The Design Of Catalysts And Study Of Performance For CO₂ Electrochemical Reduction

Converting carbon dioxide(CO2)into renewable energy plays an important role in our global efforts to mitigate both the energy shortage and climate change.In particular,electrochemical reduction of CO2 to value-added chemicals such as carbon monoxide(CO)and formate(HCOO-)can realize carbon-neutral cycle so as to reduce the accumulation of carbon in the atmosphere.In the sense,this conversion can also be regarded as a new type of energy storage,which has great potential for practical application.However,the efficiency of this conversion depends heavily on the catalytic performance of electrode.Therefore,designing and constructing a catalyst with high efficiency is crucial to realize this technology.Herein,a series of highly selective catalysts are elaborately constructed with simplified synthesis strategy to address the problems of low Faradaic efficiency for CO2 electroreduction and complicated synthesis route of electrode.The metal organic frameworks(MOFs)are employed as substrates,utilizing its pore structure to uniformly adsorb the single metal precursor.After a simple process of pyrolysis,a metal-doped carbon framework catalyst can be fabricated.A series of single-atom/nano materials with different metal doped are prepared through this simple and effective strategy Moreover,the preparation of bismuth(Bi)electrocatalyst is simplified by one-step reduction method.The electrocatalytic performance of these single-atorm/nano catalysts was then investigated.The main achievements are as follows:(1)Nickel-single-atom catalyst:Zeolitic imidazolate frameworks(ZIF-8),doping with Ni and dicyandiamide,are used as precursor to fabricate coordinatively unsaturated Ni-N sites through one-pot pyrolysis.Afterward,its catalytic performance for CO2 electroreduction and corresponding reaction mechanism were investigated.Ni in the catalyst is atomically dispersed on the surface of the carbon nanotubes.Different from Ni plate or nanoparticles,nickel-single-atom catalyst shows remarkable catalytic activity and selectivity for CO2 electroreduction,which solves the problem of low Faradaic efficiency caused by favorable hydrogen evolution reaction on most metal electrodes.(2)Fe/Ni nano-alloy catalyst:A uniformly dispersed and stable catalyst of Fe/Ni nano-alloy was fabricated by pyrolyzing Fe and Ni salts modified ZIF-8 Electrochemical measurements verified its remarkable intrinsic catalytic activity for electroreduction CO2 to CO.Due to the electrons transferred from Fe/Ni nano-alloy,the nitrogen-doped carbon framework would be in an electron-rich state,promoting the reduction of CO2 on graphene shell.Worth noting that this particular 3D carbon frameworks offer an enlarged specific surface area,which greatly improves its electrocatalytic performance.(3)Bismush nanostructure:A facile and one-pot synthesis strategy of Bi nanostructure was reported by using Sodium borohyUrlde to reduce Bi3+.Thanks to the enhanced electrochemical active area,which exposed more edges,steps,defect and high-index planes,remarkable catalytic performance with high activity and selectivity was achieved.Experimental results show that CO2 can be efficiently reduced to formate on Bi nanostructure.Density functional theory(DFT)calculation shows that the formation of*OCHO has much lower energy barrier on Bi high-index planes,particularly on Bi(012),leading to the generation of formate in the end.Most importantly,its simplified synthesis strategy gives the catalyst great potential in practical application.