Design And Preparation Of CuFeO₂-based Photocathodes For Photoelectrochemical Water Splitting

The exploitation and utilization of environmentally friendly renewable energy is crucial to solve the energy crisis and environment pollution issues facing rapidly developed human society.Hydrogen being a fascinating high density energy carrier returns only water to nature when used to produce heat or power,it has been regarded as a most promising energy carrier candidate to replace traditional fossil fuels,because of its rich resources.Photoelectrochemical（PEC）water splitting promises the storage of solar energy in the form of hydrogen,offering an ideal,renewable method of hydrogen production for cycling use of green hydrogen.Therefore,it is highly desirable to develop PEC water splitting technique for future potential application of hydrogen energy.The semiconductor photoelectrode is the essence component of a PEC cell,which produces non-equilibrium carriers on light absorption and drives the minority ones towards the semiconductor/liquid interface,where a redox reaction can be triggered,such as the reduction of H⁺to H₂for a p-type semiconductor,directly determining the power conversion efficiency of the PEC cell.p-type CuFeO₂semiconductor as an ideal photocathode candidate material for hydrogen production has advanced features of suitable band gap and band alignment,low cost and simple synthesis.However,CuFeO₂performing as photocathode faces the low separation efficiency of photogenerated carriers and poor stability issues operation,limiting its PEC water splitting performance.To solve the above-mentioned issues,this thesis focuses on the design and modification of CuFeO₂active layer and its interface with current collector and electrolyte,proposes to introduce a hole selective layer at CuFeO₂/current collector interface and a protective（and catalytic）layer at CuFeO₂/electrolyte interface,respectively,improving the separation efficiency of photogenerated carriers and inhibiting occurrence of photo corrosion in the CuFeO₂photocathode.Consequently,it is anticipated to obtain high performance and stable CuFeO₂based photoelectrode.The specific research contents are as follows:1.A strong coupled NiO/CuFeO₂laminated heterojunction photocathode was constructed by using a simple one-step thermal treatment of a Ni/Cu_0.5Fe_0.5C₂O₄·2H₂O laminated film on the FTO in air,in which the NiO layer performs as a hole selective layer（HSL）to promote carrier separation in the CuFeO₂active layer.In specific,a Ni film was first sputtered on the FTO surface.Then,a Cu_0.5Fe_0.5C₂O₄·2H₂O precursor film was in-situ grown on the Ni film by using chemical bath deposition（CBD）technique.Finally,the strong coupled NiO/CuFeO₂laminated heterojunction photocathode was obtained by heating the Ni/Cu_0.5Fe_0.5C₂O₄·2H₂O laminated film on the FTO in air.On the premise of controlling thicknesses of Ni and Cu_0.5Fe_0.5C₂O₄·2H₂O films,the thickness of NiO and CuFeO₂layers in the heterojunction photocathode can be optimized for the performance improvement.Meanwhile,the heteroatomic interdiffusion can be triggered across the NiO/CuFeO₂heterojunction with increasing heating treatment temperature.The obtained Cu:NiO/Ni:CuFeO₂laminated heterojunction photocathode possesses an improved carrier separation efficiency and thus delivers an enhanced PEC water splitting performance.A photocurrent density of 0.9 m A cm^-2has been obtained at 0.2 V（vs.RHE）under AM 1.5G sunlight irradiation,which is the maximum value of reported bare CuFeO₂based photocathode in the literature.2.A TiO₂/Pt protective/catalytic composite layer and a NiS_xcompact layer were constructed on the surface of NiO/CuFeO₂laminated heterojunction photocathode for the improvement of PEC water splitting activity and stability.In detail,a TiO₂protective layer was first deposited on the surface of the CuFeO₂light-absorbing layer by magnetron sputtering,and then load the Pt cocatalyst by photochemical deposition.The performance and stability of PEC water splitting were optimized by adjusting the thickness of the magnetron sputtered TiO₂layer and loading amount of Pt cocatalyst.Further,a NiS_xcompact catalyst layer was deposited on the surface of NiO/CuFeO₂heterojunction photoelectrode by using the successive ionic layer adsorption and reaction method to replace the TiO₂/Pt composite layer.Finally,the photocurrent density is improved by 30%as compared with the pristine NiO/CuFeO₂heterojunction photoelectrode after the surface modification,and the attenuation of photocurrent is also weakened.