Design And Synthesis Of Visible-Light-Responsive Non-noble Metal Nanomaterials And Their Application In Catalytic Hydrogen Generation From Ammonia Borane

Hydrogen is considered as one of the ideal alternative energy sources because of its high calorific value and no pollution after burning,and the key to hydrogen energy utilization is to develop new hydrogen storage materials and explore the efficient release of hydrogen from these materials under mild conditions.Ammonia borane?NH3BH3?,which has high hydrogen content?19.6 wt%?,is a promising hydrogen storage material.Compared with the noble metal catalysts,which can catalyze the hydrolytic hydrogen generation from NH3BH3,the non-noble metal catalysts have low activities and thus cannot satisfy the application requirement.In the catalytic hydrogen generation reaction?NH3BH3+2H2O?NH4BO2+3H2?,the reduction reaction is dominant.So increasing the electron density of catalytically active centers in a catalyst can benefit the enhancement of its activity.To this end,photocatalysis is one of the effective ways to realize this design.Based on these above considerations and from the angle of regulating the electronic density of catalytically active metal nanoparticles,we designed and synthesed three kinds of non-noble metal nanocatalysts containing visible light responsive supports and systematically investigated the performance of the photocatalytic hydrogen generation from NH3BH3.The main contents are listed as follows:?1?On the basis of that some metals particles such as Cu with surface plasmon resonance?SPR?effect can produce free electrons under light irradiation with specific band,a series of Cu particles with different morphologies including cube,eight faces,rhombic dodecahedron and sphere are designed and synthesized.Meanwhile,a series of Co and Ni nanoparticles supported by Cu particles are constructed and their room-temperature photocatalytic performance on the hydrogen generation from NH3BH3 is studied.The results show that the electrons can be transfered from Cu particles to the catalytically active centers Co and Ni in the catalysts under the visible light irradiation,leading to that the activities of catalysts is significantly increased and thus the Co/Cu catalysts have the total turnover frequency?TOF?values in the range of 83.3-176.5 min-1.In addition,the different morphologies of the Cu particles result in the different catalytic activities of catalysts,among which the catalyst based on cube Cu has the highest activity and the catalyst based on the dodecahedronic Cu has the lowest activity.?2?Taking full advantage of the good conductivity of graphene,Cu nanoparticles are deposited on the reduced graphene oxide?rGO?to form the composite Cu-rGO as catalyst support and then corresponding supported Co and Ni catalysts were designed and synthesized.Also,their room-temperature photocatalytic performance on the hydrogen generation from NH3BH3 is studied.The results show that rGO inhibits the recombination of photogenerated electrons and holes on the surface of Cu nanoparticles.As a result,the photoinduced electron utilization efficiency of Cu nanoparticles and the activities of catalysts for the hydrogen generation from NH3BH3 are significantly enhanced.Specially,the TOF value of Co/Cu-rGO reaches 280.1 min-1.When the insulator SiO₂ is introduced to the rGO surface and the electron transport channel is constructed,the activity of Co/Cu-rGO-SiO₂ is greatly enhanced and its TOF value reaches 407.1 min-1,which is the highest value of the activities of the non-noble metal catalysts reported so far.In addition,the systematic investigation of the catalytic performance under the single-wavelength light irradiation shows that the activity of the catalyst is the highest under the light irradiation of 550 nm.This testifies that the catalytic activity of the catalyst is caused by the SPR effect of Cu nanoparticles.?3?On the basis of that the different band structures of semiconductors can influence their photocatalytic performance and graphene can improve the photoinduced carrier separation efficiency of semiconductors,a series of composite supports C3N4-rGO with different band gaps and the corresponding supported Co catalysts are designed and synthesized.Also,their room-temperature photocatalytic performance on the hydrogen generation from NH3BH3 is studied.The results show that compared with the catalyst only containing C3N4 as support,the catalysts containing C3N4-rGO as the supports have the significantly improved activities.Specially,when the mass ratio of C3N4 to rGO is 2:1 in the composite support,the activity of the catalyst was the highest and the TOF value reachs 208.6 min^-1.