Study On The Preparation And The Overall Water Splitting Performance Of Multiple Heterojunctions Of Rare Earth Oxide/Amorphous Nickel Oxide

With a series of environmental problems caused by traditional fossil fuels,hydrogen energy,as a renewable and clean energy,is of significance in solving energy crisis and environmental pollution due to its good combustion performance,no greenhouse gas generation and high energy efficiency.At present,most of the hydrogen production methods are converted from traditional fossil fuels such as coal,coke,natural gas or oil,which not only consumes a large number of mineral deposits but also has high production costs.The electrolysis of water for hydrogen production has attracted much attention due to its high conversion efficiency,environmental friendliness,and broad application prospects.However,its slow reaction kinetics and energy loss caused by high overpotential limit its large-scale industrial application.Currently,platinum-carbon（Pt/C）is the commercial catalyst for HER,and iridium oxide（Ir O₂）or ruthenium oxide（Ru O₂）is the commercial catalyst for OER,but the high cost and scarcity of precious metals limit its large-scale application.Therefore,the development of high-efficiency,stable,and low-cost catalysts for water electrolysis is of great significance for the development of energy devices.In this paper,the heterojunction of amorphous nickel oxide（NiO）and metallic nickel（Ni）was prepared on the carbon cloth by three-electrode electrochemical deposition process using the plasma-cleaned carbon cloth as the substrate.Rare earth oxides（REO_x）are deposited on NiO to form erbium oxide（Er₂O₃）and cerium oxide（Ce O₂）.The prepared catalysts（Er₂O₃/Ni-NiO and Ce O₂/Ni-NiO）will construct numbers of amorphous and crystalline heterojunctions on the surface,resulting in a variety of defects and unsaturated coordination bonds on the surface of the catalyst.Exposing more catalytically active sites can enhance the electrocatalytic performance of HER and OER.The main work is as follows:（1）Oxygen plasma was used for pretreatment to improve the functional group structure of the carbon cloth surface to enhance the hydrophilicity of the carbon cloth surface.In this paper,scanning electron microscopy（SEM）was used to characterize the changes in the morphology of different samples.With the increase of treatment time,more catalysts were attached to the surface of the carbon cloth,indicating that the hydrophilicity of the carbon cloth surface also increased with the increase of plasma treatment time.Enhanced accordingly.In order to further determine the effect of different treatment time on the catalyst,X-ray diffraction（XRD）was used in this paper to detect the difference between different samples.The results showed that the peak intensity of Ni was also strengthened with the increase of treatment time,indicating that the attached catalyst increased with the increase of treatment time.The improvement of the hydrophilicity of the carbon cloth increases.Afterwards,X-ray spectroscopy（XPS）and high-resolution transmission（HRTEM）were performed on the samples treated with plasma for 60 s,which proved the successful preparation of the Ni-NiO catalyst heterojunction.In order to study the difference in catalytic performance of different samples,electrochemical tests of HER and OER were carried out on different samples in this paper,and it was found that when the plasma treatment time was 60s,the carbon cloth showed the best catalytic performance after electrochemical deposition(HER:85 m V@10 m A cm^-2,OER:385 m V@50 m A cm^-2).This lays the foundation for the further improvement of the catalytic performance.（2）In order to further improve the electrocatalytic performance,Er₂O₃/Ni-NiO and Ce O₂/Ni-NiO catalysts were prepared by the second-step electrodeposition process on the basis of the previous step.In order to determine the phase structure of the prepared catalyst,the results of XRD showed that the catalyst only contained the peaks of metallic Ni and REO_x,indicating the successful introduction of Ni and REO_x.It can be seen that the catalyst retains the morphology of the nanosheets by SEM.In order to further determine the structural composition of the catalyst,HRTEM and XPS were used to characterize the structure of the sample in detail.The results showed that the multiple heterojunctions of metallic Ni and amorphous NiO and REO_x and amorphous NiO were successfully prepared.Through electrochemical tests,the results showed that the HER(39 m V@10 m A cm^-2)and OER(318 m V@50 m A cm^-2)of Er₂O₃/Ni-NiO and Ce O₂/Ni-NiO were better than those of the single component（Ni-NiO）.The catalytic activity of m A cm^-2)was improved.In this paper,the establishment of its heterostructure and the introduction of metallic Ni enhances the electron transport,thereby obtaining a high-performance catalyst.