Carbon-based Nanocomposites For High-efficiency Hydrolysis Of Ammonia Borane

Caused by increasing consumption of traditional fossil fuels,the environmental contamination has become a serious problem.New-style clean energy has been concerned,such as solar energy,wind energy,hydrogen energy and so on.Among of them,hydrogen energy has many advantages,namely,environmental conservation,extensive abundance,automatic renewability.Therefore,a large number of researchers are engaged in developing "hydrogen energy economy".There are two problems urgent to be solved in the process:safe storage and controlled release of hydrogen.Much attention has been paid to ammonia borane?NH₃BH₃,AB?due to its high hydrogen content?19.6 wt%H₂?,nontoxicity,and stability under ambient condition.Hydrogen stored in ammonia borane can be released through the pyrolysis,alcoholysis and hydrolysis.Compared with the first two ways,hydrolysis of ammonia borane has relatively low cost,controlled release rate,and mild reaction conditions such as normal pressure and neutral aqueous solution.Catalyzed by the suitable catalysts,1 mole?mol?ammonia borane can release 3 mol H₂.The main work of this thesis is to prepare efficient catalysts to accelerate the hydrolysis of ammonia borane.?1?we build up Pt O₂ nanoparticles on Carbon nanotubes?CNTs?for the high-efficiency hydrolysis of AB.The PtO₂/CNTs catalyst can achieve a high total turnover frequency of 736?H₂?mol?Cat-metal?mol^-1min^-1,which is one of the best values ever reported for Pt-based catalysts.The catalyst also shows a good stability by keeping 80%activity after 5 runs.Synchrotron radiation-based X-ray absorption spectroscopy is used to probe the electronic structure of the Pt element,which reveals that Pt is+4 in the catalyst.X-ray absorption spectroscopy also reveals the reduction of oxygen groups on CNTs after the decoration of PtO₂,which can accelerate the charge transfer between PtO₂ and CNTs for better performance.The understanding of catalytic process may help to design new efficient catalysts.?2?we build up a cube-like Cu_0.5Co_0.5O nanostructure on reduced graphene oxide?rGO?for the high-efficiency hydrolysis of AB.The Cu_0.5Co_0.5O-rGO catalyst can achieve a high total turnover frequency of 81.7?H₂?mol?Cat-metal?mol^-1min^-1,which is one of the best values ever reported for noble metal-free catalysts.The catalyst also shows a good stability by keeping 88.3%activity after 5 runs.Synchrotron radiation-based in-situ X-ray absorption spectroscopy is used to probe the catalytic mechanism,which reveals that the Cu sites in catalyst can activate water and then cooperate with Co to anchor the AB molecules for high catalytic activity.The high performance of Cu_0.5Co_0.5O-rGO can be attributed to both the coordination of Cu and Co in the cube-like structure and the metal-support interaction.The in-depth understanding of catalytic process may significantly pave the way for the rational design of highly efficient catalysts.?3?The study of induction period in the hydrolysis of ammonia borane.Recent research results show that the P-based catalysts had excellent catalytic activity and a high sustainability in the hydrolysis of ammonia borane.But they typically had a long catalytic induction period in neutral aqueous solution.According to our previous results,CuO/rGO can quickly activate the water molecules and shorten the pre-reaction time.We use Cu O/rGO to regulate the pre-reaction time of the NiCoP/rGO catalyst and have got good catalytic performance.