Synthesis Of Hierarchical Porous Carbon Supported Silver Nanoparticles And The Studied Of Their Performance For Electrocatalytic CO₂ Reduction

Electrocatalytic reduction of carbon dioxide(ECR)as high value-added chemicals is one of the effective strategies to alleviate the current climate crisis and energy crisis.However,due to the inherent thermodynamic stability and kinetic inertia of CO2 molecules,excellent electrocatalysts are needed to achieve efficient ECR process.It has been reported that Ag-based catalysts can reduce CO2 to CO with high selectivity,but they are still difficult to be applied in industrial applications due to low current density and high cost.Selecting a suitable carrier for Ag-based nanomaterials can not only provide a larger specific surface area and more active sites,improve the catalytic activity of Ag,but also reduce the manufacturing cost of the catalyst.In this paper,porous carbon loaded silver nanoparticles composites were designed and prepared and the electrocatalytic reduction performance of CO2 are investigated.The main works are summarized as follows:1)The nickel-nitrogen co-doped three-dimensionally(3D)ordered macro-/mesoporous carbon material(Ni-N-OMMC)is fabricated through a dual-templating method approach by the use of silica colloidal crystal(opal)as a hard template and F127 as a mesoporous template.The prepared porous carbon material has a three-dimensional ordered interconnection of macroporous with a diameter of about 255 nm.The macroporous wall is covered with ordered mesopores with the pore size is about 15 nm.Macroporous and mesoporous can provide efficient mass/charge transport and a large specific surface area.In addition,the material has abundant Ni-Nx and Pyridine-N active sites which can promote ECR activity.Therefore,it is an excellent material as a carrier of Ag nanoparticles.2)Ni-N-OMMC@Ag,OMMC@Ag and XC-72R@Ag composites with Ag loading of 40wt%are prepared by chemical reduction method using Ni-N-OMMC,OMMC and carbon black(XC-72R)as carriers,respectively.The Ag particles on the three different carriers have uniform size and distribution,with the particle sizes of 6.6 nm,6.9 nm and 8.4 nm,respectively.Compared with XC-72R,the Ag particles which loaded on OMMC and Ni-N-OMMC are smaller,indicating that the mesoporous limit the growth of Ag particles.The ECR test find that Ni-N-OMMC@Ag has the best ECR performance,the Faradic efficiency of CO is as high as 98.7%,and the current density of CO can reach 33.3 mA·cm-2.3)Using Ni-N-OMMC as carrier,two kinds of composite materials Ni-N-OMMC@Ag-20wt%and Ni-N-OMMC@Ag-60wt%are prepared by the same chemical reduction method.From the physical characterization,it can be known that the Ag particles on Ni-N-OMMC@Ag-20wt%have uniform size and distribution,with an average particle size of 7.1 nm.The Ag particles on Ni-N-OMMC@Ag-60wt%have appeared obvious agglomeration and some larger particles with an average particle size of 10.5 nm.Through the ECR test,it is found that the ECR performance of Ni-N-OMMC@Ag-20wt%is slightly worse than Ni-N-OMMC@Ag-40wt%because of the less silver content.And Ni-N-OMMC@Ag-60wt%showed the worst ECR activity due to the larger Ag particle size,which enhanced HER reaction.