Ni/TiO2: A promising low-cost photocatalytic system for solar H2 production from ethanol-water mixtures

Abstract

Low-cost semiconductor photocatalysts that can efficiently harvest solar energy and generate H2 from water or biofuels will be critical to future hydrogen economies. Here, we evaluate the performance of low-cost Ni/TiO2 photocatalysts (Ni loadings 0-4 wt.%) for H2 production from ethanol-water mixtures (0-100 vol.% EtOH) under UV excitation. Ni(II) was deposited on P25 TiO2 by the complex precipitation method, followed by H2 reduction at 500 °C for 2 h to obtain Ni/TiO2 photocatalysts. TGA, TEM, XRD, Ni 2p XPS, Ni L-edge NEXAFS, Ni K-edge EXAFS, UV-Vis and photoluminescence measurements confirmed that Ni0 was the dominant nickel species on the surface of the Ni/TiO2 photocatalysts, with the Ni particle size ∼1-2 nm. The photocatalytic activity of Ni/TiO2 photocatalysts was highly dependent on the Ni loading, with the optimal Ni loading being 0.5 wt.%, which afforded a H2 production rate of 11.6 mmol g-1 h-1 (or 0.258 mmol m-2 h-1) at an EtOH:H2O volume ratio of 10:90 and a UV flux comparable to that in sunlight. High H2 production rates were achieved over a wide range of EtOH:H2O concentrations, with a 95:5 volume ratio affording the highest rate (24.3 mmol g-1 h-1). The 0.5 wt.% Ni/TiO2 photocatalyst displayed superior photocatalytic activity to a 2 wt.% Au/TiO2 reference photocatalyst at low ethanol concentrations (1-15 vol.%), which is attributed to the high co-catalyst dispersion achieved in the Ni/TiO2 system. Results suggest that Ni/TiO2 photocatalysts are promising alternatives to M/TiO2 (M = Pd, Pt or Au) photocatalysts for solar H2 production from biofuels.