HER Response of Titanium Oxynitride/Mesoporous Carbon Composites in Sulfuric Acid: Implications for TiON-Based...

Titanium oxynitride (TiN_1-x O _x , hereafter denoted as TiON) has attracted attention as a support material in electrocatalytic systems, including those for the hydrogen evolution reaction (HER). Understanding the baseline cathodic response of TiON under acidic HER conditions is important for interpreting and developing TiON-containing composite electrodes. Here, the HER response of titanium oxynitride/mesoporous carbon composites (TiON/MPC) in sulfuric acid was examined as a model system relevant to TiON-based supports. TiON/MPC was prepared by ammonia nitridation of TiO₂/MPC precursors at 750, 800, and 850 °C, and hydrogen evolution was evaluated by chronoamperometry coupled with gas chromatographic quantification. Measurable H₂ evolution was confirmed for the TiON/MPC samples nitrided at 750 and 800 °C, with the highest rate observed for the 800 °C sample, whereas the response of the 850 °C sample was strongly suppressed and the mesoporous carbon control showed negligible activity under the same conditions. X-ray diffraction and X-ray photoelectron spectroscopy showed that increasing the nitridation temperature increased the bulk TiN fraction and modified the surface oxygen/nitrogen composition. The sample nitrided at 800 °C exhibited the highest hydrogen evolution response, indicating a nonmonotonic dependence of the HER response on nitridation temperature. These findings provide fundamental information for interpreting TiON-containing composite electrodes and TiON-based support materials in HER-related catalyst systems.