Synthesis And Performance Of Ultra-high Activity Nickel Catalysts For Hydrogen Production From Ammonia Borane Hydrolysis

In the context of the“double carbon”target,the global energy structure is shifting from fossil energy to renewable energy.Hydrogen,as a secondary energy source,has become one of the key pillars of the global energy sector in all carbon-neutral routes due to its high calorific value of combustion,clean and non-pollution.Ammonia borane（NH₃BH₃,AB）has been considered a great potential chemical hydrogen storage material because of its high mass hydrogen storage density of 19.6 wt%,safety and stability at room temperature,easy storage and transportation,and controlled hydrogen production capacity.In order to obtain high purity,high-speed hydrogen stream,the design of high activity,economical catalysts for ammonia borane hydrolysis is a key challenge to achieve practical applications of ammonia borane.Nickel catalysts have been widely studied for their low price and environmental friendliness,but generally suffer from poor catalytic activity and slow reaction kinetics.To address these problems,a series of highly efficient nickel nanocatalysts were designed and synthesized in this paper to achieve highly active and selective hydrogen production from ammonia borane at room temperature.The main research contents are given as follows:The transition metal Ni is homologous to the noble metal Pt and is promising in ammonia borane hydrolysis reaction.Ordered mesoporous silica SBA-15 was used as a substrate,and Mo O₂ was introduced to modify SBA-15 hydrophilically using an anchored assembly strategy.Ni nanoparticles with ultrafine size and electron-rich surface were successfully obtained by further deposition of Ni nanoparticles on ultra-hydrophilic Mo O₂-SBA-15 substrates.The optimized Ni/Mo O₂-SBA-15 nanocatalyst exhibits remarkable catalytic activity for hydrogen generated from ammonia borane hydrolysis with a turnover frequency（TOF）value of 143.9 min^-1 at 298 K,and the TOF value further elevates to as high as 253.2 min^-1 in the help of Na OH additive.Characterization and experimental results indicated that the excellent catalytic performance of Ni/Mo O₂-SBA-15 for the hydrolysis of ammonia borane was attributed to the excellent hydrophilicity of Ni/Mo O₂-SBA-15,which promoted the cleavage of O-H bonds in H₂O molecules.And the strong interaction between Ni and Mo O₂-SBA-15 facilitates the formation of ultra-fine（1.5 nm）Ni nanoparticles with electron-rich surfaces,which accelerates the cleavage of B-H and B-N bonds in NH₃BH₃ molecules,resulting in the rapid release of hydrogen.The heteromolecular co-activation strategy provides a unique and novel insight for the development of nanocatalysts with excellent hydrophilicity and outstanding catalytic activity for hydrolysis reactions.Due to the ability of MoC to activate and dissociate H₂O at low temperatures,phosphorus-nitrogen co-doped porous carbon encapsulated MoC nanomaterials（MoC@PNC）were obtained by a facile one-step calcination method and subsequently used to anchor Ni nanoparticles to obtain Ni/MoC@PNC nanocatalysts for efficient hydrogen production from ammonia borane.A series of characterization and performance tests showed that the nanoparticles with a mean size of about 1.7 nm were uniformly embedded in the carbon layer,and the introduction of MoC and the doping of heteroatoms in the carbon layer played an important role in improving the catalytic activity.Thanks to the electron modulation induced by strong metal-support interaction（SMSI）,the anchoring effect of heteroatom doping,and the effective activation of O-H bonds by MoC,the optimized Ni/MoC@PNC showed excellent catalytic performance for ammonia borane hydrolysis with a TOF value of 120 min^-1 at 298 K,and the TOF value further elevates to as high as 225.0 min^-1 in the help of Na OH additive.