RESUMEN
Addressing the inherent holes transport limitation of BiVO4 photoanode is crucial to achieve efficient photoelectrochemical (PEC) water splitting. The construction of the hole-transfer bridge between co-catalysts and BiVO4 photoanode could be an effective way to overcome sluggish hole-transfer kinetics of BiVO4 photoanode. Herein, CxNy/BiVO4 photoanode was prepared by coupling carbon nitride hydrogel (CNH) containing unsaturated N on the BiVO4 photoanode during annealing. CxNy/BiVO4 photoanode exhibited excellent PEC performance and stability. Photoelectrochemical tests proved that the coupling of CxNy accelerated holes transfer and enhanced oxygen evolution kinetics. X-ray photoelectron spectroscopy (XPS) and theoretical calculations confirmed the existence of the BiNV bond between BiVO4 photoanode and CxNy, which could serve as the hole-transfer bridge to significantly accelerate separation and transfer of carriers driven by the interfacial electric field. Moreover, it was found that the coupling of CxNy effectively inhibited the dissociation of metal ions through changing their coordination environment, resulting in the excellent stability of CxNy/BiVO4 photoanode. This result provides unique insights into vital roles of the interfacial structure, which might have a significant impact on the construction of PEC devices.
RESUMEN
Facilitating the charge separation of semiconductor photocatalysts to increase the photocatalytic CO2 reduction activity has become a great challenge for sustainable energy conversion. Herein, the surface halogen-modified defect-rich Bi2 WO6 nanosheets have been successfully prepared to address the aforementioned challenge. Importantly, the modification of surface with halogen atoms is beneficial for the adsorption and activation for CO2 molecules and charge separation. These properties have been analyzed by experimental and theoretical methods. DFT calculations revealed that the modification of the Bi2 WO6 surface with Br atoms can decrease the formation energy of the *COOH intermediate, which accelerates CO2 conversion. All halogen-modified defect-rich Bi2 WO6 nanosheets showed an enhanced photocatalytic CO2 reduction activity. Specifically, Br-Bi2 WO6 exhibited the best CO generation rate of 13.8â µmol g-1 h-1 , which is roughly 7.3 times as high as the unmodified defect-rich Bi2 WO6 (1.9â µmol g-1 h-1 ). Moreover, in the presence of a cocatalyst (cobalt phthalocyanine) and a sacrificial agent (triethanolamine), Br-Bi2 WO6 exhibited an even further improved CO generation rate of 187â µmol g-1 h-1 . This finding provides a new approach to optimize the CO2 reduction pathway of semiconductor photocatalysts, which is beneficial to develop highly efficient CO2 reduction photocatalysts.
RESUMEN
In this work, Zn(OH)F is prepared by an initiative, simple post-synthesis method, in which the molar ratio of F/Zn (RF) was varied to investigate the effect of the NH4F amounts added on the samples. Further, we have mainly investigated their energy bands and photochemical properties. Under UV light irradiation (λ£420nm), the samples (RF=0,1,2) show the high degradation activities of methylene blue (MB) dye, namely, 80% of MB can be degraded after 8min. It is found that the hydroxyl and fluorine have greatly down shifted the conduction band (CB, 0.99eV) and valence band (VB, 4.17eV) of Zn(OH)F, compared with ZnO (CB=-0.31eV, VB=2.89eV), but with the nearly same band gap. For the degradation of MB dye, the main oxidative species are holes and hydroxyl radicals for ZnO and Zn(OH)F, respectively. This study suggests that this simple post-synthesis fluorination approach could be extended to develop the other photocatalysts; moreover, we can facilely tune the band structure and photocatalytic activity by introducing or removing hydroxyl and fluorine, which could benefit to develop new photocatalysts.
RESUMEN
Developing a high energy density micro-supercapacitor still remains a big challenge. In this paper, a two-dimensional (2D) CoMoO4 ultrathin nanosheet (NS)-based asymmetric supercapacitor (ASC) is fabricated. It is found that the CoMoO4 NS electrode processes a high specific capacitance (153.2 F g-1) at a current density of 1 mA cm-2 and this ASC can deliver an energy density of 0.313 mWh cm-3 at a power density of 80 mW cm-3, which is higher than that reported in the literature. Moreover, the ASC can drive a light emitting diode (3 mm diameter, red) to work for 6 min after being charged for 10 s. After 5000 cycles, 77.37% of capacitance still remains. We maintain that the ultrathin thickness can significantly shorten the diffusion paths for both electrons and ions, thus leading to fast electron transport and ion diffusion rates. Our results demonstrate that 2D ultrathin NSs could be a new, promising candidate for energy conversion/storage devices, which could offer more accommodating sites for ion intercalation.
RESUMEN
The photochemical properties of crystal facets with obviously distinct atomic and geometric structures have been studied widely to date. However, little work has been performed for two or more facets with very similar atomic and geometric structures. Herein, we mainly report the photochemical properties of {001} and {100} facets of Bi2O2(CO3)1-xSx with very similar atomic and geometric structures. The simulation and experimental results show that over {100} facets, sulfur prefers to substitute for the carbonate anion, leading to the formation of an interesting serpentine internal electric field that greatly inhibits the charge recombining of electrons and holes, which has rarely been demonstrated; over {001} facets, however, sulfur preferentially adsorbs in oxygen vacancies, which greatly reduces the surface energy of {001} facets, leading to 80% of the high-energy {001} facets exposed. As a result, the photochemical properties of nanosheets have been greatly improved. This study could help us to fully understand the photochemical properties of semiconductors.
RESUMEN
In this study, the supercapacitive properties of six new TiO2 nanostructures-including nanodishes, three-layer nanosheets, ancient Chinese coins, single-layer nanosheets, hollow nanocubes, and commercial rutile TiO2 are investigated mainly by cyclic voltammetry, chronopotentiometry, and electrochemical impedance spectroscopy. The results show that among them, the TiO2 nanodishes have the highest discharging capacitance at 1792 mFg(-1), which is 6.4 and 1.5 times higher than that of TiO2 single-layer nanosheets and commercial rutile TiO2, respectively. We found that the electrochemical properties of the TiO2 samples are predominated primarily by the high-energy facets exposed, instead of by the Brunauer-Emmett-Teller area. An important and previously unknown finding of our work is that the electrochemical properties of electrode materials can be improved by controlling the high-energy facets.
RESUMEN
It is still a big challenge for Ag3PO4 to be applied in practice mainly because of its low stability resistant to photo corrosion, although it is an efficient photocatalyst. Herein, we have mainly investigated its activity and stability under indoor weak light for the degradation of dye pollutants. It is amazing that under indoor weak light irradiation, rhodamine B (RhB) can be completely degraded by Ag3PO4 polypods after 36 h, but only 18% of RhB by N-doped TiO2 after 120 h. It is found that under indoor weak light irradiation, the degradation rate (0.08099 h(-1)) of RhB over Ag3PO4 polypods are 46 times higher than that (0.00173 h(-1)) of N-doped TiO2. The high activity of Ag3PO4 polypods are mainly attributed to the three-dimensional branched nanostructure and high-energy {110} facets exposed. After three cycles, surprisingly, Ag3PO4 polypods show a high stability under indoor weak light irradiation, whereas Ag3PO4 have been decomposed into Ag under visible light irradiation with an artificial Xe light source. This natural weak light irradiation strategy could be a promising method for the other unstable photocatalysts in the degradation of environmental pollutants.
