Nanosized Fe/Co-N-C Electrocatalysts Derived From Cationic MOFs For Oxygen Reduction:Design,Preparation And ORR Catalysis

In this paper,two cationic MOF metal-organic framework compounds（MOFs）[Co（TTPPDA-4）]（ClO₄）₂.nS（hereinreferredtoCo-TTPPDA-4）and{[Cd（TTPPDA-4）（HCOO）]（ClO₄）·9H₂O·DMF}_n（herein referred to Cd-TTPPDA-4）were synthesized based on the ligand of TTPPDA-4 with four 1,2,4-triazole groups by sol Vothermal method.Nanosized carbon-based electrocatalysts for oxygen reduction reaction（ORR）are prepared by two different methods:（1）Direct high-temperature carbonization of MOF to obtain catalysts Co-N-C and N-C;（2）After introducing[Fe（CN）₆]^3-and[Co（CN）₆]^3-into MOF ca Vity by ion exchange,Fe-Co-N-C,Fe-N-C and Co-N-C catalyst were prepared by high temperature carbonization.The ORR electrocatalytic acti Vity of the nanocatalysts obtained by the abo Ve two methods was studied and correlated with the catalyst morphology,chemical composition and microstructure,the influencing factors of the oxygen reduction catalytic acti Vity of the catalyst were discussed in depth.The specific work was as follows:Co-TTPPDA-4 is a three-dimensional non-interpenetrating structure of a cationic framework based on a linear trinuclear cobalt cluster as a 12-linked inorganic node,with one-dimensional pore contains exchangeable ClO₄^-anion.The catalyst Co-N-C-x（x represents the temperature）was obtained by directly carbonizing Co-TTPPDA-4 at different temperatures.The Co-N-C-900 exhibits the best catalytic acti Vity(E_onset=0.92 V,E_1/2=0.84 V)which is much worse compared with Pt/C(E_onset=1.02 V,E_1/2=0.88 V);Co-TTPPDA-4 is soaked in different concentrations of K₃[Fe（CN）₆]solution to exchange anion[Fe（CN）₆]^3-into the Co-TTPPDA-4 pores,and then carbonized to gi Ve Fe-Co-N-C-x-y（y represents the percentage concentration of K₃[Fe（CN）₆]solution）.The ORR catalytic acti Vity of Fe-Co-N-C-900-2(E_onset=0.97 V,E_1/2=0.86 V)catalyst shows optimal ORR catalytic acti Vity that is close to the reference Pt/C catalyst.Cd-TTPPDA-4 is also a three-dimensional non-interpenetrating structure containing exchange ClO₄^-anions.Cd-TTPPDA-4 was directly carbonized at different temperatures to obtain a catalyst N-C-x（x indicates temperature）,where in N-C-1000(E_onset=1.02 V,E_1/2=0.90 V)shows excellent ORR catalytic acti Vity comparable to Pt/C(E_onset=1.04 V,E_1/2=0.89 V).Cd-TTPPDA-4 was soaked in different concentrations of K₃[Fe（CN）₆]solution for ion exchange,and carbonized to gi Ve Fe-N-C-1000-y（y represents the percentage concentration of K₃[Fe（CN）₆]solution）.Compared with N-C-1000,the catalytic acti Vity of the catalyst Fe-N-C-1000-2(E_onset=1.05 V,E_1/2=0.91 V)obtained under the optimal conditions has been further impro Ved,eVen exceeding the benchmark Pt/C catalyst.In a similar manner,Cd-TTPPDA-4 was soaked in different concentrations of K₃[Co（CN）₆]solution for ion exchange,and carbonized to obtain Co-N-C-1000-z electrocatalysts（z represents the concentration of K₃[Co（CN）₆]solution）.How eVer,the catalytic acti Vity of the catalyst Co-N-C-1000-2(E_onset=1.0 V,E_1/2=0.87 V)was found to be deteriorated with regard to N-C-1000.