RESUMO
To meet increasing requirement for innovative energy storage and conversion technology, it is urgent to prepare effective, affordable, and long-term stable oxygen electrocatalysts to replace precious metal-based counterparts. Herein, a two-step pyrolysis strategy is developed for controlled synthesis of Fe2O3 and Mn3O4 anchored on carbon nanotubes/nanosheets (Fe2O3-Mn3O4-CNTs/NSs). The typical catalyst has a high half-wave potential (E1/2 = 0.87 V) for oxygen reduction reaction (ORR), accompanied with a smaller overpotential (η10 = 290 mV) for oxygen evolution reaction (OER), showing substantial improvement in the ORR and OER performances. As well, density functional theory calculations are performed to illustrate the catalytic mechanism, where the in situ generated Fe2O3 directly correlates to the reduced energy barrier, rather than Mn3O4. The Fe2O3-Mn3O4-CNTs/NSs-based Zn-air battery exhibits a high-power density (153 mW cm-2) and satisfyingly long durability (1650 charge/discharge cycles/550 h). This work provides a new reference for preparation of highly reversible oxygen conversion catalysts.
RESUMO
Due to its adverse environmental and human health hazards, addressing the elimination of nitric oxide (NO) has become a pressing concern for modern society. Currently, electrochemical NO reduction provides a new alternative to traditional selective catalytic reduction technology under mild reaction conditions. However, the complexity and variability of products make the coverage of NO an influencing factor that needs to be investigated. Hence, this study delves into the coverage-sensitive mechanism of electrochemical NO reduction on cost-effective perovskite catalysts, using SrTiO3 as an example, through density functional theory calculations. Phase diagrams analysis reveals that the coverage range from 0.25 to 1.00 monolayer (ML) coverage is favorable for NO adsorption. Gibbs free energy results indicate that the selectivity is significantly influenced by NO coverage. NH3 is likely to be generated at low coverage, while N2O and N2 are more likely to be produced at high coverage through a dimer mechanism. Charge analysis suggests that the charge transfer and Ti-O bond strength between reactants and catalysts are crucial factors. This work not only provides deep insights into coverage-sensitive reaction mechanisms but also is a guideline towards further rational design of high-performance perovskite catalysts.
RESUMO
The application of covalent organic frameworks (COFs) for the photocatalytic reduction of CO2 is mostly limited by severe charge recombination and low sunlight utilization. Herein, a triazine-based COF with an electron-rich and large π-conjugated system (TCOF) was employed as a building block and integrated with CuInS2 (CIS) to construct a noble-metal-free and high-efficiency photocatalyst for CO2 reduction. The in situ growth of CIS nanosheets on TCOF creates a p-n heterojunction, named CIS@TCOF. Compared with TCOF, the CIS@TCOF heterostructure exhibits a dramatically boosted photocatalytic performance in the reduction of CO2. The produced HCOOH yield over 10 wt % CIS@TCOF can be up to 171.2 µmol g-1 h-1 under visible light irradiation with good reproducibility, which is about 3 times as high as that over TCOF. Further in-depth studies indicate that the introduction of CIS not only enhances the visible light utilization but also restrains the recombination of photogenerated electron-hole pairs efficiently and facilitates the photoinduced charge transfer via the p-n heterojunction system due to the unique structural and compositional features. This research shows the great potential of COFs as efficient photocatalytic carbon fixation materials and provides a versatile route to construct semiconductor-COF heterostructures for photocatalysis.
