Controlled-Synthesis Of Platelet Carbon Nanofibers Supported PtCo Catalysts For Enhanced Kinetics Of Hydrogen Generation

Carbon material is a kind of significantly important support of industrial catalysts.As a one-dimensional carbon material,platelet carbon nanofiber(p-CNF),consisting of ordered arrangement of graphene sheets,possesses not only tunable structural,chemical and electronic properties,but also edge-rich planes compared to the traditional carbon materials.Such unique characteristics are beneficial for well fabrication and optimization of highly efficient yet stable supported metal nanocatalysts.In this thesis,a catalytic chemical vaper deposition(CCVD)method is employed to synthesize p-CNF via Fe catalyzed CO disproportionation.The regulation of the p-CNF microstructures is achieved by changing the Fe catalyst structures and process parameters.Over the optimal p-CNF,a series of PtCo catalysts are prepared,and then microstructural and electronic properties are correlated with the hydrogen generation activity,kinetics behavior as well as stability for hydrogen evolution reaction(HER)and ammonia borane hydrolysis,aiming to clarify the underlying nature of the catalyst structure-performance relations.Finally,the highly efficient and stable PtCo/p-CNF catalysts are developed.The main findings are shown below:(1)The regulation of p-CNF microstructures is revealed by changing the Fe catalyst structures and the growth temperature.It is found that the p-CNF with the higher specific surface area and graphitization degree is synthesized via the catalytic CO disproportionation at 600? over Fe3O4 precursor prepared by a colloid method.Subsequently,a series of PtCo/p-CNF catalysts with different Pt/Co ratios are prepared for ammonia borane hydrolysis.Combining various characterizations with kinetics analysis indicates that the catalyst with the Pt/Co ratio of 1/5 exhibits an outstanding synergistic effect for showing the lowest activation energy and the highest hydrogen generation activitiy.Meanwhile,the catalyst also shows excellent durability owing to the effective anchoring of highly dispersed PtCo alloy nanoparticles by the edge-rich sites of p-CNF.(2)A new method for precise fabrication of Pt-CoO interfaces is developed by employing p-CNF as the support and using atomic layer deposition technology.It is found that the p-CNF can effectively facilitate the transfer of electrons and anchoring of highly dispersed Pt and CoO nanoparticles.Meanwhile,the fabricated Pt-CoO interfaces can significantly regulate the electronic structures of Pt nanoparticles.The as-obtained Pt-CoO/p-CNF catalyst delivers extremely improved HER activity and stability in comparison to the commercial Pt/C catalysts.Specifically,such unique catalyst exhibits a very low overpotential of 26 mV under a current density of 10 mA cm-2.Moreover,the Tafel kinetics analysis demonstrates the change in the dominant HER mechanism from Volmer-Heyrovsky mechanism to Volmer-Tafel mechanism with the increase of the Pt electron binding energy,leading to a great increasement for the HER activity.