Preparation And Performance Study Of Catalysts For Hydrogen Storage Through Ammonia Synthesis And Hydrogen Production From Hydrazine Borane Decomposition

Hydrogen energy（H₂）is celebrated for its clean,pollution-free nature and wide range of applications,earning its reputation as the most promising secondary energy source of the 21st century.It holds the potential to replace fossil fuels,offering a solution to issues such as energy depletion,environmental pollution,and global warming.However,the safe storage,efficient transportation,and controllable release of H₂ have restricted the large-scale development and utilization of H₂.The chemical hydrogen storage materials have the characteristics of high safety and good convenience,which can effectively solve the problems of H₂ storage,transportation and safe utilization.Among chemical hydrogen storage materials,ammonia（NH₃）and hydrazine borane（N₂H₄BH₃,HB）have high hydrogen content and stability and have received extensive attention.Among them,the hydrogen content of NH₃ is 17.8 wt%,its liquefaction temperature,hydrogen storage volumetric density,and ignition point are all much higher than liquid hydrogen,making liquid ammonia a more suitable and safer hydrogen storage medium for transportation.At present,the industrial synthesis of NH₃ mainly relies on the Haber-Bosch process.However,this process has high energy consumption and high CO₂emission.In contrast,the conversion of N₂ to NH₃by a plasma-coupled electrochemical method with water as the hydrogen source,air as the nitrogen source,and sustainable electricity as the driving force,is another strategy that achieves"green electricity"conversion and"green hydrogen"storage simultaneously,and can solve issues of"green hydrogen"production,storage,and transportation.However,the research on this method is still in its infancy,and there are numerous critical issues that need to be addressed before it can be applied to industrial synthesis of NH₃.The hydrogen content of HB is 15.4 wt%,and its mass hydrogen storage capacity can reach 10.0 wt%in HB-3H₂O.Under the influence of suitable catalysts,HB can selectively release H₂.However,achieving efficient and highly selective HB decomposition for hydrogen production still presents significant challenges.Whether it is the synthesis of NH₃ for hydrogen storage or the decomposition of HB for hydrogen production,the efficiency of hydrogen storage and release depends on the design and regulation of the catalyst.Therefore,developing economical and efficient catalysts to enhance both the synthesis of NH₃ and HB decomposition for hydrogen production is critical to promoting the development of hydrogen energy.The research content of this thesis mainly includes the following aspects:1.N₂ can be activated effectively by plasma,which can overcome the difficulty of N≡N triple bond dissociation of N₂ in conventional electrochemical reactions and the low solubility of N₂ in aqueous solution.In this thesis,a two-step plasma coupled electrochemistry method（"N₂→NO_x^-→NH₃"）is used to synthesize NH₃.First,we set up a plasma-assisted N₂ oxidation reactor（p NOR）to obtain nitrate/nitrite（NO_x^-）intermediates.Secondly,foam Co-supported Co-W alloy（Co W/CF）self-supporting catalyst is developed for NO_x^-reduction synthesis of NH₃（e NO_xRR）.The theoretical and experimental results show that the alloying of W and Co can change the adsorption energy of reactant/intermediate,reduce the energy barrier of the rate-determining step in e NO_xRR,and inhibit the hydrogen evolution reaction.Under conditions of 0.2 M NO_x^-and-0.7 V,the reaction achieves excellent NH₃ yield(164.3 mg h^-1 cm^-2),high Faraday efficiency（98.1%）,and ampere-scale current density(1559 m A cm^-2).In addition,a gram-level NH₃ yield(4.771 g h^-1)can be obtained by expanding the reactor,further confirming the excellent performance of the catalyst.2.On the basis of the above,to further improve the synthesis efficiency of NH₃,a nickel foam supported cobalt-phosphorus(Co-P_11.1/NF)bifunctional catalyst is developed to efficiently catalyse both p NOR and e NO_xRR processes.The experimental results show that the doping of P not only enhances the adsorption of N₂,accelerates the rate-limiting step of p NOR process,and achieves excellent NO_x^-yield(171.3 mmol h^-1).It can also provide more active H*in the e NO_xRR process,promote the hydrogenation step in the electrochemical process,and obtain a high NH₃ yield(319.2mg h^-1 cm^-2)and Faraday efficiency（99.2%）.In addition,a scalable integrated system for the synthesis and separation of NH₃ has been successfully developed.This system links the p NOR and e NO_xRR reactions in series,allowing these two steps to operate synchronously online.This setup enables the direct and efficient conversion of N₂ to NH₃,with a high yield rate of 1.53 g h^-1.These results provide a green,efficient and fast way for large-scale synthesis of NH₃ to store hydrogen in the future.3.Nanoparticles（NPs）have a large surface area and a considerable number of edge atoms,which are conducive to improving catalytic performance.However,the high surface energy of small particles often leads to massive aggregation during the reaction process,causing a loss in catalytic performance.Anchoring NPs onto carrier materials with high surface areas is an effective method to alleviate particle aggregation.Based on this,a room-temperature synthesis of NH₂-functionalized N-doped graphene support（NH₂-N-r GO）with good hydrophilicity is achieved.After loading Mo O_x-modified Ni Pt alloy catalyst onto the NH₂-N-r GO,a preparation of Ni_0.9Pt_0.1-Mo O_x/NH₂-N-r GO NPs with ultrafine particle size is successfully accomplished.Experimental results show that there is a strong interaction between the metal particles and the carrier,the NH₂-N-r GO carrier has successfully dispersed the NPs,and the addition of Mo O_x has modulated the electronic structure of the Ni Pt alloy,thereby enhancing catalytic performance of the HB decomposition.Under conditions of 323 K,Ni_0.9Pt_0.1-Mo O_x/NH₂-N-r GO NPs demonstrate 100%H₂ selectivity and conversion rate,with a turnover frequency of 4412 h^-1,surpassing the performance of the most reported catalysts.Additionally,the inclusion of Ni effectively reduces the cost of the catalyst,making the potential practical application of HB as a hydrogen storage material feasible.