| Energy crisis and environmental pollution are two big challenges in today’s world. As a kind of storable and environmentally benign fuel, hydrogen is considered as an ideal energy source. In this paper, the Ni anode of an industrialized alkaline electrolytic cell for water electrolysis was modified by photocatalyst. The water electrolysis was coupled with photocatalytic decomposition of water by irradiation on the anode. And a feasible process for the hydrogen preparation of water electrolysis assisted by photocatalysis (WEAP) was proposed and experimental confirmed. Several kinds of Tio2-based nanocomposite films were designed and synthesized. The effect of the morphology and structure of photocatalyst film on the efficiency of hydrogen preparation was investigated.Our home-made device for hydrogen generation was based on the U-type alkaline electrolytic cell of water electrolysis. The anode was Ni, and the cathode was Ni-Cr alloy. The anodic and cathodic compartments were separated by a nano filtration (NF) membrane. TiO2nanotubes with an average diameter of10.0nm were synthesized by a simple hydrothermal method, and spin coated on the Ni anode. The modified Ni substrate was applied as anode in photoassisted water electrolysis. The H2-production rate of WEAP was increased by61%than that of with pure Ni anode. And applied voltage reduced by14.5%compared to traditional water electrolysis. In WEAP process, the maximum hydrogen evolution rate was obtained at concentration of NaOH electrolyte (15%), however, for the sole Ni anode system occurs at higher concentration (20%). The results show that the concentration of NaOH could be reduced, making the operating conditions much more moderate in WEAP.For improving the electron transfer in photocatalytic films on WEAP anode, TiO2films with different morphologies:P25nanoparticles (TiO2NP), random nanotubes (TiO2RNT), orientation nanotubes array (TiO2NTA) and three dimensional (3D) TiO2nanotube network, have been fabricated on Ni substrate. TiO2NP has much more contact interface boundary than TiO2nanotube film. Compared with TiO2RNT. TiO2NTA vertically arranged on Ni substrate, one end of TiO2nanotube is directly contact with Ni electrode. Electrons can transfer to the Ni substrate directly along the nanotubes without interface boundary. This unique3D nanotube network structure not only possesses a large surface area but also decreases the recombination rate of generated electrons and holes. In comparison with traditional alkaline electrolytic cell for water electrolysis with Ni anode,H2-production rate increased by145%and139%in WEAP with photoactive Ni anode modified by3D TiO2nanotube network and TiO2NTA, respectively.For enhancing the visible-light utilization of WEAP photocatalysis films, nanostructured films of rhombohedral Ni3S2/TiO2nanotube were hydrothermally synthesized on Ni anode. A possible mechanism is proposed to explain the formation of rhombohedral Ni3S2nanostructures. The results of UV-vis spectrophotometric studies indicate that optical absorption spectrum of Ni3S2/TiO2nanotube composite films could be extended to the visible region. The hydrogen production rate under visible and UV-visible light irradiation are1.63ml/h·cm2and2.79ml/h-cm2, shows41%and141%improvement in comparison with that of pure Ni anode. The probable mechanism of Ni3S2/TiO2film on the enhancement of photoassisted water electrolysis was proposed.Two types of p-n junction of NiO/TiO2nanotube composite films were directly synthesized on Ni substrate. First, NiO/TiO2nano p-n junctions were prepared on the surface of the round NiO nanosheet. The hydrogen production rate under UV and UV-visible light irradiation are2.68ml/h·cm2and3.01ml/h-cm2, shows131%and159%improvement compare to that of pure Ni anode. Second, we synthesized TiO2/NiO nanoflake tubular array on Ni substrate. Under UV and UV-visible light irradiation, the hydrogen production rate are2.92ml/h·cm2and3.16ml/h·cm2, respectively. |
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