Study On Preparation,Performance And Mechanism Of Cobalt-Based Catalysts For Oxygen Reduction Reaction

Oxygen reduction reaction?ORR?is one of the vital important processes of the energy conversion devices such as fuel cells?FCs?and metal-air battery?MAB?.However,the reaction process of the ORR is very complicated and has sluggish reaction kinetics.It needs a large number of catalysts to improve the efficiency of the ORR.So far,the Pt is the most popular ORR catalyst for FCs and MAB.But the Pt suffers from the high price,low durability and low poison resistance,which restrict the wild application of the above-mentioned energy conversion devices.Thus,it is urgent to investigate high-activity,good-stability,and low-prices non-noble catalysts to replace the noble catalysts.In this paper,a series of cobalt-based ORR catalysts were designed and prepared.And the paper deeply studied the catalytic activity and performance of the catalysts by combining the physical and electrochemical characterization results.The main research results of the paper are as follows:Firstly,self-standing and binder-free porous N-Co carbon nanofiber?N-Co/CNF?cathodes are prepared for Zinc-air batteries?ZAB?by an in-situ electrospinning/plasma-etching method.The morphology and activity of the prepared electrodes are investigated by several characterization techniques.The prepared specimens exhibit a multi-layered CNF structure,and a new CoN compound is produced after plasma-etching treatment.The N-Co/CNF-300-10cathode demonstrates excellent electrocatalytic performance toward ORR,with an onset potential?Eonset?and half-wave potential(E_1/2)of 0.995 and 0.853 V?vs.RHE?,respectively,which is comparable to that of 20%Pt/C.The N-Co/CNF-300-10 cathode acting as a self-standing electrode for ZAB exhibits a discharge maximum power density as high as 229mW cm^-22 and a specific capacity of 659.6 mAh g_Zn^-1,which are much higher than those of the commercial catalysts,benefiting from the self-standing porous structure,N-doping,more defects and active sites induced by plasma-etching.In this paper,a core-shell cobalt nanoparticles-embedded honeysuckle-like N-doped carbon nanotube?Co@NCNT?catalyst is synthesized through programmed carbonization with the plasma etching.The Co@NCNT displays a uniform core-shell honeysuckle-like nanostructure and exhibits comparable ORR performance to the commercial 20%Pt/C.The Eonset and E_1/2/2 of the Co@NCNT are 1.030 V and 0.872 V?vs.RHE?,and the potential decay in E_1/2/2 is only 9 mV after 5,000 cycles accelerated durability test.Moreover,a ZAB with Co@NCNT cathode catalyst exhibits a peak power density of 162.5 mW cm^-22 and high rate capability as well as excellent durability.The excellent performance of the Co@NCNT is mainly attributed to the synergistic effect of unique core-shell nanostructure,more defects and active sites as well as more tiny rifts in the carbon-shell induced by the plasma etching.Finally,an N-doped carbon nanotubes-encased Co₂Ni₁ alloy nanoparticles?Co₂Ni₁@NCNT?electrocatalyst is prepared via programmed-pyrolysis combined with plasma etching technology.The characterization results confirm that the Co₂Ni₁@NCNT shows unique space confinement nanostructure,and more defects and N-doping are induced after plasma etching.Benefiting from the unique space confinement,N-doping in carbon and metal,and more defects on the carbon layer surface,the prepared Co₂Ni₁@NCNT exhibits excellent bifunctional oxygen reaction catalytic activity.As demonstrated in electrochemical measurements,the Co₂Ni₁@NCNT exhibits a high E_1/2/2 of 0.866 V?vs.RHE?for ORR and a low overpotential of 349 mV at a current density of 10 mA cm^-22 for OER.Moreover,using the Co₂Ni₁@NCNT as the cathode catalyst,the self-assembled rechargeable ZAB exhibits an excellent peak power density of 171mW cm^-2,and a good charge-discharge performance.