Synthesis Design Of Mesoporous Carbon/Nickel Nanocomposites For Electrochemical Energy Storage And Catalytic Methane Decomposition

Incorporation of Ni active species with mesoporous carbon and the resulting composite materials have received much attention due to their nature of flexibility derived from a confluence of metallic and carbonic properties and numerous textural advantages inherited from mesoporous carbon substrates,contributing to their versatility in adsorption,catalytic hydrogen storage,electrochemical energy storage and other fields.In traditional composite materials,there is often a problem that metal active components tend to agglomerate and fall off,and the low accessibility results in reduced utilization of active components,and the structural and functional advantages of the two materials are not fully exploited.Hence,the technical key of this study lies in the design and development of highly integrational nickel-carbon nanocomposites with complementary performance advantages and uniformly dispersed active components.Compared with other mesoporous carbon materials,the three dimensionally ordered mesoporous carbon possesses a unique FCC structure matrix composed of highly ordered mesopores,and the interspaced pores can be used as a buffer to nucleate the active substances independently and avoid excessive agglomeration growth,which is a good carrier and template for the growth of nickel species.Based on this,starting from the design and preparation of composite materials,the confined space synthesis of nickel species within three dimensionally ordered mesoporous carbon（3DOMC）by steam-assisted crystallization was propose in this paper.Different types of highly hybrid composites were prepared through structural regulation and directional transformation of metallic nickel species.At the same time,the crystal structure,microstructure transformation,electronic structure and chemical state of the composites were systematically correlated with the specific properties of different applications.1)A series of Ni（OH）₂/3DOMC composite electrode materials were designed and fabricated.Dual forms of high-crystalline nanosheet-like Ni（OH）₂ severally distribute within mesopores or over the outer surface of 3DOMC particles depending on the loading amount of Ni（OH）₂.Benefitted from the highly hybrid combination and efficient electrolyte diffusion,the obtained Ni（OH）₂/carbon nanocomposites exhibit an excellent electrochemical performance,and the optimal sample of 6%＿Ni（OH）₂/3DOMC with confined extra-small Ni（OH）₂nanosheets as dominant shows the highest specific capacitance of 552.5 F·g^-1 at 1.0 A·g^-1,which is 330%higher than the contrast sample by using activated carbon as the support.Furthermore,the assembled hybrid supercapacitor displays an energy density of 11.7 Wh·kg^-1 at 288.1 W·kg^-1 and a superior charge/discharge stability.It is expected that the flexible component,well-defined structure,and superior electrochemical performance could promote a great application potential of Ni（OH）₂/3DOMC nanocomposites as supercapacitor electrodes and in other energy storage devices.2)Ni/3DOMC composites were designed and prepared for catalytic methane decomposition.And the bimodal size distribution of the Ni nanoparticles exhibited in Ni/3DOMC composites,the external-grown Ni particles presented a mean size of～85 nm and partially embedded in the 3DOMC,indicating the positive reduction effect by the 3DOMC support leading to the highly effective dispersion of Ni particles.On the other hand,the Ni⁰confined within the mesopores of 3DOMC with regularly spherical shape and uniform particle size close to the mesopore diameter of 3DOMC.And the reduced sample of Ni/3DOMC is further used as a catalyst for methane decomposition to produce COx-free hydrogen and contributes a maximum CH₄ conversion of 66.5%and H₂output rate of 7.4 mmol·g^-1_cat·min^-1at 850℃,which are 37%higher in CH₄ conversion and 39%higher in H₂output rate than the Ni-incorporated active carbon（Ni/AC）catalyst.Moreover,the Ni/3DOMC catalyst also exhibits a higher initial reaction rate attributed to the abundant homodispersed Ni active sites by its highly hybrid structure.The purpose of this paper is to design and exploitation new composite materials.Three-dimensional ordered mesoporous nickel-carbon composites with different metal types were prepared according to different application requirements,which solved the problems of metal shedding and agglomeration in traditional composites.This work not only develops a confined space synthesis strategy to prepare highly hybrid composites,but also expands the template utilization direction of the three-dimensional ordered mesoporous carbon to effectively regulate the crystalline characteristics and species types of metallic nickel.