| The shortage of fossil fuels and the environmental problems brought about by the extensive use of fossil fuels have become an obstacle to the sustainable development of human society.It is necessary to find a sustainable,clean,efficient energy as substitutes for fossil fuels.Hydrogen is an ideal clean energy,and hydrogen production by water splitting is an important way to obtain high purity hydrogen molecules in the future.The oxygen evolution reaction is a multi-electron process with slow kinetics and relatively high overpotential,which is the bottleneck problem of the electrolysis water.The catalytic efficiency of noble metal oxides can usually meet the requirements,but the high price limits its practical application.Therefore,it is of great significance to develop inexpensive non noble metal catalysts.Layered transition metal silicates have been widely used in the fields of optical materials,catalysis,gas sensors and water treatment agents because of their unique crystal structure and their abundant resources,simple preparation and stable performance.In this paper,we use different modification methods to improve the ability of the transition metal silicate to catalyze the decomposition of water.The main research contents are as follows:1.Firstly,Multiwalled Carbon Nanotubes（MWCNTs）were purified by a certain concentration of nitric acid.Then,SiO2 was synthesized by sol-gel method and uniformly loaded on MWCNTs to obtain MWCNTs@SiO2.Finally,a simple hydrothermal reaction will be used to intimate growth of the nickel-cobalt silicate hydroxide nanosheets on the outer surfaces of multiwalled carbon nanotubes（MWCNTs@NCS）.Scanning electron microscope（SEM）,transmission electron microscope（TEM）,the X-ray diffraction（XRD）,X-ray photoelectron spectroscopy（XPS）and other methods were used to analyze the morphology,phase and composition.The properties of the oxygen evolution of the electrode material was measured in 0.1 M KOH electrolyte,and the overpotential of MWCNTs@NCS-2 was about 440 mV at the current density of 10 mA·cm-2,and the Tafel slope was about 96 mV/dec.The excellent propertie of oxygen evolution of MWCNTs@NCS was due to the synergistic effect between the layered transition metal silicate and carbon nanotubes.2.The monodisperse silica spheres were prepared by sol-gel method.（Ni,Co）3Si2O5（OH）4 hollow nanospheres（NCS）composed of nanosheets were synthesized by a hydrothermal method.Finally,（Ni,Co）3Si2O5（OH）4-P（NCS-P）was obtained by phosphorus modification method under low temperature.Changing the temperature of phosphorus modification to optimize the conditions,so that find out the optimum temperature for the phosphorus modification of nickel-cobalt silicate hydroxide.SEM,TEM,XRD,XPS and other methods were used to analyze the morphology,phase and composition.The properties of the oxygen evolution of the electrode material was measured in 1 M KOH electrolyte,and the overpotential of NCS-P-275 was about 394 mV at the current density of 10 mA·cm-2,and the Tafel slope was about 67 mV/dec.Phosphorus modification was used to increase the electrochemical active sites in catalysts,which improved the electrocatalytic performance of transition metal silicate from another point of view.3.Because of the bare nickel-cobalt silicate hydroxide after phosphorus modified treatment can greatly improve the electrocatalytic performance for oxygen evolution,we were going to have phosphorus modification on the basis of the first work to explore better electrode materials.Firstly,the layered nickel-cobalt silicate hydroxide nanosheets on the outer surfaces of multiwalled carbon nanotubes were synthesized by the same method as above.Then,the MWCNTs@NCS-P-400 was obtained by phosphorus modification.Controlling experiments without sodium hypophosphite and other conditions（such as heat treatment temperature and time）remain unchanged.SEM,TEM,XRD,XPS and other methods were used to analyze the morphology,phase and composition.The properties of the oxygen evolution of the electrode material was measured in 1 M KOH electrolyte,and the overpotential of MWCNTs@NCS-P-400 was about 328 mV at the current density of 10 mA·cm-2,and the Tafel slope was about 49 mV/dec.The synergistic effect between layered transition metal silicate and carbon nanotubes and electrochemical active sites induced by phosphorus modification can further improve the electrocatalytic performance of OER. |
