Fluorinated carbon encapsulated NiO cluster/TiO2 nanotubes as a robust photocatalyst for hydrogen evolution

Abstract

Synergies gained from different material engineering methods endow heterostructured catalysts with rapid interfacial charge transfer, high activity and excellent surface binding properties for efficient solar energy to fuel conversions, e.g., photocatalytic hydrogen evolution reaction (HER). Guided by density functional theory (DFT) predictions, the present work demonstrates rational material design of highly dispersed NiO clusters (<1.8 nm) decorated on TiO₂ nanotubes that are encapsulated with fluorinated amorphous carbon (FNT-x) as robust HER photocatalysts. Effective tuning of the work function alignment at the NiO/TiO₂ interface by controlling the NiO size, along with changes in the energy barriers of interfacial charge transfer and surface hydrogen adsorption free energy of the composite were predicted. The interfacial electron flow from TiO₂ to NiO, advanced kinetics of the electron injection and photocatalytic HER activity significantly improve the overall HER performance. Without using a precious metal cocatalyst (e.g., Pt), the FNT-x composites produced an optimal HER efficiency of 16.5 mmol g⁻¹ h⁻¹, showing steady reproducibility during the cyclic HER test. The HER efficiency is 41-fold and four-fold higher than that of the TiO₂ nanotubes (ca. 0.4 mmol g⁻¹ h⁻¹) and the NiO cluster/TiO₂ nanotubes (NT-1, 3.8 mmol g⁻¹ h⁻¹), respectively.