Study On The Construction And Performance Of The Catalytic Materials For Efficient Hydrogen Production Under Electromagnetic Wave Field

Hydrogen is a clean energy carrier with high energy density and can also be used as a chemical in various hydrogenation processes.Therefore,it is of great importance to achieve efficient and sustainable hydrogen production.As two forms of the electromagnetic waves,visible light and microwave are essentially the same and simply differ in wavelength.Visible light can be harvested directly from the sun and microwave is available from unstable and non-fossil fuel based power units(such as solar or wind electricity generation system).Thus,the catalytic hydrogen production processes driven by visible light or microwave would help to achieve the goal of producing green and sustainable hydrogen resources.For the visible light driven H₂evolution process,H₃PO₂modification and the NH₄Cl-assisted“bottom-up”synthesis strategy were employed,and the controllable preparation of graphitic carbon nitride(g-C₃N₄)nanosheets with significant nitrogen vacancies was readily achieved via a facile one-step in-situ reduction process.The differences between the g-C₃N₄nanosheets synthesized with H₃PO₂and H₃PO₄modification highlighted the importance of the phosphorus valence states on the synthesis of g-C₃N₄-based materials.H₃PO₂induced multiple modifications to g-C₃N₄by introducing nitrogen vacancies and protonation,which synergistically enhance the visible light harvesting,charge carrier separation and migration and thereby boost the H₂evolution performance of the g-C₃N₄nanosheets through water splitting,with the apparent quantum yield at 420 nm being 40.4%.In the microwave-driven process,the nickel catalysts were rationally promoted by incorporating the excellent microwave response capability and multivalent states characteristics of manganese oxides.Manganese oxides could help the nickel catalysts to achieve an equilibrium state with balanced methane cracking and carbon gasification rates,and consequently improve the anti-coke ability of the catalyst and stabilize the microwave absorption and transformation.A simple nickel catalyst has very strong potential to crack methane into solid carbon and hydrogen,and will consequently result in filamentous carbon deposition.The filamentous carbon would cover the nickel active sites and induce weakened microwave absorption,and then result in extremely poor H₂production via methane dry reforming.While,the manganese oxides-introduced Mn³⁺/Mn²⁺redox pair promoted the nickel catalyst to retain a high concentration of surface lattice oxygen species,which are beneficial to the gasification of the deposited carbon.In return,the excellent anti-coking ability would help the catalysts maintain stable dielectric properties to absorb and convert microwaves for achieving efficient and robust methane reforming to produce hydrogen.In view of the goal for H₂production and fully considering the two key factors such as electromagnetic wave response and conversion,the catalytic materials which are suitable for the visible light and microwave processes were constructed,respectively.With the help of the characterizations such as composition,morphology and chemical state of each element and also the density functional theory(DFT)simulations,the effects of the promoters such as H₃PO₂and manganese oxides were thoroughly analyzed.In addition,the H₂evolution performances of the catalysts were carefully correlated with their intrinsic properties,which would provide theoretical guidance for constructing efficient catalysts to convert renewable energy or produce green and sustainable hydrogen under electromagnetic wave fields.