Designed Synthesis Of Nickel And Nitrogen Co-doped Carbon Electrocatalysts For CO₂ Reduction

Due to the rapid development of social economy,human activities have led to an increase in the atmospheric CO₂ content year by year.Thus,the greenhouse effect has become more and more obvious.And a series of environmental problems such as the global warming,melting glaciers,and ocean acidification etc.have emerged which further affected the ecological balance of nature.Capturing the CO₂ in the atmosphere and converting it into high value-added chemicals can realize the social economic value of CO₂ and maximize the use of resources.Currently,among all CO₂ conversion technologies,the electrochemical method has become a hot spot for researchers due to its advantages such as mild conditions,adjustable product compositions,simple equipment,and environmental-friendly.The structure of CO₂ molecular is stable,hence a high overpotential is needed for the activation process.Therefore,it is necessary to use highly active electrocatalysts to lower the overpotential and reduce energy consumption.Carbon materials have the advantages of high conductivity,controllable pore structure,excellent stability,low cost,etc.,but their catalytic activity is not high,so non-noble metal porous carbon-based catalysts have received great attention.Herein,we took transition metal porous carbon-based catalyst as the research object,and realized the adjustment of the distribution of CO₂ electroreduction products through component adjustment and structure optimization.The main contents and results are as follows:?1?Melamine,triphenylphosphine and nickel acetate were used as precursors to synthesize ternary nanocomposites,pyrolyzed at 850?,melamine as nitrogen source and carbon source,triphenylphosphine as phosphorus source,and finally get a nickel phosphide in-situ growth on nickel-nitrogen-carbon matrix electrocatalyst.Nickel phosphide is a common hydrogen evolution catalyst,Ni-N-C has a high selectivity for the reduction of CO₂ to CO,therefore,the obtained electrocatalysts were used to catalyze CO₂-H₂O to prepare syngas with different proportions.The influence of triphenylphosphine content in the precursor on the morphology,pore structure,and surface element composition of materials was explored.It was found that as the amount of triphenylphosphine in the precursor increases,the specific surface area of the catalyst increases,which is mainly because of the activation of the gas generated during the pyrolysis of triphenylphosphine,which can increase the pore structure and specific surface area of the materials.The species of nickel phosphide changed from Ni₁₂P₅ to Ni₂P.The CO₂reduction tests show that the CO/H₂ ratio can be adjusted from 10:1 to 1:4 at the potential range of-0.5^-1.1 V?vs.RHE?.And results showed a linear correlation between the synthesis gas ratio and the surface nickel phosphide/Ni-N_x value at the same potential.This part of work provides a new synthesis idea for the preparation of syngas.?2?Crystalline coordination polymers containing repeated Cu-N₄ motifs was synthesized as precursor.Next,an edge-riched ultra-polar carbon was prepared after pyrolysis and acid washing.In this work,the nitrogen doping amount,nitrogen species distribution and pore structure of the materials synthetized at temperature of 600?and 900?were studied.A nickel-nitrogen-carbon catalyst was prepared by Ni?NO₃?₂ impregnation and applied in CO₂electroreduction.N₂ and CO₂ adsorption results showed that the materials are rich in micropores,which are beneficial to the anchoring of nickel atoms and provides reactive sites.According to TG-MS analysis,it was found that the prepared ultra-polar carbon contains large numbers of edge sites compared with the nonpolar carbon material EC600JD.The result of water vapor adsorption showed that the adsorption volume of the as-prepared ultra-polar carbon at low relative humidity is significantly greater than that of nonpolar carbon material EC600JD,indicating a greater polarity.Stability test result showed that UPC-2%Ni electrolyzed at-0.77V?vs RHE?for 9 h can still maintain a Faraday efficiency of more than 90%,indicating a good stability.This work provides a reference for the application of hydrophilic carbon in CO₂reduction.