Design And Construction Of ZIFs-derived Carbon-containing Composites And Their Electrochemical Performance

With the increasing environmental contamination and scarcity of resources,sustainable energy conversation technologies,such as regenerative fuel cells,metal-air batteries,and water splitting devices,are gaining more and more attention.The electrocatalysis processes,including oxygen reduction reaction（ORR）,oxygen evolution reaction（OER）and hydrogen evolution reaction（HER）,directly determine the energy conversion and storage efficiencies of these energy devices.The shortcomings of high-cost,single catalytic activity and poor stability make the noble metal catalysts fail to meet the requirements of these new technologies.Therefore,it is imperative to develop multifunctional electrocatalysts with excellent activity,good stability and low-cost.In this paper,based on the optimization and regulation of morphology,pore structure and active ingredients for zeolite imidazolate frameworks（ZIFs）material,a series of ZIFs-derived carbon nanocomposites with rational morphology and hierarchical porosity as well as multiple active ingredients were designed and applied to electrocatalytic reactions（ORR,OER,HER）.The main results are summarized as follows:（1）The morphology,pore structure and composition of ZIF-8 derived carbon material are successfully tuned by the co-pyrolysis of potassium ferricyanide and ZIF-8.Potassium ferricyanide is employed as a multifunctional iron precursor,which not only can generate Fe-N_x sites and Fe/Fe₃C nanocrystal,but also transform ZIF-8derived carbon material from 3D polyhedron into flake-like nanostructure,as well as induce abundant mesopores.Benefitting from the flake-like nanostructure,hierarchically pore structure and the synergistic effect of Fe-based active sites,the optimized Fe-N-C material displays a comparable ORR activity to Pt/C in alkaline media as well as a better long-term stability and methanol tolerance,and also exhibits high specific capacitance and outstanding rate capability.（2）Using the mild redox reaction between Fe（Ⅱ）-doped ZIF-8（Fe（Ⅱ）ZIF）and cobalt（Ⅲ）acetylacetonate,the partial fragmentation of nanoparticle and cobalt-doping for Fe（Ⅱ）ZIF are achieved,which can reduce the nanosize of pyrolysis products and also increase the ratio of mesopores,as well as generate bimetal-N active sites.The as-obtained FeCo-NC-850 possesses an excellent bifunctional oxygen catalytic activity with a low reversible potential gap（ΔE）of 0.81 V for ORR/OER.（3）A novel ternary metal-based ZIFs with hollow structure and Ru-doping are synthesized using the combination of tannic acid etching and ion-exchange method.TheCo-Ru bimetal electrocatalyst is prepared via carbonization and the subsequent controllable air-annealing.This strategy successfully integrates Co-Ru bimetal active ingredients with multiple valence state into N-doped hollow carbon matrix,and also induces a Ru-rich surface with abundant oxygen vacancies.The as-prepared CoRu-O/A@HNC-2 catalyst displays a superior trifunctional catalytic activity of ORR/OER/HER in alkaline electrolyte,which endows an ultralow potential gap of0.662 V between OER and ORR in 0.1 M KOH,and the as-fabricated water splitting cell based on the above-mentioned materials only needs a voltage of 1.558 V to achieve the current density of 10 mA·cm^-2 in 1 M KOH.