A Study Of Magnetron-sputtering Alloy Electrodes And Their Electrocatalysis

Nowadays, the world is facing the energy crisis. Fuel cell is a renewable energy power system, if combined with the solar energy conversion technology; it would realize the effective utilization of solar energy and solve energy and environmental problems. In recent years, both fuel cell and water electrolysis research are focused on the study of alloy catalysts, whose preparations usually require high annealing temperature and thus are very time-consuming. Furthermore, since the alloy’s morphology and composition are largely affected by the preparation method, it is difficult to make alloys with uniform morphology and composition. It would be more difficult to make alloys between metals and non-metals, such as metal silicide, whose traditional preparation need annealing temperature over800℃. In the present work, we study the preparation of two-component alloy electrodes through magnetron sputtering, and their applications to typical electrochemical reactions. The main results are summarized as follows.1. The Au-Cu alloys with different compositions were prepared through a series of magnetron sputtering experiments, including optimizing sputtering pressure, sputtering time, sputtering power and sputtering mode, etc. The composition, crystal orientation, surface electronic structure and surface morphology of the alloys were characterized by various methods. Upon alloying with Cu, the catalytic activity of Au toward the oxygen reduction reaction(ORR) was enhanced significantly, which could be originated from the ligand effect between Au and Cu. Pt/Au, Pt/AU3CU and Pt/AuCu were prepared by the method of CO controlling electrodeposition, the lattice size of the surface Pt layer was thus modulated. The lattice expansion of Pt was found to benefit the catalytic activity toward the formic acid oxidation reaction(FAOR). H underpotential deposition(H-upd) controlling electrodeposition was also applied to control the thickness of the deposited Pt layer. It was found that, upon increasing the thickness of Pt surface layer, the catalytic activity decreased toward the FAOR but increased toward the ORR.2. Intermetallic Pt2Si and Pt3Si electrodes were prepared using magnetron sputtering. Systematic characterizations have proven the intermetallic structure of Pt2Si and Pt3Si. By incorporating Si, the affinity of Pt to surface oxygenated species enhanced, and the catalytic activity toward the ethanol oxidation reaction(EOR) increased. It seemed that the higher EOR activity of Pt2Si and Pt3Si were attributed to the enhanced efficiency of C-C bond cleavage and of surface poison removal. As for ORR catalysis, the as-prepared Pt2Si and Pt3Si were not better than Pt. But after electrocchemical CO annealing, the catalytic activity of Pt2Si and Pt3Si was markedly increased due to the surface segregation of Pt. The kinetic current density of Pt2Si and Pt3Si at0.9V were2.5times and3.2times of that of Pt(magnetron sputtering),6.3times and8.2times of that of Pt/C(JM), respectively.3. Amorphous Pd-Si alloys were prepared by magnetron sputtering, and the amorphous structures were proved by several physical characterizations, such as XRD, HRTEM, and DSC. The cyclic voltammetrys of Pd2Si and Pd3Si indicated the enhancement of adsorption energy of surface oxygenated species. The CO stripping experiment indicated that the Pd2Si and Pd3Si amorphous alloys were favourable to the CO oxidative stripping on the surface. The catalytic activity of Pd2Si and Pd3Si toward the formic acid oxidation reaction(FAOR)were also increase in comparison to pure Pd, which may be due to the advantage of oxidative stripping of surface poisoning species, as well as more defect sites exposed at amorphous alloy surface.4. Au-Si alloys were prepared by magnetron sputtering. These alloys were characterized to be amixture of amorphous structures and nanocrystals. Upon increasing the Si component, the Au-Si alloy electrodes took on an interesting feature: H underpotential deposition appeared in CVs, which is an indication for catalytic activity toward the hydrogen evolution reaction(HER). It turned out that the apparent activity of these alloys was closed to pure Pt and superior to those reported non-Pt catalysts. The HER currents normalized by the electrochemical areas were found to be independent to the Si content, indicating that the active sites on Au-Si alloy surfaces were the Au component, rather than the Si component.