【摘要】 析氧反应（OER）是电解水制氢的关键步骤,开发高效、稳定、廉价的OER电催化剂是目前该领域的研究热点.碱性电解液中的OER电催化剂成分以Mn、Fe、Co、Ni等为主,其中单一组分的Fe基化合物催化活性不高,但碱性电解液中的痕量铁杂质极易掺入Ni、Co等非Fe基材料的结构中,极大影响其OER催化性能,即现有大部分非Fe基化合物无法回避Fe的影响.为探究Fe基多金属电催化剂的活性规律,本文以结构清晰、组分可控的Fe基金属有机框架材料为基底,通过掺入Mn、Co、Ni等元素构建双元金属化合物Fe₂M-MIL-88B（M=Mn, Co, Ni）,并围绕上述Fe基双金属电催化剂的构效关系展开研究.扫描电镜、透射电镜、X射线衍射光谱、红外光谱等表征结果表明,所制备的Fe基双金属材料均为具有MIL-88B构型的纳米棒,其特征三核金属簇Fe3O中的一个铁原子被第二元金属所替代,从而形成相应的三核混合金属簇Fe₂MO.上述Fe基双金属催化剂的析氧催化活性顺序为:Fe₂Ni> Fe₂Co> Fe₂Mn> Fe （0.1 M KOH电解液）.其中, Fe₂Ni-MIL-88B电催化剂在10 m A cm^-2析氧电流对应的过电位仅需307 m V,明显低于OER基准电催化剂20 wt%Ir/C（376 m V）.结合材料的元素组成、电化学活性比表面积（ECSA）及金属价态分析发现,第二元金属的引入会在不同程度上降低Fe的价态,其中Ni的影响程度最大, Co次之, Mn的影响最小.借助分子轨道理论对上述实验现象进行了解释.处于低自旋态的Ni²⁺与邻近桥氧O^2-之间存在电子排斥作用,因此部分电子将从Ni²⁺经O^2-转移至高自旋态的Fe³⁺,从而在Ni²⁺和Fe³⁺之间形成了较强的电子耦合作用.Co²⁺具有和Ni²⁺相似的构型,但影响稍小.而Mn²⁺和Fe³⁺同为高自旋态,对Fe³⁺的电子结构影响最小,导致活性改善程度最低.密度泛函理论计算得到的自旋态变化情况印证了上述推测.该系列Fe基双金属材料的催化性能主要受金属活性位点的电子结构影响, Fe与邻近金属间形成的电子耦合作用修饰了金属活性位点的电子结构,从而提高了材料的OER本征催化活性.更多还原

【Abstract】 First-row transition metal compounds have been widely explored as oxygen evolution reaction（OER） electrocatalysts due to their impressive performance in this application. However, the activity trends of these electrocatalysts remain elusive due to the effect of inevitable iron impurities in alkaline electrolytes on the OER; the inhomogeneous structure of iron-based（oxy）hydroxides further complicates this situation. Bimetallic metal-organic frameworks（MOFs） have the advantages of well-defined and uniform atomic structures and the tunable coordination environments, allowing the structure-activity relationships of bimetallic sites to be precisely explored. Therefore, we prepared a series of iron-based bimetallic MOFs（denoted as Fe₂ M-MIL-88 B, M = Mn, Co, or Ni） and systematically compared their electrocatalytic performance in the OER in this work. All the bimetallic MOFs exhibited higher OER activity than their monometallic iron-based counterpart, with their activity following the order Fe Ni > Fe Co > Fe Mn. In an alkaline electrolyte, Fe₂ Ni-MIL-88 B showed the lowest overpotential to achieve a current density of 10 m A cm^–2（307 m V） and the smallest Tafel slope(38 m V dec^–1). The experimental and calculated results demonstrated that iron and nickel exhibited the strongest coupling effect in the series, leading to modification of the electronic structure, which is crucial for tuning the electrocatalytic activity.更多还原