Boosting the performance of visible light‐driven WO3/g‐C3N4 anchored with BiVO4 nanoparticles for photocatalytic hydrogen evolution

In this article, a ternary WO₃/g‐C₃N₄@ BiVO₄ composites were prepared using eco‐friendly hydrothermal method to produce efficient hydrogen energy through water in the presence of sacrificial agents. The prepared samples were characterized by scanning electron microscopy (SEM), scanning transmission electron microscopy (STEM), transmission electron microscopy (TEM), X‐ray diffraction (XRD), ultraviolet‐visible (UV‐vis), Brunauer‐Emmett‐Teller (BET) surface area, and photoluminescence spectroscopy (PL) emission spectroscopy. The experimental study envisages the formation of 2‐D nanostructures and observed that such kinds of nanostructures could provide more active sites for photocatalytic reduction of water and their inherent reactive‐species mechanism. The results showed the excellent photocatalytic performance (432 μmol h^?1 g^?1) for 1.5% BiVO₄ nanoparticles in WO₃/g‐C₃N₄ composite when compared with pure WO₃ and BiVO₄. The optical properties and photocatalytic activity measurement confirmed that BiVO₄ nanoparticles in WO₃/g‐C₃N₄ photocatalyst inhibited the recombination of photogenerated electron and holes and enhanced the reduction reactions for H₂ production. The enhanced photocatalytic efficiency of the composite nanostructures may be attributed to wide absorption region of visible light, large surface area, and efficient separation of electrons/holes pairs owing to synergistic effects between BiVO₄ and WO₃/g‐C₃N₄. The prepared samples would be a precise optimal photocatalyst to increase their suppliers for worldwide applications especially in energy harvesting.     

CNT/g‐C3N4 photocatalysts with enhanced hydrogen evolution ability for water splitting based on a noncovalent interaction

Graphite carbon nitride (g‐C₃N₄) as a novel photocatalyst has attracted growing attention, but its photocatalytic efficiency should be further improved. Based on the large work function and fast electron conductivity of carbon nanotubes (CNTs), here CNT/g‐C₃N₄ photocatalysts with improved H₂ evolution ability and stable water splitting ability were synthesized. The improvement was attributed to the synergistic effect between CNTs and g‐C₃N₄. As for the mechanisms, CNTs strongly attracted photoelectrons and, because of excellent conductibility, rapidly transferred photoelectrons from the catalyst interface. Thereby, the photoelectron migration rate and the photogenerated charge separation and the use efficiency of photoelectrons in g‐C₃N₄ were improved, which largely enhanced the hydrogen production ability. Moreover, the addition of CNTs improved the service life and stability of g‐C₃N₄‐based photocatalytic H₂ production. After 10 hours of visible light irradiation, the maximum H₂ yield from the 12‐mg/L CNT/g‐C₃N₄ (CG12) was 138.7 times larger than that of g‐C₃N₄ (6548.4 vs 47.2 μmol/g), and the H₂ evolution rate was 138.7 times that of g‐C₃N₄ (654.8 vs 4.72 μmol/g/h). After 50 hours, the apparent quantum efficiency of CG12 was up to 37.9%, indicating that the addition of CNTs improved the photocatalytic splitting and stability of g‐C₃N₄. The mechanism of photocatalytic hydrogen production and the roles of CNTs in improving water splitting were discussed through characterization and activity experiments. It was found that the addition of CNTs accelerated the migration, separation, and utilization of photoelectrons and thereby significantly enhanced the photocatalytic performance.     

Catalytic properties of Ag promoted ZnO/Al2O3 catalysts for hydrogen production by steam reforming of ethanol

Ag promoted ZnO/Al₂O₃ catalysts were prepared by using the incipient wetness impregnation method. The catalytic properties of steam reforming reaction for hydrogen production on the prepared catalysts were evaluated with H₂O:C₂H₅OH molar ratios of 3:1 at 450 °C and atmospheric pressure. Ag promoted ZnO/Al₂O₃ catalysts show higher SRE catalytic activity than ZnO/Al₂O₃ catalysts. H₂ and CH₃CHO are the major products on Ag promoted catalysts, and C₂H₄ is also produced probably due to acid sites on Al₂O₃. SRE mechanism on Ag promoted ZnO/Al₂O₃ catalysts, which contains C-C scission, is different from that on ZnO/Al₂O₃ catalysts. A method based on thermogravimetry (TG), differential scanning calorimetry (DSC) and mass spectrometry (MS) was used to analysis the coking behavior on catalyst surface. The surfaces of Ag promoted ZnO/Al₂O₃ catalysts show two different types of coking, and suffer higher coke deposition during the steam reforming reaction.     

Electrochemical performance of Nd0.6Sr0.4Co0.5Fe0.5O3−δ–Ag composite cathodes in intermediate temperature solid oxide fuel cells

The electrochemical performances of Nd_0.6Sr_0.4Co_0.5Fe_0.5O_3−δ–Ag composite cathodes have been investigated in intermediate temperature solid oxide fuel cells. The Nd_0.6Sr_0.4Co_0.5Fe_0.5O_3−δ–Ag cathodes prepared by ball milling followed by firing at 920 °C show the maximum performance (power density: 0.15 W cm⁻² at 800 °C) at 3 wt.% Ag. On the other hand, the Nd_0.6Sr_0.4Co_0.5Fe_0.5O_3−δ–Ag composite cathodes with 0.1 mg cm⁻² (0.5 wt.%) Ag that were prepared by an impregnation of Ag into Nd_0.6Sr_0.4Co_0.5Fe_0.5O_3−δ followed by firing at 700 °C (but the electrolyte–Nd_0.6Sr_0.4Co_0.5Fe_0.5O_3−δ assembly was prepared first by firing at 1100 °C) exhibit much better performance (power density: 0.27 W cm⁻² at 800 °C) than the composite cathodes prepared by ball milling, despite a much smaller amount of Ag due to a better dispersion and an enhanced adhesion. AC impedance analysis indicates that the Ag catalysts dispersed in the porous Nd_0.6Sr_0.4Co_0.5Fe_0.5O_3−δ cathode reduce the ohmic and the polarization resistances due to an increased electronic conductivity and enhanced electrocatalytic activity.