Synthesis Of Co-LDHs And CoP Electrocatalysts For Their Catalytic Performance

Metal-organic frameworks（MOFs）,a type of emerging organic-inorganic materials with tunable components and porous structures,which are excellent precursors for carbon-/metal-based inorganic materials.In order to establish a bridge between the MOFs and its corresponding inorganic materials,and provide a solid foundation for the large-scale application of materials,this paper selected cobalt zeolitic imidazolate framework material（ZIF-67）and cobalt layered double hydroxides（Co-LDHs）as a model to explore,develop a simple,low-cost,environmentally-friendly strategy to selectively prepare ZIF-67 and Co-LDHs.On this basis,use Co-LDHs as the precursor templates to prepare hydrogen evolution electrocatalyst cobalt phosphide（CoP）,and its electrocatalytic properties in acid and alkaline solutions were studied.The specific research contents include the following two aspects.（1）The classical methanol synthesis system of ZIF-67 was selected.ZIF-67,Co-LDHs and their composite materials were designed and synthesized by adjusting the concentration and molar ratio of cobalt nitrate and 2-methylimidazole in the reaction system.Further explore the changing trend of product at different temperatures,and establish an intuitive“phase diagram”.ZIF-67 nanocrystals are favorably produced at low concentration of cobalt nitrate and 2-methylimidazole or low molar ratio of Co（NO₃）₂/Hmim.Conversely,Co-LDHs are easily formed.The synthetic strategy was further successfully expanded to bimetallic Zn and Co systems,and similar trends were observed.At the same time,Co-LDHs synthesized using this strategy demonstrated similar or better catalytic performance than prepared Co-LDHs using other synthetic methods,further demonstrating the reliability of the synthesis strategy.（2）Using Co-LDHs as precursors,cobalt phosphide assembled with sheets was prepared by low temperature phosphating,and the catalytic hydrogen production performance in acid and alkali solutions was further researched.Lamellar CoP has the best hydrogen evolution catalytic activity in acid and alkali solution.In 0.5M H₂SO₄,when the current density is 10mA cm^-2,the hydrogen evolution overpotential is only 115 mV,and the corresponding Tafel slope is 47.3 mV dec^-1.In 1M KOH,when the current density is 10 mA cm^-2,the overpotential is 125 mV,and the corresponding Tafel slope is 48.1 mV dec^-1.