Controllable Construction Of Ni-NC Based Catalysts And Their Reaction Mechanism Of Electrocatalytic CO₂ Reduction

The concentration of carbon dioxide（CO₂）in the atmosphere increases rapidly owing to the abundant use of fossil fuels,resulting in a series environmental problems such as global warming and ocean acidification,etc.The electrochemical reduction of CO₂ to high value-added chemicals and fuels by renewable electricity is undoubtedly a promising strategy to balance the global carbon emissions.The suitable catalyst plays vital role in reducing the energy barrier as well as improving the selectivity of final products.In this paper,the electrocatalytic activity of Ni-NC based materials were greatly improved by introducing N-rich triazine rings and zirconia（ZrO₂）nanoparticles to the carbon structure.A novel porous nickel-porphyrin framework based catalyst（NiPTFs-600）was successfully prepared by using pyrrole and p-cyanbenzaldehyde as basic building blocks,followed by a trimerization treatment under ionothermal conditions.Ni was coordinated with nitrogen and the Ni-Nx sites were atomically dispersed on carbon structure.The nitrogen content of the catalyst was 8.43 at.%result from the introduction of triazine rings.The Faradaic efficiency（F.E.）of NiPTFs-600 towards carbon monoxide（CO）was nearly 97.6%,and it could maintain the CO F.E.higher than 90%in a wide potential range from-0.55 to-0.95 V.Due to the synergistic effect of Ni-Nx active sites and N from triazine rings,the adsorption of CO₂ was promoted,thereby greatly enhancing the ECR performance of the catalyst.Besides,in order to solve the problems of high overpotential and low current density of the catalyst during the ECR process,a metal oxide containing catalyst denoted as ZrO₂@Ni-NC was prepared by hydrothermal,carbonization,and then NH4Cl etching.The particle size of ZrO₂ was around 5 nm,and the single Ni atoms were uniformly distributed in the material.The F.E.of ZrO₂@Ni-NC was 98.6%at-1.0 V,and the overpotential was only 190 mV.Additionally,by applying the gas diffusion electrode,the current density of ZrO₂@Ni-NC could reach as high as 200 mA cm-2.The introduction of ZrO₂ nanoparticles might change the reaction path of CO by increasing the adsorption of CO₂ and the proton transfer rate.