Preparation And Electrocatalytic Properties Of MOF Derived Nanomaterials

The depletion of fossil fuels and environmental pollutions are global challenges in the 21st Century human society.Zinc-air batteries?ZABs?and hydrogen production by water splitting have become energy conversion technologies that can effectively deal with energy problems.At the core of these technologies are oxygen evolution reactions?OER?,oxygen reduction reactions?ORR?and hydrogen evolution reactions?HER?,each combining to satisfy a specific electrochemical application.Metal-Organic Frameworks?MOFs?derived nanomaterials were used as catalysts for various electrochemical reactions due to their adjusted active sites activities and numbers,as well as the robust mechanical nanostructures.This paper aims to develop bifunctional electrocatalysts for MOF derived nanomaterials with high exposure active sites and low price.In this paper,a self-supporting electrocatalytic material?CCVG@CoNC_T?was prepared by inducing the growth of ZIF-67 on the vertical graphene?VG?of carbon cloth surface under the assisted pyrolysis of melamine.The presence of MWCNTs,metallic Co and Co-N_xC sites,as well as in-situ formed Co oxides,will synergistically contribute to the electrocatalytic performance of OER and ORR.Taking advantage of the unique hierarchical nanostructures and the free-standing electrode obtain excellent bifunctional OER and ORR activities.The O₂ reduction peak of CCVG@CoNC₈₀₀ was around 0.866?V vs.RHE for ORR,and the overpotential at current density 10 mA cm^-2is 357 mV for OER,the zinc-air battery assembled by CCVG@CoNC₈₀₀ has a charging and discharging stability of 25 h.In order to further optimize the electrochemical properties of the materials mentioned above,introducing of heteroatoms into crystal lattices has been proved to be an effective approach to enhance the intrinsic activity.Based on this idea,a series of component-controllable CC/CNTs@CoS_xSe_2?1-x?was synthesized by the ZIF-67nanocrystals as the precursor.It is worth noting that the lattice distortion caused by the different radius between Se and S generated polarized electric field for easy adsorption of the intermediate products and boost the electrocatalytic activity.CoS_0.74Se_0.52exhibited that the overpotential for HER and OER are 225 mV and 285 mV to reach the current density of 10 mA cm^-2,respectively.Meanwhile,the as-prepared electrocatalysts could act as both the cathode and the anode in water electrolyzer,showing a cell voltage of 1.74 V to deliver 10 mA cm^-2.Finally,a strategy using ZIF-67 as template is proposed for in situ coupling of CoP and CNTs to obtain the hybrid of CNTs@CoP,and the water splitting voltage was further reduced by using the organic substrates assisted technology.Its unique beaded hierarchical structure can effectively expose active sites while maintaining good conductivity,making it have excellent HER and OER performance.CNTs@CoP exhibited that the overpotential for HER and OER are 169 mV and 321 mV to reach the current density of 10 mA cm^-2,respectively,and the overall water splitting requires1.74 V at 10 mA cm^-2.The catalyst also showed excellent performance of glucose oxidation reaction?GOR?,After GOR was used instead of the OER process,the overall water splitting voltage was reduced to 1.42 V at 10 mA cm^-2.The three MOF-derived electrocatalytic materials prepared by this subject all have excellent bifunctional properties,which provide a new perspective for the design and synthesis of MOF-derived electrocatalytic materials.