Elucidating the Effect of Nitrogen Occupancy on the Hydrogen Evolution Reaction for a Series of Titanium Oxynitride Electrocatalysts

Titanium nitride (TiN) shows desirable properties for use as an electrocatalyst and catalyst support, as it possesses high electrical conductivity and excellent corrosion resistance. However, the effect of oxygen content in the nitride lattice on its ability to drive the hydrogen evolution reaction (HER) is not well understood. Here, a series of titanium oxynitrides (TiN_xO_1-x) with varied nitrogen occupancy (0.53≤x≤1.0) in the bulk have been fabricated by ammonolysis. Their specific activities towards the HER were normalised by the surface areas determined by BET and electrochemical methods. We show that the specific activities of these oxynitrides are strongly correlated with the bulk nitrogen occupancy, despite the similar surface composition derived from XPS analysis. Furthermore, a removal of the oxygen content in the bulk or at the surface was attributed to the upgraded performance (up to 25 % increase) seen during extended chronoamperometry (CA) tests. Our results show that minimising bulk oxygen content in this class of material is critical to achieve a more conductive and active material for the HER.