Zhongshui Li

A green one-pot synthesis of Pt/TiO2/Graphene composites and its electro-photo-synergistic catalytic properties for methanol oxidation

A facile and green one-pot method was used to synthesize Pt/TiO2/Graphene composites with ethanol as a reducing agent under microwave irradiation. The as-prepared composites were characterized by SEM, TEM, EDX, XPS, XRD and Raman. Electrocatalytic performance of the Pt/TiO2/GNs composites was investigated by cyclic voltammetry (CV), chronoamperometric (CA), COad stripping voltammetry and electrochemical impedance spectrum (EIS). All experimental data have revealed that TiO2 (P25) not only enhanced the reduction ability of ethanol under microwave irradiation but also promoted Pt heterogeneous nucleation to form Pt nanoclusters which are around P25 and loaded on graphene nanosheets (GNs) surface. Electrochemical experiments showed that Pt/TiO2/GNs had much higher catalytic activity and stability toward methanol oxidation reaction (MOR) and better resistance to CO poisoning compared with Pt/GNs and the commercially available Johnson Matthey 20% Pt/C catalyst (Pt/C-JM). Especially under UV irradiation with 20min, Pt/TiO2/GNs composites showed an ultrahigh forward peak current density of 1354mAmg(-1), nearly 2.5 times higher than that of Pt/C-JM, which indicated that the electrocatalytic and photocatalytic properties of Pt/TiO2/GNs had been integrated to boost the catalytic performance for MOR.

The synergistic effect of graphene and polyoxometalates enhanced electrocatalytic activities of Pt-{PEI-GNs/[PMo12O40]3−}n composite films regarding methanol oxidation

The {PEI-GNs/PMo12}n composite films are prepared by an LBL electrostatic assembly technique, and their uniform and homogeneous traits have been verified by UV-vis and cyclic voltammetry. The {PEI-GNs/PMo12}n composite films are used as a novel catalyst support for electro-deposition of Pt particles in situ. Pt particles immobilizing on the surface of {PEI-GNs/PMo12}n composite films were confirmed by XPS, EDX, XRD and FE-SEM. The interesting seashell-like Pt micro–nano-clusters can be obtained when {2PEI-GNs/PMo12} composite films are used as catalyst supports. Pt-{PEI-GNs/PMo12}n composite films present good electrocatalytic activity regarding methanol oxidation and improved tolerance of CO. These results indicate that poly(ethyleneimine) functionalized graphene (PEI-GNs) preserves the superior electric conductivities of graphene sheets in the composite films, and the introduction of electroactive [PMo12O40]3− (PMo12) into the composite films helps to convert intermediate species CO into CO2 from the Pt nanoparticles. The synergistic effect of PEI-GNs and PMo12 remarkably enhanced the electrocatalytic activity and stability regarding methanol oxidation.

One-step microwave synthesis of Pt (Pd)/Cu2O/GNs composites and their electro-photo-synergistic catalytic properties for methanol oxidation

A facile one-pot method was used to synthesize Pt/Cu2O/GNs and Pd/Cu2O/GNs composites. Pt or Pd nanoparticles are deposited onto graphene sheets (GNs) and Cu2O via synchronous reduction of K2PtCl4 (K2PdCl4), Cu(OH)2 and graphene oxide (GO) with glucose as a reducing agent under microwave irradiation. The formation of Cu2O promotes the nucleation of Pt(0) or Pd(0) particles and favors more complete reduction of PtCl42− or PdCl42−. Catalytic properties of as-prepared composites for methanol oxidation reaction (MOR) were evaluated by cyclic voltammetry (CV), chronoamperometry, COads stripping voltammetry and electrochemical impedance spectrum (EIS). Electrochemical experiments showed that Pt/Cu2O/GNs and Pd/Cu2O/GNs had much higher catalytic activity and stability for MOR and better resistance to CO poisoning compared with the commercially available Johnson Matthey 20% Pt/C catalyst (Pt/C-JM) and Sigma-Aldrich 20% Pd/C catalyst (Pd/C-SA). Especially under the UV irradiation, the total peak current density and catalytic stability of Pt/Cu2O/GNs and Pd/Cu2O/GNs drastically increase, which may result from the synergistic effect between the electro-catalytic and photo-catalytic properties. In brief, the cooperation among Pt (Pd), Cu2O and GNs promotes remarkably the catalytic performance for MOR on Pt/Cu2O/GNs and Pd/Cu2O/GNs either without light or with UV irradiation.

In situ electro-deposition of Pt micro-nano clusters on the surface of {[PMo12O40]3−/PAMAM}n multilayer composite films and their electrocatalytic activities regarding methanol oxidation

The {[PMo(12)O(40)](3-)/PAMAM}(n) multilayer films are prepared by LBL electrostatic assembly technique, and their uniform and homogeneous traits have been verified by cyclic voltammetry. The {[PMo(12)O(40)](3-)/PAMAM}(n) multilayer films with PAMAM as the outmost layer, having an open structure and exhibiting good penetrability for the solvent molecules at low pH, are used as matrices for electro-deposition of Pt micro-nano clusters in situ. X-ray photoelectron spectroscopy (XPS) analysis and field emission scanning electron microscope (FE-SEM) characterization show that the unique Pt micro-nano clusters with flower-like structure have been immobilized on the surface of {[PMo(12)O(40)](3-)/PAMAM}(n) multilayer films. The morphologies of Pt micro-nano clusters are influenced by electro-deposition conditions such as deposition potential, deposition time, and the number of layers of {[PMo(12)O(40)](3-)/PAMAM}(n) multilayer films. Pt(-clusters)-{PMo(12)/PAMAM}(3) composite films demonstrate good electrocatalytic activities regarding methanol oxidation and improved tolerance of CO.

Preparation of Pt/{PDDA-GN/PSS-GN}n multilayer films and their electrocatalytic activity regarding methanol oxidation

The stable aqueous dispersion solutions of polymer-modified graphene were prepared by reduction with hydrazine hydrate in situ from exfoliated graphite oxides in the presence of poly (diallyldimethylammonium chloride) (PDDA) and poly(sodium 4-styrenesulfonate) (PSS), respectively. The multilayer films consisting of PDDA-GN and PSS-GN were fabricated on the substrate by layer-by-layer self-assembly technique and characterized by ultraviolet-visible spectroscopy (UV-vis). The multilayer films were used as a novel catalyst support for electrodeposition of Pt nanoparticle clusters in situ. X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscope (FE-SEM), and X-ray diffraction (XRD) analysis demonstrated that Pt particles had been immobilized on the surface of {PDDA-GN/PSS-GN}(n) multilayer films. Cyclic voltammetry and chronoamperometric curves were used to study electrocatalytic activity of Pt/{PDDA-GN/PSS-GN}(n) multilayer films regarding methanol oxidation. The results indicated good electrocatalytic activity of the titled multilayer composites toward methanol oxidation in the 0.5 M H(2)SO(4).

Visible light assisted electro–photo synergistic catalysis of heterostructured Pd–Ag NPs/graphene for methanol oxidation

In this work, a facile method was used to synthesize the heterostructured bimetallic catalyst Pd–Ag/graphene (simplified as Pd–Ag/GNs). In order to achieve the heterostructured Pd–Ag nanoparticles (NPs), Ag2O was firstly produced on GNs from AgOH under UV irradiation, then the heterogeneous phase between the precursor Pd2+ and Ag2O contributes to the formation of the highly dispersed heterostructured Pd–Ag NPs with the average diameter of 5 nm on GNs after a synchronous reduction process. Electro-catalytic performances of Pd–Ag/GNs were investigated by cyclic voltammetry (CV), chronoamperometry, COad stripping voltammetry, and electrochemical impedance spectroscopy (EIS). It is shown that Pd–Ag/GNs has a much higher catalytic activity (595 mA mg−1) and stability for methanol oxidation reaction (MOR) and improved tolerance of CO compared with the counterpart Pd/GNs and the commercial 20% Pd/C catalyst (Pd/C-SA). And under visible light irradiation, the catalytic activity and stability of Pd–Ag/GNs are remarkably enhanced. Especially, its mass activity is 1128 mA mg−1 which is 1.9 times higher than that without light irradiation. The significantly improved performance benefits from the efficient electro–photo synergistic catalysis for MOR under visible light irradiation, which is in favor of harvesting sunlight to produce clean energy.