Preparation and Application of Platinum Group Metals and Alloy Nanomaterials

Abstract:

Pd, Pt, Ir and Ru powders and IrRu, PtNi and PtNiCo alloy powders with 3D-nano-framework structure were successfully prepared by spray drying method combined with calcination and reduction using noble metal salt as raw material and ammonium chloride (NH₄Cl) as pore making agent. The effect of NH₄Cl concentration on the morphology of atomized powder was studied. It is found that with the increase in NH₄Cl concentration, the average particle size of atomized (NH₄)₂PdCl₄ powder shows an increasing trend, the sphericity gradually decreases, and the dispersion becomes worse. The effects of calcination temperatures on the morphology of palladium powder were studied. It is found that palladium powder reduced by calcination at 300 ℃ has an inherited effect on the precursor shape. Due to the nano-pores left by the gas spilling during calcination, palladium powder has a spheroidal 3D-nano-framework structure and a large specific surface area (28–40 m²/g). When the calcination temperature rises to 400 ℃, the 3D-nano-framework is gradually broken to form dense Pd powders. Therefore, when the concentration of NH₄Cl is 5–10 g/L and the calcination temperature is controlled at 300 ℃, it is conducive to the preparation of spherical 3D-nano-framework platinum group metal powders with high specific surface area. In addition, Pt, Ir, Ru, IrRu, PtNi and PtNiCo platinum group metals and alloy powders with 3D-nano-framework have been successfully prepared using the optimal preparation parameters, which proves that the method is universal in the preparation of other platinum group metals and alloys. Finally, in order to prove the feasibility of the synthetic materials, the catalytic methanol oxidation reaction of the PtNiCo 3D-nano-framework materials prepared in this study was tested in fuel cell anode. The results show that the catalytic methanol oxidation performance of PtNiCo nanomaterials (1117 mA/mg(Pt)) is 6.5 times higher than that of commercial Pt black (170 mA/mg(Pt)), and it also has excellent anti-toxicity and stability. It is proved that excellent performance of platinum group metal alloy nano-catalyst could be achieved by the preparation method in this study.