Metal–Support Interaction between Titanium
Oxynitride and Pt Nanoparticles Enables Efficient Low-Pt-Loaded High-Performance
Electrodes at Relevant Oxygen Reduction Reaction Current Densities
posted on 2024-02-02, 09:03authored byArmin Hrnjić, Ana Rebeka Kamšek, Lazar Bijelić, Anja Logar, Nik Maselj, Milutin Smiljanić, Jan Trputec, Natan Vovk, Luka Pavko, Francisco Ruiz-Zepeda, Marjan Bele, Primož Jovanovič, Nejc Hodnik
In the present work,
we report on a synergistic relationship between
platinum nanoparticles and a titanium oxynitride support (TiOxNy/C) in the
context of oxygen reduction reaction (ORR) catalysis. As demonstrated
herein, this composite configuration results in significantly improved
electrocatalytic activity toward the ORR relative to platinum dispersed
on carbon support (Pt/C) at high overpotentials. Specifically, the
ORR performance was assessed under an elevated mass transport regime
using the modified floating electrode configuration, which enabled
us to pursue the reaction closer to PEMFC-relevant current densities.
A comprehensive investigation attributes the ORR performance increase
to a strong interaction between platinum and the TiOxNy/C support. In particular, according
to the generated strain maps obtained via scanning transmission electron
microscopy (STEM), the Pt-TiOxNy/C analogue exhibits a more localized strain in Pt
nanoparticles in comparison to that in the Pt/C sample. The altered
Pt structure could explain the measured ORR activity trend via the
d-band theory, which lowers the platinum surface coverage with ORR
intermediates. In terms of the Pt particle size effect, our observation
presents an anomaly as the Pt-TiOxNy/C analogue, despite having almost two times
smaller nanoparticles (2.9 nm) compared to the Pt/C benchmark (4.8
nm), manifests higher specific activity. This provides a promising
strategy to further lower the Pt loading and increase the ECSA without
sacrificing the catalytic activity under fuel cell-relevant potentials.
Apart from the ORR, the platinum-TiOxNy/C interaction is of a sufficient magnitude
not to follow the typical particle size effect also in the context
of other reactions such as CO stripping, hydrogen oxidation reaction,
and water discharge. The trend for the latter is ascribed to the lower
oxophilicity of Pt-based on electrochemical surface coverage analysis.
Namely, a lower surface coverage with oxygenated species is found
for the Pt-TiOxNy/C analogue. Further insights were provided by performing a
detailed STEM characterization via the identical location mode (IL-STEM)
in particular, via 4DSTEM acquisition. This disclosed that Pt particles
are partially encapsulated within a thin layer of TiOxNy origin.