Controllable Synthesis Of Carbon/Transition Metal Chalcogenide Hybrids For Multifunctional Electrocatalysis

Energy without carbon footprints has become a significant concern in the modern era.Electrocatalytic water splitting has been considered a vital candidate for obtaining clean hydrogen fuel.Developing a cost-effective and highly abundant catalyst for overall water splitting is highly desirable.Noble metals(Pt,Ir and Ru)have been proven to be the best electrocatalysts to date.However,the scarcity of these noble metals highly hampered their application on a commercial scale.Therefore,it is essential to design an earth-abundant electrocatalyst that requires low overpotential with a better electronic structure.The main contents are as follows.(1)1D nitrogen-doped carbon coated ternary NiCo2O4 nanorods(NiCo2O4@NC)derived from metal-organic frameworks(MOFs),which display low overpotential(η≈1296 mV@10 mA cm-2),small Tafel slope(53 mV dec-1)and excellent durability for OER in alkaline medium,which is higher than the commercially available Ir/C electrocatalyst(η≈350 mV@10 mA cm-2).Such higher electrochemical properties are primarily attributed to the high electrochemical surface area,the synergistic effect from chemical compositions and unique mesoporous architecture having support of nitrogen-doped carbon species.The proposed strategy for controlled design and finetuning of MOFs derived functional materials provides projections for producing remarkably active and stable electrocatalysts in electrochemical energy devices.This portion of the dissertation presents a meaningful approach to understanding the effect of morphological engineering on electrocatalytic OER activity.(2)A feasible approach to fabricate a catalyst based on phase-separated heterointerfaces in which heterostructured NiSe2 and FeSe2 are supported on reduced graphene oxide composite(NiSe2/FeSe2/rGO),that may improve the intrinsic properties of materials.The as-prepared catalyst shows excellent oxygen evolution reaction(OER)(260 mA cm-2),hydrogen evolution reaction(HER)(101@10 mA cm-2)and total water splitting(1.57 V@10 mA cm-2)activities in alkaline solution.The NiSe2/FeSe2/rGO catalyst also exhibits fast charge transfer ability,longterm stability,and large electrochemically active surface area.The multi-metal active sites generate a remarkable synergistic effect and carbon channels also support the electron transmission during water splitting process.(3)Adding urea into water not only produces energy-saving hydrogen but also treat urea-rich wastewater.A feasible strategy to design a metal organic framework derived transition metalbased catalyst(Ni-Co9S8@NC).Taking advantage of optimum Nickel doping the electronic structure of Co9S8 is improved,resulting in the high charge transfer capacity and high electrical conductivity.Moreover,the as prepared catalyst demonstrates UOR at current density of 10 mA cm-2 with overpotential of 1.42 V vs.RHE,HER at 10 mA cm-2 with 107 mV and 1.52 V is required for overall urea electrolysis to achieve current density of 10 mA cm-2.Such efficient electrochemical activities are mainly attributed to optimal nickel incorporation and fine support of carbon channels.This part of thesis offers a significant approach to design an efficient and costeffective electrocatalyst to obtain H2 fuel.