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 (TiNxO1-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. Titanium nitride (TiN) shows desirable properties for use as an electrocatalyst and catalyst support, as it possesses high electrical conductivity and excellent corrosion resistance. Any oxygen and humidity present or incomplete nitridation during the synthesis process of nitrides can lead to an increasing oxygen content. However, the role of oxygen contents or nitrogen occupancies in the bulk of the nitrides during the electrocatalytic reactions is not well understood. In this work, we have synthesised a series of titanium oxynitrides with varied bulk nitrogen occupancies by ammonolysis at different temperatures. Higher ammonolysis temperatures will give a higher nitrogen occupancy but result in a lower surface area. The geometric activities towards the hydrogen evolution reaction (HER) have been normalised by the electrochemically active surface areas (ECSA) and the BET surface areas to get the specific activities. Their specific activity towards the HER is found to be strongly correlated with the bulk nitrogen occupancy and a higher bulk nitrogen occupancy is beneficial to the specific HER activities.image

Automated summary

Titanium nitride has desirable properties for electrocatalysis and catalyst support. The oxygen content in the material plays a critical role in its ability to drive the hydrogen evolution reaction. Minimizing bulk oxygen content is important for achieving a more conductive and active material.