Design Of Fe/Heteroatom Co-doped Carbon Electrocatalysts With Highly Dispersed Activated Site For Oxygen Reduction Reaction

Fuel cells convert chemical energy directly into electrical energy showing the advantages of high power density,quick-start ability,and no pollutants generation.Fuel cell is considered to be the most promising energy storage and conversion device in future.However,the high cost of platinum catalysts has greatly hindered the commercialization of fuel cells due to the application of platinum based precious metal to accelerate the slow oxygen reduction reaction（ORR）at the cathode.Thus,it is imperative to develop an inexpensive,high-performance ORR catalyst.Currently,transition metal/heteroatom-doped carbon shows excellent ORR activity and stability in acid electrolytes,and is expected to replace precious metal catalysts.This work is devoted to develop catalyst with high density catalytic active sites and the intrinsic activity of catalytic sites through smart design.Under this premise,Fe/N/C-DT,Fe-N/P/C-850 and catalyst with corresponding similar structure are systematically studied.The specific research work of this article are as follows:1.Silicon dioxide and zinc acetate are used as dual templates to regulate the porous structure of the catalyst,and the iron source ferrocene formaldehyde（Fc-CHO）is incorporated into the molecular chain of polyimide（PI）,which increases the steric hindrance effect of iron atoms.After heat treatment at 900℃and acid etching,a porous catalyst（Fe/N/C-DT）with highly dispersed active sites is successfully prepared.The results show that Fe/N/C-DT displays a high specific surface area(484m² g^-1)and a porous net structure,which is conducive to supporting high-density active sites and fascinating mass transfer efficiency.In 0.1 M KOH,Fe/N/C-DT shows the best ORR activity.Its onset potential and half-wave potential are 1.043 and 0.9 V,respectively.Its activity and electrochemical stability are better than 20%commercial platinum carbon.Fe Cl₂/N/C-DT and Fe SO₄/N/C-DT using FeCl₂ and FeSO₄ as iron sources,respectively,are prepared for comparison,and after DFT theoretical calculation,to further confirm the superiority of Fc-CHO.In addition,the potential difference at the oxygen cathode△E(△E=E_j=10,OER–E_1/2,ORR)is 0.76 V.Fe/N/C-DT can be used as the cathode of a zinc-air battery,showing a higher peak power density(220 m W cm^-2),open circuit voltage（1.451 V）,and a certain charge-discharge performance.2.The characteristics of low boiling point（about 200℃）and decomposition temperature（about 400℃）of ferrocene are innovatively used to synthesis high dispersion iron doped graphite catalyst.Phosphorus and nitrogen-rich porous polyaniline gel（PANi）is used as a precursor during heat treatment.After the ferrocene was volatilized and decomposed,highly dispersed active sites were obtained on the surface of porous carbon.The experimental results show that iron atoms can be“anchored”in porous carbon pores by the complexation of P and N,and the synergistic effect of co-doping P and N can adjust the metal electronic structure and plane charge distribution,which greatly improving ORR catalytic activity.When the heat treatment temperature is 850℃,Fe-N/P/C-850 exhibits the highest ORR activity and electrochemical stability,with an onset potential of 1.06 V and a half-wave potential of 0.87 V.