Electrochemical oxidation behavior of titanium nitride based electrocatalysts under PEM fuel cell conditions

Abstract

Titanium nitride (TiN) is attracting attention as a promising material for low temperature proton exchange membrane fuel cells. With its high electrical conductivity and resistance to oxidation, TiN has a potential to act as a durable electrocatalyst material. Using electrochemical and spectroscopic techniques, the electrochemical oxidation properties of TiN nanoparticles (NP) are studied under PEM fuel cell conditions and compared with conventional carbon black supports. It is observed that TiN NP has a significantly lower rate of electrochemical oxidation than carbon black due to its inert nature and the presence of a native oxide/oxynitride layer on its surface. Depending on the temperature and the acidic media used in the electrochemical conditions, the open circuit potential (OCP) curves shows the overlayer dissolved in the acidic solution leading to the passivation of the exposed nitride surface. It is shown that TiN NP displays passive behavior under the tested conditions. The XPS characterization further supports the dissolution argument and shows that the surface becomes passivated with the O–H groups reducing the electrical conductivity of TiN NP. The long-term stability of the Pt/TiN electrocatalysts is tested under PEM fuel cell conditions and the trends of the measured electrochemical surface area at different temperatures is shown to agree with the proposed passivation model.