Study On Electrocatalytic Performance Of Transition Metal Sulfides

With the rapid development of global economy,the demand for energy is increasing,and the pollution caused by the consumption of fossil fules has already affected people’s normal life.Thus,more and more researchers are focusing on the development of clean and renewable energy alternatives.At present,hydrogen energy,a sustainable green energy source,has attracted extensive attention owing to its high energy density and pollution-free.Hydrogen produced from electrocatalytic water splitting is widely regarded as a safe and sustainable technology.Electrocatalytic water splitting includes two half reactions:the anodic oxygen evolution reaction（OER）and the cathodic hydrogen evolution reaction（HER）.However,the low catalytic performance of this reaction is mainly attributed to the inevitable overpotential.Therefore,people need to find inexpensive and abundant materials to boost the catalytic efficiency of this reaction.The transition metal materials have become a research hotspot in the field of electrocatalytic water splitting due to their advantages of abundant electron orbitals and multivalent activity states.Cu,Co and Ni based sulfides,phosphides and oxides show excellent performance in electrocatalytic water splitting.Based on the above discussion,this thesis mainly aims to design and synthetize self-supported transition metal（Cu,Co,Ni）sulfides on porous Cu or Ni foam for electrocatalytic water splitting.The obtained samples were characterized by XRD,SEM,TEM,XPS,LAMER and ICP-OES,et al.This thesis includes three chapters:The electrodeposition method was used to grow Co₉S₈-Cu S materials with nanosheet morphology on the porous Cu foam by using cobalt nitrate and copper nitrate as the cobalt and copper sources.Co₉S₈-Cu S materials show excellent OER catalytic activity in 1 M KOH solution,which leads to a low overpotential of 370 m V at the current density of 50 m A cm^-2,along with low Tafel slope of 108 m V dec^-1.The catalytic activity is superior to those of most other reported mono-metal sulfides.The outstanding activity can be attributed to its large surface area and adundant catalytic active site,as well as the strong synergistic effect between Co₉S₈ and Cu S.Co₉S₈@Ni₂S₃/NF with nanosheet morphology was obtained via a facile hydrolysis-etching technique,followed by vulcanization process by using Co-MOF as the precursor.Co₉S₈@Ni₂S₃/NF exhibits an excellent OER activity,which shows the lowest overpotentials of230 m V and 280 m V to reach current densities of 50 m A cm^-2and 100 m A cm^-2 with small Tafel slope of 62 m V dec^-1.Co₉S₈@Ni₂S₃/NF exhibits an HER activity with a low overpotential of 129m V to achieve the current density of 100 m A cm^-2,which is much higher than Co（OH）₂@Ni（OH）₂/NF counterpart.The remarkable activity can be ascribed to its large catalytic area and more active sites.Paintbrush-like Co-Cu₃P/CF was synthesized by a simple three-step cation exchange-hydrothermal-phosphorization method.The OER and HER activity of Co-Cu₃P/CF were tested in 1 M NaOH solution.The Co-Cu₃P/CF electrode exhibited outstanding electrocatalytic performance toward hydrogen and oxygen evolution with a specific current density of50 m A cm^-2 being achieved at small overpotentials of 250 and 270 m V,respectively.Furthermore,we assembled overall water splitting cell by using the optimized Co-Cu₃P/CF as both cathode and anode catalysts.The potential to reach a current density of 10 m A cm^-2 in 1 M KOH is1.55 V.The excellent electrocatalytic performance of Co-Cu₃P/CF can be attributed to its paintbrush-like hierarchical architecture,which provides a large number of active sites and speeds up the electrolyte penetration.