Electronic structure modification of platinum on titanium nitride resulting in enhanced catalytic activity and durability for oxygen reduction and formic acid oxidation

Abstract

It is very important to improve the mass activity and durability of platinum (Pt) catalysts for oxygen reduction and the oxidation of small organic molecules for fuel cell applications. A strong interaction between Pt and the support materials can change the electronic structures of platinum, enhancing catalytic activity and durability. Here, we deposited various amounts of Pt on TIN supports and characterized these catalysts using electron microscopy, H-2 uptake, XANES, XPS, and valence-band XPS. The Pt nanoparticles had very small sizes (<2 nm) with a narrow size distribution. Compared to a commercial Pt/C catalyst, the Pt surface in Pt/TiN catalysts was in a higher reduction state, and the Pt d-band center was downshifted. The results of OFT calculations confirmed that Pt could be stabilized on the TiN surface and that the Pt d-band center is downshifted relative to bulk Pt. The activity and durability of the Pt/TiN catalysts was enhanced for the oxygen reduction reaction and formic acid oxidation over that of the Pt/C catalyst. For the oxygen reduction reaction at 0.9 V (vs. RHE), the mass activity was 0.29 A/mg(Pt) for the 10 wt% Pt/TiN catalyst and 0.17 A/mg(Pt) for the Pt/C catalyst. After 5000 cycles of an accelerated durability test, the Pt/TiN exhibited a mass activity of 0.24A/mg(Pt), whereas the Pt/C catalyst exhibited a mass activity of 0.12 A/mg(Pt). The Pt/TiN catalyst followed a direct pathway with fewer surface-poisoning intermediates for formic acid oxidation, which enhanced the activity of the Pt/TiN catalyst over that of the Pt/C catalyst. The modification of the electronic structure of Pt catalysts by interaction with TiN supports can significantly enhance the activity and durability of the catalyst.