Manipulation of Pt^∧Ag Nanostructures for Advanced Electrocatalyst

Abstract

Attempts are made in this study to manipulate nanostructures of Pt-flecks on Ag nanoparticles (Ptm∧Ag) for advanced electrocatalysts by reflux citrate reduction of Pt from PtIICl42− or PtIVCl62− ions in solution containing Ag colloids at different atomic Pt/Ag ratio (m). Characterizations with UV−vis, SERS, XPS, and XRD showed a gradual Pt covering of the Ag colloids with increasing m when PtIICl42− was the precursor of Pt (Ptm∧Ag−A samples). However, due to an involvement of the galvanic replacement reaction between PtIVCl62− and the metallic Ag colloids during the citrate reduction of PtIVCl62− ions, a distinct alloying of Pt with the underlying Ag particles took place at the surface region of the colloidal Ag particles when PtIVCl62− was the precursor of Pt (Ptm∧Ag−B samples). Cyclic voltammetry (CV) measurement of the electrochemically active surface area (EAS) showed that the Pt utilization (UPt) in Ptm∧Ag−A increased with the decrease in m. The mass-specific activity (MSA) of Pt for the electrooxidation of either methanol or formic acid increased linearly with UPt in Ptm∧Ag−A, but was enhanced significantly with proper Pt−Ag alloying in Ptm∧Ag−B catalysts. Fine-tuning the extent of Pt−Ag alloying resulted in optimized Ptm∧Ag−B catalyst at 0.47 ≤ m ≤ 0.53, whose activity by MSA of Pt was 1 order of magnitude higher in methanol electrooxidation and six times higher in formic acid electrooxidation than its Ptm∧Ag−A counterpart of similar UPt.