Preparation And Electrocatalytic Properties Of Cobalt-based Hydroxide Nanostructured Materials

The shortage of energy and environmental problems caused by large-scale use of fossil fuels have aroused wide concern in recent years.Therefore,developing efficient,clean and renewable new energy sources'has attracted immense research interest.As a representative new type of clean energy,hydrogen is expected to replace traditional fossil fuels in the future due to its high calorific value and no pollution.Electrochemical water splitting has the advantages of high efficiency,clean and easy operation,and it is regarded as a promising and sustainable strategy to produce hydrogen.At present,traditional noble metal-based catalysts(Pt,Ir,Ru,etc.)hold the benchmark for HER and OER,which have high catalytic activity and stable performance.But the scarcity and high cost greatly impede their scalable utilization.Thus,it is of great necessity to develop efficient,stable and economical nonprecious electrocatalysts for water splitting.In recent years,some progress has been made in the study of high-efficiency electrocatalysts.However,compared with noble metal-based electrocatalysts,nonprecious electrocatalysts still have poor catalytic performance.Especially in terms of HER catalysis,it is difficult to achieve the catalytic effect of commercial Pt/C catalysts.Herein,considering the low-cost and efficient characteristics of cobalt-based nanomaterials,cobalt-based electrocatalyts with excellent electrocatalytic properties are fabricated via design of its morphology and structure.The phase,morphology and chemical state of the materials are characterized by certain test and analysis methods to explore the mechanism of the electrocatalytic reaction process.At the same time,the electrocatalytic properties of the obtained nanomaterials are studied.1.Interface Engineering of Co(OH)2/Ag/FeP Hierarchical Superstructure as Efficient and Robust Electrocatalyst for Overall Water SplittingFeP nanorods grown on Ti substrates are fabricated by hydrothermal and low-temperature phosphating,and Ag nanoparticles are loaded by modified UV-assisted reduction method.Subsequently,ultrathin Co(OH)2 nanosheets are further grown on the surface of Ag/FeP through electrodeposition method,fabricating the heterostructure composed of zero-dimensional Ag nanoparticle,one-dimension FeP nanorod,and two-dimension Co(OH)2 nanosheet grown on Ti foils.In this composite,FeP and Co(OH)2 have high catalytic activity for HER and OER,respectively,as well as the good conductivity of Ag.This hierarchical superstructure not only reveals increased well-exposed active sites but also generates new bonding mode,resulting in a changed electronic and interf-acial structure.The optimal Co(OH)2/Ag/FeP heterostructure shows low overpotentials of 118 and 236 mV to reach a current density of 10 mA cm 2 for HER and OER in 1.0 M KOH,respectively.Furthermore,the overall water splitting can be delivered with Co(OH)2/Ag/FeP-Co(OH)2/Ag/FeP hybrid catalytic couple at a low operation ?10 voltage of 1.56 V with approving durability for 50 h,which is superior to the commercial Pt/C-IrO2 couple and most of up-to-date nonprecious electrocatalysts.2.Effect of surface modification of CoOOH with nonmetallic atoms(N,P,S)on oxygen evolution reaction activityThe Co(OH)2 nanosheets are synthesized at room temperature and then further converted to CoOOH nanosheets.The doping of different non-metal on the surface of the CoOOH nanosheets is fabricated by the method of low-temperature calcination under inert atmosphere with suitable S.P.and N sources.The electrocatalytic activity of the electrocatalysts have a great relationship with the surface state in OER process.The surface is doped with non-metal ions,which changes the surface state of CoOOH.The phase,morphology and chemical state of the material are analyzed by X-ray powder diffraction(XRD),transmission electron microscopy(TEM)and X-ray photoelectron spectroscopy(XPS).Furthermore,the OER electrocatalytic activity of a series of materials is conducted to investigate the effect of CoOOH surface state on its electrocatalytic properties.