Synthesis of Ni/Au/Co trimetallic nanoparticles and their catalytic activity for hydrogen generation from alkaline sodium borohydride aqueous solution

Abstract

A series of poly (N-vinyl-2-pyrrolidone) stabilized colloidal Ni/Au/Co trimetallic nanoparticles (TNPs) were synthesized by co-reduction of their corresponding metal precursors via dropwise addition of NaBH₄. Ultraviolet-visible spectrophotometry (UV-Vis), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), powder X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HR-TEM) combined with energy dispersive spectrometry (EDS) were used to characterize the morphology, crystalline structure and electron distribution of the as-prepared TNPs. The effects of metal composition on the size distribution and hydrogen generation from catalytic hydrolysis of alkaline NaBH₄ aqueous solutions were also investigated. The results indicated that the as-prepared alloy-structured Ni₄₅Au₄₅Co₁₀ TNPs showed a maximum catalytic activity of 1170 mol-H₂ per h per mol-M, which is several times higher than that of the as-prepared Au, Ni or Co monometallic nanoparticles (MNPs), or Au₅₀Ni₅₀, Au₅₀Co₅₀ or Ni₅₀Co₅₀ bimetallic nanoparticles (BNPs). The enhanced catalytic activity of the TNPs compared with the MNPs and BNPs could be attributed to the presence of electron charge transfer effects among Au, Ni and Co atoms, which is supported by the results of X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT) calculation. The apparent activation energy of the as-prepared Au₄₅Ni₄₅Co₁₀ TNPs in hydrolysis of NaBH₄ aqueous solution was determined as 18.8 kJ mol⁻¹.