Study On The Characteristics And Influencing Factors Of Synergistic Catalytic Ammonia Borane Hydrolysis By Multi-Regulation Metal-Semiconductor Catalysts For Hydrogen Production

Ammonia borane（AB）has the characteristics of high hydrogen storage density,solidstate at room temperature,stable physical and chemical properties,no environmental toxicity and convenient hydrogen storage and release.AB reacts by pyrolysis when heated to produce hydrogen.AB is easily soluble in water and organic alcohol solution,and its water or alcohol solution can be catalyzed and hydrolysis or alcoholysis to produce high purity hydrogen.These excellent characteristics make AB become a portable hydrogen storage material with great application potential.In this paper,the reaction path and hydrogen production mechanism of AB（pyrolysisand hydrolysis）were studied by experiments and DFT simulation.Combined with the application background of vehicle-borne hydrogen production,this paper focuses on the catalytic hydrolysis of AB for hydrogen production.Based on the principle of conventional metal-catalyzed AB hydrolysis and semiconductor photocatalyst photocatalyzed AB hydrolysis,the technology of metal-photocatalyzed co-catalyzed AB hydrolysis to produce hydrogen were studied.A metal-photocatalytic bifunctional catalyst was constructed by modifying the semiconductor catalystβ-SiC with precious metal deposition to enhance the performance of AB hydrolysis for hydrogen production.The study revealed the conventional metal-catalyzed hydrogen production mechanism of AB hydrolysis,the photocatalyzed mechanism of AB hydrolysis and their synergistic mechanism.Based on the synergistic effect of bimetallic,precious metal Ru and transition metal Cu were used to construct bimetallic catalyst RuCu,which solved the shortcomings of expensive precious metal Ru catalyst and low activity of transition metal Cu catalyst for hydrolyzing AB for hydrogen production.Then,the catalytic performance of AB for hydrogen production was further enhanced through the construction of heterojunction catalyst RuCu/β-SiC and semiconductor catalysts Bi₂O₃and Cu₂O.Finally,the influencing factors and operating parameters of the catalytic hydrolysis of AB for hydrogen production were investigated.The main innovative research contents of this paper are as follows:The reaction path and hydrogen production mechanism of AB pyrolysis and hydrolysis to produce hydrogen were studied by DFT calculation,and a micro AB hydrolysis for hydrogen production-hydrogen supply fuel cell power experimental system was built,which verified the technical adaptability of AB catalytic hydrolysis for hydrogen production technology applied to the vehicle power system.The determination of hydrogen composition and concentration of hydrogen produced by AB hydrolysis confirmed that the hydrogen produced by AB hydrolysis was high purity hydrogen,and no toxic gas composition was detected,which met the purity requirements of hydrogen source for hydrogen fuel cell.Hydrogen production from AB hydrolysis-hydrogen supply fuel cell power experimental system was designed.In the continuous cycle hydrogen production experiment,the power system basically ran stably,which further verified that the technology of AB hydrolysis for hydrogen production could continuously support the power system of hydrogen fuel cell work stably.The bifunctional metal-photocatalytic catalysts Pt/β-SiC NWS and Ru/β-SiC NWS were constructed by the precious metal deposition method.The study confirmed that the photocatalytic technology can catalyze the hydrolysis of AB to produce hydrogen,and also confirmed the feasibility of the conventional metal catalytic and photocatalytic coupling and synergistic catalytic technology for the hydrolysis of AB to produce hydrogen.The deposition of precious metals Pt and Ru in the photocatalystβ-SiC NWs reduces the band gap and increases the spectral response range of the photocatalystβ-SiC NWs,and the modification of precious metals Pt and Ru is beneficial to the formation and transfer of photogenerated electron-hole pairs,which can improve the photocatalytic performance of AB hydrolysis for hydrogen production.DFT calculation shows that the modification ofβ-SiC band structure by Pt and Ru is realized by the hybridization of Pt and Ru atomic orbitals toβ-SiC electron orbitals.The existing literature reports the mechanism of photocatalytic AB hydrolysis to produce hydrogen,which believe it is similar to photocatalytic degradation of rhodamine B（Rh B）,is associated with dissolved oxygen in solution,but it does not have the rationality through experimental verification,and we puts forward a feasible mechanism of photocatalytic AB hydrolysis to produce hydrogen.Considering the mechanism of metal catalytic AB hydrolysis to produce hydrogen and photocatalytic AB hydrolysis to produce hydrogen and metal modified photocatalyst mechanism,we summarizes the metal catalytic-photocatalytic coupling synergetic mechanism.In the Pt-Ru/β-SiC NWs catalytic AB hydrolysis reaction system,Pt and Ru plays two roles,on the one hand,the precious metals Pt and Ru can directly catalyze the hydrolysis of AB for hydrogen production.At this time,β-SiC NWs as the carrier of the catalytic active metals,which plays the role of carrying and dispersing the active metal components,and improves the catalytic efficiency of the precious metals Pt and Ru.On the other hand,Pt and Ru are also used as modifiers for the modification ofβ-SiC NWs,which play a role in regulating the band structure ofβ-SiC NWs and promoting the excitation and timely transfer of photogenerated electron-hole pairs.No matter in the absence or presence of the light condition,the catalytic activity of bimetallic catalyst CuRu/β-SiC NWs is much higher than the pure Cu/β-SiC NWs catalyst,and has the same activity as noble metal catalyst Ru/β-SiC NWs.The repetitive experiments showed bimetallic catalyst CuRu/β-SiC NWs has a good catalytic stability,which is of great significance in reducing catalyst cost.Bimetallic alloy catalyst CuRu/β-SiC NWs is outstanding for the mechanism of catalytic activity of double metal RuCu alloy electron transfer between the phenomenon and Ru+Cu-heterogeneous species,response to ammonia borane catalyzed hydrolysis to produce hydrogen with positive synergies.The mechanism of the excellent catalytic activity of bimetallic catalyst CuRu/β-SiC NWs is the existence of electron transfer phenomenon between bimetallic RuCu alloys and the formation of Ru⁺Cu^-heterogeneous species,which has a positive synergistic effect on the catalytic hydrolysis of AB for hydrogen production.The band structure ofβ-SiC can be regulated by the electron orbital doping between RuCu andβ-SiC,which reduces the band gap width ofβ-SiC,enlarges the spectral response range ofβ-SiC,and improves the performance of hydrogen production from AB hydrolysis.The modification of Ru on transition metal catalyst Cu/β-SiC not only improves the metal-catalyzed hydrogen production efficiency of Cu/β-SiC,but also improves the photocatalyzed efficiency of hydrogen production.Under the same quality of active metal and light conditions,the hydrogen production efficiency of Ru/β-SiC on AB hydrolysis is higher than that of transition metal catalyst Cu/β-SiC,or even slightly higher than that of Ru/β-SiC.In the experiments of hydrogen production from AB hydrolysis catalyzed by RuCu/β-SiC NWs,Cu₂O-RuCu/β-SiC NWs andα-Bi₂O₃-RuCu/β-SiC NWs,the heterojunction effect has the effect of enhancing the photocatalytic performance of hydrogen production from AB hydrolysis,and Cu₂O-RuCu/β-SiC NWs shows a better catalytic performance for hydrogen production from AB hydrolysis than Bi₂O₃-RuCu/β-SiC NWs.This may be due to the fact that the photogenerated electrons of Cu₂O and the photogenerated holes of RuCu/β-SiC NWs transfer to each other respectively,resulting in the decrease of the substantial band gap,the decrease of the photon energy required for electron transition and the increase of the number of transition free electrons.The number of electron-hole involved in AB hydrolysis increases,and the catalytic efficiency of AB hydrolysis increases.Although the photogenerated electron-holes of Bi₂O₃-RuCu/β-SiC NWs Z-Type heterojunction have a high oxidation-reduction ability,but the number of electronic-hole patterns is lower than（TypeⅡ）heterojunction,so under the same condition,Cu₂O-RuCu/β-SiC NWs have a high catalytic ability of AB hydrolysis for hydrogen production.Both acid and base can improve the hydrogen production performance of AB hydrolysis,but the mechanism of acid and base to improve the performance of AB hydrolysis is different.The alkali（Na OH）does not react with AB,while the acid（HCl,C₆H₈O₇,CH₃COOH）reacts with AB to improve the catalytic hydrolysis performance of AB for hydrogen production.Through experimental investigation,we speculated that OH^-in alkaline solution improve the performance of hydrogen production in the reaction of AB hydrolysis by activating H-O bond in H₂O molecule under the action of catalyst.In addition,the mechanism of hydrogen production by the reaction of AB with acid was also proposed.Reaction temperature is a significant factor affecting the catalytic hydrolysis of AB for hydrogen production,with the increase of temperature,the rate of hydrogen production from the catalytic hydrolysis of AB increases significantly.The rate of hydrogen production in the AB catalytic hydrolysis has a poor correlation with the concentration of AB,but the amount of catalyst is positively correlated with the rate of hydrogen production in the AB hydrolysis,and the above rule is not affected by the illumination of the reaction system.In order to broaden the application temperature range of AB hydrolysis technology,adding a certain proportion of methanol,ethanol or ethylene glycol into the reaction solution can effectively overcome the defects of low rate of hydrogen release and incomplete hydrogen release of pure methanol,ethanol or ethylene glycol,it also can solve the problem of high freezing temperature of water.Therefore,it is a feasible technical scheme to broaden the temperature range of hydrogen production from AB catalytic hydrolysis.