Activity enhancement of platinum oxygen-reduction electrocatalysts using ion-beam induced defects

High activity is one of the primary requirements for the catalysts in proton exchange membrane fuel cell applications. Platinum (Pt) is the best known catalyst, especially for oxygen reduction at the cathode; however, further activity improvements are still required. Previous computational studies suggested that the catalytic activity of Pt nanoparticles could be enhanced by a $\mathrm{Pt}\text{−}\mathrm{carbon}$ (C) support interaction. We have recently found that an enhanced electronic interaction occurs at the interface between an argon-ion (${\mathrm{Ar}}^{+}$)-irradiated glassy carbon (GC) surface and Pt nanoparticles. Here, we report a more than twofold increase in specific activity for the Pt nanoparticles on the ${\mathrm{Ar}}^{+}$-irradiated GC substrate compared to that on the nonirradiated GC substrate. The mechanism of this activity enhancement was investigated by local structure analysis of the interface. ${\mathrm{Ar}}^{+}$ irradiation of the carbon support led to the formation of $\mathrm{Pt}\text{−}\mathrm{C}$ bonding, thus protecting the deposited Pt nanoparticles from oxidation.

Figure 1

Pt nanoparticles on the GC substrates irradiated with Ar ions as oxygen reduction catalysts. (a) CV curves for Pt nanoparticles on the ${\mathrm{Ar}}^{+}$-irradiated GC substrates in an ${\mathrm{N}}_2$-saturated 0.1 M ${\mathrm{HClO}}_4$ solution at a scan rate of 50 mV/s. (b) ORR polarization curves for Pt nanoparticles on the ${\mathrm{Ar}}^{+}$-irradiated GC substrates in an ${\mathrm{O}}_2$-saturated 0.1 M ${\mathrm{HClO}}_4$ solution at a sweep rate of 20 mV/s and a rotation rate of 1600 rpm.

Figure 2

ORR performance of all the samples. (a) Enlarged view of the ORR polarization curves for all the samples. (b) Tafel slopes derived from the mass-transport correction of the corresponding RDE data. Current densities are normalized to the ECSA of platinum within the samples. Inset: Current densities of all the samples at 0.85 V.

Figure 3

XAFS spectra of Pt nanoparticles on the ${\mathrm{Ar}}^{+}$-irradiated GC substrates. (a) The normalized XAFS spectra of the Pt $M_3$-edge measured in the TEY mode using the BL-27A of the KEK-PF. The inset shows an enlarged view of the white-line peaks. (b) The normalized XAFS spectra of the Pt $L_3$-edge measured in the transmission mode at the BL14B1 of SPring-8.

Figure 4

Sample preparation schematic for the Pt $L_3$-edge XAFS measurements at SPring-8.

Figure 5

(a) $k^2$-weighted EXAFS spectra, and (b)–(d) Fourier transform of the EXAFS spectra.

Figure 6

(a) Calculation models of the irradiated GC and Pt nanoparticles. The interface was modeled as an icosahedral ${\mathrm{Pt}}_{13}$ cluster and three layers of graphene with (b) SV, (c) DV, (d) 2SV, and (e) 2DV.