Preparation And Performance Study Of Cu-Cu₂O-Al₂O₃/C Catalyst For Electrochemical Reduction Of Carbon Dioxide Into Ethylene

Recently,CO₂ conversion by the electrochemical tool into value-added chemicals has been considered as one of the most promising strategies to offer sustainable development in energy and environment due to low-cost and efficient process.To develop and figure out the efficient and stable metal-based electro-catalysts is a pertinent task to enhance the selectivity and stability toward C₂ products to fulfil the fuel and energy need and also applicable for industrial purpose as well.Apart from the commonly used strategies for improvement of hydrocarbons by using surface structural and compositional regulation in copper-based catalysts,the oxides derived copper-based catalyst through electrochemical treatment from 2D materials is an alternative and effective strategy to enhance the surface area,highly dispersed exposed reactive sites for increasing the electro-catalytic reactivity toward C₂ products during CO₂reduction reaction.The aim of this thesis,to devise a strategy for utilization of electro-derived catalysts from layered double hydroxides（LDH）composite,which would be energy efficient,environmentally friendly,cost-effective and efficient toward CO₂ reduction reaction（CO₂RR）.The purpose of devising the electro-catalysts to explore the role and interfacial effect of LDH layered structure as supporting material for derived copper and its oxides from LDH;and role of other supporting material for LDH derived catalyst.These influential factors in LDH based catalysts are revealed toward CO₂RR accordingly.First,copper（Cu）based LDHs was designed through standard co-precipitation method with adjustable copper ration and further,the derived Cu-Cu O_x-Al₂O₃ nanocomposite by electrochemical treatment strategy.In electrochemical reduction（ER）treatment strategy,different potential vs.time was applied to obtained different derived nanocomposites to optimize the applied potential vs.time and Cu ratio as well through CO₂RR process accordingly.Herein,the ER-Cu₅-LDH was the best one as compared to other derived catalysts due to high faradaic efficiency（44%）toward C₂H₄ along with good stability up to 22 h.The partial current density was?6.8 m A/cm² higher than other derived electro-catalysts.Subsequently,the detailed analysis exhibited that this unique strategy for electro-derived composite from LDH having small nanoparticles stacked each other grown on the layered structure would provide new insight to improve the durability of O-Cu combination catalysts for C-C coupling products during electrochemical CO₂ conversion by suppressing hydrogen evolution reaction（HER）.The X-ray diffraction（XRD）,high resolution transmission electron microscopy（HRTEM）,scan electron microscopy（SEM）,Tafel slop,electrochemically active surface area（ECSA）and X-ray photoelectron spectroscopy（XPS）analyses confirmed that the long-term ethylene selectivity of ER-Cu₅-LDH.Later,the catalyst performance was compared with ER-Cu₂O and found higher efficiency toward C₂H₄.The designed composite catalyst significantly enhances the stability and selectivity,and also decreases the over-potential for CO₂ electro-reduction.Second,to improve the current density and catalytic activity,the Cu₅Al-CO₃ LDH with different graphene oxide（GO）ratios were designed and passed through electrochemical treatment to derive electro-composites Cu-Cu₂O-Al₂O₃/r GO（reduced graphene=r GO）.In order to optimize the GO with LDH via efficient C₂H₄performance,the derived-catalyst were passed through an efficient CO₂ reduction reaction（CO₂RR）.Interestingly,the ER-Cu₅-LDH/r GO-3 catalyst presented a higher C₂H₄ production selectivity（54%）than the ER-Cu₅-LDH C₂H₄FE（44%）catalyst without r GO.The obtained ER-Cu₅-LDH/r GO-3catalyst exhibited a high C₂H₄ FE up to 54%and a high C₂H₄ partial current density of?11.64 m A/cm² at?1.2 V vs.RHE.It also exhibited excellent stability up to 50 h which is higher than ER-Cu₅-LDH catalyst stability（22 h）.The morphological changes during CO₂RR were monitored using SEM analyses.ER-Cu₅-LDH/r GO-3 post CO₂RR SEM morphologies remained stable up to 50 h but the ER-Cu₅-LDH catalyst morphology is turned into deforming after 22 h.The influences of p H on the electro-catalytic performance of ER-Cu₅-LDH/r GO-3 were studied.To reflect the superiority of LDH precursors,a control catalyst containing Cu₂O nanoparticles supported on r GO（ER-Cu₂O-Al₂O₃/r GO）was prepared and comparatively studied.The high C₂H₄ FE,high C₂H₄ partial current density,and the excellent stability of ER-Cu₅-LDH/r GO-3 can be attributed to the good dispersion of active copper species along with the high electric conductivity of r GO.Finally,to extend this study,the Cu₅Al-CO₃ LDH with hexaaminetetraphenyl（HATP）COF（covalent organic framework）was designed to improve the current density,performance toward C₂H₄and also investigate the role COF nitrogen combined carbon as support material.The derived-catalysts were comparatively analyzed for efficient CO₂RR analysis.Among all,the ER-Cu₅-LDH/COF-2 catalyst represented the highest C₂H₄ FE（63%）and stability up to 75 h which is higher than that other derived catalysts.Hence,the detailed HRTEM,XPS,SEM analysis revealed that the exfoliation of COF and interaction of Cu with nitrogen play a vital role in enhancement of catalytic activity toward C₂H₄selectivity and stability.Moreover,highly dispersed Cu-Cu₂O-Al₂O₃ nanoparticles also a key factor for selectivity and stability.These results are very useful for the rational design of catalysts for a variety of processes,as has been demonstrated in this work for the CO₂ electrochemical oxidation.We are hopeful that the design of electro-engineering for LDH based electro-derived composites will be applied for further stable and selective electro-catalysts development for CO₂ reduction to value-added products especially C₂H₄.