Preparation Of Cobalt-based Multistage Composite And Study On Its Catalytic Hydrolysis Of NaBH₄ For Hydrogen Production

With the development of economy,the demand for energy increases gradually,but the large consumption of traditional energy（coal,oil,natural gas,etc.）causes serious environmental pollution.In order to create a better living environment,the development of green and renewable new energy to supersede traditional energy has become a pressing matter of social and economic development.In recent years,hydrogen energy（H₂）has attracted extensive attention due to its high combustion energy density(120 MJ kg^-1,3 times higher than traditional gasoline,44.4 MJ kg^-1),no contamination of combustion products（the only product of combustion is water）and wide sources.Traditional industrial hydrogen production methods are mainly prepared through steam reforming of methane,and the by-products（CO,CO₂,etc.）of this method will also cause serious environmental pollution.Therefore,the development of electrochemistry and chemical hydrogen production technology has gradually attracted the attention of mounting number of scientists.On account of the low density of H₂,there are great hazards in storage and transportation.Therefore,the development of a portable and on-demand hydrogen production system is of great significance for promoting economic development and facilitating life.Hydrogen storage materials represented by ammonia borane,hydride and borohydride have gradually become the source of chemical catalytic hydrogen production materials due to their high hydrogen storage content,high density,stable chemical properties and convenient transportation.Among them,sodium borohydride（NaBH₄）is widely recognized as the most potential hydrogen storage material due to its advantages such as low price（1/30 of the price of ammonia borane）,high hydrogen content（10.8 wt%）and environmental friendliness of reaction products.According to the catalytic hydrolysis reaction equation of NaBH₄（NaBH₄+2H₂O=NaBO₂+4H₂?）,1.0 mol NaBH₄ can produce 4.0 mol H₂,which indicating a high hydrogen production efficiency.To be more flexible in controlling the rate of hydrogen production,this reaction is usually carried out under alkaline conditions.Under alkaline conditions,researchers have developed a variety of catalytic materials.According to the properties of materials,they can be roughly divided into two categories:one is noble metal catalysts based on Pt,Pd and Ru;another is non-noble metal catalysts based on Co,Ni,Fe,etc.Up to now,most of the non-noble metal catalysts have low catalytic activity and cycle stability,while the noble metal catalysts have high load capacity,high price and are easy to be poisoned by BO^2-,etc.,which makes it difficult to be commercialized and widely promoted.Based on the above analysis,we first used flexible experimental means to design the composite catalyst of low loading RuP₃ nanoparticle modified CoP nanosheet array,the folded CoP-Ni₂P non-noble metal composite catalyst,and the composite catalyst of low loading PdO modified Co₃O₄ nanosheet array.Secondly,in combination with a variety of characterization test methods,we explored in detail the hydrogen evolution rate,conversion frequency（TOF）,multiple cycle use and other characteristics of this series of catalysts in the process of catalyst produces H₂ by hydrolysis of NaBH₄,and analyzed the relevant catalytic mechanism in detail.The specific research content is as follows:1.Co-Ru-P@NF catalyst:We have developed a controllable strategy to fabricate a seriesof hierarchically structured cobalt-ruthenium-phosphide arrays on nickel foam（Co–Ru–P@NF）as a highly efficient and stable catalyst for hydrogen generation from NaBH₄ hydrolysis in alkaline media.SEM and TEM analyses show that the interconnected rugae-like Co–Ru–P arrays are vertically grown on the surface of Ni foam,together with uniformly distributed RuP₃nanoclusters on the surface of CoP nanosheets.More importantly,the optimized Co–Ru–P@NF catalyst exhibits an outstanding catalytic performance on NaBH₄ hydrolysis in alkaline media with a high turnover frequency（TOF）of 2123.6 mol_H22 min^-1mol _Ru^-1at 25?C,which is one of the highest known so far.In addition,the catalytic reaction of low activation energy(40.3 kJ mol^-1),indicate that the catalytic reaction has fast dynamic cycle stability.The cyclic stability study found that after 5 consecutive cycles,the catalyst had only a small decline（8.0%）.These excellent catalytic activity and stability are caused by the synergy between the RuP₃ and CoP species,among them:the effect of electron transfer between the two species of catalytic hydrogen production,and unique morphology（large specific surface area and open channels）for solute transportAdsorption,and rapid emission of end product gas（H₂）.2.Co-Ni-P@NF catalyst:We report a series of hierarchical rugae-like CoP-Ni₂P nanoarrays decorated Ni foam（Co-Ni-P@NF）catalyst,which are fabricated by consecutive two-step electrodeposition and phosphating treatment.A series of characterizations（XRD,SEM,TEM,XPS,ICP,EDS）of the prepared catalysts were carried out to determine the composition,morphology,valence state of each element and other physicochemical parameters.The optimized Co-Ni-P@NF catalyst shows a superior catalytic H₂ generation by NaBH₄ hydrolysis in alkaline media,affording a specific H₂ generation rate of 4323.0 mL min^-11 g^-11 at 25?C,low activation energy of 30.2 kJ mol^-1and demonstrates a high level of reusability,far superior than all comparable catalysts and most previously reported catalysts.3.Co₃O₄-PdO@NF catalyst:We use the electrodeposition,metal-organic ligand and calcination treatment method of the preparation of the Co₃O₄-PdO@NF.At first,the Co-spices@NF were prepared by electrodeposition,afterwards,the interaction between metal and organic coordination was used to obtain Co-MOF@NF in aqueous solution,then the composite materials modified by Pd（OAc）₂ was obtained by immersion method,the final target catalyst is obtained in air calcined.The catalyst was characterized by XRD,SEM,TEM,EDS,XPS,etc.to determine the chemical composition microstructure and the element valence state of the catalyst.Performance test showed that the catalyst of hydrogen evolution rate of 3707.5mL min^-1g^-1,TOF value of 1604.3 mol min^-1mo1_Pd^-1,the excellent catalytic performance is significantly improved by the unique MOFs structure of precious metal dispersion and the coordination between different species（Co₃O₄/PdO）catalysis is a common cause.