Research On Two-dimensional Co-based Oxide Nanofilms Catalyzing Hydrogen Generation From Ammonia Borane

Energy is the core of economic development,so it is urgent to exploit sustainable green energy.Hydrogen,as an excellent renewable energy carrier,has the advantages of high calorific value,high energy density and environment friendly,has been obtained wide attention.The development of chemical hydrogen storage materials provides a new perspective for hydrogen conversion.Among them,Ammonia borane（AB）is one of the ideal chemical hydrogen storage materials for its high hydrogen storage capacity,non-toxic,low molecular weight,high solubility and stably.However,the AB hydrolysis at room temperature depends on catalysts.Therefore,it is of great significance to develop the efficient and low-cost non-noble metal catalysts,especially transition metal Co,which have been favored by many researchers.Nevertheless,Co catalyst has problems such as unsatisfactory activity and poor stability.In this study,the catalysts with two-dimensional nanofilm structure were prepared by doping Fe and Cu elements respectively.The catalytic performance was significantly improved in comparison with monometallic Co/Co O_x catalyst.（1）Co/Co Fe O_x-X bimetallic oxide nanofilm catalysts having an amorphous structure were prepared on an（IL）/water interface for AB hydrolysis.The Co²⁺and Fe²⁺precursors were added rapidly within 30 s for inhibiting the rearrangement of metal nuclei to construct an amorphous structure.There is a“volcano”relationship between the catalytic activities of the Co/Co Fe O_x-X catalysts for AB hydrolysis and the Fe doping amounts.The optimal Co/Co Fe O_x-25 catalyst catalyzed the AB hydrolysis without alkaline medium within 3.8 min with TOF value of 12.25 mol_H2·mol_Co^–1·min^–1at 298 K,much higher than that of the monometallic Co/Co O_x.Without separation of catalyst,the catalytic performance remained 65.2%of the initial activity after 5th recycle.The results indicate that Fe can modulate the electronic structure of Co,the electronic synergistic effect between Co and Fe enhances the adsorption and activation of AB and H₂O molecules,meanwhile,the ultrathin amorphous two-dimensional nanofilm structure can expose more metal active sites to enhance the catalytic performance.（2）A series of Co Cu/Co Cu O_x-X nanofilm catalysts were prepared for the AB hydrolysis by using an ionic liquid/water interface method.The result shows that the hydrogen generation rate of AB hydrolysis by Co Cu/Co Cu O_x-25 catalyst can reach4140.8 m L·min^–1·g_Co^–1 without alkaline medium,the values of TOF at 298 K and E_a are9.97 mol_H2·mol_Co^–1·min^–1 and 39.53 k J/mol respectively.This ultrathin two-dimensional nanofilm structure has high specific surface area,which can expose more metal active sites and facilitate the rapid transfer of AB molecules on the catalyst surface to accelerate the hydrolysis kinetic.Meanwhile,Cu can regulate the electronic structure of Co,the catalytic activity of Co Cu/Co Cu O_x-25 can be effectively improved by synergistic interaction between Cu and Co.Although the catalytic activity decreased due to the collapse of the nanofilm structure and the reduction of Cu²⁺during the cycling process,it can still completely catalyze AB hydrolysis to produce hydrogen.