Study Of Plasma Reduction On Carbon-based Materials

The use of fossil fuel brings about tremendous problems of resource and environment, which hydrogen energy has become the favorite of the energy scientific community. There are three key technologies in the use of hydrogen energy, namely, hydrogen production, hydrogen storage and fuel cells. Hydrogen is the carrier of hydrogen energy. If hydrogen energy takes place petroleum products as fuel of transport, it is necessary to solve the problem of the high density hydrogen storage. However, catalyst performance issues result in the fuel cell is far away from the commercial applications. Therefore, this thesis puts forward how to improve their performance by glow discharge plasma preparing high-load and high-dispersed carbon-based methanol fuel cell catalysts and hydrogen storage materials. Moreover, this paper discussed the characteristics of the preparation of nanoparticles in the way of plasma reduction.We have presented a glow discharge plasma reduction method for noble metal ions on wafers. HAuCl₄,PdCl₂,H₂PtCl₆ and AgNO₃ can be reduced to nanoparticles using an Ar-plasma without the addition of any reducing agents. The mechanism of plasma reduction may be related to two processes. One is the high-energy electrons generated by plasma reduction reduced the metal ions through a recombination route. Another is the solvated electrons eaq^- and H^·atoms are indeed the strongest reducing agents that are responsible for reduction of the metal ions to the metallic state. The plasma reduction shows a modification of particle shape, producing more flattened nanoparticles. So it is easier to form metal films on substrate. Pd membranes were prepared on substrate by this mechanism.In this thesis, in order to reducing the high loaded Pt catalyst and improving the electricatalytic activity of the Pt catalysts, the plasma reduction were used to prepare the Pt/Vulcan XC-72 catalysts with high dispersibility and utramicro particles. The size of Pt particles on 20 wt% and 40 wt% Pt/C by plasma is 1.43 nm and 1.5 nm, respectively. In the cyclic voltammogram obtained in the 0.5 mol/L H₂SO₄+1 mol/L CH₃OH solution, the magnitude of the peak at 0.73 V is directly proportional to the amount of methanol oxidized at the Pt/C electrode. The peak current for methanol oxidation of 20 wt%Pt/C-plasma is about 35.2 mA/cm²,40 wt%Pt/C-plasma is about 68.9 mA/cm². The electrocatalytic activities for the methanol oxidation for the Pt/C catalyst prepared with plasma method are much better than that of the Johnson Mattey commercial Pt/C catalyst.Hydrogen adsorption properties of a superactived carbon (AX-21) doped with Pt nanoparticles by using plasma reduction were studied, and were compared with that by using traditional H2 reduction. The hydrogen storage capacity was significantly increased by plasma reduction. The H2 storage capacity on Pt-doped AX-21 at 298K and 10 MPa was increased from 1.19 wt % (by H2 reduction) to 1.46 wt % on the sample obtained by plasma reduction. The plasma reduced sample produced 1.5-3 nm Pt particles that were highly dispersed on carbon and most interestingly, the metal particles were recessed into the carbon substrate. Both isosteric heats of adsorption and the activation energies for spillover were decreased by plasma reduction, which was evidence that the energy barrier for H spillover was lowered by plasma treatment, resulting in faster rates as well as higher spillover capacities.Hydrogen storage capacity by hydrogen spillover on metal-doped carbons were significantly enhanced by introducing surface oxygen functional groups to the carbon. On the Pt-doped on O2-plasma treated carbons, Pt/TC-O and Pt/AX-21-O, the hydrogen uptakes at 10 MPa were enhanced to 1.74 and 1.48 wt %, respectively. For comparison, Pt/TC and Pt/AX-21 had a hydrogen storage capacity of 1.17 wt % and 0.98 wt%. Oxygen plasma treatment generated mainly semiquinone groups. Ab initio molecular orbital calculations showed that the binding energies between the spiltover hydrogen and different groups followed the order: Lactone > Semiquinone > Carboxyl > Basal Plane. XPS results showed the very strong (and irreversible) binding of the spiltover hydrogen with the lactone groups. The main groups of semiquinone remain functional as receptor sites upon cycling.