Study On Structural Regulation Of Active Sites On Co-based Phosphide And Catalytic Mechanism For Hydrogen Generation

Hydrogen storage technology plays an important role in the development of next-generation energy.The safe and convenient storage and transportation of hydrogen is a challenge.Ammonia borane（NH₃BH₃）as hydrogen carriers can release high-purity hydrogen in situ with catalyst and is of great value for the safe and efficient use of hydrogen energy.How to design and construct the structure of non-noble metal based catalysts with efficient active sites to improve the intrinsic catalytic activity of catalysts and clarify the catalytic mechanism is still a challenge.Therefore,the rational structural design and composition regulation accurately constructs the structure of cobalt-based active sites,changes the valence state and chemical environment of active sites is the key to enhancing the catalytic activity of hydrogen generation from ammonia borane（NH₃BH₃）.The introduction of phosphorus has promised to effectively regulate the electronic structure of metals,thus significantly improving the intrinsic catalytic activity.Herein,Co-based phosphide catalysts with dual-active sites are constructed by regulating the structure of active sites of cobalt-based phosphide to improve the hydrogen generation activity of NH₃BH₃ hydrolysis.The effect of the constructed Co-based phosphides catalysts on the catalytic mechanism of NH₃BH₃ hydrolysis is also investigated.The main contents of the research are as follows:（1）The design of active sites of CoP/Co₂P@SC heterostructure regulated by oxygen modification and the catalytic mechanism for enhanced hydrogen generation of NH₃BH₃ hydrolysis.The O-modified CoP/Co₂P@carbon heterostructure（O-（CoP/Co₂P）@SC）is designed through controlled oxygen（O）modification and phosphorus-inducing（P-inducing）strategy.The experimental results confirm that the constructed catalyst consisting of Co-O and Co-P presents potent catalytic activity and a TOF of 35 min^-1 is achieved.Density functional theory（DFT）testifies that the O modification and phosphorus-inducing strategy have a key role in decreasing the reaction activation energy of NH₃BH₃ and H₂O molecules on the surfaces of catalysts.The O modification adjusts the electronic configuration of CoP/Co₂P and changes the reaction dissociation energy,thus optimizing the catalytic kinetics of NH₃BH₃ and H₂O.Moreover,Conearby Co-O activates H₂O and Conearby Co-P activates NH₃BH₃.This research is important for boosting catalytic reaction and enhancing the catalytic activity.（2）The design of B-Co-P atomic bridge structure on h-BN and the catalytic mechanism for enhanced hydrogen generation of NH₃BH₃ hydrolysis.The atomic-bridge structure of B-Co-P containing dual-active sites is designed through a one-step Na BH₄ reduction and local phosphorus-inducing strategy.The constructed Co₃B-CoP/h-BN consisting of Co-B and Co-P dual-active sites presents a TOF of 37min^-1.Both experimental investigation and theoretical calculations reveal that the constructed atomic-bridge structure of B-Co-P adjusts the electronic structure and chemical coordination environment of Co-based active sites,enhance the dissociation ability of catalysts towards to NH₃BH₃ and H₂O molecules,thus accelerating the catalytic activity.Explanatorily,Co-B activates H₂O and Co-P activates NH₃BH₃.This discovery provides a reference for designing the catalysts with highly active structure.（3）The design of hydroxyl-rich CoP/h-BN_OH nanosheets and the catalytic mechanism for enhanced hydrogen generation of NH₃BH₃ hydrolysis.The CoP/h-BN_OHwith B_OH and Co-P dual-active sites is designed through a hydroxyl-assisted and phosphors-inducing strategy.Experimental investigations demonstrate that the designed and synthesized catalysts containing B_OH and Co-P dual-active sites express superior catalytic activity than the catalysts with a single active site.And the TOF reaches up to43 min^-1.The construction of the dual-active sites of B_OH and Co-P significantly improves the catalytic activity of CoP/h-BN_OH to catalyze the hydrogen generation from the hydrolysis of NH₃BH₃.Experimental investigation and DFT calculations reveal that the dual-active sites of B_OH and Co-P promote the adsorption and dissociation of NH₃BH₃ and H₂O molecules,reduce the activation energies of reaction molecules,and increase the catalytic activity of hydrogen generation.Noteworthily,B_OH activates H₂O,and Co-P activates NH₃BH₃.This work enriches the chemical toolbox for the construction of active structures in heterogeneous catalytic reactions.（4）The design of bifunctionally active interface of Co（OH）₂ and CoP on Ti₃C₂（MXene）and the catalytic mechanism for enhanced hydrogen generation of NH₃BH₃hydrolysis.A structure of bifunctionally active interfacial Co（OH）_xP_y consisting of Co（OH）₂ and CoP on MXene is successfully constructed through in situ hydroxylation and P-inducing strategy.The experimental results confirm that the presence of MXene stabilizes Co（OH）₂,promotes the formation of the bifunctional active interface of Co（OH）_xP_y.The TOF of the constructed catalyst reaches up to of 41 min^-1 during the hydrolysis of NH₃BH₃.Both experimental and computational results manifest that the constructed bifunctional active interface reduces the reaction activation energies of NH₃BH₃ and H₂O molecules,and expedites the catalytic activity.Summarily,Co（OH）₂activates H₂O and CoP activates NH₃BH₃.This work provides an experimental basis for rationally designing the structure of active interface and clarifying the catalytic mechanism of the bifunctional active interface.