Synthesis Of Functional Metal-Organic Frameworks(MOFs) Materials And Electrocatalytic Applications

The design and development of electrochemical catalysts with high efficiency and low consumption is one of the research hotspots in the field of electrochemistry.Metal-organic frameworks?MOFs?have attracted much attention due to their large specific surface area,adjustable composition and structure.However,the applications of MOFs in the field of electrocatalysis are limited by their weak conductivity and poor stability.Therefore,functionalizing MOFs has become one of the important research directions to improve their conductivity and stability,and broaden their applications in the field of electrochemistry.In this paper,ZIF-67,MOF-74 and Co-MOFs were functionalized by composited with carbon fibers and template method to prepared several MOFs-based functional materials,namely,MOFs composite materials and MOFs-derived transition metal based materials,including ZIF-67/carbon fiber composite?ZIF-67/PCF and ZIF-67/SCF?,CuCo coated nitrogen-enriched porous carbon polyhedron?CuCo@NPCP?,bimetal?CoFe,CoCu,CoNi?embedded nitrogen-doped carbon frameworks?CoM?M = Fe,Cu,Ni?-NC?,porous rod-like cobalt-nickel bimetal nitrides?Co_xNi_yN?,and hollow bimetallic carbides/nitrogen-doped carbon nanotube?Co₆Mo₆C₂@NCNT?.These materials modified electrodes were applied to electrochemical sensing,electrochemical water spiltting and oxygen reduction reaction,respectively,and obtained good catalytic performance.The main contents of the paper are as follows:1.Novel ZIF-67@carbon fiber composites were fabricated by a simple stirring method and used to construct electrochemical sensors for nitrobenzene and l-cysteine.In order to explore the influence of carbon fiber structure on the electrocatalytic efficiency of the ZIF-67,different structural carbon fibers?hollow porous carbon fiber?PCF?and solid carbon fiber?SCF??were used for preparing ZIF-67/carbon fiber catalysts.Thanks to excellent hollow structural characteristic of PCF,ZIF-67/PCF possesses more exposed active sites,smaller particle size of ZIF-67,more mass transport channels as well as superior electrocatalytic abilities than ZIF-67/SCF.Furthermore,ZIF-67/PCF?1:1?sample-modified glassy carbon electrode presents a linear range to nitrobenzene that is composed by two line segments,i.e.from 0.3 to 50 ?M with a sensitivity of 454.7 ?A mM^-1and from 50 to 390 ?M with a sensitivity of 132.0 ?A mM^-1,and a low detection limit of 0.16 ?M.It also exhibits a wide linear response to L-cysteine in the range of 5 to 160 ?M and 160 to 1580 ?M with a rapidly response within 1.0 s as well as good stability and anti-interference ability.2.CuCo coated nitrogen-enriched porous carbon polyhedron?CuCo@NPCP?materials were synthesized as a highly sensitive electrochemical luteolin sensor through pyrolysis of Cu-doped ZIF-67.As characterized byX-ray diffraction,scanning electron microscopy,transmission electron microscopy,X-ray photoelectron spectroscopy,N₂ adsorption-desorption isotherms and electrochemical methods,CuCo@NPCP materials possess high specific surface area,3D porous framework,amounts of available active sites,which all contribute to the adsorption and catalysis for luteolin.Meanwhile,vast mesoporous structure of CuCo@NPCP further affords more mass transport channels and enhances the mass transfer capacity.Thanks to above-mentioned characteristics,optimal Cu₁Co₃@NPCP presents superior analytical performance: a wide linear range from 0.2 nM to 2.5 ?M,a ultrahigh sensitivity of 134.57 ?A ?M^-1,a low detection limit of 0.08 nM,as well as satisfactory selectivity,reproducibility,and long-term stability.3.A family of bimetal?CoFe,CoCu,CoNi?embedded nitrogen-doped carbon frameworks?CoM?M = Fe,Cu,Ni?-NC?were synthesized through a facile and simple thermal conversion strategy of metal-doped zeolitic imidazolate frameworks?CoM-ZIF-67?.CoM?M = Fe,Cu,Ni?-NC were used as bifunctional electrocatalysts for water splitting.Thanks to collaborative superiorities of abundant M-N-C species,modulation action of secondary metal,template effect of MOFs and unique porous structure,bimetal embedded nitrogen-doped carbon frameworks materials manifest good catalytic activity toward oxygen evolution reaction?OER?and hydrogen evolution reaction?HER?in alkaline solution.Especially,after modulating the species and molar ratio of metal sources,optimal Co_0.75Fe_0.25nitrogen-doped carbon framework catalyst just requires a low overpotential of 303 mV to achieve 10 mA cm^-2with a low Tafel slope(39.49 mV dec^-1)for OER,which even surpasses that of commercial RuO₂.In addition,the optimal catalyst can function as an efficient bifunctional electrocatalyst for overall water splitting with satisfying activity and stability.4.We design and synthesize porous rod-like cobalt-nickel bimetal nitrides?Co_xNi_yN?as high-efficiency HER electrocatalysts in wide pH range through nitridation from bimetal-organic framework?MOF-74?precursor.Thanks to collaborative superiorities of high surface areas,abundant mesporous structure,perfect metal element dispersion and electron modulation effect,the as-prepared Co_xNi_yN possess the superior catalytic ability toward HER at all pH values.In particular,the optimal Co₂Ni₁N requires overpotentials of 102.6,92.0 and 152.8 mV to afford a current density of 10 mA cm^-2in alkaline,acidic and neutral solution,respectively.In addition,it also presents excellent stability under different pH conditions.5.A novel hollow bimetallic carbides/nitrogen-doped carbon nanotube?Co₆Mo₆C₂@NCNT?was synthesized as multifunctional electrocatalysts for oxygen reduction reaction?ORR?,HER and OER through the simple pyrolysis of polypyrrole-supported MOFs composite.Remarkable characteristics of the large surface area,unique porous structure,rich active sites and synergistic effect between Co₆Mo₆C₂andNCNT arouse high catalytic efficiency.Notably,the Co₆Mo₆C₂@NCNT presents excellent ORR catalytic activity(a high half-wave potential of 0.875 V and diffusion-limited current density of 6.22 mA cm^-2)via a four-electron pathway,together with outstanding stability and methanol tolerance over commercial Pt/C.The composite also exhibits superior HER performance,delivering a low overpotential of 122.14 mV at current density of 10 mA cm^-2,as well as good catalytic performance for OER.