A Template-mediated Reaction Strategy For The Synthesis Of MOFs-based Nanoarray Architectures For Electrocatalytic Water Splitting

Water electrolysis to produce high-purity hydrogen is an efficient electrochemical conversion process to store and utilize renewable energy.The adjustment of the material internal structure and the construction of unique and controllable morphology are equally important considerations for improving the catalytic activity of HER and OER.Compared with various electrocatalysts,metal organic framework（MOF）has been widely studied due to their internal specific surface area and orderly adjustable porous structure.However,there are still massive gaps in the construction of MOFs-based hierarchical micro/nanoarrays on conductive substrate due to the more difficult binding with inorganic substances.The works mainly focus on the classical MOFs with relatively mild synthesis conditions,such as ZIF-8,ZIF-67,Uio-66,HKUST,MIL,etc.For most MOFs,their reference value is limited.In view of this situation,this paper carries on the following research:1.Solvothermal reactions of Co（NO₃）₂·6H₂O,3-amino-1,2,4-triazole,and 1,2,4,5-benzenetetracarboxylic acid afforded a Co-MOF.Furthermore,a unique metal-organic-framework-based pine-needle-like nanocluster hierarchical architecture has been rationally designed and prepared on a nickel foam skeleton via a simple solvothermal method based on the Co（OH）F intermediate and directly adopted as an optimum bifunctional electrocatalyst for overall water splitting.The optimal catalyst is obtained by adjusting the ratio of metal salt and Co（OH）F.In 1.0 M KOH solution,the overpotential for OER to achieve the current density of 50 m A cm^-2 is only 266 m V,and for HER the overpotential is 115 m V at 10 m A cm^-2.At the same time,the catalyst exhibited excellent stability during the OER process,and the overpotential was only increasing about 9.4% after reacting for 100 h at a current density of 20m A cm^-2.In addition,the cell voltage of the electrolytic cell assembled by bifunctional Co-MOF/NF at a current density of 10 m A cm^-2 is only 1.55 V.This excellent catalytic performance is mainly due to the unique pine needle-like nanocluster structure,which has dense and accessibility catalytic active sites,increased specific surface area,and the interaction between organic ligands and cobalt ion centers to promote the reversible chemisorption of oxygen species.After the OER stability test,further SEM,TEM,and XPS analysis showed that the formation of Co₃O₄ and the loose internal structure within the catalyst,and the good maintenance of morphology of the catalyst are the main reasons for the stable and high catalytic activity.This work expands the application of MOFs in the field of electrocatalysis.2.The Co（OH）F-ZIF67/NF composites were prepared by a solvothermal method using the Co（OH）F hierarchical nanosheets as self-sacrificing templates.The growth process of ZIF-67in different solvents and its influence on the catalytic performance of OER were also discussed.Under the condition of water as the solvent,benefit to the unique coupling structure between Co（OH）F and ZIF-67,and the good maintenance of morphology during the reaction process,the optimal catalyst reveals excellent OER catalytic activity by adjusting the reaction temperature,reactants concentration and the reaction time.With the current density of 10 m A cm^-2 in an alkaline medium,the overpotential is only 241 m V.Meanwhile,the catalyst with high catalytic stability and kinetic characteristics for OER.The Tafel slope is 65 m V dec^-1,and the catalytic can still be maintained at 20 m A cm^-2 current density for 20 h.