Manipulation of PtΛAg Nanostructures for Advanced Electrocatalyst

Attempts are made in this study to manipulate nanostructures of Pt-flecks on Ag nanoparticles ((PtmAg)-Ag-Lambda) for advanced electrocatalysts by reflux citrate reduction of Pt from (PtCl42-)-Cl-II or (PtCl62-)-Cl-II 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 (PtCl42-)-Cl-II was the precursor of Pt ((PtmAg)-Ag-Lambda-A samples). However, due to an involvement of the galvanic replacement reaction between (PtVCl62-)-V-II and the metallic Ag colloids during the citrate reduction of (PtCl62-)-Cl-II ions, a distinct alloying of Pt with the underlying Ag particles took place at the surface region of the colloidal Ag particles when Pe(IV)Cl(6)(2-) was the precursor of Pt ((PtmAg)-Ag-Lambda-B samples). Cyclic voltammetry (CV) measurement of the electrochemically active surface area (EAS) showed that the Pt utilization (U-Pt) in (PtmAg)-Ag-Lambda-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 U-Pt in (PtmAg)-Ag-Lambda-A, but was enhanced significantly with proper Pt-Ag alloying in (PtmAg)-Ag-Lambda-B catalysts. Fine-tuning the extent of Pt-Ag alloying resulted in optimized (PtmAg)-Ag-Lambda-B catalyst at 0.47 <= m <= 0.53, whose activity by MSA of Pt was I order of magnitude higher in methanol electrooxidation and six times higher in formic acid electrooxidation than its (PtmAg)-Ag-Lambda-A counterpart of similar U-Pt.