Using reactivity predictors to enhance or control the electrocatalytic activity of materials is a fascinating concept. This is especially true for the development of alternative platinum metal group-free materials as it facilitates the rational design of active catalytic materials for the oxygen reduction reaction (ORR). In previous work, we have found that the peripheral and non-peripheral electron-withdrawing effects and the electron-pull effect from axial extraplanar ligand in iron-phthalocyanine (FePc) are key factors in improving the binding energy between the active Fe site and O₂ resulting in an increase of the electrocatalytic activity of FePcs for the ORR. In this work, we have utilized fundamental principles of electrocatalysis and DFT calculations to design and synthesize FeN4 molecular catalysts to increase their catalytic performance for the ORR through the "pull" effect. To achieve this, by chemical synthesis, we have incorporated pyridinium functional groups (N⁺py) in peripheral and non-peripheral positions into the porphyrazine cyclic ligands. In this fashion we obtain the porphyrazinium molecular catalysts, [Fe(II)2,3-(TMe)TPyPz]⁴⁺ and [Fe(II)3,4-(TMe)TPyPz]⁴⁺. Because these new compounds are not commercially available and, to the best of our knowledge, they have not been tested for ORR. In order to determine their effectiveness, we have compared porphyrazinium with neutral analog porphyrazine compounds (Fe(II)TPyPz) and perfluorinated and perchlorinated iron phthalocyanines, which are currently the best molecular catalysts for ORR. The electrocatalytic activity was determined for each molecular catalyst deposited on the edge plane of a graphite electrode (EPG) surface in an alkaline medium. Only for the purpose of comparison we include two Fe porphyrins studied previously, which show low activity for ORR. Although the DFT theoretical analysis of porphyrazinium complexes suggests a high activity for these catalysts, our experimental findings revealed the opposite trend. Therefore, this finding makes us reconsider the interfacial effects, such as the counter-ions effects on N⁺_py that could influence the electron-pull effect, opening new insights for designing molecular catalysts considering interface engineering. Moreover we report for the first time, the reactivity linear relationship between the metal-centered redox potential gap (E°_Fe(III)/(II) – E°_Fe(II)/(I))) with the electrocatalytic activity for ORR for all catalysts studied, emerging this potential gap as a possible and promising new reactivity descriptor for ORR in MN4 catalyst.

使用反应性预测器来增强或控制材料的电催化活性是一个令人着迷的概念。对于替代性无铂金属族材料的开发尤其如此，因为它有助于氧还原反应（ORR）活性催化材料的合理设计。在前期工作中，我们发现铁酞菁（FePc）中的外围和非外围吸电子效应以及轴面外配体的电子拉力效应是提高活性Fe位点与O之间结合能的关键因素。 ₂导致 FePcs 对 ORR 的电催化活性增加。在这项工作中，我们利用电催化和DFT计算的基本原理来设计和合成FeN4分子催化剂，通过“拉”效应提高其对ORR的催化性能。为了实现这一目标，通过化学合成，我们将外围和非外围位置的吡啶鎓官能团（N ^{+ py）掺入四氮杂萘环状配体中。}通过这种方式，我们获得了四氮杂卟啉分子催化剂，[Fe(II)2,3-(TMe)TPyPz] ⁴⁺和 [Fe(II)3,4-(TMe)TPyPz] ⁴⁺。因为这些新化合物尚未上市，而且据我们所知，它们尚未经过 ORR 测试。为了确定其有效性，我们将四氮杂卟啉与中性类似四氮杂卟啉化合物 (Fe(II)TPyPz) 以及全氟化和全氯化铁酞菁进行了比较，它们是目前最好的 ORR 分子催化剂。在碱性介质中测定了沉积在石墨电极（EPG）表面边缘平面上的每种分子催化剂的电催化活性。仅出于比较的目的，我们纳入了之前研究的两种铁卟啉，它们对 ORR 的活性较低。尽管紫菜络合物的 DFT 理论分析表明这些催化剂具有高活性，但我们的实验结果却揭示了相反的趋势。所以，⁺ _py可能会影响电子拉力效应，为考虑界面工程的分子催化剂设计提供新的见解。此外，我们首次报告了金属中心氧化还原电位间隙（E° _Fe(III)/(II) – E° _Fe(II)/(I))）与ORR电催化活性之间的反应性线性关系对于所有研究的催化剂，将这种潜在的差距作为 MN4 催化剂中 ORR 的可能且有前途的新反应性描述符。