Scaffold-Like Titanium Nitride Nanotubes with a Highly Conductive Porous Architecture as a Nanoparticle Catalyst Support for Oxygen Reduction

We designed a scaffold-like porous titanium nitride (TiN) nanotube (NT) as a catalyst support for Pt to facilitate the oxygen reduction reaction. Bulk titanium nitride, which is known as an electrically conductive material, is compatible with other metals. As the size of TiN particles decreases, however, they lose their intrinsic high electrical conductivity, due to a series of nanoparticle grain boundaries acting as electron reservoirs and traps. A designed grain-boundary-free scaffold-like porous TiN NT which is analogous to the shape of the one-dimensional porous human spine exhibits high electrical conductivity in spite of having a surface area similar to that of TiN nanoparticle (NPs). The electrical conductivity of TiN NTs is ca. 30-fold higher than that of spherical TiN NPs. The electrochemical oxygen reduction measurements between porous TiN NT and TiN NPs after Pt loading clearly exhibit the superiority of TiN NT as a catalyst support. The results from various electrochemical measurements suggest that the electrocatalytic activity per site did not change from a kinetic viewpoint, but the utilization (the amount of triggered catalytic active sites) in the catalyst layer on the electrode decreased. The Pt/TiN NT composite catalyst exhibited higher activity in comparison to TiN NPs as well as conventional Pt/C catalysts. The accelerated durability test (ADT) revealed that this nanotubular supporting material dramatically enhanced the durability of the catalyst and maintained the electrochemically active surface area (ECSA) of Pt nanoparticles, thus exhibiting performance higher than that of the commercial Pt/C catalyst. X-ray spectroscopy results verified the strong metal–support interaction between Pt nanoparticles and the TiN NT support. This approach opens a reliable path for designing innovative transition-metal oxides, nitrides, or carbides as catalyst supports for use in a wide range of energy conversion applications.