Oxygen Reduction Reaction Electrocatalytic Activity of Glancing Angle Deposited Platinum Nanorod Arrays

Abstract

The electrocatalytic oxygen reduction reaction (ORR) activity of vertically-aligned Pt nanorods has been evaluated utilizing cyclic voltammetry (CV) and rotating-disk electrode (RDE) techniques in a 0.1 M HClO 4 solution at temperatures ranging from 20 to 60 C. A glancing angle deposition (GLAD) technique was used to fabricate Pt nanorod arrays on glassy carbon (GC) electrodes. GLAD catalyst nanorods, without any carbon support, have been produced at different lengths varying between 50 and 400 nm, corresponding to 0.04-0.32 mg/cm 2 Pt loadings, with diameter and spacing values ranging from about 5 up to 100 nm. The scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD) results reveal that Pt nanorods are well-isolated, vertically aligned, and single-crystal. Crystal orientation analysis demonstrates that large surface area Pt nanorod sidewalls are mainly dominated by Pt(110) planes, which is known to be the most active crystal plane of Pt for the ORR. Compared to a commercial high-surface-area-supported Pt (Pt/C) catalyst, the CV results show that the Pt-nanorod electrocatalyst exhibits a more positive oxide reduction peak potential, indicating that GLAD Pt nanorods are less oxophilic. Moreover, the nanorods exhibit enhanced stability against loss of electrochemically-active surface area as a result of potential cycling in acidic electrolyte as compared to the Pt/C catalyst. Specific ORR activities determined by the RDE technique for GLAD Pt nanorods of different lengths are analyzed and compared to literature values for polycrystalline Pt, nano-structured thin film Pt (3M NSTF Pt), and to those measured for Pt/C. RDE results reveal that Pt-nanorod electrocatalysts exhibit higher area-specific activity, higher electron-transfer rate constant, and comparable activation energy for ORR than those of Pt/C due to their larger crystallite size, single-crystal property, and dominance of the preferred crystal orientations for ORR. However, Pt nanorods show lower mass specific activity than that of Pt/C electrocatalyst due to the large diameter of nanorods.

Perspectives on oblique angle deposition of thin films: From fundamentals to devices

“…Gall et al [425][426][427][428] and Karabacak et al [127,[429][430][431] have extensively applied OAD methodology to the fabrication of Pt-based cathodes for PEMFCs and develop Pt/C cathodes through the dynamic MS-OAD of carbon nanorods (a $ 85 ) onto flat, pre-patterned substrates, followed by posterior decoration of their tips with Pt deposited by MS in the classic (non-oblique) configuration [426]. The use of these pre-patterned surfaces yielded C layers that were highly porous in the vicinity of the substrate, but became rather compact and similar to thin films obtained by conventional MS at their ends.…”

“…Karabacak et al [429][430][431] focused their investigations on the MS deposition of well-crystallized Pt nanorods to improve their efficiency in oxygen reduction reactions without carbon support. To achieve this, they studied the formation of well-isolated, single-crystalline and vertically aligned Pt nanorods formed by dynamic OAD at an oblique angle of 85°, finding that the Pt OAD films exhibit a higher specific activity, higher electron-transfer rate and comparable activation energy when compared to conventional Pt/C electrodes.…”

Pt3M (M: Co, Ni and Fe) Bimetallic Alloy Nanoclusters as Support-Free Electrocatalysts with Improved Activity and Durability for Dioxygen Reduction in PEM Fuel Cells

“…9d. Hence, the MA of Pt-Co decreased nearly 47 % and comparatively higher than Pt-Ni (55 %) and Pt-Fe (44 %) and which led by the negative shift of half-wave potential, and details were given in Table 3, also compared with other Pt-based catalysts from recent literatures [25,27,47,48,50,[58][59][60][61][62][63][64][65]. From the ADT studies, all the three Pt-M bimetallic alloy nanoclusters are competing with the standard bench mark catalysts in terms of both activity and durability and Pt-Co was notified to have great potential compared with other combinations for cathode oxygen reduction for low temperature fuel cells.…”

Nb-doped TiO2/carbon composite supports synthesized by ultrasonic spray pyrolysis for proton exchange membrane (PEM) fuel cell catalysts

“…6(a), oxide reduction potential of 20wt% Pt 0.62 Pd 0.38 /25 wt% (Nb 0.07 Ti 0.93 O 2 )-75 wt% C synthesized at 600 C is 0.784 V and 40 mV more positive than the oxide reduction potential of commercial Pt/C. This may be indicative that the 20wt%Pt 0.62 Pd 0.38 / 25 wt% (Nb 0.07 Ti 0.93 O 2 )-75 wt% C is less oxophillic than Pt/C [18]. Although the experimental data supports complete alloying between Pt and Pd, the effect of Pd on hydrogen adsorption and desorption onto PtPd alloy catalyst sites could introduce significant unknowns into ESA calculations.…”