Enhanced Photocatalytic Hydrogen Evolution with TiO₂–TiN\nNanoparticle Composites

Abstract

Metal\nnitrides have potential in energy applications because of\ntheir physical and optical properties. Nanoparticle composites of\ntitanium nitride (TiN) and titanium dioxide (TiO₂) were\ninvestigated for their photocatalytic hydrogen (H₂) evolution\nactivity via methanol reformation. Physical mixing of the nanoparticulate\nTiO₂ and TiN was employed to prevent the oxy-nitride formation\nand particle aggregation observed in thermal preparations. This convenient\ncombination of TiO₂ and TiN demonstrated a substantial\nsynergistic effect with enhanced activity (9.4 μmol/h TiO₂–TiN vs 1.8 μmol/h TiO₂) under combined\nUV/vis light. Irradiation under only UV light resulted in a similar\nenhancement factor compared to using combined UV/vis light, demonstrating\nthat the enhanced activity of the composites occurs essentially for\nUV-driven photocatalysis. No activity/enhancement was observed with\nonly visible light irradiation; however, minor enhancement was observed\nwhen switching between UV and UV/vis irradiation, suggesting a contribution\nfrom the TiN plasmon. We propose that the plasmonic contribution is\ndependent on the band gap excitation of TiO₂, which reduces\nthe degree of band bending at the TiO₂/TiN interface. This\npromotes the migration of hot electrons from TiN away from the TiO₂/TiN interface to be used for H₂ evolution.