Xu-Lei Sui

A newly-designed sandwich-structured graphene–Pt–graphene catalyst with improved electrocatalytic performance for fuel cells

A novel sandwich-structured graphene–Pt–graphene (G–P–G) catalyst has been synthesized by a convenient approach. The obtained G–P–G catalyst has been characterized by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy, high resolution transmission electron microscopy, and electrochemical measurements. Structural characterization shows that the G–P–G catalyst has a well-defined sandwich-like morphology. The results of electrochemical measurements indicate that the G–P–G exhibits 1.27 times higher activity for methanol electrooxidation than that of the Pt/graphene catalyst. Importantly, the results of the accelerated potential cycling test demonstrate that the G–P–G catalyst possesses 1.7 times higher stability than that of Pt/graphene. The significantly enhanced electrochemical performance is ascribed to its unique sandwich-like structure. Pt nanoparticles are anchored between the two adjacent graphene sheets, substantially enhancing the metal–support interaction, and graphene could act as a “mesh bag” to prevent the Pt species from leaking into the electrolyte, so its stability has considerably been enhanced. The effect of composited graphene amount on the stability of the hybrid has also been systematically studied. The stability of the catalyst increases with the increase of the introduced GO amount and the G–P–G50 shows optimized electrocatalytic performance. These findings suggest that the sandwich-structured G–P–G catalyst holds tremendous promise for fuel cells.

Graphitic carbon nitride nanosheet coated carbon black as a high-performance PtRu catalyst support material for methanol electrooxidation

PtRu supported on a C@g-C3N4 NS (g-C3N4 nanosheet coated Vulcan XC-72 carbon black) catalyst has been prepared by a microwave-assisted polyol process (MAPP). The results of electrochemical measurements show that the PtRu/C@g-C3N4 NS catalyst has excellent activity due to more uniform dispersion and smaller size of PtRu nanoparticles (PtRu NPs), and higher stability ascribed to the stronger metal–support interaction (SMSI) between PtRu NPs and the composite support. Physical characterisation using techniques such as X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) has indicated that the bulk g-C3N4 shell outside of the as-prepared C@bulk g-C3N4 (bulk g-C3N4 coated Vulcan XC-72 carbon black, C@bulk g-C3N4) indeed exfoliated to layered g-C3N4 nanosheets and formed a composite material of Vulcan XC-72 coated with g-C3N4 nanosheets. Furthermore, the results indicate that the mass catalytic activity of the PtRu/C@g-C3N4 NS catalyst substantially enhanced, which is a factor of 2.1 times higher than that of the PtRu/C catalyst prepared by the same procedure and the accelerated potential cycling tests (APCTs) show that the PtRu/C@g-C3N4 NS catalyst possesses 14% higher stability and much greater poison tolerance than as-prepared PtRu/C. The significantly enhanced performance of the PtRu/C@g-C3N4 NS catalyst is ascribed to the following reasons: the inherently excellent mechanical resistance and stability of g-C3N4 nanosheets in acidic and oxidative environments; the increased electron conductivity of the support by forming a core–shell structure of C@g-C3N4 NS; SMSI between metal NPs and the composite support. Based on this novel approach to fabricate a C@g-C3N4 NS hybrid nanostructure, many other interesting applications might also be discovered.

3D Hierarchical Pt-Nitrogen-Doped-Graphene-Carbonized Commercially Available Sponge as a Superior Electrocatalyst for Low-Temperature Fuel Cells

Three-dimensional hierarchical nitrogen-doped graphene (3D-NG) frameworks were successfully fabricated through a feasible solution dip-coating method with commercially available sponges as the initial backbone. A spongy template can help hinder the graphene plates restacking in the period of the annealing process. The Pt/3D-NG catalyst was synthesized employing a polyol reduction process. The resultant Pt/3D-NG exhibits 2.3 times higher activity for methanol electro-oxidation along with the improvement in stability as compared with Pt/G owing to their favorable features including large specific surface area, high pore volume, high N doping level, and the homogeneous dispersion of Pt nanoparticles. Besides, Pt/3D-NG also presents high oxygen reduction reaction (ORR) performance in acid media when compared with Pt/3D-G and Pt/G. This work raises a valid solution for the fabrication of 3D functional freestanding graphene-based composites for a variety of applications in fuel cell catalysis, energy storage, and conversion.

Multiphase sodium titanate/titania composite nanostructures as Pt-based catalyst supports for methanol oxidation

Sodium titanate/titania composite nanotubes/nanorods (STNS) are synthesized from anatase titania by the hydrothermal method and subsequent annealing in the range of 300–700 °C. The changes in the composition and morphology of STNS are investigated by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The results reveal that the composition of STNS changes from “Na2−xHxTi2O5” to “Na2Ti6O13” and their morphology changes from nanotubes to nanorods. The products obtained at 400 °C and 600 °C correspond to the intermediate state of reactions. Pt-based catalysts are prepared by a microwave-assisted ethylene glycol process, and are also characterized by physical analysis and electrochemical measurements. The variations of the catalytic activity and stability of Pt/C-STNS catalysts show the interesting “M” shape with the increase of the annealing temperature of STNS. The Pt nanoparticles supported on STNS-400 nanotubes and STNS-600 nanorods exhibit more uniform dispersion and superior electrocatalytic performance for methanol electrooxidation. The main reason seems to be that both of them are multiphase composites with a large number of phase interfaces and crystal defects, which is conducive to the deposition of Pt nanoparticles. The uniform dispersion of Pt nanoparticles plays an essential role in the electrochemical performance of catalysts. In addition, the presence of the “anatase TiO2” phase in both of them can further enhance the electrochemical performance due to the metal–support interaction. Moreover, compared to commercial Pt/C, the Pt/C-STNS-600 catalyst exhibits higher electrochemical activity and stability, suggesting that superior catalysts can be developed by designing the structure and composition of the supports.

A rapid synthesis of TiO2 nanotubes in an ethylene glycol system by anodization as a Pt-based catalyst support for methanol electrooxidation

In this paper, we report a rapid method to synthesize titania nanotubes as the support for a Pt-based catalyst. The titania nanotubes can be obtained during 1200 s in an ethylene glycol system by the anodization method. Pt nanoparticles were successfully deposited on a mixture of carbon and as-prepared TiO2 nanotubes by a microwave-assisted polyol process. The electrochemical results show that the electrochemically active specific surface area and the activity for methanol electrooxidation of the as-prepared catalyst are both much higher than those of the commercial Pt/C. Whether it is through the constant potential test or cycling potential test, the durability of the as-prepared catalyst is higher than that of the commercial Pt/C. Such remarkable performance is due to the strong corrosion resistance of titania, metal–support interactions and hydrogen spillover effect between Pt and titania, the better electronic conductivity, as well as the good dispersion of the Pt nanoparticles. These studies indicate that titania nanotubes are a promising catalyst support for methanol electrooxidation.

Graphitic-C3N4 quantum dots modified carbon nanotubes as a novel support material for a low Pt loading fuel cell catalyst

For developing low Pt loading and high performance catalysts for direct methanol fuel cells, a graphitic-C3N4 quantum dots (g-C3N4 QDs) modified CNT (CNT-QDs) composite material was constructed via a π–π stacking method, in which the g-C3N4 QDs act a bridged unit between the CNTs and metal nanoparticles (NPs). Compared to conventional acid-functionalized CNTs used for supporting novel metal NPs, the CNT-QDs have less structural damage leading to their high stability. Moreover, the electrochemical test results indicate that the mass catalytic activity of the PtRu/CNT-QDs catalyst is 2.3 times higher than that of PtRu/CNT, leading to a 56.5% reduction of novel metal loading. The accelerated potential cycling tests (APCTs vs. RHE 0–1.2 V) show that the PtRu/CNT-QDs catalyst possesses 15.1% higher stability than that of the conventional acid-functionalized CNTs supported PtRu (PtRu/T-CNT) catalyst. The significantly enhanced performance obtained for the PtRu/CNT-QDs catalyst was ascribed to the homogeneous dispersion of PtRu NPs on the composite support due to its abundant Lewis acid sites for anchoring the PtRu NPs and the excellent mechanical resistance and stability of the g-C3N4/CNT composite materials in acidic and oxidative environments, as well as the strong metal–support interaction (SMSI) between the metal NPs and g-C3N4.

Hierarchical carbon coated molybdenum dioxide nanotubes as a highly active and durable electrocatalytic support for methanol oxidation

Molybdenum dioxide (MoO2) has been adopted as an advanced auxiliary support material for its outstanding electrical properties to anchor metal nanoparticles (NPs). To overcome the drawback of MoO2 electronic conductivity, a novel hierarchical carbon coated molybdenum dioxide (MoO2@C) nanotube built from ultra-thin nanosheets was utilized as a nanostructured support. Pt NPs were uniformly deposited onto the MoO2@C support and a hierarchical Pt-based anode catalyst was successfully synthesized. Benefitting from several favourable features, including high exposed surface area, short diffusion distance, fast charge transfer and homogeneous Pt NPs dispersion, the Pt/MoO2@C catalyst exhibited an improved activity along with enhanced stability for methanol electrooxidation when compared with that of the Pt/C catalyst. This novel hierarchical structure is helpful for the further applications in hydrogen evolution reaction, supercapacitors and batteries.

One-pot synthesis of a three-dimensional graphene aerogel supported Pt catalyst for methanol electrooxidation

A three-dimensional (3D) structured Pt/graphene aerogel has been synthesized by a facile one-pot solvothermal process. The as-synthesized catalyst is characterized by X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy, and electrochemical tests. It has been found that the Pt/graphene aerogel catalyst exhibits a well-developed 3D interconnected porous graphene framework with Pt nanoparticles (NPs) decorated on the surface of the graphene aerogel. More importantly, the as-made Pt/graphene aerogel catalyst exhibits a much higher electrocatalytic activity and stability than the Pt/graphene for methanol electrooxidation. The enhancement may result from the unique 3D graphene architecture, and the efficient assembly between the Pt NPs and graphene aerogel. These outstanding properties suggest that the Pt/graphene aerogel catalyst holds tremendous potential for fuel cell applications.

Three-dimensional TiO2@C nano-network with high porosity as a highly efficient Pt-based catalyst support for methanol electrooxidation

The development of highly active and durable Pt-based catalysts is an important issue for methanol electrooxidation. Research into highly efficient supports provides a feasible method to achieve such catalysts. In this paper, carbon-coated TiO2 nanowires with a unique three-dimensional network structure are prepared as a Pt-based catalyst support by the carbonization of a resorcinol–formaldehyde polymer. Physical characterization confirms that this unique structure can provide a large specific surface area, high porosity and efficient transport channels. The abundant heterogeneous interfaces between the TiO2 nanowires and carbon provide numerous Pt loading sites, which greatly improves the utilization of Pt. Strikingly, electrochemical measurements show that the as-prepared catalyst has much better activity and durability than commercial Pt/C for methanol electrooxidation. Furthermore, the single direct methanol fuel cell test demonstrates that the as-prepared catalyst has higher power density and polarization current. We attribute this excellent catalytic performance to the unique nano-network structure, the numerous Pt anchoring sites, and the synergetic effect of the different components.

Effect of core/shell structured TiO2@C nanowire support on the Pt catalytic performance for methanol electrooxidation

At present, low platinum catalysts have attracted much attention in the whole world. It is an effective strategy for reducing platinum loading to use an efficient support to enhance the catalytic activity. In this paper, a uniform structure of carbon and TiO2 nanowires is synthesized through a two-step hydrothermal reaction and used as an efficient Pt-based anode catalyst support. Physical characterization confirms the special core/shell structure. The carbonization temperature greatly affects the graphitization degree, porosity and surface chemical properties of the carbon shell. Electrochemical measurements indicate that the catalyst obtained at 800 °C has excellent electrochemical activity and durability. Its electrochemically active specific surface area is much higher than that of Pt/C. Its activity for methanol oxidation is about 1.4 times higher than that of Pt/C. The enhanced performance is attributed to the design of the special core/shell structure. The uniform dispersion of carbon and titania nanowires produces a strong synergistic effect and generates highly active Pt loading sites. The carbon shells can greatly improve the electronic conductivity and suppress the crystal growth of TiO2 during calcination. Meanwhile, a large number of defects within the carbon shells are also conducive to the dispersion of Pt nanoparticles. In addition, the core of TiO2 nanowires can enhance the hydrophilicity of the carbon shell and produce a strong metal–support interaction with Pt nanoparticles, which improve the activity and durability of catalysts.