Research On Construction And Photoelectrochemical Performances Of Tungsten Oxide Homojunction Composite Photoelectrode

Photoelectrochemical?PEC?water splitting based on semiconductor photoelectrodes can convert absorbed solar energy into hydrogen energy,which is considered as a golden key to solve the current energy crisis and environmental issuses.Therefore,exploring and developing efficient and stable semiconductor materials as photoelectrodes to achieve efficient PEC water splitting has become a hot topic.Among numerous semiconductor materials,tungsten oxide?WO₃?as a kind of n-type semiconductor corresponding to visible light is widely concerned because of its suitable optical band gap,excellent electronic transport characteristics and chemical stability.However,the high recombination efficiency of photo-generated carrier seriously restricts the practical application of a single WO₃ photoelectrode.In this paper,the one-dimensional?1D?WO₃ nanorod nanoarrays were firstly fabricated on FTO conductive glass substrates via hydrothermal method.In order to improve the separation and transfer efficiency of photocarriers of the WO₃photoelectrodes,the 1D Mo-WO₃/Fe-WO₃ homojunction and 1D HTA-WO₃/2D WO_3-x homojunction were constructed,and they were employed as photoanode in the PEC water splitting system.The morphology structure,and optical properties of the as-prepared composite photoelectrodes were characterized,the PEC performances were studied,the process of photo-generated carriers separation and transfer in the composite photoelectrodes was analyzed,and the PEC mechanism of the composite photoelectrodes was studied.The results show that the 1D Mo-WO₃/Fe-WO₃ homojunction composite photoelectrode was successfully prepared by two hydrothermal and one annealing treatments,and the photocurrent density reached 0.92 mA/cm² at 1.23 V vs.RHE,which is 2.97 times than that of WO₃ photoelectrode?0.31 mA/cm² 1.23 V vs.RHE?.The great improvement can be attributed to the built-in electric field generated by the different Fermi energy levels due to Mo and Fe doping can promote the carrier separation and transfer.Besides,the homojunction can effectively eliminate lattice mismatch,reduce the concentration of defects at the interface,thereby significantly improving its PEC performances.In addition,the 2D WO_3-x-x nanoarray with oxygen-rich vacancies was hydrothermally grown on the high temperature annealed WO₃ nanorod nanoarrays?HTA-WO₃?,the obtained 1D HTA-WO₃/2D WO_3-x-x photoelectrode showed a photocurrent value of 0.98 mA/cm²?1.23 V vs.RHE?,which is 3.16 times than that of WO₃ photoelectrode.On the one hand,high temperature annealing improves the crystallinity of the sample,reduces defects in the bulk and the surface,and increases the carrier concentration.On the other hand,oxygen vacancies increase the carrier concentration of the sample and increase the band bending at the photoelectrode/electrolyte interface,at the same time,the homojunction structure effectively promotes carrier separation and transfer,and reduces the concentration of defects at the interface,thereby achieving effective carrier separation and transfer.Therefore,due to the synergy effect of the high temperature annealing treatment and the oxygen-rich vacancy homojunction,the PEC performances has been significantly improved.