Research On Preparation And Performances Of Nanostructured Cobalt-based Electrocatalytic Materials For Hydrogen Evolution Reaction

The over-utilization of traditional fossil fuels makes the world energy crisis and environmental pollution more and more serious.In order to relieve the present situation,it is of great practical significance to develop clean energy with characteristics of rich in source,environmentally friendly,efficient and recyclable.Hydrogen energy is regarded as an ideal substitute for traditional fossil fuels because of its high combustion heat value,non-pollution and sustainability.Among many hydrogen generation technologies,water splitting is considered to be a mature and effective way because of simple peration and high purity of hydrogen.At present,exploration of noble metal-free hydrogen evolution catalysts with low price,low overpotential,high current density and good stability has become the key to promote the development of hydrogen generation through water splitting.Cobalt,as a type of transition metal,has attracted much attention because of its abundant reserve on earth.So far,many cobalt-based catalysts have been used in the field of electrocatalysis.Combined with hydrothermal,electrodeposition,high temperature pyrolysis and chemical reduction methods,etc.,four nano-structured cobalt-based catalytic materials have been successfully prepared,and the physical characteristics as well as hydrogen evolution reaction performances have been studied in this thesis.The main research contents are as follows:?1?Melamine has been used as raw material to synthesize multi-layered g-C₃N₄ by high temperature pyrolysis.Using g-C₃N₄ as substrate along with NaBH₄ and NaH₂PO₂ as reducing agents,ternary Co-B-P/g-C₃N₄ has been successfully synthesized by chemical reduction method.Catalytic performances towards hydrogen evolution reaction of the catalysts prepared with different molar ratios of NaBH₄ to NaH₂PO₂ have also been discussed.The results show that when the molar ratio of NaBH₄ to NaH₂PO₂ is 7:3,ternary Co-B-P-3/g-C₃N₄ shows larger electrochemical activity surface area,higher catalytic activity and better stability.At the current density of 10 mA cm^-2,ternary Co-B-P-3/g-C₃N₄ needs an overpotential of only 174 mV.In addition,ternary Co-B-P-3/g-C₃N₄ exhibits high catalytic activity even after 24 h of stability test.?2?CoMoO₄ precursor has been synthesized through hydrothermal method.By high temperature pyrolysis of CoMoO₄ and melamine,Co-Mo₂C/N-C has been in-situ synthesized.The results show that when the mass ratio of CoMoO₄ to melamine is 1:15,as-prepared Co-Mo₂C/N-C-15 shows nanocoral-like appearance assembled from nanoparticles.While CoMoO₃ nanoparticles prepared without melamine exhibit obvious aggregation and the particle size is larger than that of Co-Mo₂C/N-C-15.The electrochemical tests show that when the current density is 10 mA cm^-2,Co-Mo₂C/N-C-15requires an overpotential of 212 mV,which is 140 mV lower than that of CoMoO₃.The high catalytic activity of Co-Mo₂C/N-C-15 is due to the fact that nitrogen-doped carbon,produced by pyrolysis of melamine,effectively disperses Co-Mo₂C nanoparticles and makes the active surface area of Co-Mo₂C larger,leading to increasing number of available active sites and thus promoting the process of hydrogen evolution reaction.?3?Using NaH₂PO₂ as reductant as well as P source,and RGO as substrate,ternary Co-Ni-P/RGO nanospheres have been one-step prepared with different molar ratios of Co²⁺to Ni²⁺by electroless deposition method.The results show that when the molar ratio of Co²⁺to Ni²⁺is 7:3,the catalytic activity of as-prepared ternary Co-Ni-P-4/RGO nanospheres is significantly higher than that of binary Ni-P/RGO or Co-P/RGO.Ternary Co-Ni-P-4/RGO nanospheres exhibit a current density of 10 mA cm^-2 only at an overpotential of 217 mV and high catalytic activity even after 30 h stability test.?4?Based on the special 4f,5d electronic configuration of Sm and three-dimensional porous structure as well as high conductivity of nickel foam,three-dimensional honeycomb-like Sm₂O₃-Ni-Co has been one-step prepared on the frame of nickel foam.The effects of Sm₂O₃content on catalytic performances towards hydrogen evolution reaction have been investigated under alkaline condition.The results show that the addition of Sm₂O₃obviously changes the micro-morphology of Ni-Co film and improves the catalytic activity and stability.To achieve a current density of 10 mA cm^-2,the required overpotential of Sm₂O₃-Ni-Co/NF?prepared under optimal condition?is 276 mV,which decreases by 25 mV than that of unmodified Ni-Co/NF.Besides,Sm₂O₃-Ni-Co/NF exhibits high catalytic activity even after 30 h of stability test.