Nanorod PEM Fuel Cell Cathodes with Controlled Porosity

Abstract

Arrays of 1 m long C nanorods were grown by glancing angle deposition on flat and patterned Si wafers, coated with 0.1 mg/cm 2 Pt catalyst by magnetron sputtering, removed from the substrates, and tested as cathode electrodes in proton exchange membrane ͑PEM͒ fuel cells. Deposition on flat substrates yields a nearly fully dense nucleation layer with Ͻ5 nm wide pores, followed by the formation of separated rods with an average width that strongly increases with rod height, from Ͻ30 to 190 nm. In contrast, deposition on a patterned surface results in regularly spaced 50 nm wide pores and a rod width that only moderately increases with height, from 95 to 155 nm. Polarization curves on pure H 2 and O 2 for the two sample types are identical at high potential E Ͼ 0.55 V. However, the cathodes deposited on the patterned substrates yield considerably higher currents at low potential, with a 2 times higher limiting current density i L = 0.73 A/cm 2 than those grown on flat substrates. The higher current in the mass-transport-limited regime is attributed to the 10 times wider engineered pores that facilitate O 2 transport to the active catalyst sites, resulting in a 5 times lower mass transport resistance R MT = 1.5 ⍀ cm 2 at E = 0.50 V, as quantified by electrochemical impedance spectroscopy.

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.…”

“…One possibility in this regard that has been widely explored in the case of OAD films is the search for chemically stable substrates other than carbon where substrate oxidation and the resulting loss of Pt nanoparticles can be avoided or minimized. With this in mind, the use of Pt/Ti-OAD nanocolumnar systems [432], Pt/CrN cathodes [426] or Pt decorated Cr nanorods [431] have all been proposed. In the case of the latter two examples, nanostructured CrN and Cr layers prepared by MS-OAD act as supporting layers.…”

GLAD Pt–Ni Alloy Nanorods for Oxygen Reduction Reaction

“…Gasda et al deposited platinum catalyst layers onto gas diffusion layer (GDL) substrates by GLAD and tested them as cathodes in PEFCs. They have extended this approach to normal-incidence-angle-deposited Pt on chromium nitride (CrN) nanoparticles, patterned carbon nanorods, and electrochemically etched carbon nanorod array supports . The design and fabrication of multicomponent nanostructures with different morphologies by GLAD have been reviewed by He and Zhao .…”

GLAD Cr Nanorods Coated with SAD Pt Thin Film for Oxygen Reduction Reaction

“…5 Due to these limitations, extensive efforts are underway to develop high-performance, durable, carbon-free, and low cost (low Pt loading) catalysts with alternative support materials. [6][7][8][9][10][11][12][13] The 3M company has demonstrated the improved durability and area-specific activity of nano-structured thin film Pt (3M NSTF Pt) electrocatalyst layers consisting of a large-grained polycrystalline Pt thin film deposited on and encapsulating oriented crystalline whiskers of an organic pigment material. 6 A potential disadvantage of their support material, however, is the decomposition of the organic whiskers at elevated temperature (≥350 • C), which limits thermal treatment, such as catalyst annealing, to temperatures lower than 350 • C. 7 Low-cost and abundant base metals with established catalytic activity enhancement for ORR can be used as a support for deposition of Pt.…”