【作者】 刘博；

【导师】 王振波；

【作者基本信息】 哈尔滨工业大学 ， 化学工程与技术， 2022， 硕士

【摘要】 质子交换膜燃料电池（PEMFC）与锌-空气电池（ZAB）是新型的高能、环保储能与转换器件,但其阴极氧还原反应（ORR）过程过电位高、机理复杂,Pt族金属（PGM）催化剂成本高昂,合成低成本、高活性的非贵金属ORR催化剂是这两类电池商业化应用的关键步骤。针对非贵金属催化剂本征活性不足的问题,本论文基于沸石咪唑酯骨架（ZIF-8）材料制备了高活性的锰基双金属氧还原催化剂,并对Mn元素对催化剂活性提升的作用机理进行了相关研究。以ZIF-8材料为前驱体,通过化学掺杂-限域吸附两步法制备了含有Co、Mn双金属的氮掺杂碳催化剂。化学掺杂法引入的Co位点具有一定的ORR催化活性,对经过工艺优化后的Co-N掺杂碳材料（Co NC）通过限域吸附法引入Mn元素后,催化剂的活性得到显著提升。通过调节Mn盐的吸附量和热活化温度,所制备的Co-Mn-N掺杂碳（Co Mn NC）催化剂在酸性体系下的旋转圆环圆盘电极（RRDE）极化曲线半波电位达到了0.80 V（vs.RHE）,碱性体系下的半波电位高达0.92 V（vs.RHE）,锌-空气电池测试的最大功率密度可达193.5 m W·cm^-2,并具有优异的长时间放电稳定性。密度泛函理论计算的结果表明,向Co N₄位点附近引入Mn N₄结构后,Co位点的d带中心下降,其对O₂分子的活化能力得到提升,使速度控制步骤O=O双键的断裂更加容易进行。另外,以ZIF-8材料为基础,通过一步化学掺杂法同时引入Fe、Mn两种金属元素,制备了含有Fe Mn双金属的氮掺杂碳催化剂。通过研究不同Fe³⁺、Mn²⁺占比对催化剂活性的影响,发现在所制备的Fe-Mn-N掺杂碳（Fe Mn NC）催化剂中,Fe元素为主要活性位点,Mn元素起到了调控Fe位点活性的作用。密度泛函理论计算揭示了Mn N₄位点对Fe N₄位点ORR催化活性的调控机理,Mn位点的引入增强了Fe位点的自旋极化,通过COHP计算证明这种极化有利于削弱Fe-O键,降低OH*脱附的能垒。所制备的非贵金属Fe Mn NC催化剂具有优异的ORR催化活性,在酸性体系下的RRDE极化曲线半波电位达到0.83 V（vs.RHE）,接近商业Pt/C催化剂。氢燃料电池测试的最大功率密度可达501.7 m W·cm^-2,具有应用前景。更多还原

【Abstract】 Proton exchange membrane fuel cells（PEMFC）and zinc-air batteries（ZAB）are novel high-energy and environmentally friendly energy storage and conversion devices,but their cathodic oxygen reduction reaction（ORR）processes have high overpotentials and complex mechanisms.Due to the high cost of Pt group metal（PGM）catalysts,the synthesis of low-cost,high-active non-precious metal ORR catalysts is a key step for the commercialization of these two types of batteries.To address the problem of insufficient intrinsic activity of non-precious metal catalysts,this thesis prepared highly active manganese-based bimetallic ORR catalysts based on zeolitic imidazolate framework（ZIF-8）materials and investigated the mechanism of the effect of Mn elements on catalyst activity enhancement.Nitrogen-doped carbon catalysts containing Co and Mn bimetals were prepared by a two-step doping/adsorption method using ZIF-8 material as the precursor.The Co sites introduced by the chemical doping method had certain ORR catalytic activity,and the activity of the catalysts was significantly enhanced after the introduction of Mn elements by the adsorption method for the Co NC materials after process optimization.By adjusting the adsorption amount of Mn salt and thermal activation temperature,the prepared Co Mn NC catalysts reached a half-wave potential of 0.80 V（vs.RHE）of polarization curve at the rotating circular disc electrode（RRDE）in the acidic system and up to 0.92 V（vs.RHE）in the alkaline system,with a maximum power density of 193.5 m W·cm^-2 in the zinc-air cell test and excellent long-term discharge stability.The results of density functional theory calculations showed that the introduction of the Mn N₄ structure into the vicinity of the Co N₄ site decreases the d-band center of the Co site,and its activation ability of the O₂ molecule was enhanced,making the breakage of the O=O double bond in the velocity control step easier.In addition,nitrogen-doped carbon catalysts containing Fe Mn bimetals were prepared based on ZIF-8 material by introducing two metal elements,Fe and Mn,simultaneously through a one-step chemical doping method.By investigating the effects of different Fe³⁺,Mn²⁺and Zn²⁺ratios on the catalyst activity,it was found that in the prepared Fe Mn NC catalysts,Fe element was the main active site and Mn element played the role of regulating the activity of Fe site.Density functional theory calculations revealed the mechanism of modulation of the Mn N₄ site on the catalytic activity for the Fe N₄ site ORR.The introduction of the Mn site enhanced the spin polarization of the Fe site,and this polarization was demonstrated by COHP calculations to be conducive to weakening the Fe-O bond and reducing the energy barrier for OH*desorption.The prepared non-precious metal Fe Mn NC catalyst had excellent ORR catalytic activity,and the RRDE half-wave potential of polarization curve in the acidic system reached 0.83 V（vs.RHE）,which was close to that of commercial Pt/C catalysts.The maximum power density tested for the hydrogen fuel cell can reach 501.7 m W·cm^-2,which is promising for application.更多还原