Design Of Carbon-based Materials And Their Catalytic Applications In Hydrogen Evolution Reaction

Water splitting is the mainpart of contemporary energy conversion and storage engineering.Especially,the cathodic reaction of water electrolysis-hydrogen evolution reaction?HER?is one of the most efficient strategies to produce high purity H₂.Although Pt-based catalysts display superb catalytic ability,the shortage of resources,fancy price and poor stability largely suppress the commercial application.Design of highly active,inexpensive HER electrocatalysts plays a vital role in the development of sustainable energy system.Owing to the wide availability,high surface area and controlled chemical composition,nanocarbon materials show a high application value in the field of energy.Combined nanocarbon materials with active metal phases may decline the cost,improve the activity and durability.Based on this,this thesis focuses on the preparation of low loading noble metal-based carbon composites and non-noble metal-based carbon composites,respectively.Furthermore,this dissertation gives more in-depth analysis of their catalytic activities and reaction mechanism.Herein,in the second part,D-Glucosamine hydrochloride?GAH?,a widely available and cost-effective N-containing biomass,was selected as both the C and N sources.Melamine,a common industrial chemical,played the part of the artificial template for the preparation of graphitic carbon.Metal Ru was selected as active component,which was cheaper than metal Pt?RuCl3 served as metal source?.Highly dispersed Ru nanoparticles hybridized with graphitic carbon?Ru@CN?was abtained via one-pot calcination process.The Ru particles size was as small as 2.37 nm,and Ru content was as low as 3.18 wt%.During the low-temperature region,melamine polymerized to form carbon nitride?g-C₃N₄?.Meanwhile,GAH was condensed to form a carbon skeleton in the interlayer of the g-C₃N₄,and Ru particles were confined in the sandwich-like structure.High-temperature?>700 ??annealing finally led to the thermal decomposition of g-C₃N₄ and the formation of graphene-like nanosheets.The as-prepared Ru@CN exhibited outstanding HER activity and stability in a wide pH range.To reach the current density of 10 mA cm^-2,the optimal catalyst delivered low overpotential?32 mV?,which was close to commercial Pt/C?20 wt%?.Besides,the activity of Ru@CN maintained even after continuous 2000 cycles CV test.Because of the low cost and low mass loading of Ru,the prepared Ru@CN was an ideal electrocatalyst to substitute for Pt/C.Although Ru@CN displayed superior performance,it still needs to use the precious metals,Whether can we design effective non-noble metal catalysts to replace noble metal catalysts?Nickel is typically used in industry for water reduction in basic medium.The preparation of sole NiOx-based nanohybrid materials for HER in alkaline medium is still a massive challenge.The third part of this thesis employed the similar synthetic method in the second part.Here,we substituted Ni?NO₃?2·6H₂O for RUCl3.The results showed that the product?NiOx-GCNTs?was no longer sheet-like structure,but formed nanotubes.Differ from the morphology of commercial CNT,the inner diameter of NiOx-GCNTs was 50-70 nm,and the sidewalls of the nanotubes were composed of multilayer graphene,which inspired our curiosity.By regulating the mass ratio of precursors and pyrolysis process,we concluded that GCNTs evolution should proceed via graphitic carbon to protrusions?baby nanotubes?,finally to typical GCNTs.The early formation of graphitic carbon was conductive to the growth of GCNTs,and the fluctuation of active metals catalyzed the growth of GCNTs from graphitic carbon.NiOx-GCNTs was applied to HER,and the catalyst showed potential activity for hydrogen generation.In order to deeply explore the intrinsic factors that dominated the activity of NiOx-based catalysts,the fourth part of this thesis was on the basis of the third section,in which NiOx hybridized with bamboo-like carbon nanotubes?NiOx@BCNTs?was synthesized through pyrolysis of melamine/Ni?NO₃?2·6H₂O mixture.The as-prepared NiOx@BCNTs was served as cathode material to disclose the veil of the active components.The growth mechanism of bamboo-like carbon nanotubes was similar to that of chemical vapor deposition method.Pleasingly,NiOx@BCNTs generated a low overpotential of?79 mV at 10 mA cm^-2.Experimental results confirmed that the catalytic activity of NiOx@BCNTs was closely related to Ni0 content.With the aid of H₂-temperature programmed reduction?H₂-TPR?technique,we designed a series of Ni-based catalysts with different reduction degree.Combined experimental data with density functional theory?DFT?calculation,we for the first time fundamentally validated that the inherent high Ni0 ratio and the Ni0 on the interface of Ni/NiO played a vital role in the outstanding HER catalytic performance.Particularly,the Ni0 on the interface of Ni/NiO endowed distinguished ability for water splitting compared with bulk Ni0.In order to simplify the electrode preparation process,and increase the catalyst loading,design of cheap and binder-free electrode materials is crucial to achieving sustainable hydrogen economy.However,the reported carbon cloth?CC?-based electro catalysts suffered from low specific surface area,poor pore structure and unsatisfactory stability.Besides,researchers often evaluated the electrocatalytic activity at room temperature.Developing efficient electrocatalysts for HER at low temperature is of revolutionary significance in harsh climate region.Therefore,in the fifth part,we followed the above idea by choosing CC as conductive substrates,melamine as both C and N sources.Commercial CC was first dipped in Co?NO₃?2·6H₂O solution,and then calcined with melamine.The obtained 3D porous electrode?CoO_x-CNT-CC?featured CoO_x nanoparticles and carbon nanotubes growing on activated carbon fibers.Because of the high-temperature conditions and the corrosive gas atmosphere,the carbon fiber was activated,forming multilevel channels.The achieved 3D electrode acted as efficient electrocatalysts as well as current collectors for hydrogen production,greatly simplifying the electrode preparation process.The current density of CoOc-CNT-CC can reach up to-720 mA cm^-2,overpotential of-99 mV is required to reach current density of 20 mA cm^-2,and it functions with robust durability up to 70 hours.Beyond that,the electrode can still show impressive catalytic properties under low temperature?even at 278 K?and neutral medium.Based on the experiments analysis,the outstanding performance of CoO_x-CNT-CC can be associated with the well-developed porous structure,high conductivity and the synergistic interaction between the activated CC and CoO_x-CNT.To sum up,we utilized the lamellar structure of carbon nitride and its thermal instability,and focused on the melamine/biomass/metal salt system,via one-pot pyrolysis strategy to design a series of low-cost,highly efficient catalysts for HER.This strategy is facile in operation and wide availability of raw materials.It provides a possibility for the large-scale preparation of catalysts.Furthermore,this dissertation deeply studied the factors that affects the nature of the HER performance.It provides guidance for the rational design of highly active,cheap and stable non-noble metallic catalysts,and promotes the development of water industry.