Yunjie Huang

Development of electroless NiP–PTFE–SiC composite coating

Electroless nickel (EN) and EN composite coatings with polytetrafluoroethylene (PTFE) and/or SiC were deposited by chemical deposition. The microstructure analysis was conducted with scanning electron microscopy and X-ray diffraction. Differential scanning calorimetry was used to study the phase transition of the coating during the heat treatment. The mechanical and tribological properties were measured using hardness indentation, scratch test and pin-on-disc wear test. The surface energy was analysed using water droplet surface contact angle measurement. The synergistic effects of SiC and PTFE on the wear and anti-sticking properties of the coatings are discussed.

Available hydrogen from formic acid decomposed by rare earth elements promoted Pd‐Au/C catalysts at low temperature

The usage of hydrogen as a clean, efficient power carrier for stationary and mobile applications is attracting more and more attention. Much effort has been made towards hydrogen application technologies, especially in fuel cells. Nevertheless, the production and storage of hydrogen is the bottleneck of hydrogen economy. In transportable energy applications, hydrogen is generally produced from reforming organic molecules, such as gasoline, methanol, ethanol and so on. Hydrogen production suffers from various problems such as low efficiency, high operating temperature, huge volume, weight loading, and excessive formation of CO. On the other hand, hydrogen storage technologies are limited by low efficiency and possible danger. Notably, formic acid is a promising hydrogen carrier with advantages of considerable hydrogen content (4.4 wt %), and non-toxic and non-flammable properties. It has been reported that Au-based, Pd-based, 10] Pt-based, and metal (e.g. , Ru, Ir, Rh, Fe) complex catalysts can be used for the decomposition of formic acid (DCFA). The hydrogen from the DCFA also has been used in proton exchange membrane fuel cell (PEMFC). 21] In our previous study, the Au or Ag additive overcame the deactivation of Pd catalyst. Furthermore, the addition of Ce further improved the activity of the Pd–Au and Pd–Ag catalysts. Then, it is necessary to understand the promotion effect of other rare earth elements (REs) and design new and highly active catalysts. Here, we systematically studied the promotion effect of three REs (Dy, Eu, and Ho) on the Pd–Au/C catalysts in the DCFA reaction. In addition, the application of reforming gas in fuel cell is studied. Figure 1 a shows the output rates of reforming gas from DCFA catalyzed by Pd–Au/C, Pd–Au–Dy/C, Pd–Au–Eu/C, and Pd–Au–Ho/C. All the REs (Dy, Eu, Ho) could significantly promote the activity of Pd-Au/C catalyst. The activity order of the four catalysts was Pd–Au–Dy/C>Pd–Au–Eu/C>Pd–Au–Ho/C> Pd–Au/C. All activities increased with the temperature exponentially. In addition, these catalysts were even active at room temperature temporarily and above 325 K steadily. The activation energies for the DCFA reaction on the prepared catalysts were also calculated according to the Arrhenius equation. Figure 1 b and Table 1 show that all the REs-promoted Pd–Au/C catalysts have lower activation energies of DCFA than Pd–Au/C. Among the REs catalysts, Pd–Au–Eu/C had the lowest value of 84.2 7.4 kJ mol . However, the most active was Pd–Au–Dy/C, which had a decomposition rate of 1198 mL min 1 g 1 Pd and a turnover frequency (TOF) of 269 202 h 1 at 365 K. This catalytic performance of Pd–Au–Dy/C can provide output power of 106 W g 1 Pd theoretically, which is promising to be used in portable applications. Generally, promotion effect comes from three aspects, that is, distribution improvement of nanoparticles, electronic effect, and synergistic effect. The promotion effect of REs in these three aspects is stated as follows. Firstly, the particle size distributions of the prepared catalysts were measured by transmission electron microscopy (TEM), as shown in Figure 2 A and Figure 2 B. The relationships among the average particle size, activity, TOF, and activation energy are shown in Figure 3. The activity of REs promoted Pd–Au/C catalysts increased from 431 to 1198 mL min 1 g 1 Pd with the size decrease from 4.6 1.5 to 2.0 1.5 nm (Figure 3 a). The activity of REs-promoted catalysts can be improved by decreasing the particle size, likely due to the increasing surface-tovolume ratio. However, the TOF and activation energy Ea are not clearly dependent on the particle size as shown in Figure 3 b and Figure 3 c. Interestingly, Figure 3 d shows that TOF increased with decreasing activation energy, indicating that the activation energy determines the catalytic activity of the Figure 1. a) The activity of Pd–Au/C, Pd–Au–Dy/C, Pd–Au–Eu/C, and Pd–Au– Ho/C catalysts at different temperatures; the activity is expressed by the output gas per minute and per gram Pd. b) lnk vs T 1 plot for the DCFA reaction according to Arrhenius equation. The activation energies are shown in Table 1.

The size-controlled synthesis of Pd/C catalysts by different solvents for formic acid electrooxidation.

The size-controlled synthesis of Pd/C catalyst for formic acid electrooxidation is reported in this study. By using alcohol solvents with different chain length in the impregnation method, the sizes of Pd nanoparticles can be facilely tuned; this is attributed to the different viscosities of the solvents. The results show that a desired Pd/C catalyst with an average size of about 3 nm and a narrow size distribution is obtained when the solvent is n-butanol. The catalyst exhibits large electrochemically active surface area and high catalytic activity for formic acid electrooxidation.