Preparation Of CuFeO₂ Nanomaterials And Their Photoelectrochemical Properties

Photoelectrochemical reduction of water is an effective way to make rational use of solar energy.Photoanode materials with good stability and low cost are very common.Several common p-type semiconductors such as p-Si,p-GalnP2 and p-WSe2 are in widely use.Although the photocathode exhibits superior performance,it relies on expensive and energy-intensive deposition or processing techniques in the fabrication process,which makes large-scale production of stable and low-cost photocathodes difficult to achieve.CuFeO2 is a typical p-type semiconductor material with a copper-iron structure.It is composed of three elements of Cu,Fe and O,which are abundant in the earth’s crust.It has suitable light absorption properties and good stability,so it has a wide range of applications prospect.In this paper,the photoelectrochemical performance of CuFeO2 as photoelectrochemical reduction water cathode material is improved by changing the surface structure of CuFeO2 material and constructing heterojunction in order to solve the serious problem of photo-generated carrier in CuFeO2 material.The main work of this paper is as follows:(1)The CuFeO2 photoelectrodes with different particle sizes were prepared by drop coating and spin coating respectively.The photocurrents of CuFeO2 photoelectrodes prepared by different methods were tested under the same conditions.The photoelectric properties of CuFeO2 photoelectrodes prepared by different preparation methods were studied.Impact.The hydrothermally synthesized CuFeO2 nanoparticles were arranged as a suspension by a drop coating method,and were dropped on the FTO conductive surface to prepare a CuFeO2 photoelectrode.The photocurrent of the CuFeO2 photoelectrode prepared by the drop coating method is 5 μA/cm2 at-0.5 V(vs.Ag/AgCl),The photocurrent of the CuFeO2 photoelectrode prepared with sulfate is decayed after long-term illumination measurement 3 μA/cm2 and remains unchanged.The solution of Cu(NO3)2 and Fe(NO3)3 in ethylene glycol methyl ether was directly dispersed on the surface of FTO by spin coating,and heated to form a CuFeO2 photoelectrode.After the thickness of the CuFeO2 photoelectrode prepared by spin coating reaches 400 nm,the thickness of the CuFeO2 thin layer does not change.The photocurrent of the CuFeO2 photoelectrode is constant at 20 μA/cm2,The surface of the photoelectrode is tested,and no electron accumulation occurs.(2)By adding Mg2+to the hydrothermal reaction precursor,One step hydrothermal synthesis of Mg2+ doped CuFeO2 nanomaterial crystal powder with different concentrations.Then CuFeO2 with different Mg2+doping concentration was prepared into a photoelectrode,and the effect of Mg2+ doping concentration on the photoelectric properties of CuFeO2 was investigated.The experimental results show that Mg2+ doping not only increases the concentration of p-type carriers in the material,but also improves the conductivity of CuFeO2,which facilitates the transport of carriers in the material and prolongs the lifetime of photogenerated carriers.By adjusting the doping ratio,it was found that when the relative mass ratio of Mg2+ reached 0.1%,the lifetime of photogenerated carriers was the longest(0.8485 s),which was 94%higher than that of pure CuFeO2.Further increase in the amount of doping,the increase in the amount of Mg2+ introduced will in turn reduce the photoelectric properties of the material.(3)In order to improve the utilization efficiency of photogenerated carriers in CuFeO2 by constructing a heterojunction.There is a self-built electric field at the interface of CuFeO2/CuO heterojunction,and the self-built electric field causes the photo-generated carriers to be directionally separated,thereby improving the separation efficiency of the charges.In the experiment,a CuFeO2/CuO heterojunction photocathode was prepared by spin coating for photoelectrochemical reduction of water.The experimental results show that at a potential of-0.5 V(vs.Ag/AgCl),a high photocurrent of 50 μA/cm2 after 600 s white light irradiation is higher than the sum of photocurrents of CuFeO2 and CuO alone.The interfacial electric field of the CuFeO2/CuO heterojunction prolongs the lifetime of the photo-generated carriers and improves the separation efficiency of the charge,thereby improving the photoelectrochemical reduction water performance.