Preparation And Performance Study Of AgCo/N-C Electrocatalyst For Oxygen Reduction By High Gravity Method

Fuel cells have become one of the most eye-catching new energy supply technologies in recent years,due to their high efficiency,energy conservation,and environmental friendliness.However,the oxygen reduction reaction,as the cathode reaction of fuel cells,has a complex reaction mechanism and slow kinetic characteristics.Therefore,it is necessary to develop highly active ORR catalysts.Currently,precious metal Pt-based catalysts have become the main catalysts for fuel cells,whereas the high cost and susceptibility to methanol poisoning make them unable to be widely used.The non-noble metal catalysts-transition metal nitrogen carbon（M-N-C）have attracted widespread attention from researchers,owing to its good ORR catalytic activity.In this paper,we prepare Co/N-C and Ag Co/N-C catalysts with good ORR catalytic activity and stability via high-gravity technology,which can uniformly load transition metals Co and Ag on nitrogen doped carbon（N-C）materials.The micro morphology and structure of the catalyst are examined in terms of the effect of the preparation process conditions.And the structure-activity relationship between the catalyst elemental composition,structure and its electrocatalytic activity are explored.The paper’s primary research material and outcomes are as follows:（1）Co（NO₃）₂ 6H₂O as the Co source,Na BH₄ as the reducing agent,and polyvinyl pyrrolidone（PVP）as the modifier and nitrogen source,Co nanoparticles were in-situ loaded on carbon black carriers using high gravity method combined with thermal annealing technology to prepare Co/N-C catalysts.The optimal preparation conditions are studied and determined:the Co loading amount is 3.40 wt%;The reaction time is 15 minutes;The reaction temperature is 0℃;The molar ratio of Na BH₄/Co（NO₃）₂6H₂O is 5:1;The RPB speed is 2000 rpm;The annealing temperature is 500℃.The average particle size of Co nanoparticles in the prepared Co/N-C catalyst is approximately 10.8nm.Co elements exist in the catalyst in the form of Co⁰ and Co²⁺,with some Co elements achieving N doping and forming Co N compounds.In comparison to the traditional kettle stirring technique,the high-gravity technology can reduce reaction time from 1 h to 15 min,while the size of the Co nanoparticles loaded is reduced and the particle size distribution is narrowed by thus generating a more dynamic site and enhancing the catalyst’s quality and activity.The electrochemical test results show that the Co/N-C catalyst has high catalytic activity(E_onset=0.914 V vs.RHE,E_1/2=0.823 V vs.RHE).Stability of excellent magnitude and robust immunity to methanol poisoning were also present.（2）Using the prepared Co/N-C catalyst as the carrier,Ag Co/N-C catalyst was prepared using the high gravity method.The optimal preparation conditions are studied and determined:Ag loading amount is 5.7 wt%;The reaction time is 7 minutes;The mass ratio of Ag NO₃/PVP is 6:1;The solvent p H is 11;The annealing temperature is 170℃.Ag nanoparticles with an average particle size of approximately 5 nm are uniformly distributed on the surface of the carrier and exist in the form of Ag⁰.There is a certain interaction between Co and Ag,which is beneficial for enhancing the adsorption energy of Ag for oxygen.Compared with the kettle stirring method,the high gravity method can better control the particle size of Ag nanoparticles and make them evenly dispersed on the carrier.The electrochemical test results show that the ORR catalytic effect of Ag Co/N-C is significant(E_onset=0.939 V vs.RHE,E_1/2=0.845 V vs.RHE),and the catalyst has good stability.After 50000 s of stability testing,its catalytic activity remains basically unchanged.