【作者】 张萌；

【导师】 胡适；

【作者基本信息】 天津大学 ， 化学， 2020， 硕士

【摘要】 目前可再生能源的利用存在区域性和间歇性等问题,通过各种形式的可再生能源转化得到清洁的二次能源电源,经由电能与化学能之间的高效转化实现能量的存储和利用将会大大提高清洁能源的利用率,有效缓解目前的能源危机和环境恶化问题。电催化在清洁能源转换中扮演着越来越重要的作用,在各种电能和化学能的转换技术中,电催化还原二氧化碳（CO₂ reduction reaction,CO₂RR）和水分解制氢均可获得清洁燃料,这对全球能源安全、环境和经济的可持续发展意义重大。研发高效、低廉的电催化剂是使得这些清洁能源技术得以广泛普及的关键所在。本论文的主要目的是通过合理的设计开发具有良好活性的非贵金属电催化剂,用于电催化CO₂还原反应（CO₂RR）和水分解析氧反应（oxygen evolution reaction,OER）,其主要内容如下:1.采用了级联锚定策略,以多孔碳为基底,镍盐或铁盐为金属源,通过调节镍盐和铁盐的摩尔比,成功合成了Ni-N-C单原子催化剂（Single atom catalyst,SAC）、Fe-N-C SAC和双金属掺杂的碳基单原子催化剂(Ni_xFe_1-x-N-C SAC)。通过一系列的表征,发现成功制备出目标催化剂。2.电催化CO₂还原反应结果表明,该系列催化剂(Ni_xFe_1-x-N-C SAC)的还原产物只有CO和H₂两种,可制备合成气。其中,单位点的Ni-N-C SAC表现CO₂-to-CO的优异选择性,CO的法拉第效率可达98%;而Fe-N-C SAC利于HER的进行。通过调节材料合成中镍盐和铁盐的摩尔比,便可调控还原产物中CO/H₂（合成气）的比例。当材料中的x从0逐渐变为0.8时,即可在-0.86 V（vs.RHE）的电压下实现合成气（CO/H₂）宽比例（0.14-10.86）的调控。经过与密度泛函理论（Density Functional Theory,DFT）计算相结合,发现Ni-N-C位点是CO₂RR的催化活性中心,而Fe-N-C是HER的活性中心。3.电催化OER结果表明,与单金属掺杂的多孔碳（Fe-N-C SAC和Ni-N-C）相比,双金属位点的Ni_xFe_1-x-N-C SAC有着优异的OER催化活性。并且x与η_j=10(电流密度为10 m A cm^-2下的过电势)呈“倒火山”关系,具体表现为:随着x的逐渐增大,η_j=10先下降后上升,在x=0.5时具有最低值(即x=0.5时,η_j=10为319 m V,具备最优的OER活性)。更多还原

【Abstract】 At present,there are regional and intermittent problems in the use of renewable energy.Through various forms of renewable energy conversion,a clean secondary energy source can be obtained.The efficient storage and utilization of energy through the efficient conversion between electrical energy and chemical energy will be greatly improved.The utilization rate of clean energy effectively relieves the current energy crisis and environmental degradation.Electrocatalysis plays an increasingly important role in the conversion of clean energy.In various conversion technologies of electrical energy and chemical energy,clean fuel can be obtained by electrocatalytic reduction of carbon dioxide（CO₂ reduction,CO₂RR）and water decomposition to produce hydrogen.This is of great significance to global energy security,environmental and economic sustainable development.The development of efficient and inexpensive electrocatalysts is the key to the widespread use of these clean energy technologies.The main purpose of this paper is to develop a non-noble metal electrocatalyst with good activity through reasonable design for electrocatalytic CO₂ reduction reaction（CO₂RR）and oxygen evolution reaction（OER）.The main contents are as follows:1.A cascade anchoring strategy is adopted with porous carbon as substrate and nickel or iron salts as the metal source.By adjusting the molar ratio of nickel salt and iron salt,Ni-N-C single atom catalyst（SAC）,Fe-N-C SAC and bimetal doped carbon- based single atom catalyst(Ni_xFe_1-x-N-C SAC)were successfully synthesized.Through a series of characterization,it was found that the target catalysts were successfully prepared.2.The results of electrocatalytic CO₂RR show that the reduction products of this series of catalysts(Ni_xFe_1-x-N-C SAC)are only CO and H₂,which can be used to prepare syngas.Among them,the Ni-N-C SAC shows the excellent selectivity of CO₂-to-CO,the Faraday efficiency of CO can reach 98%;and Fe-N-C SAC is beneficial to HER.By adjusting the molar ratio of nickel and iron salts in the synthesis of materials,the ratio of CO/H₂（syngas）in the reduction product can be adjusted.When the x in the material gradually changes from 0 to 0.8,the width ratio（0.14-10.86）of the syngas（CO/H₂）can be adjusted at a voltage of-0.86 V（vs.RHE）.Combined with Density Functional Theory（DFT）calculations,it is found that the Ni-N-C site is the catalytic active center of CO₂RR,and Fe-N-C is the active center of HER.3.The electrocatalytic OER results show that Ni_xFe_1-x-N-C SAC with bimetallic sites have excellent OER catalytic activity compared to single-metal doped porous carbon（Fe-N-C SAC and Ni-N-C SAC）.x andη_j=10(overpotential at a current density of 10 m A cm^-2)have an"inverted volcano"relationship,which is specifically expressed as:as x gradually increases,η_j=10 decreases first and then rises,it has the lowest value at 0.5(that is,when x=0.5,η_j=10=319 m V,the best OER activity).更多还原