Structure And Photoelectrochemical Properties Of CuCrO₂/CuO Nano-Multilayer Films

In the field of photocatalysis,composite semiconductor materials are often used to improve the separation efficiency of photo-generated carriers,multilayer materials are also used to improve the response of visible light.Therefore,the comb ination of composite heterostructures and nano-multilayer structures is expected to improve light absorption properties and the separation efficiency of photogenerated electron-hole pairs.In this paper,CuCrO₂ and CuO films were alternately deposited by magnetron sputtering method to form nano-multilayer films with CuCrO₂/CuO heterojunction as the basic unit.The effects of modulation parameters?such as modulation periods,modulation ratios?and temperatures on structure,absorption,electrical properties,chemical impedance spectroscopy,polarization curves,and photocurrent response of CuCrO₂/CuO nano-multilayer films were studied.On the basis of this,their hydrogen production activities were discussed:1)CuCrO₂/CuO is selected as the basic modulation unit according to the band structure and its matching,as well as the heterojunction structure.From the viewpoints of light absorption capacity,electrical conductivity,photoelectrochemical performance,catalytic activity and growth continuity,the following parameters of multilayer film structure are designed:modulation periods are 6,8,10,and modulation ratios?ratios of CuCrO₂:CuO?are?2:1?,?1:1?,?1:2?,the surface material is CuO and CuCrO₂,respectively.Three temperature conditions are deposition of CuCrO₂ at 200°C,deposition at room temperature,room temperature deposition and annealing at 200°C.The multilayer films were formed by alternately depositing CuCrO₂ and CuO films on the substrate by RF magnetron sputtering and DC magnetron sputtering,respectively.2)The effects of these parameters on the structure and microstructure of the multilayer films were analyzed by XRD,XPS and FE-SEM.The results show that increasing the modulation period and modulation ratio is beneficial to refining the grain of CuO layer.The deposition of CuCrO₂ at 200°C and the deposition of CuCrO₂ at room temperature as well as annealing at 200°C are beneficial to improve the crystallinity of CuO layer,while CuCrO₂ exists in an amorphous form.XPS confirms that the multilayer film consisted of CuCrO₂ and CuO.The film has nano-scale multilayer characteristics.The reduction of the modulation period and the modulation ratio makes the interlayer interface and the columnar features of the CuO more obvious.Increasing of temperature is not conducive to the formation of a layered periodic interface of the multilayer film.3)The performance test results of CuCrO₂/CuO nano-multilayer film show that the improvement of light absorption capacity largely depends on the decrease of the thickness of the periodic layer or the increase of CuO in the ratio,that is high modulation period and small modulation ratio.The increase of deposition temperature reduces the light absorption performance,while the annealing treatment increases the absorbance of the material.4)The I-V characteristic curve and photocurrent are related to the modulation structure of the multilayer film:the current transmission mechanism is combined by hot carrier emission mechanism and tunneling mechanism.The increase of the modulation period makes the tunneling mechanism play a major role,and the modulation ratio has little effect.5)The increasing of the modulation period and modulation ratio,depositing at room temperature and coating with CuCrO₂ on the surface are beneficial to increase photocurrent and the separation and migration efficiency of photogenerated carriers.The charge transfer between the film surface and the solid/liquid interface and the reaction activity of the surface were promoted.The increase in temperature is unfavorable for the transport of charge to the interface and decreases the reaction reactivity.Compared with CuCrO₂ layer and CuO layer,the multilayer film has obvious photocatalytic hydrogen evolution activity.In summary,among the 20 kinds of multilayer films designed and prepared,the multilayer film with a modulation ratio of?2:1?,10 period,and surface layer of CuCrO₂has the optimal performance.The light absorption range can be extended to the visible light.The photocurrent response is as high as 35.14?A/cm².It has a charge transfer resistance of as low as 8.98?/cm² and a reaction potential of-0.423 V under illumination.it has the highest photocatalytic hydrogen evolution activity,whose hydrogen production is 1.8046?mol/?h.cm²?.