Design,Preparation And Catalytic Performance Of The Polyoxometalate-based Photo-and Electro-catalysts

POMs,the abbreviation of Polyoxometalates,are a kind of nanosized inorganic metal-oxygen cluster with abundant composition,structure and chemical propreties.POMs have potential applications in the field of photocatalysis,electrocatalysis,proton conduction,medicine chemistry,organic catalysis,electrochromism.In this paper,a series of POMs-based photocatalysts are constructed and these composites show high performance toward degradation of dyes under visible light irradiation.Furthermore,carbide molybdenum/tungsten HER catalysts were fabricated with keggin POMs and organic precursor.The high HER catalytic activity of these electrocatalysts are attributed to the propreties of abundant composites and nanostructure of POMs.1.A series of 2D layered Bi₂O_xS_3-x/Nb6O17?Bi/Nb?heterostructures photocatalysts were synthesized through a facile hydrothermal vulcanization method between Bi³⁺exchanged K₄Nb₆O₁₇ and thiourea?NH2CSNH2?.XRD result confirms that the heterostructures were composed of Bi2 Ox S3-x and Nb6O17.HRTEM indicate that Bi₂O_xS_3-x was successfully intercalated into layers of K₄Nb₆O₁₇.Such large interfacial contacts can be benefical to the transfer and the separation of photogenarated charge carriers.Thus the composites exhibit good photocatalytic performance for the degradation of methyl orange?MO?under visible light irradiation?? > 400 nm?.The radical capture tests reveal that photogenerated hole h+ and O₂^-played an important roles in the photodegradation of MO.These 2D layer composites can be used as high activity and promosing photocatalysts in the purification of waste water and environment repair.2.A series of polyoxometalates mediated g-C₃N₄?POMs/C₃N₄?composites were fabricated using g-C₃N₄ and various keggin polyoxoanions?polyoxoanions = SiW12O404-,PW12O403-,PMo12O403-?.The results of XRD,TEM,XPS and EDAX reveal that a small amount of polyoxoanions have been modified on the surface of g-C₃N₄ by the electrostatic and hydrogen bond interactions.Photocatalytic experiments indicate that the composites exhibit enhanced photocatalytic activity for the degradation of methyl orange?MO?and water splitting H2 production under visible light irradiation compared to C₃N₄.The loading amount and type of polyoxoanions can regulate the photocatalytic performance of the composites.Among the samples,5 % SiW12 modified C₃N₄ has the best photocatalytic performance.The study of photocatalytic mechanism reveals that polyoxoanions can act as the different electron traps,which can efficiently promote the separation of photogenerated charge carriers of C₃N₄,thus resulting in the enhanced photocatalytic peformance of the composites.This work can promote the study of POM-based composite photocatalyst.3.we report a P-modified tungsten carbide encapsulated in N-doped carbon?P-W₂C@NC?as an efficient and stable HER electrocatalyst at all pH range?0-14?by annealing polyoxometalate?H3PW12O40·xH2O?and dicyandiamide at high temperature.Electrocatalytic tests show that to achieve current density of 10 mA cm^-2,the P-W₂C@NC required overpotential of 89 mV in acid,63 mV in alkaline solution and 185 mV in neutral solution.DFT calculation indicated that the combination of W2 C and N-carbon can decrease the ?GH of H atom which resulted in enchanced catalytic performance.Furthermore,the introduction of P dopant can also promote the activity of catalyst.More important,the carbon layers on the W2 C can not only protect the core from aggregation but also from correction in the basic solution.It is the first case about tungsten-carbide-based HER electrocatalyst operated at all pH values with high activity and stablity,which might provide some new pave to explore tungsten-based Pt-like electrocatalyst for HER.4.P-modified Mo₂C loaded on the N-carbon layers?P-Mo₂C/NC?was successfully synthesized from low-cost and eco-friendly Urea-formaldehyde resin?UF?and H3PMo12O40 via annealing at high temperature for the first time.The UF with 3D framework facilitate the uniform distribution of POMs clusters which can avoid the aggregation of Mo2 C particles at annealing process.The particles size of catalyst was nanosized?av.7nm?and the size distribution of particles are uniform?5-12nm?.The as-synthesized P-Mo₂C/NC displayed excellent HER performance and long-term stability at all pH values.To achieve current density 10 mA cm^-2,only 109 mV,159 mV and 83 mV was required for P-Mo₂C/NC in 0.5 M H2SO4?pH = 0?,0.1 M phosphate buffer?pH = 7?and 1 M KOH?pH = 14?,respectively.This non-noble metal HER catalyst may provide new avenue to explore low-cost,eco-friendly carbon source to fabricate high efficient and stability HER catalyst.