Platinum Systems Electrodeposited in the Presence of Iron or Palladium on a Gold Surface Effectively Catalyze Oxygen Reduction Reaction

Abstract

In this study, Pt and Pd catalysts (in the absence and presence of Fe) and a Pt−Pd alloy were generated on a polycrystalline Au surface by means of a direct electrodeposition approach. The electrochemical profile of these materials was investigated using cyclic voltammetry and microgravimetry (electrochemical quartz crystal microbalance). The electrocatalytic activity toward oxygen reduction reaction (ORR) was studied using hydrodynamic cyclic voltammetry. Physical characterization of samples was performed using scanning electron microscopy, energy dispersive X-ray microanalysis, and atomic force microscopy. Electrodeposited catalysts containing Pt exhibited high electrocatalytic activity toward ORR, stability in terms of specific activity, and repeatability of responses, even at low Pt concentrations in the electrodeposition solution, thus suggesting the possibility of applying these catalysts to acid fuel cells. The Au electrode modified with Pt(0.75)/Fe(0.25) exhibited a nanorounded, low-roughness structure, whereas the Au electrode modified with Pd(0.75)/Fe(0.25) showed poor electrocatalytic activity, a nanospaghetti-shaped structure, and enhanced roughness.

Catalysts for oxygen reduction reaction based on nanocrystals of a Pt or Pt–Pd alloy shell supported on a Au core

“…Nonetheless, large current densities related to oxygen productionc an be seen above 1.50 V( positive-direction scan), in competition with Pt-oxide or Pd-oxide production ( Figure 1B). [31] Most important was the absence of ap ronounced reduction peak at around 1.17 V( ap eak characteristico fA u oxide reduction-see black curve,F igure 1B)a nd the presence of aw ell-defined reductionp eak at around 0.64 V[ characteristic of Pt (and Pd oxide reduction)i nt he negative-direction scan]. [31] These responses demonstrate complete coverage of the Au-core surfaced uring PNSs ynthesis, in agreement with the EDX mapping images shown in Table 1a nd Ta ble S1.…”

“…[31] Most important was the absence of ap ronounced reduction peak at around 1.17 V( ap eak characteristico fA u oxide reduction-see black curve,F igure 1B)a nd the presence of aw ell-defined reductionp eak at around 0.64 V[ characteristic of Pt (and Pd oxide reduction)i nt he negative-direction scan]. [31] These responses demonstrate complete coverage of the Au-core surfaced uring PNSs ynthesis, in agreement with the EDX mapping images shown in Table 1a nd Ta ble S1. The sole exception was Pd@Au PNSs, for which ap ronounced reductionp eak can be observed around1 .…”

“…These differences in the E 1/2 values, of 70 mV on average,s upport the assumption that the absence or presence of PtO x or PdO x influences ORR catalysis at these modifiede lectrodes. [30,31] The modified GC electrodes shown in Figure 2B Figure 2A;s ee also Equations (S1) and (S2) in the Supporting Information, which were used to calculate the percentage of H 2 O 2 formation,X H 2 O 2 ]. [31,32] (Table S4).…”

“…[30,31] The modified GC electrodes shown in Figure 2B Figure 2A;s ee also Equations (S1) and (S2) in the Supporting Information, which were used to calculate the percentage of H 2 O 2 formation,X H 2 O 2 ]. [31,32] (Table S4). H 2 O 2 production was highest for Pd@Au PNSs (1.9 %) and lowest forP d black (0.5 %) and Pd PNSs (0.3 %) at 0.12 Vi nt he forward HV scans (inset of Figure S2 A).…”

“…Calculated ECSA values for modified GC electrodes are shown in Figure 2C (see also Ta ble S4), peaking at 9.3 cm 2 (48 times highert han the GC electrode geometric area) for Pt' PNSs. Figure 2D (see also Ta bleS4) shows calculated specific ECSA values, peakinga t4 2m 2 g À1 for Pt-Pd@Au and 37 m 2 g À1 for Pt-Pd@Au' PNSs;t he values were obtained with Pt-Pd alloy loadings of 94.5 and 88.4 mgcm À2 (Table S4), resulting in mass-specific activity (MSA)v alues of 0.48 and 0.46 mA mg À1 at 0.9 V, for Pt-Pd@Au and Pt-Pd@Au' PNSs, respectively (Figure 2E)[ see Equations (S3) and (S4) in the Supporting Information, which were used to calculate Pt-group metals (PGM)-specific ECSA [30,31,33,34] andP GM MSA values]. [30,31] The highest specific activity (SA)v alues calculated [see Equation (S5) in the Supporting Information, which was used to calculate the SA values] [30,31,33,35] at 0.9 V, 1.15 and 1.24 mA cm À2 , were obtainedf or Pt-Pd@Au andP t-Pd@Au' PNSs, respectively.T hese values were better,i ns omec ases, than those reported elsewhere( Ta ble S4), even if compared with commercial Pt and Pd blacks.…”