Effect of pH Value of Reaction System on Dispersibility of Pt Powder by Chemical Liquid Phase Reduction

Na₂PtCl₆ solution with platinum mass concentration of 10 g·L⁻¹ was dropped into N₂H₄·H₂O solution with 1% mass fraction with an equal volume. The pH value of the reaction system （2.5–10） was controlled by NaOH solution and HCl solution. Pt powder was prepared by the chemical liquid phase reduction method. The variation laws of the micromorphology, particle size distribution and dispersibility of Pt powder with pH value were studied. The results show that when the pH value of the reaction system was controlled at 10, the Pt powder particles were small and aggregated in a flocculent form, and had wide particle size distribution; the difference between the particle size with a cumulative distribution ratio of 90% （D₉₀） and that with a cumulative distribution ratio of 10% （D₁₀） was 4.48 μm. With increasing pH value, the particle size of Pt powder increased, the dispersibility of the particles was improved, and the particle size distribution was narrated. When the pH value was 6 to 7, the particle size of Pt powder remained basically unchanged, the particle dispersibility was good, and the particle size distribution became wider. As the pH value continued to decrease, the particle size and the dispersibility of the particles decreased, the degree of agglomeration of small particles was intensified, and the particle size distribution was broadened. When the pH value of the reaction system was 8, the dispersibility of Pt particles was the best, with D₉₀−D₁₀ being only 2.29 μm. With decreasing pH value, the diffraction peak intensity of the prepared Pt powder was significantly weakened, and the half-peak width increased. The grain size of the Pt powder prepared in the alkaline system was relatively large, while that prepared in the acidic system was relatively small.