Spongelike Nanoporous Pd and Pd/Au Structures: Facile Synthesis and Enhanced Electrocatalytic Activity

This paper reports the facile synthesis and characterization of spongelike nanoporous Pd (snPd) and Pd/Au (snPd/Au) prepared by a tailored galvanic replacement reaction (GRR). Initially, a large amount of Co particles as sacrificial templates was electrodeposited onto the glassy carbon surface using a cyclic voltammetric method. This is the key step to the subsequent fabrication of the snPd/Au (or snPd) architectures by a surface replacement reaction. Using Co films as sacrificial templates, snPd/Au catalysts were prepared through a two-step GRR technique. In the first step, the Pd metal precursor (at different concentrations), K₂PdCl₄, reacted spontaneously to the formed Co frames through the GRR, resulting in a snPd series. snPd/Au was then prepared via the second GRR between snPd (prepared with 27.5 mM Pd precursor) and Au precursor (10 mM HAuCl₄). The morphology and surface area of the prepared snPd series and snPd/Au were characterized using spectroscopic and electrochemical methods. Rotating disk electrode (RDE) experiments for oxygen reduction in 0.1 M NaOH showed that the snPd/Au has higher catalytic activity than snPd and the commercial Pd-20/C and Pt-20/C catalysts. Rotating ring-disk electrode (RRDE) experiments reconfirmed that four electrons were involved in the electrocatalytic reduction of oxygen at the snPd/Au. Furthermore, RDE voltammetry for the H₂O₂ oxidation/reduction was used to monitor the catalytic activity of snPd/Au. The amperometric <i>i</i>–<i>t</i> curves of the snPd/Au catalyst for a H₂O₂ electrochemical reaction revealed the possibility of applications as a H₂O₂ oxidation/reduction sensor with high sensitivity (0.98 mA mM^–1 cm^–2 (<i>r</i> = 0.9997) for H₂O₂ oxidation and −0.95 mA mM^–1 cm^–2 (<i>r</i> = 0.9997) for H₂O₂ reduction), low detection limit (1.0 μM), and a rapid response (<∼1.5 s)