Search

In this study, a nanoflower structured WO3 thin film has been prepared on an etched titanium substrate using a WO3 seeds-assisted hydrothermal reaction method. The WO3 nanoflower-like structure appeared when the growth time arrived at 4.75 h. Subsequently, this film went into a rapid growth stage. The nanoflower (NF) structured WO3 thin film with 8 h of hydrothermal reaction possessed the best photoelectrochemical performance. The photoinduced current density was 2.0 mA·cm−2 at a bias potential of 1.23 V (vs. Ag/AgCl) under the illumination by a simulated sunlight (100 mW/cm2) with a filter air mass (AM) 1.5 G. The improvement of the photoelectrochemical performance of the nanoflower structured WO3 can be attributed to three aspects. Firstly, the light absorption capacity could be increased by the nanoflower structure. Secondly, the reactive sites could be enhanced due to the increased specific surface area of the nanoflower structured WO3. Finally, a direct transfer channel for the photogenerated electrons could be formed by the definite 2-dimentional WO3 nanoflakes linked with the Ti substrate.

Copper element was employed to achieve the interlayer doping and intralayer doping in g-C3N4 (CN). Univalent Cu single atom prefer to dope into the interlayer site of CN to form a steady bridged bond structure. Further increasing the doping amount of Cu, except for the univalent Cu at the interlayer, some divalent Cu single atoms can be doped on the intralayer site of CN to form an unstable but active-catalysis structure. Electrochemical and theoretical calculation results reveal that Cu-interlayer doping can form an energy gradient between the different CN layers to decrease the charge transfer energy barrier between them. More importantly, these interlayer photogenerated electrons will converge on the divalent Cu, a catalysis active site for the photogenerated electrons, inducing more superoxide radicals and high activity. This two-sites modified CN, can mineralize a refractory antibiotic Norfloxacin (NOR) to CO2 and H2O completely under visible light stimulation, and the two-sites co-doping method provides a reference for CN photocatalyst modification to solve the questions of insufficient redox energy and low photons quantum efficiency of CN.

The hydrogen storage properties and mechanisms of the Ca(BH4)2-added 2LiNH2–MgH2 system were systematically investigated. The results showed that the addition of Ca(BH4)2 pronouncedly improved hydrogen storage properties of the 2LiNH2–MgH2 system. The onset temperature for dehydrogenation of the 2LiNH2–MgH2–0.3Ca(BH4)2 sample is only 80 °C, a ca. 40 °C decline with respect to the pristine sample. Further hydrogenation examination indicated that the dehydrogenated 2LiNH2–MgH2–0.1Ca(BH4)2 sample could absorb ca. 4.7 wt% of hydrogen at 160 °C and 100 atm while only 0.8 wt% of hydrogen was recharged into the dehydrogenated pristine sample under the same conditions. Structural analyses revealed that during ball milling, a metathesis reaction between Ca(BH4)2 and LiNH2 firstly occurred to convert to Ca(NH2)2 and LiBH4, and then, the newly developed LiBH4 reacted with LiNH2 to form Li4(BH4)(NH2)3. Upon heating, the in situ formed Ca(NH2)2 and Li4(BH4)(NH2)3 work together to significantly decrease the operating temperatures for hydrogen storage in the Ca(BH4)2-added 2LiNH2–MgH2 system.

The introduction of RbF into the Mg(NH2)2-2 LiH system significantly decreased its (de-)hydrogenation temperatures and enhanced its hydrogen-storage kinetics. The Mg(NH2)2-2 LiH-0.08 RbF composite exhibits the optimal hydrogen-storage properties as it could reversibly store approximately 4.76 wt % hydrogen through a two-stage reaction with the onset temperatures of 80 °C for dehydrogenation and 55 °C for hydrogenation. At 130 °C, approximately 70 % of hydrogen was rapidly released from the 0.08 RbF-doped sample within 180 min, and the fully dehydrogenated sample could absorb approximately 4.8 wt % of hydrogen at 120 °C. Structural analyses revealed that RbF reacted readily with LiH to convert to RbH and LiF owing to the favorable thermodynamics during ball-milling. The newly generated RbH participated in the following dehydrogenation reaction, consequently resulting in a decrease in the reaction enthalpy change and activation energy.

Potassium hydride (KH) was directly added to a Mg(NH2)2-2LiH system to improve the hydrogen storage properties; the corresponding mechanisms were elucidated. The Mg(NH2)2-2LiH-0.08KH composite displays optimized hydrogen-storage properties, reversibly storing approximately 5.2 wt% hydrogen through a two-stage reaction and a dehydrogenation onset at 70 °C. The 0.08KH-added sample fully dehydrogenated at 130 °C begins to absorb hydrogen at 50 °C, and takes up approximately 5.1 wt% of hydrogen at 140 °C. Adding KH significantly enhances the de-/hydrogenation kinetic properties; however, an overly rapid hydrogenation rate enlarges the particle size and raises the dehydrogenation temperature. A cycling evaluation reveals that the KH-added Mg(NH2)2-2LiH system possesses good reversible hydrogen storage abilities, although the operational temperatures for de-/hydrogenation increase during cycling. Detailed mechanistic investigations indicate that adding KH catalytically decreases the activation energy of the first dehydrogenation step and reduces the enthalpy of desorption during the second dehydrogenation step as a reactant, significantly improving the hydrogen storage properties of Mg(NH2)2-2LiH.