Facile Synthesis of PtNi Intermetallic Nanoparticles: Influence of Reducing Agent and Precursors on Electrocatalytic Activity

In this paper, a nonaqueous synthesis of PtNi nanoparticles is presented using multiple reducing agents and metal precursors. Through this investigation, it was found that all the species present in solution have an impact on the resulting nanoparticles. Metal precursor choice has a major effect on the resulting nanoparticles and their behavior. When using acetylacetonate (acac) precursors, the acac ligands bind tightly with the resulting metal particles and cannot be easily removed through washing. After annealing to nucleate the intermetallic phase, these ligands decompose into a carbonaceous coating rendering the particles inactive toward formic acid oxidation. This led to the development of a chloride precursor Li2NiCl4, not previously used for synthesis of inorganic nanoparticles, which is soluble in ether solvents unlike NiCl2 and many other metal chlorides. Using the lithium metal chloride as a precursor, the organic content of the nanoparticle products is greatly reduced as seen by lower weight losses in TGA, TEM imaging, lower intermetallic formation temperatures, and greatly enhanced catalytic activity for formic acid oxidation. Additionally, by changing the alkali metal of an alkali metal alkylborohydride reducing agent and thus the resulting salt byproduct, the particle size of the resulting intermetallic nanoparticles can be controlled. These new LixMCly precursors and synthesis techniques have opened the door to the synthesis of a broad range of intermetallic Pt-M nanoparticles and will allow their study as electrocatalysts.