Synthesis Of ZIFs-derived Composite Nanomaterials And Their Electrocatalytic Properties For Oxygen Reduction

Proton exchange membrane fuel cells(PEMFCs)plays an important role in conversion and storage of renewable energy.However,kinetically-sluggish oxygen reduction reaction(ORR)at the cathode may unfavorably damage the performance of PEMFCs,thus restricting their commercialization.Pt is considered as one of the most active ORR catalysts,but its practical application is limited by the scarcity,high cost,and poor durability.Consequently,developing low-Pt and Pt-free catalysts as low-cost alternatives should be essential to support high-performance ORR catalysis in the longer term.On this basis,we propose novel designs for N-doped carbon(NC)-coated Pt-based ternary alloy(Pt-CoZn@NC)and 2D leaf-like Fe-NC catalysts,which combine with the merits of high porosity,nitrogen self-doping and tunable active sites towards ZIFs-derived materials.The main research contents are listed as follows:(1)Using Pt@CoZn-ZIF as precursors,the hybrid catalyst consisting of NC-coated Pt-CoZn ternary alloy nanoparticles(denoted as Pt-CoZn@NC)were successfully synthesized via a facile pyrolsis route.Through systematically adjusting the pyrolysis temperatures and loading amount of Pt,the best catalyst Pt-CoZn@NC-800-10%exhibited excellent activity and stability,with a half-wave potential of 0.917 V and only 1 mV loss after 5,000 cycles during accelerated durability test.Besides,both of mass activity and specific activity are superior to commercial Pt/C catalyst and binary alloy hybrid catalysts(PtCo@NC-800-10%and PtZn@NC-800-10%).This Pt-CoZn@NC ternary-alloy hybrid catalyst shows significant advantages in ORR electrocatalysis,which can be attributed to the electron transfer between Pt,Co,and Zn,as well as the accessibility of active sites given by the NC structures.(2)A kind of Pt-free catalysts,i.e.2D Fe-NC catalysts with 2D leaf-like morphology were synthesized via stepwise pyrolysis with ammonium ferric citrate modified Zn-ZIF-L as precursors.By optimizing Fe content in the precursors,the Fe-NC-1%catalyst was found to exhibit the outstanding ORR performances in both acidic and alkaline electrolytes.Especially in alkalic ORR,the half-wave potential(E1/2)of 0.897 V,kinetic current density(j0.85v)of 26.70 mA·cm-2 and durability(ΔE1/2=5 mV)after 5,000 cycles all were better than those of commercial Pt/C catalyst.The significant enhanced ORR performances of Fe-NC-1%are mainly attributed to the large specific surface area with hierarchical porosity,high graphitization degree,and abundant N-containing active species.