Synthesis And Electrocatalytic Properties Of MOF-Derived Iron-based Composites

Developing renewable and clean energy is an effective strategy to address the current environmental challenges and energy crisis caused by the overuse of fossil fules.Therefore,related energy conversion and storage technologies?such as water splitting devices and metal-air batteries?have become one of the most popular research fields.The oxygen reduction reaction?ORR?,hydrogen evolution reaction?HER?and oxygen evolution reaction?OER?are curial electrochemical reaction in the renewable energy conversion and storage technologies.At present,noble metal-based catalysts are highly efficient for these reactions,specifically Pt for HER and ORR,Ru O₂ and Ir O₂ for OER.However,the high cost,scarcity and instability severely limites their widespread applications.Hence,the development of highly efficient and durable non-noble electrocatalysts plays an important role in energy conversion and storage.In recently years,the porous carbon composites coating iron species have attracted extensive attention due to their unique structure and excellent performance.Metal-organic frameworks?MOFs?have been selected as self-sacrificed template/precursor for the preparation of transition metal iron-supported carbon catalysts due to their good designability and controllable composition.Compared with the traditional ways to prepare the iron-based porous carbon materials,the carbon composites prepared with MOFs as precursors can achieve the uniform distribution of desired elements by directional design of organic ligands and metal components.At the same time,the metal atoms in the MOFs can be converted into metal compounds confined in the carbon matrix,preventing them from further agglomeration and sintering during the catalytic reaction,making it has excellent stability under continuous operation and harsh reaction conditions.Based on the above research background,using the dicyandiamide-based Fe-MOF as precursors,we obtained carbon-based nanocomposites containing different iron species through template etching and heteroatom doping under high-temperature calcination.The structure and composition of the composites were characterized by a series of characterization methods,the electrocatalytic performance of prepared composites were studied in detail.The specific research contents are as follows:?1?The 3DOM Fe?dca?₂pyz was prepared by adding the polystyrene microsphere as porogens during the synthesis of Fe?dca?₂pyz.A hierarchically three-dimensional ordered macroporous N-doped carbon framework encapsulating iron and iron-nitrogen alloy nanoparticles?3DOM Fe/Fe-NA@NC?was obtained by the direct pyrolysis of single-source 3DOM Fe?dca?₂pyz under nitrogen atmosphere.Experimental results indicate that the catalyst prepared at 800°C?3DOM Fe/Fe-NA@NC?has excellent ORR performance under alkaline conditions,with the half-wave potential of 0.88 V,meanwhile,it shows better stability and methanol tolerance.In addition,we investigated its performance of the Zn-air battery with the3DOM Fe/Fe-NA@NC-800 as the cathode material.?2?By adding triphenyl phosphorus during the calcination of Fe?dca?₂pyz,the material with N and P co-doped carbon matrix encapsulating iron phosphide nanoparticles was obtained by one-step phosphation?Fe_xP@NPC?.XPS and EDS proved that phpsphorus atoms were successfully doped into the carbon matrix.Due to the introduction of phosphorus atoms and the generation of iron phosphide active species,the prepared composite materials have multifunctional catalytic activity.The results indicate that the material calcined at 800°C?Fe_xP@NPC-800?has the best catalytic performance.The HER and OER overpotentials are 218 m V and 382 m V to deliver a current density of 10 m A cm^-2 in 1 M KOH solution,and the half-wave potential is 0.86 V for ORR.Because of its excellent oxygen catalytic activity,the performance of Zn-air battery with the material of Fe_xP@NPC was studied.