Fabrication Of Nanoporous Nickel Electrode With Super Capacitive Performance

With the extensive dependence and consumption of fossil fuels,mankind is facing significant environmental pollution and energy resource crisis.To achieve the goal of replacing fossil energy with new energy sources and easing the energy crisis,it is the necessary to option to develop and use of new energy sources for sustainable development and new energy devices.As a kind of new energy storage device,supercapacitor has the advantages of both higher power than traditional capacitors and bigger energy density than the battery.Consequently,more and more attention and interests have been attracted into this field.Electrode material was the most dominating factor for the comprehensive performance of supercapacitor.At present,one of the favorable development directions of electrochemical capacitors is to develop new electrode materials with high capacity on the basis of existing research.This work introduces strategies based on design of materials with high electrical conductivity and specific surface area.We have conducted the design,synthesis and performance research of a series of 3D porous Ni based metal nanoelectrodes.To further improving the capacitance performance of the supercapacitor materials,we explored the design and fabrication of three dimensional porous structural,and the composite of porous metal materials with transition metal oxide.The main purpose of this work is to obtain electrode materials for supercapacitors with high capacitance and good cycling performance.Detailed experiments and conclusions are as follows:（1）The effect of the ratio of initial alloys elements on material catalytic performance.Nanoporous nickel（NPN）was fabricated by Ni-Al alloy as precursors with the method of electrochemical dealloying,and then we explored the effects of initial alloy composition on the microstructure and electrochemical performances of nanoporous nickel.The results showed that NPN₁ was prepared by dealloying with Ni_33.5Al_66.5 alloys,and it had the irregular bicontinuous ligament structure on the surface.NPN₂ was prepared by Ni_30.8Al_69.2 alloys in the same conditions of dealloying,and it had the uniform bicontinuous ligament structure on the surface.The specific capacitance of NPN₁(1.134 F cm^-2)is 4.3 times higher than that of NPN₂(0.261 F cm^-2)at a current densities of 7 mA cm^-2.The results indicated that the ratio of initial alloys elements determines the phase composition and morphology of nanoporous nickel.The existence ofα-Al phase accelerates the process of dealloying,which causing the cracks on the surface of the material,and resulting in an open pore structure with larger specific surface area.（2）The effect of the corrosion potential on the material performance.Taking the Ni-Mn alloy with 25%Ni as the precursor,nanoporous nickel（NPN）was fabricated by electrochemical dealloying,and the effect of corrosion potential on the material microstructure and electrochemical performance was studied in the article.In the literature,the surface of the material obtained by Ni₂₅Mn₇₅ with corrosion potential of-750 mV shows a"mud crack"structure.However,when the corrosion potential is-900 mV and the material prepared by the same precursor alloy under the same corrosion time not only has retained the alloy frame,but also reduced and shallower the large cracks on the surface of the material and the small cracks increase accordingly.After a deep research,it was found that the corrosion potential determines the morphology and structure of porous material.This was due to the fact that corrosion rate became quicker when the corrosion voltage was higher and the degree of corrosion increased accordingly;as the dissolution of Mn,precursor alloy defects increased,it would lead to the internal stress increased.In addition,the diffusion rate of Ni was so low that it couldn’t refill the vacancy of Mn timely,and then more cracks occurred.Therefore,there were significant differences for the number and size of cracks.The electrochemical performance tests show that the specific capacitance of NPN was 1.58 F cm^-2 at a current densities of 7 mA cm^-2.（3）Preparation of nanoporous nickel thin film materials.In order to improve the electrical conductivity of NiO,the nanoporous nickel oxide film materials were fabricated by the method of interfacial electroless plating.The nickel was deposited on the surface of the substrate with three-dimensional nano-porous structure,and then the Ni is converted to NiO after exposure to oxygen in the air.In practical devices,thin electrode material,small resistance volume and big specific surface accelerate the catalyzing reaction.High hardness and melting point of Ni make it hard to make the film material by melting alloy.In this passage,we attempted to use porous gold as the support structure,which not only provided the continuous conductive and porous ion conducting structure,but also made its own as current collector,without conductive agent and binder,so it is much easier to set the capacitor.Furthermore,the substrate material can have a synergy with the nickel.Compared to the particle material,the prepared nanoporous nickel overcomes the aggregation among particles,enlarges the specific surface area of NiO,and improves the double layer capacitance.Meanwhile,it should be possible to greatly improving the redox active sites of material.Thus,the ensemble performance of the material is improved.The mass specific capacitance is 378 F g^-11 and volumetric specific capacitance can reach to 973 F cm^-3,While the slope of impedance curve is much larger than 45 degree,indicating that ions diffused quickly between the interface of the materials and electrolyte,exhibiting near the excellent performance of pure capacitance.