Boron-doped Conductive Metal-organic Frameworks For Electrocatalytic Ammonia Synthesis

Due to the advantages of large specific surface area,diversified coordination types and modes,and adjustable morphology,metal-organic frameworks（MOFs）have been widely applied in fileds of gas storage and separation,catalysis,biosensing and biomedicine.Among many MOFs,two-dimensional（2D）conductive d-πconjugated MOFs（c MOFs）demonstrate high-conjugated nanostructures,high hydrophobicity and excellently electrochemical activity,beneficial to the improvement of the electrocatalytic performance.In this work,the heterojunctions of 2D c MOFs and boride nanomaterisl were prepared as electrocatalysts for realzing the electrochemical nitrogen reduction reaction（NRR）.The main content of this thesis is provided as follows:（1）A bimetallicsemiconductorMOFwasparepaedusing2,3,6,7,10,11-hexamethylenebenzene（HITP）as ligand and Co²⁺and Ni²⁺as metal nodes by hydrothermal method[Co_xNi_3-X（HITP）₂].Subsequently,by coupling with with boron nanosheets（BNSs）,a novel Van der Waal heterojunction hybrids[Co_xNi_3-X（HITP）₂/BNSs]was obtained,following by modified by plasma etching,affording plenty of active sites and abundant defects[Co_xNi_3-X（HITP）₂/BNSs-P].The Co_xNi_3-X（HITP）₂/BNSs-P hybrid exhibited the graphene-like structure,excellent electrochemical activity,and effective nitrogen adsorption abilities,as well as high proton transport capability and catalytic activity toward the NRR.Electrochemical tests showed that NH₃yield of Co_xNi_3-X（HITP）₂/BNSs-P was as high as 131.6（±2.8）μg h^-1mg^-1_cat.with Faraday efficiency（FF）of 64.08%.When using Co_xNi_3-X（HITP）₂/BNSs-P as a anode catalyst,the assembled aqueous rechargeable Zn-N₂battery had a peak power density of 2.5 m W cm^-2and an energy density of 240 m W h g_zn^-1,accompanying with the synthesis rate of NH₃of 15.6（±0.8）μg h^-1cm^-2.（2）Based on the above analysis and results,a series of heterojunctions of copper-based MOF[Cu₃（HITP）₂]and hexagonal boron nitride nanosheets（h-BN NSs）were prepared by the hydrothermal method.The graphene-like structure of Cu₃（HITP）₂provided high-speed electronic transmission path due to copper single atom sites,while the electronic distribution of Cu₃（HITP）₂/h-BN cwas adjusted by h-BN.Meanwhile,the prepapred hybrid nanocatalyst greatly promoted increase the NRR ability.The results of electrochemical measurements revealed that the NH₃yield was as high as 142.7（±1.48）μg h^-1mg^-1_cat.with the high Faraday efficiency of 42.52（±0.34）%.The Cu₃（HITP）₂/h-BN-catalyzed Zn-N₂battery illustrated the peak power density of 1.59 m W cm^-2,and the energy density of 123.7 m W h g _Zn^-1,along with the synthesis rate of NH₃of 8.1（±0.3）μg h^-1cm^-2.In summary,in the present work,boron-doped c MOFs were prepared as heterojunction electrocatalyst.Combining the excellent electrochemical activity,large specific surface area,rich active sites,and unsaturated metal coordination caused by B（N）could remarkably facilitate the adsorption and activation of N₂active center and nitrogen activation performance,realizing the NRR with high yield and Faraday efficiency.Further,these developed MOFs-based NRR electrocatalysts showed the promising applications for the assmbeling the aqueous Zn-N₂batteries,leading to the electrochemical synthesis of ammonia along with the external energy supply.Therefore,the present work can supply experimental basis and theoretical reference for the construction of efficient electrocatalysts of the NRR based on MOF-based heterostructures.