Jing-Jia Zhang

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.

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.

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.

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.

Effect of N-doped carbon quantum dots/multiwall-carbon nanotube composite support on Pt catalytic performance for methanol electrooxidation

N-Doped carbon quantum dots (NCQDs)/multiwall-carbon nanotube (MWCNT) supports are synthesized by a one pot hydrothermal treatment process at different contents of precursor. NCQDs–MWCNT as support can be widely used in the process of electrocatalysis. In this paper, the Pt/NCQDs–MWCNT catalysts are prepared by a microwave-assisted polyol process (MAPP) method and the effects of NCQDs with different contents on the performance of Pt-based anode catalysts for methanol oxidation reaction (MOR) are systematically demonstrated. The electrochemical tests reveal that the Pt/NCQDs–MWCNT catalyst exhibits the best performance for MOR when precursor content is 3 g. In terms of the electrochemical and characterization results, the moderate content of precursor for NCQDs plays multiple roles in the electrocatalytic performance: promoting the dispersion of untreated MWCNT significantly in solution; providing the plentiful oxygen-containing groups to deposit Pt nanoparticles; and facilitating the formation of homogeneous Pt nanoparticles.