Synthesis And Catalytic Performance Of Supported Nibased Alloy And Ir-Ru-B Catalysts For Hydrogen Generation From Hydrazine Monohydrate Decomposition

Hydrogen is a clean and highly efficient energy carrier,which is expected to play an important role in the future clean energy economy.However,the widespread implementation of hydrogen economy is severely impeded by a series of grand scientific/technical challenges in hydrogen production,hydrogen storage,and hydrogen use.Among them,hydrogen storage is generally recognized as the most challenging bottleneck due to multiple stringent technical specifications.In recent years,the emerging and rapid development of chemical hydrogen storage technology have provided an opportunity to overcome the bottleneck of hydrogen storage.Among the known chemical hydrides,hydrazine monohydrate(N₂H₄·H₂O)is an appealing candidate thanks to its favorable combination of high hydrogen density(8 wt%),low cost,and satisfactory stability at ambient conditions.More importantly,N₂H₄·H₂O does not yield any solid byproduct in its catalytic reactions,which is highly beneficial for the design and practical application of H₂-source systems.The synthesis of highly active,selective and durable catalysts is a central issue for the development of the N₂H₄·H₂O-based hydrogen generation system.For decades,extensive research activities have been directed toward the development of supported Ni or Co-based catalysts by employing a combination of alloying,nanostructure modulation and basic support immobilization strategies,which enabled a complete decomposition of N₂H₄·H₂O at ambient temperatures.But as a whole,the bimetallic alloys composed of a combination of precious metals and nonprecious metals(like Ni and Co)are currently the main body of research on the active phase of catalysts.In addition,the existing catalysts are still far from reaching the level demanded by real-world applications in terms of activity and durability.Based on the state of art research,this thesis abides by the general goals of developing a highly efficient and stable catalyst for H₂ generation from N₂H₄·H₂O.Three excellent catalysts were successfully synthesized under the elaborate investigation which optimized the composition/structure of supported Ni-based alloy catalysts and expanded the scope of the catalyst composition.Besides,the inherent connections of structure-activity relationships were also taken into consideration.The main progress achieved is as follows:(1)The powdery Ni₁₀Mo/Mo-Ni-O catalyst was prepared by a combination of hydrothermal and annealing treatment.Thus-obtained catalyst is superior to the reported non-precious metal catalysts in terms of reaction activity(54.5 h^-1)and cycle stability.The favorable properties of the powdery Ni₁₀Mo/Mo-Ni-O catalyst inspired us to further prepare a monolithic Ni₁₀Mo/Mo-Ni-O/NF catalyst using a similar method.Thus-prepared monolithic Ni₁₀Mo/Mo-Ni-O/NF catalyst was used in combination with the commercially available 85 wt%N₂H₄·H₂O solution to constitute a high-capacity hydrogen generation system.The system has rapid dynamic response at mild conditions and its hydrogen storage capacity reaches up to 6.2 wt%.This work demonstrated that the usage of non-noble monolithic catalyst enabled rapid and high-density hydrogen generation from commercial N₂H₄·H₂O solution.Our results may encourage further exploration of the N₂H₄·H₂O-based system for practical H₂ source applications.(2)Development of high-performance catalysts requires a comprehensive consideration of intrinsic activity,number of active sites and mass transfer.A hierarchically nanostructured Ni-Pt/N-doped carbon catalyst(Ni-Pt/NC)was successfully synthesized using a simple method involving chelation and template removal steps to address the three key issues.It was found that the catalytic activity and H₂ selectivity of Ni-Pt/NC catalyst for N₂H₄·H₂O decomposition was closely related to the composition and heat treatment temperature.Such variation of apparent activity is mainly ascribed to the changes of intrinsic activity and the number of active sites of the composite catalyst.In addition,the alloy-substrate interaction was also an important factor affecting the catalytic activity of Ni-Pt/NC catalyst.When the Ni/Pt molar ratio was 6/4,and the reductive temperature was maintained 700?,the catalyst exhibited the best catalytic properties.It enabled complete decomposition of N₂H₄·H₂O to generate H₂ at a reaction rate of1602 h^-1 at 50? in the presence of 2 M Na OH.In addition,the catalyst well maintained a 100%H₂ selectivity but showed an activity loss of?35%after ten cycles.This catalytic performance outperformed most existing N₂H₄·H₂O decomposition catalysts.This work highlights the importance of multi-factor synergistic modification,and provides an experimental basis for the design of the composition and structure of the high-performance N₂H₄·H₂O decomposition catalyst.(3)A series of Ir-Ru-B/CeO₂ catalyst was prepared by using a chemical reduction method followed by reductive annealing,which was the first report of B-doped noble metal alloy catalyst for N₂H₄·H₂O decomposition.The Ir-Ru-B/CeO₂ catalyst prepared under optimal conditions show an unprecedented activity,the reaction rate for the 600?-annealed Ir₇₀Ru₃₀-B/CeO₂ catalyst reached up to 11510 h^-1 at 50?.This catalytic performance outperformed an over 4-fold higher activity for N₂H₄·H₂O decomposition than those of the state-of-the-art catalysts.Furthermore,it showed exceptionally high stability in catalyzing N₂H₄·H₂O decomposition under alkaline condition,which showed an activity loss of?18%after ten cycles.Control experiments show that the improved stability of the B-doped catalyst should be ascribed to the B-doping induced weakening of binding strength of the reaction intermediates/products to the catalyst surface.This work expands the research scope of catalytic materials for H₂generation from N₂H₄·H₂O while reveals a new way for development of highly durable catalyst.