Preparation And Electrochemical Performance Of Cobalt-based Transition Metal Nanomaterials

With the gradual consumption of global fossil energy and the increasingly serious environmental pollution,the exploration of new renewable and green energy storage and conversion methods has become an important and challenging research subject.The traditional noble metal catalysts,which are expensive,scarce and slow in catalytic kinetics,greatly limit the process of large-scale commercialization of new energy technologies.Therefore,it is an urgent task to develop efficient and low-cost electrocatalysts to reduce the reaction energy barrier and improve the selectivity of catalysts to specific products.Transition metal-based nanomaterials have been widely studied and applied in fields such as lithium-ion batteries,overall water splitting,metal-air batteries,fuel cells and supercapacitors because of their rapid reaction kinetics,high natural abundance,low-cost and environmental friendliness and the catalytic activity and stability have the potential to increase,thus it is considered to be the preferred alternative to noble metal catalysts.In this paper,we used electrospinning technique,NaCl template method and sol-gel method to prepare various cobalt-based nanomaterials,which were used as lithium-ion battery electrode materials,oxygen evolution reaction electrocatalysts and Zn-air battery bifunctional oxygen electrocatalyst,respectively and showed higher specific capacity and cycling stability and high efficiency catalytic activity.The research shows that the synthesis method developed in this paper is simple and effective,which can be extended to the macro-controlled preparation of other transition metal materials and provides some ideas for the design and controllable synthesis of efficient and cheap catalysts in the field of energy storage and conversion technology.The main research contents are as follows:?1?A facile and novel synthesis strategy of hybrid Sn O₂-Co₃O₄ nanotube was developed by employ electrospinning technology.Polyvinylpyrrolidone?PVP?was used as the carbon source,tin chloride and cobalt nitrate were used as the Sn and Co sources,respectively.The porous and uniform hybrid Sn O₂-Co₃O₄ nanotube was obtained by calcining the spinning products at temperature programming.This low cost,template-free,Kirkendall effect-derived process first yields phase-separated core-sheath PVP/Sn O₂-Co₃O₄ composites,creating highly uniform and well-dispersed nanotubes via self-assembly accompanying gradual PVP combustion.On account of the great buffering capability in hierarchical porous architecture,synergistic effect of active multi-components and the present interfacial Co nanophase,the proposed tubular hybrids possess enhanced cyclic stability and lithium storage capacity as anodes with retained capacity as high as 873 m Ah g^-1 even after 200 cycles at 100m A g^-1.The protocol paves the way for rational design of hollow hybrid nanotubes with wide applications.?2?A method was designed to prepare two-dimension?2D?flake materials by employ inert salt?NaCl?template and a nanoarray composite composed of two dimensional porous nanosheets?Co/Co_xM_y?M=N,B??was prepared by this method.The use of cobalt chloride,argon-ammonia gas?Ar/NH₃?,boric acid as sources of Co,N and B and NaCl as template and dispersant.The ultra-thin two-dimensional nanosheet materials?denoted as Co/Co_xM_y?M=N,B??were obtained by dipping method and calcination at high temperature.In the basic electrolyte,Co/Co_xM_y?M=N,B?showed better electrocatalytic activity and the initial oxidation potential was negatively shifted by 29 and 21 m V,respectively than Co/Co N and Ru O₂ for the oxygen evolution reaction at the 10 m A cm^-2.The special structure of the two-dimensional porous nanosheet and the interfacial effects as a typical schottky catalyst are the main reasons for the improvement of catalytic performance of catalyst Co/Co_xM_y?M=N,B?in in the oxygen evolution reaction?OER?.The synthesis method is universal to some extent.?3?A sol-gel method was developed to prepare the composite comprise nitrogen-doped carbon aerogel with a robust porous nano-wall framework supported Co Fe nanoparticles?denoted as Co Fe@N-CNWF?.The proposed hydrogel composed of graphene oxide?GO?crosslinked agar can efficient capture of highly active Co Fe nanoparticles after pyrolysis.NaCl was introduced to generate the novel nano-wall framework can effectively inhibit the alloy shedding and Ostwald ripening in the catalytic process.Specifically,the Co Fe@N-CNWF aerogels exhibit a positive onset?0.94 V?,half-wave?0.80 V?potentials for the oxygen reduction reaction?ORR?and a low overpotential?0.32 V?at 10 m A cm^-2 for the OER in the basic electrolyte,which is comparable to the state-of-the-art Pt/C and Ru O₂ catalysts.When used as an air-cathode catalyst for a Zn-air battery,the Co Fe@N-CNWF air cathode performs better cycling stability than Pt/C+Ru O₂ mixture catalyst.We believe that this work will offer an effective route to prepare highly-active,cost-effective and stable bifunctional oxygen reduction/evolution electrocatalysts for rechargeable Zn-air batteries.