Pt@Pd_<i>x</i>Cu_<i>y</i>/C Core–Shell Electrocatalysts for Oxygen Reduction Reaction in Fuel Cells

A series of carbon-supported core–shell nanoparticles with Pd_<i>x</i>Cu_<i>y</i>-rich cores and Pt-rich shells (Pt@Pd_<i>x</i>Cu_<i>y</i>/C) has been synthesized by a polyol reduction of the precursors followed by heat treatment to obtain the Pd_<i>x</i>Cu_<i>y</i>/C (1 ≤ <i>x</i> ≤ 3 and 0 ≤ <i>y</i> ≤ 5) cores and the galvanic displacement of Pd_<i>x</i>Cu_<i>y</i> with [PtCl₄]^2– to form the Pt shell. The nanoparticles have also been investigated with respect to the oxygen reduction reaction (ORR) in proton-exchange-membrane fuel cells (PEMFCs). X-ray diffraction (XRD) analysis suggests that the cores are highly alloyed and that the galvanic displacement results in a certain amount of alloying between Pt and the underlying Pd_<i>x</i>Cu_<i>y</i> alloy core. Transmission electron microscopy (TEM) images show that the Pt@Pd_<i>x</i>Cu_<i>y</i>/C catalysts (where <i>y</i> > 0) have mean particle sizes of <8 nm. Compositional analysis by energy-dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) clearly shows Pt enrichment in the near-surface region of the nanoparticles. Cyclic voltammograms show a positive shift of as much as 40 mV for the onset of Pt–OH formation in the Pt@Pd_<i>x</i>Cu_<i>y</i>/C electrocatalysts compared to that in Pt/C. Rotating disk electrode (RDE) measurements of Pt@PdCu₅/C show an increase in the Pt mass activity by 3.5-fold and noble metal activity by 2.5-fold compared to that of Pt/C. The activity enhancements in RDE and PEMFC measurements are believed to be a result of the delay in the onset of Pt–OH formation

Thermal decomposition synthesis of functionalized PdPt alloy nanodendrites with high selectivity for oxygen reduction reaction

Pt-based bimetallic nanostructures have found intriguing applications in electrocatalysis. However, the pristine Pt-based nanostructures generally lack the selectivity for the target reaction because of their high activity for both oxygen reduction reactions (ORRs) and fuel molecule oxidation reactions. By employing a recently developed chemical functionalization strategy, the functionalized Pt-based nanostructures have achieved their selectivity for the target reaction in fuel cells. In this work, we report a facile thermal decomposition route to synthesize the polyallylamine (PAH)-functionalized Pd–Pt bimetallic core–shell nanodendrites with a Pd-rich PdPt alloy core and a Pt-rich PtPd alloy shell (PdPt@PtPd CSNDs) by using PAH that serves as a complexant, reductant and chemical functionalization molecule. The composition, morphology and structure of PdPt@PtPd CSNDs are characterized in detail. Compared with commercial Pt black electrocatalyst, the PAH-functionalized PdPt@PtPd CSNDs show improved electrocatalytic activity and durability for the ORR, and achieve good selectivity for the ORR in the presence of ethanol molecules. The study shows a promising cathode electrocatalyst for direct alcohol fuel cells (DAFCs).MOE (Min. of Education, S’pore)Published versio