Self-Assembly Strategy To Construct Carbon Nanocomposites With Tunable Morphology And Structure For High Performance HER Catalysis

The environmental and social problems caused by the excessive consumption of fossil energy have become increasingly prominent Due to its ultra-high energy density,hydrogen energy is considered to be one of the most promising clean energy sources.Electrocatalytic hydrogen evolution reaction(HER)can convert electrical energy into hydrogen energy for storage,while the direct use of water electrolysis to produce hydrogen requires a high overpotential and brings a lot of energy consumption.Electrocatalysts can effectively reduce the overpotential,which is the focus in the development of electrocatalytic hydrogen evolution.The preparation of low-cost,efficient and stable HER catalysts is of great significance for the wide application of electrocatalytic hydrogen evolution technique.In this thesis,carbon nanocomposites with tunable morphology and pore structure are constructed by selfassembly strategy,and their HER catalytic performance is studied.Specifically,using amphiphilic poly(amic acid)(PAA)as building block,nanospheres with uniform size are prepared by self-assembly.The nanospheres can adsorb nickel ions and be calcined in N2 atmosphere to give raspberry-like carbon nanospheres(Ni@R-CSs),which possesses a rough surface with precisely controlled quantity of protrusions.In addition,the Ni@R-CSs are etched to prepare hollow carbon nanospheres(H-CNSs)with rich pore structure inside.Using the above Ni@R-CSs and H-CNSs as supports,ultrafine platinum nanoparticles can be efficiently loaded and exhibit high performance HER catalytsis.The detailed research contents are as follows:(1)The amphiphilic PAA is synthesized by stepwise polymerization,which self-assembles into nanospheres by solvent exchange method.Then the nanospheres are carbonized after in situ adsorption of Ni ions to afford of Ni@R-CSs with thin carbon layer protrusions on the surface.By adjusting the concentration of adsorbed Ni ions,the precise control of the number of protrusions on the Ni@R-CSs surface is achieved.The phase structure,graphitization degree,specific surface area and morphology of carbon nanocomposites are analyzed by XRD,Raman spectroscopy,nitrogen adsorption/desorption experiment,SEM and TEM.HER catalytic performance of catalysts is measured by electrochemical workstation and disk electrode.The results show that the thin carbon layer protrusions of Ni@R-CSs on the surface significantly enhance the graphitization degree and the specific surface area of carbon nanospheres,from 203 to 434 m2 g-1.Ultrafine Pt nanoparticles can be effectively loaded on the surface of Ni@R-CSs,and generate synergistic effect with nickel nanoparticles that promote the charge transfer between Pt and Ni nanoparticles,which achieves a significant improvement in HER catalytic performance.In 1.0 M KOH electrolyte,Pt/Ni@R-CSs can reach a current density of 10 mA cm-2 at ultralow overpotential of 7.7 mV,which is much lower than commercial Pt/C catalyst(40.3 mV)and better than most of previously reported HER electrocatalysts.At overpotential of 150 mV,the mass activity of Pt/Ni@R-CSs is 3.79 A mgPt-1,which is 3.3 times that of commercial Pt/C,showing excellent HER catalytic performance and stability.(2)H-CNS with innerly extending pore structures is fabricated by acid etching of Ni nanoparticles wrapped inside the Ni@R-CSs.The internal hole expansion of the carbon nanosphere is achieved.In the mean time,the removal of Ni nanoparticles expands the application of the catalyst in acidic electrolytes.Ultrafine Pt nanoparticles can be efficiently deposited inside the pores of H-CNS.After secondary calcination,the specific surface area of Pt/H-CNSs is significantly increased to 785 m2 g-1,resulting in a porous structure with opening on the surface.In 0.5 M H2SO4 electrolyte,the overpotential of Pt/HCNSs is only 22.8 mV to achieve a current density of 10 mA cm-2,better than Pt/C(23.5 mV).At overpotential of 150 mV,Pt/H-CNSs has the highest mass activity of 6.38 A mgPt-1,which is 3.7 times that of Pt/C.Pt/H-CNSs not only exhibite high catalytic activity,but also possesse excellent cycling stability.After 5000 CV cycles,its overpotential barely changes.The current density does not attenuate at constant voltage for more than 15 hours.Furthermore,in an alkaline environment,the potential of Pt/H-CNSs is 18.8 mV at a current density of 10 mA cm-2,which is much better than that of commercial Pt/C(40.3 mV).It is indicated that the as-prepared Pt/H-CNSs is an efficient catalyst for electrocatalytic hydrogen evolution in both alkaline and acidic environments.