Preparation Of Cobalt-based Nanofiber Catalysts By Electrospinning Technology And Their Applications In Water Electrolysis

Due to the non-renewability,traditional fossil energy will be gradually replaced by renewable energy resources in the future.As a most clean and high-efficiency energy,hydrogen stands out from many renewable energy resources.Water electrolysis is considered to be one of the most effective technique for hydrogen production due to its environmentally friendly raw materials and highly pure products.However,the excessive energy loss of the two half-reactions limits the large-scale development of water electrolysis technology.At present,noble-metal Pt,Ru/Ir-based catalysts are considered as the most efficient catalysts for water electrolysis.However,noble-metal catalysts are scarce and expensive.Therefore,it is of vital importance to develop non precious metal catalysts with low price and abundant reserves.Although transition metal sulfides and phosphides have shown good electrocatalytic activities,their poor conductivity have limited further improvement of their catalytic activities.If combined sulfides and phosphides with carbon materials,it can improve not only its conductivity,but also its dispersion,and it is expected to obtain high performance composite catalysts.Based on the above consideration,a series of cobalt-based phosphorus(sulfur)/carbon nanofiber composite catalysts were prepared by electrospinning technology,their applications in water electrolysis were studied,and expected results have been obtained.The thesis includes following three parts:(1)Several Co P/N-doped carbon nanofibers composite catalysts(Co P/N-CNFs)were prepared by carbonization and phosphorization of the precursor prepared by growing ZIF-67 on electrospinning cobalt-doped nanofibers using polyacrylonitrile(PAN)and Co(Ac)₂·4H₂O as raw materials at room temperature.The as-prepared catalysts have exhibited excellent bifunctional activities for HER,OER and water splitting in 1 M KOH.In particular,the optimum catalyst Co P/N-CNFs has shown the highest catalytic activity.When it was employed,159 and 260 m V of overpotential,and63 and 95 m V/dec of Tafel slope have been obtained for HER and OER respectively at10 m A/cm² in alkaline conditions.Also,only 1.54 V of cell voltage is needed to reach a current density of 10 m A/cm² when the catalyst was employed as overall water splitting.(2)Several nickel-cobalt oxysulfide based catalysts Ni Co₂S₄/N-C-1:X were prepared by oxidation and sulfuration of the precursors prepared by uniformly growing Co Ni-MOF on electrospinning Co-Ni-doped nanofibers using polyacrylonitrile(PAN),Ni(Ac)₂·4H₂O and Co(Ac)₂·4H₂O as raw materials at room temperature.The as-prepared catalysts have exhibited excellent activities for HER,OER and water splitting in 1 M KOH.Especially,the optimum Ni Co₂S₄/N-C-1:2 catalyst has exhibited the best catalytic activity.When it was used as catalyst for HER and OER,218 and 318m V of overpotential,and 188 and 164 m V/dec of Tafel slope were obtained at 10m A/cm²,respectively.As for water splitting,1.56 V of cell voltage is needed to reach a current density of 10 m A/cm².(3)A series of Co/Co P/N-doped carbon nanofibers(Co/Co P/N-CNFs)composites were prepared by carbonization and phosphorization of the precursors prepared by hydrothermally growing Co(CO₃)_0.5OH·0.11H₂O on electrospinning Co-doped nano fibers using polyacrylonitrile(PAN)and Co(Ac)₂·4H₂O as raw materials.The as-prepared catalysts have exhibited excellent activities for HER,OER and water splitting in 1 M KOH.When the optimum Co/Co P/N-CNFs-7-350 catalyst was employed,177 and 304 m V of overpotential,81 and 96 m V/dec of Tafel slope,and 1.58V of cell voltage were obtained for HER,OER and water splitting at 10 m A/cm²,respectively.The research results have shown that combination of transition metal phosphide(sulfide)compound with nitrogen-doped carbon fiber is an important method to improve its conductivity,dispersion,and thus the catalytic activity.The electrospinning technology is a facile and controllable method to prepare one-dimensional carbon fiber in large scale.These conclusions can be used as an important reference for the development and large-scale preparation of high-performance transition metal phosphorus(sulfide)compound/nitrogen-doped carbon composite catalysts.