Preparation Of Ternary Metal(Hydr) Oxides And Their Electrocatalytic Performance For Water Splitting

As a new and efficient energy source,hydrogen is considered to be the best alternative to fossil energy.Electrochemical water splitting is the most promising method for hydrogen production because it has the advantages of simplicity,high efficiency,and high purity of the produced hydrogen.Using efficient and stable catalyst electrodes is the key method to reducing the cost of electrochemical water splitting.Noble metal electrocatalysts such as Pt,Ir O₂ are still the most active materials now,but their expensive prices limit their large-scale practice.Recently,metal（hydr）oxides have attracted a lot of attention as a kind of promising electrocatalysts.However,the catalytic activity and stability of monometal and bimetal（hydr）oxides are unsatisfied now.Developing efficient and sable multi-metal（hydr）oxides is an efficient way to solve the above problems by utilizing the the synergistic effect in different component.We prepared two ternary metal（hydr）oxides CeO₂-CuCoO_x and Ni（OH）₂@CuCeO_x with excellent catalytic performance by one-step hydrothermal and hydrothermal-electrodeposition method.The morphology,structure,composition and wettability of the samples were acquired by field emission scanning electron microscope（FE-SEM）,field emission transmission electron microscope（FE-TEM）,X-ray diffractometer（XRD）,X-ray photoelectron spectroscopy（XPS）,Raman spectroscopy（Raman）and contact angle（CA）technology.The catalytic activity and stability tested by linear scanning voltammetry（LSV）,cyclic voltammetry（CV）,electrochemical impedance（EIS）and chronopotentiometry（CP）.We also analyzed the mechanism of the excellent performance.The main contents of this thesis are as follows:（1）The CeO₂-CuCoO_xternary metal oxides was successfully synthesized on nickel foam by a simple one-step hydrothermal method.The synthesised CeO₂-CuCoO_x was composed of cubic CeO₂ and cubic CuCoO_xwith good crystallinity.CeO₂-CuCoO_x had unique sea urchin-like morphology composed of nanofibers extending in all directions with a diameter of 50-100 nm.Electrochemical tests in 1 M KOH showed that CeO₂-CuCoO_x had excellent bifunctional electrocatalytic performance.At the current density of 10 m A cm^-2,the OER and HER overpotentials of CeO₂-CuCoO_x were 266and 93 m V,respectively.The electrochemical activity,morphology and chemical composition of CeO₂-CuCoO_x maintained stable after 20 h chronopotentiometry test.An electrolyzer composed of CeO₂-CuCoO_x as both the anode and the anode only required a voltage of 1.63 V at a current density of 10 m A cm^-2,which was equivalent to the activity of the precious metal lectrolyzer Ir O₂/NF||Pt/C/NF（requiered 1.61 V）.After25 h chronopotentiometry test,CeO₂-CuCoO_x/NF||CeO₂-CuCoO_x/NF only requiered1.65 V at a current density of 10 m A cm^-2,which was obviously lower than Ir O₂/NF||Pt/C/NF（requiered 1.70 V）.It indicated that CeO₂-CuCoO_x had better stability and brighter future in practical overall water splitting.Analyzing the characterization results,there are a few reasons for the better performance of CeO₂-CuCoO_x.CeO₂-CuCoO_x has a larger electrochemically active surface area than CuCoO_x（the ECSA value of CeO₂-CuCoO_x is nearly 7 times higher than CuCoO_x）,which can provide more Active sites.CeO₂-CuCoO_x has a smaller Rct value than CuCoO_x,the charge transport ability get promoted after incorporating CeO₂.CeO₂-CuCoO_xhas superaerophobicity and its gas contact angle is bigger than CuCoO_x,which is conducive to the release of hydrogen and oxygen bubbles during the water splitting.（2）The CuCoO_xwas firstly synthesized on nickel foam by hydrothermal,then electrodepositing Ni（OH）₂to obtain Ni（OH）₂@CuCeO_xternary metal（hydr）oxides.The synthesised Ni（OH）₂@CuCeO_x was composed of CuCeO_x and amorphous Ni（OH）_2.Ni（OH）₂@CuCeO_x showed mammillaria like morphology.Ni（OH）₂@CuCeO_x/NF has excellent HER activity in 1 M KOH,it only required a low overpotential of 90 m V at a current density of 10 m A cm^-2,and the Tafel slope is 99.6 m V dec^-1.More importantly,its HER catalytic performance is even better than commercial Pt/C when the current densitiy over-475 m A cm^-2.Ni（OH）₂@CuCeO_x/NF showed excellent durability after 25h chronopotentiometry test,which proves that it has a very bright practical application prospect.Combining control experiments and physical characterization results,it can be speculated that the main active site of the catalyst during the HER process is Ni（OH）₂and CuCeO_x has very critical synergistic effect.Fast charge transfer rate,excellent aerophobicity under liquid and good synergistic effect among the components are the main reasons for the excellent HER electrocatalytic performance of Ni（OH）₂@CuCeO_x.