WC Nanoarray Wettability Control And Applications

Fossil fuels are unsustainable and the pollution and dramatic climate change caused by fossil fuels' direct burning threatens the existence of creatures,including human beings.Development and utilization of green,clean and sustainable new energy resources is a critical approach to solve the existing and potential energy and environmental problems.Among all stripes of new energy resources,solar energy and hydrogen have drawn growing attention.In the exploitation of hydrogen and solar energy,tungsten carbide(WC)has shown great potential due to its high stability in acid and platinum-like catalytic behavior.At the same time,nanoarray structures and superwettabilities also exhibited important effects on energy resource's harvest,conversion,storage and use.In the current thesis,we focus on controlling the wettability of WC nanoarrays,and develop their applications in energy conversion,specifically,electrocatalytic water splitting in acid and solar-powered desalination(SPD)of seawater and heavy metal sewage.The content and conclusions are as follows:1.Svnthesis of tungsten oxide(WO3)nanoarrays and WC nanoarray.Twelve types of WO3 nanoarrays with different mophologies are fabricated via hydrothermal method,including nanowire arrays,nanorod arrays and nanobelt arrays.Then the WO3 nanobelt array was reduced and carbonized by thermal-decomposable solid chemicals.Thus two dimentional WC nanobelt arrays were obtained.The fabrication method is relatively safer than traditional methods,which use hydrogen and methane as the reducing agent and carbon source.By changing the species of solid reducing agents and carbon sources,we can further control the WC nanoarrays as nitrogen-doped(N-WC)or non-doped.The combination of the features of WC with nanoarray structure offers an optimal criterion for a broad range of applications.2.Superaerophobic N-WC nanoarray for electro-catalytic water splitting in acid.By electron-structure modification,nanostructure construction and wettability control,we elevated the HER performance of WC in acid from microscopical,mesoscopic,and megascopic views.Our work realized not only high current density at low overpotential(-190 mV,200 mA cm-2),but also showed high stability at large current density(100 mA cm-2).Our work will be beneficial for accelerating non-noble metal catalysts'application in water splitting for hydrogen production in acid or with proton exchange membrane.The idea of combining microscope,mesoscope and macroscope design and combining material,structure and interface construction,offers a good example for other catalysts'design.At the same time,N-WC nanoarray showed high OER catalytic activity in acid(onset potential at about 1.4 V vs.RHE).Although there are already many good non-noble metal catalysts for OER in alkline,the development of non-noble metal catalysts for OER in acid is tough.So,although N-WC is still not stable enough as an OER catalysis in acid,it shows a promising direction.When both the anode and the cathode are N-WC nanoarrays,water splitting could be powered by a single AA commercial battery,which is a breakthrough in overall water splitting in acid.3.WC nanoarrav film with sandwich wettability for highly efficient SPD.Multiscale rough nanoarray structure and thus enhanced localized surface plasmon resonance(LSPR),enable WC nanoarray high light absorption throughout a wide range(220nm-2200nm,>97.5%)in solar spectrum.Besides,the idea of applying plasmonic carbide instead of plasmonic metal nanostructures for SPD overcomes the aggregation problem of metal nanostructures under illumination.This idea not only realized broad-band absorption in the solar spectrum,but also achieved 500 hours stability without decay under illumination.Furthermore,the wettability design with sandwich structure boosts the solar-to-vapor efficiency up to 90.4%,with distilled water production rate at 1.1 kg m-2 h-1 from seawater and 1.0 kg m-2 h-1 from heavy metal sewage under normal sunlight(AM 1.5).More importantly,the desalination performance remained 98%after 1 hour x 100 times' reutilization,which is competent to face the inevitable washing and reutilization problem during desalination in practice.The design strategy is also expected to be effective toward a wide range of other solar-thermal materials and evaporation applications which will promote high efficient solar energy use and solving water crisis.Above all,by combining the intrinsic advantages of WC,nanoarray structure and wettability,we focus on exploiting their application in water splitting and solar-powered desalination.