Cun-Zhi Li

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.

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.

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.

The electrochemical sensor based on electrochemical oxidation of nitrite on metalloporphyrin–graphene modified glassy carbon electrode

In this study, 5-(4-aminophenyl)-10,15,20-triphenylporphyrin]Mn(III) (MnNH2TPP) and graphene oxide (GO) composite materials (GO–MnNH2TPP) were successfully used to modify a glassy carbon electrode (GC) by the drop casting method. The GO–MnNH2TPP/GC composite electrode was used to investigate the electrocatalytic oxidation features of nitrite ion by cyclic voltammetry (CV) and amperometric I–T curve techniques. These experimental results show the GO–MnNH2TPP/GC composite electrode has excellent electrocatalytic performance for the detection of nitrite. The oxidation peak current of nitrite ion at the GO–MnNH2TPP/GC composite electrode has shifted negatively and the intensity of the oxidation peak current increased greatly compared with that at the GC, GO/GC and MnNH2TPP/GC electrodes. A linear relationship has been established between the oxidation current and the nitrite ion concentration. The detection limit of the GO–MnNH2TPP/GC composite electrode for the detection of nitrite ion was found to be 1.1 μM and 2.5 μM (S/N = 3) using CV and amperometric I–T curve techniques, respectively. The GO–MnNH2TPP/GC electrode possesses excellent electrocatalytic activity, rapid response time, low detection limit, high selectivity for nitrite and was applied to the detection of nitrite in real water samples.

The effect of hydrothermal treatment time and level of carbon coating on the performance of PtRu/C catalysts in a direct methanol fuel cell

A carbon-riveted PtRu/C catalyst of high stability has been prepared by in situ glucose carbonization using a hydrothermal method (GICH). Its mode of action and its practical application have been investigated by X-ray diffraction, high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, a single-fuel cell test, and by conventional electrochemical measurements. The single-fuel cell test has demonstrated that the GICH hydrothermal method has high applicational usefulness. After 100 h the maximum power density of a single cell using carbon-riveted PtRu/C as anode catalyst fell by only 12.0%, from 76.6 to 67.4 mW cm−2, compared with 28.4%, from 73.2 to 52.4 mW cm−2, for traditionally prepared PtRu/C. In addition, when the optimal hydrothermal treatment time was 4 h and the level of carbon coating was 9%, a carbon-riveted PtRu/C catalyst with a 3.5 nm carbon coating gave the best stability, with similar initial activity to traditionally prepared PtRu/C. The significantly increased stability of carbon-riveted PtRu/C may be attributed to two factors: (1) the anchoring effect of the carbon nanolayer formed during in situ glucose carbonization by the hydrothermal method; and (2) the increased content of Pt(0), Ru(0), sp3-hybridized carbon and the C–OR group composition, and the clear decrease in PtO2 and RuOxHy following the carbon-riveting procedure.

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.

Nitrogen-doped carbon with mesoporous structure as high surface area catalyst support for methanol oxidation reaction

Mesoporous nitrogen-doped carbon (MNC) with a high surface area has been synthesized via carbonizing polyaniline using silica nanoparticles as template. The more silica nanoparticles, the smaller the micropore surface area is and the larger the mesoporous surface area is. Moreover, with an increase in the amount of silica nanoparticles, the electrocatalytic activity of Pt/MNC catalysts shows a downward trend after an intimal increase, and the Pt/MNC-1/6 (with the weight ratio of aniline monomer to silica nanoparticles of 1/6) catalyst has the highest activity, ascribed to the optimal Pt nanoparticles size, which is closely related to the pore structure of the support. In addition, the electrocatalytic activity and stability of Pt/MNC-1/6 catalyst are significantly superior to that of Pt/nitrogen-doped carbon (Pt/CNx) catalyst. For the same electrocatalytic activity, the Pt loading of Pt/MNC-1/6 catalyst is reduced by 33.3% compared to the Pt/CNx catalyst. The high electrocatalytic activity originates from the introduction of mesoporous structures that can facilitate mass transfer and improve the dispersion of Pt nanoparticles. Furthermore, the Ostwald ripening behavior of Pt nanoparticles is limited in the mesoporous structure of MNC-1/6, which weakens the aggregation effect of Pt nanoparticles during the electrocatalytic processes, thus enhancing the electrocatalytic stability of the catalyst.