•Compared with Pd-on-Au catalyst, Pt-on-Au catalyst exhibits higher activity for methanol oxidation in alkaline media but lower stability.•After modifying Pd surface with low amount of Pt, the activity for methanol oxidation get improved greatly.•The Pt deposited on Pd shows improved stability in comparison with the Pt deposited on Au substrate.•The total mass activity of Pt-on-Pd/CNTs for methanol oxidation is on a similar level to that of Pt/CNTs.For optimizing both the activity and stability of Pt-based catalysts for methanol oxidation reaction (MOR), several carbon nanotubes(CNTs)-supported catalysts such as Pt-on-Au/CNTs, Pd-on-Au/CNTs, Pt-on-Pd-on-Au/CNTs, Pt-on-Pd/CNTs, and Pd-on-Pt/CNTs catalysts are synthesized mainly through electrodeposition method. The activity and stability comparisons show that Pt-on-Au/CNTs has a higher MOR activity but a lower stability than Pd-on-Au/CNTs. To utilize the merits of the Pt and Pd components, Pt-on-Pd-on-Au/CNTs and Pt-on-Pd/CNTs catalysts are synthesized. The Pt-on-Pd-on-Au/CNTs and Pt-on-Pd/CNTs catalysts shows higher MOR activity than Pd-on-Au/CNTs and Pd/CNTs catalysts and higher stability than Pt-on-Au/CNTs, suggesting a synergistic interaction between Pt and Pd in catalyzing methanol oxidation reaction. Calculation shows that the total mass activity of Pt-on-Pd/CNTs with quite low Pt amount is on a similar level as that of Pt/CNTs for MOR oxidation, indicating the Pt-on-Pd catalyst could have promising potential as a low-Pt catalyst for MOR in alkaline media.By modifying Pd surface with Pt moieties, both the methanol oxidation activity and cycling stability get evidently improved.

Carbon-supported non-noble metal catalysts with Fe as the metal and tripyridyl triazine (TPTZ) as the ligand (Fe–TPTZ/C), synthesized through a heat treatment process at 900 °C, were employed to coat an electrode surface and form catalyst layers in order to optimize their catalyzed ORR activity. The formed catalyst layers containing different catalyst loads of 100, 200, 300, 400, 500, and 600 μg·cm−2 were tested using both rotating disk electrode and rotating ring disk electrode techniques. It was found that as the electrode catalyst loading increased, the ORR activity rose monotonically in the loading range of 100 to 500 μg·cm−2, then reached a saturation point with higher catalyst loading, indicating that raising the electrode catalyst loading could effectively improve the catalyst's ORR activity. In addition, the overall ORR electron transfer numbers for Fe–Nx/C catalysts were found to be in the range of 3.7–3.9 at different loadings, suggesting that the ORR process was mainly dominated by a four-electron transfer pathway to produce water.Research highlights► The effect of catalyst loading on ORR activity has been studied on glassy carbon electrode coated Fe–TPTZ/C catalyst (TPTZ: tripyridyl triazine) by both rotating disk electrode and rotating ring disk electrode techniques. ► It was found that as the electrode catalyst loading is increased, the ORR activity rose monotonically in the loading range of 100 to 500 μg·cm−2. ► The overall ORR electron transfer numbers catalyzed by Fe–Nx/C were found to be in the range of 3.7–3.9 at different loadings, suggesting that the ORR process was mainly dominated by a four-electron transfer pathway to produce water.

2,3,5,6-Tetra(2-pyridyl)pyrazine (TPPZ) was employed as a ligand to prepare an iron(II) complex (Fe–TPPZ) that served as a precursor to synthesize carbon-supported catalysts (Fe–Nx/C) through heat-treatment at 600, 700, 800 and 900 °C under N2 atmosphere. Both the structure and composition of the synthesized Fe–Nx/C were analyzed by X-ray diffraction and energy-dispersive X-ray microanalysis, respectively. The rotating disk and ring-disk electrode measurements showed that these catalysts have strong ORR activity with an overall 4-electron transfer process through a (2 + 2)-electron transfer mechanism, which was assigned to the catalytic function of the Fe–Nx center. A study on the heat-treatment temperature on the ORR activity showed that 800 °C is the optimal temperature for the synthesized catalysts. Furthermore, the effect of both catalyst and Nafion® ionomer loadings in the catalyst layer on the corresponding ORR activity was also investigated. The kinetic parameters such as the chemical reaction rate between O2 and Fe–Nx/C (adduct formation reaction), the rate constant for the rate-determining step (RDS), and the electron numbers in the ORR, were obtained. The methanol tolerance of the catalyst was also tested. To validate the ORR activity, a membrane electrode assembly in which the cathode catalyst layer contained Fe–Nx/C was constructed and tested in a real fuel cell. The results obtained are encouraging when compared with similar non-noble catalysts.Highlights► 2,3,5,6-Tetra(2-pyridyl)pyrazine (TPPZ) was employed as a ligand to prepare an iron(II) complex (Fe–TPPZ) at the first time. ► The effect of both catalyst and Nafion® ionomer loadings in the catalyst layer on the corresponding ORR activity was investigated by both rotating disk electrode and rotating ring disk electrode techniques. ► It was found that this catalyst has strong ORR activity with an overall 4-electron transfer process through a (2 + 2)-electron transfer mechanism, which was assigned to the catalytic function of the Fe–Nx center. ► The results obtained in a real fuel cell environment assembled with such a catalyst as the cathode are encouraging when compared with similar non-noble catalysts.

Using the laser monitoring observation technique, the solubilities of dimethyl fumarate in methanol, ethanol, 1-propanol, 2-propanol, 1,2-propanediol, and water have been determined experimentally from (289.95 to 347.15) K. The experimental data were correlated with the modified Apelblat equation. The calculated results showed good agreement with the experimental data.

The densities and viscosities of the (4-picoline + water) binary mixture have been experimentally determined at temperatures from T = (298.15 to 338.15) K and the mole fraction of mixture range from 0.00 to 1.00. The excess molar volume and the apparent molar volume were calculated from experimental measurements. The results were fitted to obtain the adjustable parameters and standard deviations between the measured and fitted values, respectively. The results were also briefly discussed.

To provide thermodynamic data for isonicotinic acid production, the solubilities of isonicotinic acid in water and 4-methylpyridine binary solvent mixture were determined from (287.65 to 361.15) K with the solvent mole fraction composition ranging from 0.00 to 1.00. The experimental data were correlated with the modified Apelblat equation. The calculated results show good agreement with the experimental data.