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Photoreforming biomass-derived waste such as glycerol into hydrogen fuel is a renewable hydrogen generation technology that has the potential to become important due to unavoidable CO2 production during methane steam reforming. Despite tremendous efforts, the challenge of developing highly active photocatalysts at a low cost still remains elusive. Here, we developed a novel photocatalyst with a hybrid support comprising reduced graphene oxide (rGO) and TiO2 nanorods (TNR). rGO in the hybrid support not only performed as an excellent scavenger of electrons from the semiconductor conduction band due to its suitable electrochemical potential, but also acted as an electron transport highway to the metal co-catalyst, which otherwise is not possible by simply increasing metal loading due to the shadowing effect. A series of hybrid supports with different TNR and rGO ratios were prepared by the deposition method. Pd nanoparticles were deposited over hybrid support through the chemical reduction method. Pd/rGO-TNRs photocatalyst containing 4 wt.% rGO contents in the support and 1 wt.% nominal Pd loading demonstrated hydrogen production activity ~41 mmols h−1g−1, which is 4 and 40 times greater than benchmark Au/TiO2 and pristine P25. The findings of this works provide a new strategy in optimizing charge extraction from TiO2, which otherwise has remained impossible due to a fixed tradeoff between metal loading and the detrimental shadowing effect. [ABSTRACT FROM AUTHOR]

A series of Cu(OH)2-Ni(OH)2/P25 photocatalysts was prepared by co-deposition-precipitation (total metal loading ≈1 wt %) and their performance was evaluated for H2 production. Among this series, the 0.8 Cu(OH)2-0.2 Ni(OH)2/P25 photocatalyst demonstrated very high H2 production rates in 20 vol % ethanol/water and 5 vol % glycerol/water mixtures (10 and 22 mmol h−1 g−1, respectively). Detailed analyses based on reaction kinetics, photoluminescence, X-ray photoelectron spectroscopy (XPS), and charge carrier scavenging suggest that both working catalysts are composed of Cu and Ni metals in their active phases. Cu0 is produced directly by the transfer of electrons from the conduction band of TiO2 to surface Cu(OH)2 nanoclusters, whereas Ni0 is formed indirectly through a process of gradual dissolution of Ni(OH)2 to yield aqueous Ni2+ owing to the acidic environment of the medium, followed by Ni2+ reduction by electrons from the TiO2 conduction band. The high rates of H2 production that match those obtained with noble metals can be explained owing to a considerably less negative Δ Go of Cu oxide formation when compared with that of Ni oxide formation and higher work function of Ni than that of Cu. [ABSTRACT FROM AUTHOR]

A series of composite photocatalysts based on CdS nanorods decorated with Cu/Ni hydroxides were prepared via deposition precipitation method at room temperature (total metal loading ≈ 3 wt%). The performance of these photocatalysts was evaluated for H 2 production through water dissociation reaction under direct sunlight. The 2.4Cu(OH) 2 0.6Ni(OH) 2 /CdS photocatalyst with a total 3 wt% nominal metal cocatalyst loading demonstrated an excellent hydrogen production activity of ~20 mmol h−1 g−1, that is 2 and 20 times greater than the benchmark Au/CdS and pristine CdS photocatalysts, respectively. Detailed analyses based on UV–Visible diffuse reflectance spectroscopy (DRS), X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), steady state photoluminescence (PL) and energy dispersive spectroscopy (EDS) suggested cocatalysts Cu/Ni hydroxides were transformed into their metallic states during photoreaction. Cu° was produced by the transfer of electrons due to the as available position of CdS conduction band (E° = 0.61 V) to surface Cu(OH) 2 nanoclusters (Cu(OH) 2 /Cu°, E° = 0.224 V) whereas Ni° was produced by the shift in conduction band level of CdS under continuous sunlight illumination (Ni(OH) 2 /Ni°, E° = 0.72 V). Based on these observations, the mechanism of hydrogen production from water splitting over Cu/Ni(hydroxides)-CdS was described. [Display omitted] • CdS nanorods decorated with Cu/Ni hydroxides are prepared. • The performance of these photocatalysts was evaluated for H 2 production. • The 2.4Cu(OH) 2 0.6Ni(OH) 2 /CdS photocatalyst shows hydrogen production of ~20 mmol h−1 g−1. • Cocatalysts Cu/Ni hydroxides are transformed into their metallic states during photoreaction. • The mechanism of hydrogen production from water splitting over Cu/Ni(hydroxides)-CdS is proposed. [ABSTRACT FROM AUTHOR]

Abstract A two dimensional Cu/Ni based coordination polymer [{CuII(4,4ʹ-dipy) 2 }{Ni(CN) 4 }] n ·0.7(C 2 H 6 O 2)·1.6(H 2 O) (CP-1) (4,4ʹ-dipy = 1,3-di (4-pyridyl)propane) has been demonstrated as a potential co-catalyst on TiO 2 support for hydrogen evolution under UV light. CP-1 /TiO 2 composite exhibits considerable hydrogen production in comparison with the pristine CP-1 and TiO 2 (P25), highlighting that the photocatalytic performance is significantly related with the good separation of photo generated e−/h+ pairs. Different wt. % (2.5, 5 and 7.5%) of CP-1 in CP-1 /TiO 2 composites were tested for photocatalytic hydrogen production in 5 vol % glycerol/water mixture. The 5 wt % CP-1 /TiO 2 composite displayed the greatest hydrogen production of 9.2 mmolh−1g−1. The concealed mechanism is divulged on the behalf of results obtained by cyclic voltammetry, photoluminescence and diffused reflectance/UV-visible studies which demonstrate that upon irradiation of UV light, electrons transfer from TiO 2 conduction band to CP-1. CP-1 not only grabs the conduction band electrons of titania but also performes as a co-catalyst to reduce the protons into hydrogen. These results are anticipated to direct the forthcoming advancement in creating proficient, cheap semiconductor photocatalysts for solar hydrogen production. Graphical abstract Image 1 Highlights • A composite of bimetal (Cu/Ni) coordination polymer (CP-1) and TiO 2 is synthesized. • CP-1/TiO 2 composite is utilized as photocatalyst for H 2 generation from water. • The 5 wt % CP-1/TiO 2 composite displayed H 2 production of 9.2 mmolh−1g−1. [ABSTRACT FROM AUTHOR]