Synthesis Of Ni-P-CNTs Composite Electrode For Electrocatalytic Hydrogen Evolution Reaction

Energy is the foundation to the survival and development of human society.The increasing consumption of fossil energy and accompanying the greenhouse effect as well as environmental pollution are driving the search for renewable and environment-friendly alternatives as the energy carriers.Hydrogen?H₂?is a promising energy carrier and has many advantages over hydrocarbons,such as high energy density,no harmful products when burnt,and is recognized as the future oil.Currently,hydrogen production from electrolyzed water is considered the most promising method.Hydrogen production from electrolyzed water requires a catalyst with high electrocatalytic activity to reduce the hydrogen evolution overpotential to improve hydrogen production efficiency.We know that the noble metal catalysts?such as Pt,Ir,Rh,etc.?are the most efficient electrocatalysts for electrocatalytic hydrogen evolution reaction?HER?.However,high cost and scarcity seriously limit its wide application in industry.Based on this,it is of far-reaching significance to develop high-activity non-precious metal catalysts for the large-scale application of hydrogen energy under the precondition of low energy and low-cost input.In this thesis,Carbon nanotubes?CNTs?was used to modify the transition metal phosphides?TMPs?.The Ni-P-CNTs composite electrode was successfully prepared by high temperature powder sintering method,and the relationships among microstructure,chemical composition and catalytic activity of HER were systematically studied.The morpgology and chemical composition of the composite electrodes were characterized by X-ray photoelectron spectroscopy?XPS?,X-ray diffraction?XRD?,field emission scanning electron microscopy?FESEM?and transmission electron microscopy?TEM?.The electrocatalytic hydrogen evolution activity of the composite electrode was evaluated by electrochemical correlation test method,such as linear sweep volammetry?LSV?,Tafel,cyclic voltammetry?CV?,electrochemical impedance?EIS?.The main research contents and results are as follows:?1?The chemical composition and morphology of the composite electrodes are changed with the increase of carbon nanotubes.The main change are the conversion from single catalytic phase?Ni₂P?to multiphase(Ni₂P,Ni₁₂P₅,CNTs,etc.)coexistwence,three-dimensional connected porous structure becomes to stacked particles or flower-like nanosheets hierarchical structure.Meanwhile,the addition of carbon nanotubes makes the composition of the composite electrode distributed and its mechanical strength is strengthened.?2?Ni-P-?CNTs?_x composite electrodes were prepared by high temperature powder sintering with CNTs modified nickel phosphide.The microstructure,chemical composition,electrocatalytic activity of Ni-P-0%CNTs,Ni-P-41%CNTs,Ni-P-43%CNTs and Ni-P-45%CNTs composite electrodes were systematically studied.The results show that the CNTs modified composite electrodes can significantly enhance the charge transfer inside the electrode and between the electrolyte and the electrodes.At the same time,the introduction of CNTs will greatly increase the specific surface area of the composite electrodes,and promote the preferential orientation growth of nano-grains,and highly expose the highly active?001?crystal plane,thus accelerate the diffusion of electrolyte and the shedding of bubbles on the electrode surface.Among them,Ni-P-43%CNTs composite electrode showed the best electrocatalytic activity,and the HER onset potential of Ni-P-43%CNTs was-29mV,the overpotential of 10 mA/cm^-2 and 20 mA/cm^-22 were-96mV and-159mV,and the Tafel slope was 58mV/dec.Compared with the Ni-P-0%CNTs composite electrode,the HER onset potential,Tafel slope,the overpotential of 10 mA/cm^-2 and 20 mA/cm^-2 of the Ni-P-43%CNTs composite electrode were reduced by 130 mV,128mV,128mV,99mV/dec,respectively.?3?The?Ni-P?_x-CNTs composite electrodes were prepared by changing the molar ratio of nickel to phosphorus.The microstructure,chemical composition,electrocatalytic activity of?Ni-P?_1/3-CNTs,?Ni-P?_1/2-CNTs,?Ni-P?₁-CNTs and?Ni-P?₂-CNTs composite electrodes were systematically studied.The experimental results showed that the HER activity of the composite electrode was significantly affected by the molar ratio of Ni to P.Under the experimental conditions,when the molar ratio of nickel to phosphorus is 1:1,the?Ni-P?₁-CNTs composite electrode showed the best electrocatalytic activity and excellent stability in both acidic and alkaline media.Furthermore,it was found in the experimental results that the?Ni-P?₁-CNTs composite electrode had better HER performance than alkaline electrolyte in acidic electrolyte due to the rapid decrease of proton concentration during HER.Compared with 1M KOH electrolyte,the?Ni-P?₁-CNTs composite electrode HER onset potential,10mA/cm^-2overpotential,Tafel slope decreased by 6mV,30mV,24 mV/dec in 0.5M H₂SO₄.Therefore,the chemical composition and microstructure of the composite electrode can be optimized by adjusting the composition design of the composite electrode,so as to improv the Electrocatalytic HER performance in different electrolytes.