platinum nanocubes (Pt-NCs) composites (Pt-NCs/rGO) were synthesized successfully by a water-based co-chemical reduction method, in which polyallylamine hydrochloride acted as a multi-functional molecule for the functionalization of graphene oxide, anchorage of Pt(II) precursor, and control of Pt crystal facets. The morphology, structure, composition, and catalytic property of Pt-NCs/rGO composites were characterized in detail by various spectroscopic techniques. Transmission electron microscopy images showed well-defined Pt-NCs with an average size of 9 nm uniformly distributed on the rGO surface. The as-prepared Pt-NCs/rGO composites had excellent colloidal stability in the aqueous solution, and exhibited superior catalytic activity towards the hydrogenation reduction of nitro groups compared to commercial Pt black. The improved catalytic activity originated from the abundant exposed Pt{100} facets of Pt-NCs, excellent dispersion of Pt-NCs on the rGO surface, and synergistic effect between Pt-NCs and rGO.

Self-assembly synthesis of reduced graphene oxide-supported platinum nanowire composites with enhanced electrocatalytic activity towards the hydrazine oxidation reaction

Reduced graphene oxide (RGO)-supported Pt nanocrystal composites have wide applications in catalysis and electrocatalysis. In this work, we successfully synthesize guanidine-functionalized graphene oxide composites and phosphonate-functionalized platinum nanowires (Pt-NWs). Based on self-assembly and NaBH4 reduction, RGO-supported Pt-NW composites (Pt-NWs/RGO) are obtained successfully. The as-prepared nanomaterials are detailedly characterized using various physical techniques, such as transmission electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, element mapping, etc. Physical characterization results demonstrate that the guanidine functionalization of graphene oxide is crucial for the generation of Pt-NW/RGO composites. Electrochemical results show that both the phosphonate functionalization of Pt-NWs and the introduction of RGO contribute to the improved electrocatalytic activity of Pt-NW/RGO composites towards the hydrazine oxidation reaction.

Self-assembly of amine-functionalized gold nanoparticles on phosphonate-functionalized graphene nanosheets: a highly active catalyst for the reduction of 4-nitrophenol

Graphene nanosheet (GNS) supported gold nanoparticle (Au-NP) composites (Au-NP/GNS) have attracted a lot of attention due to their important applications in catalysis, sensing, optics, medicine, and fuel cells. In this study, based on the strong electrostatic and/or hydrogen bonding interactions between the amine-functionalized Au-NP (Au-NP@NH2) and phosphonate-functionalized GNS (GNS-PO3H2), a self-assembly strategy was used to synthesize Au-NP/GNS composites. The physical and chemical properties of Au-NP@NH2, GNS-PO3H2, and the Au-NP/GNS composites were fully investigated using various physical characterization, including X-ray powder diffraction, X-ray photoelectron spectroscopy, ultraviolet-visible spectroscopy, transmission electron microscopy, and zeta potential analysis. The experimental results demonstrate that the phosphonate-functionalization of GNS was critical for the generation of high-quality Au-NP/GNS composites. The as-prepared Au-NP/GNS composites show improved catalytic activity for the degradation of 4-nitrophenol compared to functionalized Au-NP, which was ascribed to the amine-functionalization of the Au-NP and the introduction of the GNS with high electrical conductivity and large surface area.

The facile ionic liquid-assisted synthesis of hollow and porous platinum nanotubes with enhanced catalytic performances

A facile one-pot synthetic method was developed to synthesize hollow and porous Pt nanotubes (Pt-HPNTs) using silica nanorods as a template, ionic liquid as a precipitator and reductant, and in situ generated KCl as an etching agent. The work reported here might open a new route for the synthesis of hollow nanostructures.