Study On The Structure Modulation And Electrochemical Performance Of CoMoO₄ Based Nanocomposite Electrode Materials

With the development of society,energy problems have become very serious.At present,the main energy is coal,oil and natural gas.However,serious environmental pollution is caused by the burning of fossil fuels.it is very urgent to develop new energy storage systems and clean energy.Among many energy storage systems,supercapacitors have attracted extensive attention due to their fast charge/discharge capability,long cycle life and environmental friendliness.With the popularity of the sustainable development concept,the ecological environment and green energy become important.Hydrogen energy has also become the most potential candidate for replacing fossil energy in the future society owing to its unique advantages such as zero carbon emission,abundant reserves,and cycle performance.Among them,electrochemical water splitting has been identified as one of the most prosperous hydrogen production technologies.Therefore,based on the future development prospects of supercapacitors and electrochemical water splitting,the design of high-performance and low-cost electrode materials have become an important prerequisite for energy storage and conversion.Transition metal oxides have been research focuses owing to their unique physical and chemical performances.However,most of transition metal oxides can cause volume expansion or contraction during long-term energy storage and conversion,which make the structure of the material change and affect the electrochemical performance.Therefore,the reasonably design and prepare hybrid structured electrode materials with large specific surface area and multiple active sites becomes very important.In this work,CoMoO4 nanomaterials are used as the target,the effect of microstructure on the performance of supercapacitors,hydrogen evolution reaction,oxygen evolution reaction and overall water splitting have been studied,the main contents are as follows:Through a two-step hydrothermal reaction,CoMoO4@MoZn22 nanoarrays with uniform morphology and size are synthesized on a Ni foam substrate.The array provides more transmission paths for electrons.At the same time,this ultra-thin nanosheet structure facilitates the full contact between the electrolyte and the electrodes,and increases the adsorption sites of electrons.In a three-electrode system,the CoMoO4@MoZn22 structures possess a mass specific capacity of 923 C g-1 at 1 A g-1.Using it as positive electrode and activated carbon as negative electrode,the assembled asymmetric supercapacitor maintains 97%of its initial capacity after 10,000 charge/discharge at 4 A g-1.In 1 M KOH electrolyte,the prepared product exhibits an OER overpotential of 240 mV at a current density of 20 mA cm-2.The CoMoO4@Co1.62Mo6S8 core-shell structure is prepared on Ni foam by a simple hydrothermal method,and the CoMoO4@CoMoP sample is prepared by hydrothermal and chemical vapor deposition methods.The performances of Mo-based oxides,phosphides and sulfides are compared.The CoMoO4@Co1.62Mo6S8 electrode material with sheet structure exhibits the best supercapacitor and OER performance.At a current density of 1 A g-1,the mass specific capacity of CoMoO4@Co1.62Mo6S8 structure is 665 C g-1.The assembled asymmetric supercapacitor still maintains 99.5%of its initial capacity(4 A g-1)after 10,000 charge/discharge,and when the power density is 2,703.7 W kg-1,the maximum energy density reaches 277.6 Wh kg-1.For OER performance,the overpotential of CoMoO4@Co1.62Mo6S8 electrocatalyst is 200 mV at 10 mA cm-2,and the corresponding Tafel slope is 59.34 mV dec-1.In order to further improve the electrocatalytic performance of the electrode material,the highly active Ni element is added to CoMo-based material.A series of NiMoxCo2-x-LDH electrode materials are prepared by hydrothermal method.When the ratio of three elements of Ni,Mo and Co is 1:1:1,the performance of the prepared NiMoCo-LDH sample is significantly higher than other samples.NiMoCo-LDH electrode material exhibits a HER overpotential of 123 mV and excellent OER performance at a current density of 10 mA cm-2.When it is used as an electrocatalyst for overall water splitting,water splitting can be achieved at a voltage of 1.71 V,and it will maintain an excellent electrocatalytic stability even after more than 14 h.At the same time,as a supercapacitor electrode material,it delivers a high mass specific capacitance and an excellent cycling performance.NiMoCo-LDH//AC ASC shows high energy density at a power density of 2695 W kg-1,and maintains 93%of the initial capacity after 8000 charge/discharge.