Preparation Of Non-noble Metal-based Catalysts And Their Catalytic Performance For Hydrogen Production From Ammonia Borane/Hydrous Hydrazine

With the increasing of energy crisis and environmental pollution,developing clean energy is becoming more and more important.Hydrogen energy,a green energy,has been considered as one of the most effective alternative energy sources.Because storage and delivery of hydrogen storage materials are safe and efficient,searching for the effective hydrogen storage materials is one of the most difficult challenges for hydrogen energy as a energy source in future.Among various hydrogen storage materials,ammonia borane and hydrazine hydrate have attracted wide attention from researchers due to their high hydrogen content and good stability.Ammonia borane with its high hydrogen content(19.6wt%),nontoxicity and excellent stability at room temperature has recently attracted great research interests for H₂ storage materials.Hydrazine hydrate,another hydrogen storage material,has a high content of hydrogen(8.0 wt%)and low cost.Moreover,nitrogen is the only by-product of complete decomposition of hydrazine hydrate.Hydrogen generation efficiency of hydrous hydrazine and ammonia borane depends largely on the selection of catalysts.Therefore,it is urgently important to find a catalyst with high catalytic activity,environmental friendliness,low price and good stability.A lot of researchers have studied hydrogen evolution reaction catalysts.Many different catalytic systems have been developed so far.Among them,noble metal based catalysts is the most widely studied catalysts.A relatively complete system of noble metal based catalysts has been established.And noble metal-based catalysts exhibit excellent catalytic activity.However,the global reserve scarcities and exorbitant price of noble metal-based catalysts limit their extensive application as catalysts.Compared with noble metal-based catalysts,non-noble metals have some unique advantages,such as,a huge storage capacity and a wide variety of species on the earth.Noble-metal-free material and their sulfides,phosphides and carbides,also show excellent catalytic activity as catalytic materials.Due to the low cost and excellent performance of noble-metal-free catalysts,it has attracted widely attention from scholars.In this paper,three new noble-metal-free catalysts with high catalytic activity have been developed,and their catalytic performance has been studied.The specific research content of this paper are divided into three parts,and the organization as follows.Firstly,using metal organic framework ZIF-67 as the precursor and sodium hypophosphite(Na H₂PO₂)as the P source,we prepared a new type of Co-based metal organic framework derivative material by a simple method of combining calcination and phosphating.It composed of uniformly dispersed Co@Co₂P core-shell nanoparticles embedded in a N-doped carbon nanotube polyhedron(N-CNP).The prepared Co@Co₂P nanoparticles are uniformly distributed in the N-CNP without aggregation.And there is a strong coupled contacts between Co and P.This will allows the Co@Co₂P/N-CNP catalyst to exhibit excellent catalytic performance towards the hydrolysis of ammonia borane for hydrogen generation,which is embodied a high initial turnover frequency(TOF)value of18.4 min^-1 and low evaluated the activation energy(E_?)of 32.1 k J·mol^-1.The work provides a guideline for design of highly efficient supported noble-metal-free nano-catalysts with integrated architecture.Secondly,we synthesized the non-noble metal Cu_0.81@Mo_0.09Co_0.10 core-shell structure catalyst by a simple in-situ reduction method at room temperature without additional reducing agent.The catalyst uses ammonia borane with mild reducing properties as a reducing agent.A Cu@Mo Co core-shell structure is synthesized by using the difference in the reduction potential of Cu,Mo and Co.The core of the catalysts is Cu,and the shell of the catalysts is Mo Co.The incorporation of Mo into Cu@Co core-shell structure not only limits the growth of nano-catalysts,but also effectively regulates the electronic structure of catalyst.The Cu_0.81@Mo_0.09Co_0.10 core-shell nanocatalyst displays high catalytic activity towards the hydrolysis dehydrogenation of ammonia borane underambient atmosphere at room temperature.The turnover frequency(TOF)value of the catalyst is 49.6 min^-1,and the activation energy(E_?)is calculated to be 22.2 k J·mol^-1.The value of TOF is higher than most of the reported non-noble metal catalysts under the same reaction conditions.Moreover,the value of TOF reachs the level of noble metal-based catalysts.This work can provide design ideas for the efficient and convenient preparation of core-shell nanoparticle catalysts.Thirdly,We introduced Ce₂O₃ into Ni_8.1Co_1.0Pt_0.9 nanoparticles,and synthesized Ni_8.1Co_1.0Pt_0.9/Ce₂O₃ amorphous structure nano-catalysts by a facile co-reduction route.Due to the introduction of Ce₂O₃,the long-range order of the Ni_8.1Co_1.0Pt_0.9 nano-alloy with low crystallinity was broken.Then,a Ni_8.1Co_1.0Pt_0.9/Ce₂O₃ nanoparticle catalyst with a amorphous structure is synthesized.Amorphous materials have a higher concentration of active sites in the catalytic reaction because they have a high concentration of defect sites.The hydrous hydrazine decomposition reaction catalyzed by the amorphous Ni_8.1Co_1.0Pt_0.9/Ce₂O₃ catalyst with low precious metals containing exhibits 100%hydrogen selectivity at room temperature under ambient atmosphere,and the value of initial turnover frequency(TOF)is 93.75 h^-1.This work can provide a reference for the preparation of amorphous nanoparticle catalysts by simple and effective doping of metal oxides at room temperature.