Preparation Of Fe-based Single-atom And Nanoclusters Catalysts Supported On Carbon For Electrochemical Oxygen Reduction

Proton exchange membrane fuel cells?PEMFCs?and metal-air batteries with high energy density,low-cost and zero-emission of pollutant have been considered as promising devices to alleviate the energy crisis and environmental problem.Small-size metal nanoclusters,single-atom catalysts?SACs?supported on highly conductive carbon materials are regarded as promising candidates for Pt catalysts towards the PEMFC core reaction?oxygen reduction reaction?,due to their excellent catalytic performance,well-defined structure and low metal dosage.Among them,the transition metals are the focus of attention.The successful preparation of small-size nanoclusters and SACs with high-loading are the prerequisite of the practical application.However,the atoms prone to agglomerate into particles due to the surface chemical activity of metal atoms increases dramatically at the atom scale.Therefore,it is necessary to design the reasonable strategy to improving the metal loading,reducing metal size and ultimately optimize the catalytic performance.Based on improving the dispersion of metal species and guaranteeing the metal isolated state.We prepared high-loading Fe-SACs and small-size FeMn bimetallic catalysts via effective ligands and high surface area doped carbon materials strategy.The detail contents of this work are as follows:?1?High-loading?7.5 wt%?Fe single-atomic catalysts were successful prepared via a one-step metal complex with carbon-assisted pyrolysis process,which using high specific surface area N doped carbon materials?NPC?as dispersion substrates,o-phenylenediamine??-PD?as ligand,melamine as N sources and Fe?NO₃?₃?9H₂O as metal precursor,respectively.During this procedure,NPC offers the guarantee of high dispersion of metal complexes.Meanwhile,?-PD can easily coordinate to transition metals to avoid contact between the metal atoms.Besides,?-PD is also employed as additional substrates sources under metallic catalytic effect at high temperature.The chemical chelation and physical isolation are essential to synthesis high-loading Fe-SACs.The optimized 250Fe-SA/NPC-800 catalyst exhibits excellent ORR performance in alkaline electrolytes,including a positive onset potential?0.970 V vs.RHE?and half-wave potential?0.850 V vs.RHE?,which comparable to that of Pt/C.Meanwhile,it manifests remarkable electrochemical stability.?2?Small-size F-FeMn/NC bimetallic nanocluster catalysts were successful fabricated via a one-step pyrolysis process,which using high F-127,high specific surface area N-doped carbon materials?NC?as mesopore soft-template and dispersion substrates,respectively.The best-performing F-FeMn/NC-3 catalyst with a large BET surface area of 413.6 m² g^-1,delivers excellent oxygen reduction reaction activity with half-wave potential of 0.867 V?vs.RHE?in 0.1 M KOH,73,25 and 59 m V more positive than that of F-Fe/NC,F-Mn/NC and 40 wt%Pt/C,respectively.Furthermore,it provides respectable stability during long-time test.