Study On Morphology Control And Stability Of Tungsten Trioxide Nano-photoanodes

Under the dual pressures of energy crisis and environmental polution,the search for clean renewable energy instead of fossil energy is urgently needed.As a kind of clean renewable energy,solar energy has received extensive attention.The photoelectrochemical?PEC?cells to convert solar energy into hydrogen is one of the most promising ways to meet future energy needs.As a kind of earth-rich metal oxide,tungsten trioxide?WO₃?has a medium bandgap?2.5².7 eV?,a sufficient positive valence band position and good stability in acidic electrolyte,which has been widely used as PEC photoanodes.However,due to the two major defects of high recombination of photoelectron-hole pairs and poor stability in non-acid electrolytes,the PEC efficiency of WO₃ photoanode is still much lower than its theoretical value.In order to obtain high-efficiency and stable WO₃ photoanode,nanostructure engineering and passivation layer coating were considered to overcome the above defects,thus improving the photoelectrochemical performance and stability of WO₃photoanode.The main research contents are as follows:?1?Porous WO₃ nanoplate arrays with regular arrangement were prepared by hydrothermal method,and the morphology and thickness of WO₃ were successfully controlled by adjusting the addition of?NH₄?₂C₂O₄ in hydrothermal precursor liquid.With the increasing amount of?NH₄?₂C₂O₄,the WO₃ nanoplates are getting thinner,and the thinnest thickness is 20³0 nm.The photocurrent of the prepared ultra-thin porous WO₃ photoanode can reach 1.80 mA/cm² at 1.23 V?vs.RHE?.The high PEC performance of the WO₃photoanode is mainly due to its porous ultra-thin morphology and amorphous layer,which are advantageous for widening the photoresponse range of the WO₃ photoanode,increasing the electrochemical active surface area and promoting charge transfer at the photoelectrode/electrolyte interface.?2?In order to improve the photoelectrochmical stability of the WO₃ photoanode under neutral or even alkaline electrolyte,the dense TiO₂ passivation layer was covered on the WO₃photoelectrode by atomic layer deposition,compared with which was prepared by hydrothermal method.The results show that the TiO₂ passivation layer prepared by atomic layer deposition is more dense and the stability is better.At the same time,the band structure between TiO₂ and WO₃ matches each other to form a type II heterojunction.The recombination between TiO₂ and WO₃ can realize the spatial separation of electrons and holes,thereby improving the photoelectrochemical performance of the photoanode.