Electrodeposition of Composite Ni-TiO 2 Coatings from Aqueous Acetate Baths
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RESEARCH on the development of new, efficient, and environmentally friendly solar energy conversion systems has been conducted for many years. The main limitations of such systems are related to the catalytic properties of the applied materials.[1] One of the most interesting and widely studied processes is the conversion of solar energy and its storage based on photochemical hydrogen generation.[2] Hydrogen possesses a low molecular weight and high value of combustion energy. In addition, hydrogen combustionresults in water formation, making it the most environmentally friendly available energy carrier. The location of nickel on the DHMe-H log(i0) dependence as well as the properties of specially photosensitized and modified TiO2,[3,4] and its resistance to photo corrosion, semiconducting properties as well as its efficiency of UV–Vis absorption allow for the assumption that a combination of these materials may allow for the synthesis of composites of the required properties suitable for photocatalytic water splitting. Common routes concerning the design of materials for hydrogen generation by water
KRZYSZTOF MECH is with the AGH University of Science and Technology, Academic Centre for Materials and Nanotechnology, Al. A. Mickiewicza 30, 30-059 Krakow, Poland. Contact e-mail: [email protected] Manuscript submitted March 20, 2019. Article published online June 25, 2019 METALLURGICAL AND MATERIALS TRANSACTIONS A
splitting are focused on platinum group metal (PGM) alloys,[5–8] or the synthesis of new PGM-free alloys,[9,10] semiconductors,[11,12] or metal–semiconductor composite materials.[13] In the literature, there are also many reports concerning the application of TiO2-based heterostructures of increased charge carrier separation for this purpose.[14–16] The photocatalytic hydrogen generation in metal–semiconductor systems consists of two parallel processes. In the cathodic one, H+ ions are reduced to H2 while in the anodic one, under UV light oxidation, water molecules are oxidized. The process can proceed on semiconductors of band gap larger than 1.23 eV corresponding to the water splitting potential. The valence band of TiO2 is more positive than O2/H2O redox potential, and its conducting band is more electronegative than the H+/H2 redox potential. In addition, TiO2 is highly resistant to photocorrosion under UV–Vis radiation as well as to reactions taking place on its surface making it the most suitable candidate for these kinds of purposes.[17] The properties of electrochemically synthesized Ni-TiO2 have been investigated most thoroughly in terms of photoelectrochemical properties by de Tacconi et al.[18,19] The Ni-TiO2 composite has many other potential applications including selective methanation of CO,[20] selective oxidation of chloronitrobenzene to chloraniline,[21] hydrogen generation by photoelectrocatalytic glucose reformation,[22] and photoreduction of CO2 to methane.[23] One of the methods of synthesis of the Ni-TiO2 materials is electrodeposition. Mohajeri et al. reported
VOLUME 50A, SEPTEMBER
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