Based On Cu₂O Photoelectrode Film Preparation And Catalytic Water Splitting Performance Research

Cuprous oxide(Cu2O),as a narrow band p-type semiconductor material,is widely used as a photoelectrocatalyst due to its low price,non-toxicity and absorption of visible light and so on.However,there are also some challenges restricting its application.The most obvious disadvantage is that the serious charge recombinations in the bulk and on the surface of Cu2O,resulting the actual photocurrent density being much lower than the theoretical value.The other is the stability.As the redox potentials for the reduction and oxidation of Cu2O locate within the water splitting potentials,if the charge carriers could not quickly migrate apart from Cu2O or be consumed,the Cu2O material used in the photoelectrolyte suffers from serious photocorrosion.In this paper,the catalytic activity and stability of Cu2O photoelectrode were improved by constructing heterogeneous junction and loading metal as co-catalyst.The kinetic process of hydrogen evolution and the charge transfer process were also studied.On the other hand,as a visible light absorption material,Cu2O can be combined with the n-type semiconductor TiO2 and fabricate an efficient photoanode by extending the light absorption ability as well as promoting the charge separation efficiency by constructing a heterophase junction.The detail work is shown as follows:1.Fabrication of high efficiency and economical photocathode is a challenge issue in photoelectrocatalysis(PEC).In this work,Cu2S/Ni/Cu2O photocathode was constructed via electrodeposition method followed by a two-step overlayer deposition procedure including direct-current magnetron sputtering(DCMS)and ion exchange reaction.The scanning electron microscope(SEM)images and energy dispersive X-ray spectroscopy(EDX)results show that the presence of Ni in the inner-layer could not only affect the morphology but also enhance the formation rate of the outer-layer Cu2S.The XPS results indicate that the Ni should exist as NiOx instead of NiO.The photocurrent of Cu2S/Ni/Cu2O achieved two times higher of it on the pristine Cu2O.The charge dynamic characterizations,including electrochemical impedance spectroscopy(EIS),Tafel slopes and photoluminescence(PL)spectra,demonstrate that the Ni can promote the hydrogen evolution reaction follow the Heyrovsky reaction,while Cu2S shows a crucial role on the charge separation.At last,surface photovoltage microscopy(SPVM)technology was used to reveal the function of each overlayers.It gives a direct evidence for the charge transportation pathway in the system and totally explains the function of each component.It illustrates that,the photogenerated electrons will migrate from Cu2O to Ni,while the holes will transport from the VB band of Cu2O to Cu2S and further reach to the substrate.Thus,Ni can mainly contribute to the activity,while Cu2S not only behaves as a protector but also plays a crucial role on the charge separation by efficiently collecting the holes.This work provides an efficient modification method for the construction of a high performance photocathode and especially gives a deep insight into the mechanism of the PEC process.2.As an n-type semiconductor,TiO2 is widely used as a photoanode because of its strong oxidation and reducibility,good stability,low price and environmental friendliness.However,because it has a forbidden band gap of about 3.2 eV,it can only absorb the visible light(-5%in the solar spectrum),which greatly limits its application.In order to solve this problem,a two-dimensional nanowire film was prepared through hydrothermal method,and then a layer of Cu2O nanoparticles was grown on the nanowire film.The amount of Cu2O was controlled by the concentration of the copper precusor.The coupling of p-Cu2O and n-TiO2 can promote the light absorption region of TiO2 shift to the visible light,and the separation efficiency of photogenerated carriers can be improved by the presence of p-n heterojunction,so that the Cu2O/TiO2 composite photoelectrode has a higher catalytic activity than the pristine TiO2 photoelectrode.From the results of electrochemical impedance spectroscopy,the presence of Cu2O reduces the charge transfer resistance of the carriers and accelerates the separation of photogenerated electrons and holes.Therefore,a high performance photoanode was constructed by coupling of p-Cu2O and n-TiO2.