Study On Preparation Of Carbon-Based Metal Hybrid Materials And Catalytic Activities Of Hydrogen Production

Hydrogen,a renewable clean and abundant energy carrier,is considered a promising energy replacement for fossil fuels as a potential solution to increasing environmental and energy problems.At present,the two most promising routes for its large-scale production in high purity are electrochemical water splitting and chemical release from hydrogen-storage materials.Although alternative catalysts are being rapidly developed,Pt is still the most effective catalyst for electrochemical hydrogen evolution and chemical hydrogen production,the high price of Pt-based electrocatalysts has restricted their widespread adoption.Meanwhile,carbon-based metal hybrids materials with high electrical conductivity,good chemical stability,unique edge sites,and synergetic effects exhibit great potential.In this thesis,we report a facile and effective in-situ mosaic strategy through thermolysis of small molecular precursor at selected temperatures under an N₂atmosphere for preparing non-noble metal and nitrogen co-doped mesoporous carbon catalysts?denoted as Co/CoO@N-C-T?.It is found that among the catalysts,the Co/CoO@N-C-800 shows superior catalytic activity and high sustainability.The turnover frequency?TOF?and activation energy of the hydrolysis of ammonia borane are 15.6 mol_H2 mol_cat^-11 min^-1 and 54.0 kJ mol^-1,respectively.Meanwhile,this catalyst still maintains good catalytic performance after 5 cycles.On the basis of the above work,we designed and synthesized a high-efficiency and stable catalyst with low-ruthenium content CoRu nanoalloy encapsulated in porous nitrogen-doped carbon layers?CoRu_x@N-C?via pyrolysis of small organic metal molecules.We explored different proportions of Co and Ru and found the optimum Co/Ru ratio.The amount of ruthenium in the catalyst that showed the highest activity was only 5.07 wt%.CoRu_0.25@N-C can efficiently catalyze the hydrogen evolution reaction?HER?with a wide pH range and low overpotential to drive current densities of 10 mA·cm^-22 of only 27 mV?1.0 M KOH?and 94 mV?0.5 M H₂SO₄?.CoRu_0.25@N-C also showed decent durability with negligible degradation after 1000 cyclic-voltammetry cycles both in acidic and alkaline solutions.It also has excellent catalytic activity and can easily sustain ammonia borane hydrolysis with an initial turnover frequency?TOF?of 457.8 mol_H2 mol_cat^-11 min^-1 under ambient conditions and activation energy of 32.5 kJ mol^-1.Even after five cycles,the CoRu_0.25@N-C catalyst retained96.1%of its initial activity,indicating good recyclability.CoRu_0.25@N-C can readily perform both NH₃BH₃ hydrolytic dehydrogenation and electrochemical hydrogen evolution as a result of its highly specific surface area,carbon layer protection,synergistic effect,and a porous carbon matrix doped with heteroatoms.On the other hand,we further study the impact of the carrier and the supported metal crystalline states on the catalytic performance of HER.Here,the synthesis of a novel carbon-loaded ruthenium nanoparticle electrocatalyst?Ru@CDs?for the HER,using carbon dots?CDs?,is reported.CDs are more beneficial to prevent the agglomeration of supported Ru nanoparticles and Ru@CDs exhibits better catalytic activity.By studying the growth process of Ru@CDs,we found that the HER performance of Ru is highly dependent on its crystallinity.