On the stability of TiN-based electrocatalysts for fuel cell applications

摘要

The transition metal compound - titanium nitride (TiN), with its high electrical conductivity and corrosion resistance, can be a potential fuel cell material, particularly in the development of durable electrocatalysts replacing the state-of-the-art Pt/C. Compared to conventional carbon black, TiN nanoparticle (TiN NP) catalyst supports have a lower rate of corrosion under fuel cell conditions. The current research is a follow up study on the stability of TiN based fuel cell electrodes and its impact on the electrochemical activity of the Pt based electrocatalysts when used as an alternative to the state-of-the-art carbon black support in commercial fuel cell catalyst systems under fuel cell operating conditions. Through this paper, we report that an active behavior of TiN NP can be observed at the optimal conditions of 0.5 M H_2SO_4 and 60 ℃. But under increased temperature or acidic conditions, the native layer on TiN tends to dissolve in the electrolyte exposing the underlying nitride surface which then gets passivated with hydroxide groups. Electrochemical and XPS characterization is used to validate our hypothesis of active or passive nature of TiN NP due to presence or absence of surface passivating -OH groups, respectively. The synthesized Pt/TiN electrocatalyst, upon subjecting to accelerated durability test, showed the performance trends which agree well with the active and passive nature of the TiN NP supports.