Preparation Of Fe₂TiO₅-Based Photoanode For Photoelectrochemical Water Splitting By Electrospray Deposition

According to the Global Energy and Climate Outlook report,the global energy demand will increase to 37%in the next ten years,and the greenhouse gas emissions will reach 30%.Currently,the main source of energy for mankind is still petroleum fuels.However,the generation of petroleum energy requires a long and complicated cycle,and the consumption of petroleum energy will inevitably increase CO₂emissions.Therefore,seeking a clean and renewable energy sources has become an urgent challenge since the 21st century.Solar energy is recognized as one of the most promising energy sources that can replace petroleum fuels because of its zero-emission,eco-friendly,non-polluting,and inexhaustible characteristics.Photoelectrochemical（PEC）water splitting,as a process to convert and store solar energy through chemical bonds,offers a promising strategy for clean energy and environmental remediation.Unfortunately,building a set of high-efficiency,environmental-friendly,and low-cost solar-hydrogen energy converters faces many challenges,such as the selection of photoelectrode semiconductor materials.The prominent semiconductor materials should possess a suitable band gap,efficient carrier transport and separation,excellent stability and catalytic activity.Besides,the water splitting is an uphill reaction,requiring at least 237 KJ/mol Gibbs free energy.In order to ensure the progress of the water splitting reaction,the valence band potential must be more positive than O₂/H₂O redox potential,and the conduction band potential must be more negative than the H⁺/H₂ redox potential.Moreover,the photogenerated electron-hole pairs require good efficiency of separation and high mobility to avoid recombination of the bulk or surface.Electrospray is a method of preparing thin films that leads to ultrafine atomization of metal salt precursors dissolved in solvents under the influence of electrical forces.This technique applied in non-vacuum condition and possesses the advantages of low cost,short deposition time,high deposition efficiency and reduced material consumption.In this paper,nanostructured Fe₂TiO₅ thin films were prepared by electrospray technique.In addition,the strategy of doping,surface-modification and combining with other materials were used to enhance Fe₂TiO₅ photoanode PEC performance:1.Nanostructured Zn-doped Fe₂TiO₅ thin films were prepared by electrospray technique,and then an ultra-thin FeNi（OH）_x co-catalyst film was loaded on the surface of Zn-doped Fe₂TiO₅ film to significantly improved the photocurrent density.At 1.23 V_RHE,the photocurrent density increased from 0.08 m A/cm²to 0.35 m A/cm².After further loading of the FeNi（OH）_x cocatalyst,the photocurrent density was improved to 0.51 m A/cm²,which was nearly 6.25 times that of the original Fe₂TiO₅photoanode.Through systematic characterization,we found that the doping of Zn changed the electronic properties and surface state of the Fe₂TiO₅ film,improving the charge separation efficiency and suppressing the recombination of carriers in the bulk.The FeNi（OH）x cocatalyst acted as an electron-hole acceptor to reduce the overpotential and inhibit the recombination of electron-hole pairs at the electrode-electrolyte interface,which improved the charge separation and transfer efficiency at interface,and enhanced the catalytic activity of the electrode.2.Nanostructured WO₃/Fe₂TiO₅ composite thin films were prepared by electrospray technique.In detail,the nanostructured WO₃ prepared by the synthetic method had a spherical shape and a loose surface,and the Fe₂TiO₅ nanoparticles could be well attached to the surface of WO₃.The photocurrent density increased to0.21 m A/cm² at 1.23V_RHE when the film thickness ratio was 1:1.Through the analysis of the characterization results of the composite photoanode,the improvement was attributed to the formation of the heterojunction between the WO₃/Fe₂TiO₅ interface,which constituted a built-in electrical potential,promoted the separation of photogenerated electron-hole pairs in the two materials,suppressed the recombination of charges on the surface,and accelerated the transmission of charges.