Ni/TiO 2 : A promising low-cost photocatalytic system for solar H 2 production from ethanol–water mixtures Wan-Ting Chen a , Andrew Chan a , Dongxiao Sun-Waterhouse a , Toshihiro Moriga b , Hicham Idriss c , Geoffrey I.N. Waterhouse a,d,⇑ a School of Chemical Sciences, The University of Auckland, Auckland, New Zealand b Graduate School of Advanced Technology and Science, The University of Tokushima, Tokushima, Japan c SABIC, Corporate Research Institute (CRI), KAUST, Saudi Arabia d The MacDiarmid Institute for Advanced Materials and Nanotechnology, New Zealand article info Article history: Received 16 December 2014 Revised 11 March 2015 Accepted 14 March 2015 Keywords: Hydrogen production Ethanol Photocatalysis Nickel TiO 2 abstract Low-cost semiconductor photocatalysts that can efficiently harvest solar energy and generate H 2 from water or biofuels will be critical to future hydrogen economies. Here, we evaluate the performance of low-cost Ni/TiO 2 photocatalysts (Ni loadings 0–4 wt.%) for H 2 production from ethanol–water mixtures (0–100 vol.% EtOH) under UV excitation. Ni(II) was deposited on P25 TiO 2 by the complex precipitation method, followed by H 2 reduction at 500 °C for 2 h to obtain Ni/TiO 2 photocatalysts. TGA, TEM, XRD, Ni 2p XPS, Ni L-edge NEXAFS, Ni K-edge EXAFS, UV–Vis and photoluminescence measurements confirmed that Ni 0 was the dominant nickel species on the surface of the Ni/TiO 2 photocatalysts, with the Ni particle size 1–2 nm. The photocatalytic activity of Ni/TiO 2 photocatalysts was highly dependent on the Ni loading, with the optimal Ni loading being 0.5 wt.%, which afforded a H 2 production rate of 11.6 mmol g 1 h 1 (or 0.258 mmol m 2 h 1 ) at an EtOH:H 2 O volume ratio of 10:90 and a UV flux comparable to that in sunlight. High H 2 production rates were achieved over a wide range of EtOH:H 2 O concentrations, with a 95:5 volume ratio affording the highest rate (24.3 mmol g 1 h 1 ). The 0.5 wt.% Ni/TiO 2 photocatalyst displayed superior photocatalytic activity to a 2 wt.% Au/TiO 2 reference photocatalyst at low ethanol concentrations (1–15 vol.%), which is attributed to the high co-catalyst dispersion achieved in the Ni/TiO 2 system. Results suggest that Ni/TiO 2 photocatalysts are promising alternatives to M/TiO 2 (M = Pd, Pt or Au) photocatalysts for solar H 2 production from biofuels. Ó 2015 Elsevier Inc. All rights reserved. 1. Introduction The discovery of efficient, low-cost and environmentally friendly technologies for H 2 production is a key step towards the widespread development of a sustainable hydrogen economy. Currently, almost all of the world’s H 2 production is based on steam methane reforming (SMR) and the water–gas shift reaction; energy intensive processes with a significant carbon footprint [1–3]. Various alternative H 2 production technologies are now being aggressively pursued [4–7], of which photocatalytic H 2 pro- duction from water or biofuels using sunlight is amongst the most promising [7–10]. Presently, there is a strong research emphasis on the development of stable and efficient semiconductor photocata- lysts for H 2 generation, with M/TiO 2 photocatalysts (M = Pd, Pt or Au) dominating this research space due to their high activity and resistance to photo-corrosion. However, the high cost and low natural abundance of the Pd, Pt and Au co-catalysts represent a sig- nificant obstacle to the future application of M/TiO 2 photocatalysts (M = Pd, Pt or Au) for large-scale H 2 production, motivating the search for alternative, low-cost transition metal or metal oxide co-catalysts. Titania (TiO 2 ) is an archetypal semiconductor photocatalyst and has been widely studied in relation to H 2 production from water or biofuels under UV irradiation. TiO 2 exists in three different poly- morphic forms, which all have electronic band gaps in the UV region (anatase TiO 2 , E g = 3.2 eV; brookite TiO 2 , E g = 3.15–3.3 eV; rutile TiO 2 , E g = 3.0 eV) [11]. Bulk absorption of electromagnetic radiation with E > E g generates electron–hole pairs (e  –h + ), with the holes and electrons either migrating to the surface of TiO 2 par- ticles and participating in oxidation and reducing reactions, respectively, or simply recombining. TiO 2 satisfies the three basic criteria for a H 2 production photocatalyst, since: (1) the valence http://dx.doi.org/10.1016/j.jcat.2015.03.008 0021-9517/Ó 2015 Elsevier Inc. All rights reserved. ⇑ Corresponding author at: School of Chemical Sciences, The University of Auckland, Auckland, New Zealand. Fax: +64 9 373 7422. E-mail address: g.waterhouse@auckland.ac.nz (G.I.N. Waterhouse). Journal of Catalysis 326 (2015) 43–53 Contents lists available at ScienceDirect Journal of Catalysis journal homepage: www.elsevier.com/locate/jcat