Preparation Of WX_n-based (WO₃, WS₂) Nanomaterials And Their Gas-sensitivity And Electrocatalytic Properties

The rapid economic development and excessive consumption of fossil fuel have caused not only shortage of fossil energy,but also severe environmental issues,such as smog,climate change,ozone depletion etc.,threatening our wellbeing and seriously restricting the further development of modern society.As gases are everywhere,sensitive and reliable gas sensors are essential for gas analysis,public safety and envirmonental monitor.Meanwhile,development of cleaner and renewable energy is badly needed to solve the above problems.Photoelectrochemical hydrogen generation is viewed as one of the most prospective strategies to resolve the energy and environmental problems,unfortunately,developing an effective and economic catalyst appears to be the bottleneck.The present thesis completed two tasks:(i)developed effective WO3-based gas sensors,and(ii)developed WS2-based electrocatalyst for hydrogen evolution reaction(HER).Specifically:I.Ag nanoparticle-sensitized WO3 hollow nanospheres(Ag-WO3 HNSs)are fabricated via a sonochemical synthesis route.FE-SEM and TEM images reveal that the Agx-WO3 adopts the hollow nanosphere structure in which WO3 forms the outer shell framework and the Ag NPs grown on the inner wall of the WO3,and the size of the Ag NPs can be controlled by adjusting the addition amount of reactants.It is found that the Ag(15nm)-WO3 sensor shows remarkablely high sensitivity and selectivity towards alcohol vapor,and the superior detection-limit as low as 0.094 ppb.Compared with the pristine WO3,it increases the responses by 7-fold and lower the optimum working temperature of sensor from 340 to 230?.Light illumination was found to boost the sensor performance effectively,especially at 405 nm,where the light wavelength resonates with the absorption of Ag NPs,thus the improved sensor performance is attributed to the localized surface plasmon effect.II.Ag-WO3 core-shell nanospheres(CSNSs)are fabricated for gas sensor applications.Different with the traditional metal(core)-semiconductor(shell)nanostructure,Ag NPs in our study are dispersed in the core-shell nanosphere uniformly,composited with WO3,to form a hybrid nanostructure.It is found that the sensor based on Ag-WO3 CSNSs dramatically improve the sensor performance towards alcohol vapor,with significantly lower optimum working temperature(260?),superior detection limit(0.20 ppm),and extremely high responses.Moreover,we found that the Ag-WO3 sensor displays an ultrahigh sensitivity under visible light illumination.When irradiation occurred,the response increased from 62 to 160,the optimum working temperature reduced from 260 to 190?,and the detection limit enhanced to 0.032 from 0.20 ppm,significantly better than that of the pristine WO3.Thanks to the SPR effect of Ag NPs and the unique hollow yolk-shell stuctures,the resultant Ag-WO3 CSNSs can provide a more efficient way to reflect and scatter light,which makes it advantageous in significantly lower optimum operating temperature while maintaining relatively high sensor response.III.Nanowires assembled sub-WO3 urchin-like nanostructures have been fabricated via a solvothermal method.Different with the stoichiometric WO3,the WO3-x in our study displayed a significant sensor performance towards alcohol vapor at room temperature,and exhibited a typical p-type semiconductor sensor behavior.The superior sensing performance of this WO3-x sensor is ascribed to the large specific surface area and abundant oxygen vacancies.And the obvious enhancement of the gas sensing property can be very useful for the future design and development of room temperature gas sensors.IV.Layered graphdiyne-WS2 2D-nanohybrid(GD-WS2 2D-NH)was systhsined via a combination of ultrasonication and solvothermal methods in this study.Owing to the conjugated electronic structure and low reduction potential,GD is found to be an effective stabilizer and also a reducing agent during these processes.Further study shows that the layered GD-WS2 2D-NH synthesized with abundant active edges.Such loose and defect-rich structure with large surface area renders ultrahigh catalytic activity and durability for HER in acidic media.Furthermore,owing to the built-in electric field formed among dissimilar layers(GD and WS2),the enhanced charge transfer leads to high activity of the basal plane sites that were inactive for the HER.As a result,the GD-WS2 2D-NH catalyst presents a reduced HER onset potential as low as 140 mV and a superior Tafel slope of 54 mV per decade,making the GD-WS2 2D-NH a promising stable catalyst for the HER reaction.