Study On ZIFs-derived Double Transition Metal Electrocatalyst For Oxygen Reduction

With the surge of energy demand and the intensification of environmental crisis,high-efficiency and clean polymer electrolyte membrane fuel cells（PEMFCs）are considered to be one of the energy technologies with great development potential.However,due to the sluggish kinetic process of cathodic Oxygen Reduction Reaction（ORR）,a large number of commercial Pt/C electrocatalysts are used to accelerate the reaction process.Nevertheless,the limited reserves and high prices of platinum seriously impedes the large-scale application and development of PEMFCs.Therefore,the design of efficient and affordable non-precious metal electrocatalysts has become an important way to promote its development.The primary aim of this thesis is to synthesize non-precious metal electrocatalysts with superb activity,remarkable durability,and low price.Based on the precursors derived from zeolitic imidazolate frameworks（ZIFs）,high-performance electrocatalysts involving dual transition metal active sites are prepared.Our main works and results are described as follows:（1）The low-cost iron porphyrin and cobalt porphyrin containing catalytic active sites for ORR are selected as the metal source.The strategy of co-modification of ZIF-8 with two porphyrins appears to be realized by the coordination between porphyrin molecules and skeletal zinc ions.And the novel Fe CoP@ZIF-8-900 electrocatalyst is prepared by subsequent pyrolysis.It displays an improved ORR activity with the half wave potential(E_1/2)of 0.913 V（vs.RHE）and 0.803 V（vs.RHE）in alkaline and acidic solutions,respectively,comparable to that of commercial Pt/C and surpassing most of the current non-noble metal electrocatalysts.Moreover,it also exhibits an excellent durability with the decrease of E_1/2 of only 16 m V and 30m V after 3000 cycles of cyclic voltammetry（CV）scanning in alkaline and acidic solutions,respectively,relative to that of Pt/C.（2）ZIF-11 is synthesized by partial replacement of zinc ions with manganese ions,where the doping of manganese ions realizes the modification of ZIF-11.At the same time,the cobalt phthalocyanine,which is extremely inexpensive and contains catalytic active sites for ORR,is introduced to coordinate with metal ions to achieve the further modification of ZIF-11.The CoPc@Mn-ZIF-11-950 electrocatalyst obtained after pyrolysis holds an E_1/2 of 0.864 V（vs.RHE）in alkaline media,close to that of Pt/C.In addition,it also demonstrates an outstanding durability with the decrease of E_1/2 of only 15 m V after 3000 cycles of CV scanning in alkaline solution,which is much smaller than Pt/C.