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Free keywords:
electrocatalysis; nitrogen-doped carbon; platinum nanoparticles; stability; fuel cells
Abstract:
Platinum and platinum alloys supported on carbon materials are the state
of the art electrocatalysts for the essential oxygen reduction reaction
(ORR) in low-temperature fuel cells. The limited stability of such
materials under the often detrimental operation conditions of fuel cells
still remains a critical issue to improve. In this work, we explore the
impact of nitrogen-doped carbon supports on the activity and stability
of platinum-based fuel cell catalysts. We present a nitrogen-doped
mesostructured carbon material, nitrogen-doped hollow carbon spheres
(NHCS), as a support for platinum-based electrocatalysts. A detailed
study of the electrochemical activity and stability was carried out for
two Pt@NHCS materials i.e., as-made material (Pt@NHCS) with a Pt
particle size smaller than 2 nm and the corresponding material after
thermal treatment at 850 degrees C (Pt@NHCSΔT) with a Pt
particle size of ca. 23 nm. Activity in the ORR was studied by rotating
disc electrode (RDE) thin-film measurements, and electrocatalyst
stability was evaluated by accelerated aging tests under simulated
startstop conditions. The performance of the NHCS-based materials was
compared to the two corresponding nitrogen-free materials as well as to
a standard Pt/Vulcan catalyst. The underlying degradation mechanisms of
Pt@NHCS materials were investigated via identical location electron
microscopy. Our results conclusively show that nitrogen doping of the
carbon supports can offer benefits for achieving high initial mass
activities due to improved high platinum dispersion; however, it was not
found to necessarily lead to an improvement of the catalyst stability.
