Oxygen Reduction Kinetics on Electrodeposited Pt, Pt[sub 100−x]Ni[sub x], and Pt[sub 100−x]Co[sub x]

Abstract

The kinetics of the oxygen reduction reaction (ORR) on a series of electrodeposited normalPt100−xnormalNix and normalPt100−xnormalCox alloy films were examined in comparison to electrodeposited Pt and mechanically polished polycrystalline Pt. The alloys were electrodeposited at potentials positive of that required to grow the pure iron group metal. The growth process is ascribed to strong bonding enthalpy between Pt and the iron group metals that can be envisioned as iron-group underpotential deposition (upd) on Pt surface sites coupled with ongoing Pt overpotential electrodeposition. Rotating disk electrode measurements of the ORR kinetics, normalized for the H upd electroactive area, indicate a ∼1.9 to 2.7-fold catalytic enhancement on normalPt100−xnormalCox and normalPt100−xnormalNix, when x is in the range of 25–35, as compared to electrodeposited Pt films grown under similar conditions. An even greater ORR enhancement factor, between 3 and 4.8, was noted for dealloyed transition metal-rich (x75) films. Different schemes for integrating the electrodeposition (and dealloying) process into the fabrication of fuel cell membrane electrode array are also briefly discussed.

Preparation of low-platinum-content platinum–nickel, platinum–cobalt binary alloy and platinum–nickel–cobalt ternary alloy catalysts for oxygen reduction reaction in polymer electrolyte fuel cells

“…Each alloy group shows a remarkably increase in ORR activity and exhibits an optimal deposition charge, that is the dependence of i k on the electrode surface compositions before the dealloying procedure. The surface composition of the optimal electrode PtNi203 and PtCo205 is Pt 73 Ni 27 and Pt 63 Co 37 as shown in Table S1, respectively, coinciding with the reported results in some literature [18,25,26]. However, when the deposition charge density obtained 210 mC cm À2 as well as larger values, the surface compositions did not show an obviously change as shown in Table S1, whereas the ORR activity exhibited a remarkably decline.…”

Electrochemical Surface Processes and Opportunities for Material Synthesis

“…UPCD of a series of binary and ternary Pt-based alloys has been used by Moffat in combination with dealloying to prepare nanostructured electrocatalysts [128][129][130]. Pt-Ni, Pt-Ni-Pd, and Pt-Co were tested for their catalytic activity toward the oxygen reduction reaction; in comparison to Pt, these films exhibit up to 10-fold improvement in activity per unit mass of Pt.…”

Xylella fastidiosa Esterase Rather than Hydroxynitrile Lyase

“…According to the investigators, Pt‐rich iron‐group alloys were electrodeposited at more‐positive potentials than those that were required to grow the pure iron‐group metal, given the strong bonding enthalpy between Pt and the iron‐group metals, which, in a first approximation, could be envisioned as iron‐group underpotential deposition (UPD) on Pt, coupled with ongoing Pt deposition. They found that alloying Pt with Ni and Co led to increased ORR kinetics relative to Pt and observed even‐better ORR enhancement for dealloyed transition‐metal‐rich Pt 100− x Ni x and Pt 100‐ x Co x films 24. Moreover, the thicknesses of the Pt 100− x Ni x films that were electrodeposited onto Au surfaces ranged from 13–85 nm and the observed increasing activity for the ORR with increasing Ni content was attributed to a Pt skin that formed on top of the dealloyed substrate 25.…”

“…Moffat and co‐workers24–26 studied thin alloy films that were produced by electrodeposition under potentiostatic conditions for the ORR. Thin Pt, Pt 100− x Ni x , and Pt 100− x Co x films were deposited from 0.5 M NaCl electrolyte that contained 3 m M H 2 PtCl 6 , either alone (in the case of Pt deposition) or with either 0.1 M NiCl 2 or CoCl 2 (in the case of deposited Pt alloys); for example, Pt that was deposited onto a Pt rotating disk electrode (RDE) by using short deposition times (typically 2 min at −0.35 V) yielded film thicknesses on the order of 5.3 nm.…”