Synthesis Of Ammonia Borane Nanocomposites For Thermolysis Dehydrogenation

Hydrogen fuel is a promising clean energy.However,the storage and transport are technical bottleneck in large scale application of hydrogen energy.Ammonia borane?AB?is considered as an attractive chemical hydride due to its high hydrogen storage density and nontoxicity.Nevertheless,some problems,such as dehydrogenation temperature,slow kinetics of H₂ release at low temperature and simultaneous emission of volatile by-products hamper the commercial utilization of AB in fuel cell.In current research,the improvement of AB thermolysis dehydrogenation has been made a great process by achieving the nanosize of AB particles via the nanoconfinement of porous materials.Due to the special tubular structure and smaller aspect ratio,the natural silicon-based halloysite nanomaterial is well expected as a supporter and nanocontainer to nano-encapsulate AB molecules.In addition,porous carbon materials can also be used as supporters to encapsulate AB owing to its high surface area and thermal stability.Hence,in this paper,halloysite was used to support metal catalyst on its surface.Furthermore,we also prepared mesoporous carbon spheres?MCSs?and biomass multi-poplar porous catkin carbon?MPC?.And these materials were used as supporters to load AB to obtain AB nanocomposites.And then,dehydrogenation performances of these nanocomposites were investigated by thermal decomposition test.The contents and results are as follows:?1?Preparation of AB@Pd/HNTs and the study of its thermal dehydrogenationPd nanoparticles were synthesized on halloysite nanotubes?HNTs?as supporter by simple and effective strong electrostatic adsorption method?Pd/HNTs?.Characterization results revealed that Pd particles were uniformly dispersed on the surface of HNTs with an average particle size of 1.4 nm,and the loaded Pd NPs did not destroy the tubular structure of HNTs.And then AB was encapsulated into Pd/HNTs channel and coated on its surface with a uniform nano-layer of 7.7 nm using evaporating solvent,which played dual nanoconfinement effects on inner and outer surface.The as-prepared AB@Pd/HNTs hydrogen storage composite exerted a superior dehydrogenation activity with low hydrogen release temperature?60^oC?and complete inhibition of volume expansion and volatile by-products?ammonia,diborane and borazine?evolution.The synergetic catalysis of Pd NPs and surface group of HNTs,as well as nanosize of AB confined in HNTs contribute to the significate elevation in AB pyrolysis.?2?Preparation of AB/MCSs and the study of its thermal dehydrogenationMCSs were synthesized by polymerization method,in which phenolic resols as precursor of carbon and CTAB as template.And AB was supported on MCSs through evaporating solvent?AB/MCSs?.Characterization techniques showed the prepared MCSs were spherical mesoporous structures with rough surface and AB was filled into the mesoporous,achieving the nanoconfinement of AB.The AB/MCSs exhibited that a low decomposition temperature?51^oC?and high-purity H₂ desorption,namely,no by-products of ammonia,diborane,and borazine were generated during dehydrogenation process;the reaction activation energy of 51.5 k J mol^-1 in kinetic,which reduced the reaction barrier of AB.The reason can be ascribed to the synergistic effect between nanoconfinement of MCSs nanopores and interface reaction of MCSs hole-wall and AB.?3?Preparation of AB/MPC and the study of its thermal dehydrogenationPoplar carbon microsheets were prepared through pyrolysis of biomass poplar catkin at high-temperature,and the microsheets were treated to form pores on their surface by chemical activation of Fe₂O₃-assist method to obtain muti-pores carbon?MPC?.Then AB was supported on MPC via evaporating solvent?AB/MPC?.The results showed that MPC had uniform pores and rough surface with high surface area of 475.3 m² g^-1 and pore size of 5.4 nm.The composite achieved H₂ release at60^oC,and completely inhibited the release of diborane and borazine,despite a small amount of ammoia was detected during pyrolysis process.Additionally,AB/MPC had a short dehydrogen induction and low reaction barrier(58.2 k J mol^-1 of Ea)in kinetic.The nanoconfinement of porous MPC and the interaction between AB and MPC surface may be contribute to these good dehydrogenation properties.