Constructing The Structure Of CoNi/CNFs For Electrocatalytic Performance

Cathodic oxygen reduction reaction(ORR)in fuel cells can improve conversion efficiency by using electrocatalyst to reduce reaction overpotential.At present,the high price and scarce reserves of the precious metal platinum electrode used in commercial application greatly limit the application of fuel cell.Therefore,the development of environmentally friendly,low-cost and abundant non-noble metal electrode materials is very important for the development of fuel cells.In this paper,the CoNi/CNFs composites were prepared by electrospinning method,and the effects of the size and distribution of CoNi alloy particles on the electrocatalytic oxygen reduction performance were investigated.The research contents are as follows:(1)The effects of concentration of metal salts in electrospinning precursor(0.09,0.12,0.15,0.18 mol/L)on the structure and properties of CoNi/CNFs were studied.The size of CoNi nanoparticles and the graphitization degree of carbon fibers were significantly affected by the concentration of metal salts.With the increase of metal salt concentration,the content and size of CoNi alloy on carbon fiber increased.When the metal salt content was 0.15 mol/L,the CoNi-0.15 composite had the best electrocatalytic performance.The initial potential and half-wave potential of the composite were 0.96 V and 0.88 V(vs RHE),respectively,and the limiting current density reached 5.58 mA/cm2.The current retention rate is 90.7%after the timing test of 20000 s.The main reason is that when the metal salt concentration is 0.15 mol/L,the CoNi/CNFs electrode not only has a higher load of CoNi,but also has a smaller grain size(22.1 nm)and a higher graphitization degree.(2)The effects of the additional amount of thiourea in the precursor on the microstructure and electrocatalytic performance of CoNi/CNFs were studied.The addition of thiourea can effectively refine the CoNi alloy particles.When the addition of thiourea is 0.10 mol/L,the size of CoNi alloy particles decreases from 22.1 nm to 10.2 nm.The graphitization degree IG/(ID+IG)value of carbon nanofibers increased from 30%to 47%.Compared with the samples without thiourea,the initial oxygen reduction potential was increased from 0.96 V to 0.98 V(vs RHE),the half-wave potential was increased from 0.88 V to 0.91 V,and the limiting current density was increased from 5.58 mA/cm2 to 6.00mA/cm2.In addition,the CoNi/CNFs showed excellent stability,with a current retention rate of 94%after 20000 seconds of timed testing.The steric inhibition of thiourea can effectively refine the CoNi alloy particles in the carbon nanofibers,providing more active sites for electrocatalytic reaction.The improvement of graphitization degree enhances the charge transfer rate of CoNi/CNFs,which improves the electrocatalytic performance of CoNi/CNFs.(3)The effects of internal axial propelling rate(1 mm/h,1.5 mm/h,3.0 mm/h)on the microstructure and electrocatalytic performance of CoNi/CNFs were studied.The CoNi/CNFs composite electrode with the gradient structure of CoNi can be obtained by adjusting the inner axis propulsion rate.With the increase of the internal axial pushing rate,the distribution of the CoNi alloy on the carbon fibers tends to be on the surface.When the internal axial pushing rate is 1.5 mm/h,the distribution of the CoNi alloy on the carbon fibers is the most uniform.The electrocatalytic performance is the best,showing the initial potential of 0.99 V,the half-wave potential of 0.92 V,and the limit current density of 6.31 mA/cm2.At the same time,the current retention rate can reach 95.2%after 20000 s timing test,and the stability is excellent.