Departamento de Ciencias Físicas, Universidad Andrés Bello, Sazié 2212, 837-0136, Santiago, Chile.
Departamento de Química de Los Materiales, Facultad de Química y Biología, Universidad de Santiago de Chile, Santiago, Chile.
Sci Rep. 2022 May 16;12(1):8072. doi: 10.1038/s41598-022-11820-6.
Fe(III) 5,10,15,20-(tetraphenyl)porphyrin chloride (FeTPP) and Co(III) 5,10,15,20-(tetraphenyl)porphyrin chloride (CoTPP) were adsorbed on carbon Vulcan and studied as electrocatalysts for the oxygen reduction reaction (ORR) before and after pyrolysis. The pyrolysis process was also simulated through ab initio molecular dynamic simulations and the minimum energy path for the O dissociation after the interaction with the metal center of the FeTPP and CoTPP were calculated. After the pyrolysis the FeTPP showed the best performances reducing O completely to HO with increased limiting current and lower overpotential. Tafel slops for the various catalysts did not change after the pyrolytic process suggesting that the mechanism for the ORR is not affected by the heat treatment. TEM images, X-ray diffraction, XPS spectroscopy, Fe Mössbauer, and DFT simulations, suggest that there is no breakdown of the macrocyclic complex at elevated temperatures, and that the macro cyclic geometry is preserved. Small variations in the Metal-O (M-O) binding energies and the M-N bond length were observed which is attributed to the dispersive interaction between the macrocycles and the irregular surface of the Vulcan substrate induced by the heat treatment and causing better interaction with the O molecule. The theoretical strategy herein applied well simulate and explain the nature of the M-N-C active sites and the performances towards the ORR.
三价铁 5,10,15,20-(四苯基)卟啉氯化物（FeTPP）和三钴 5,10,15,20-(四苯基)卟啉氯化物（CoTPP）被吸附在碳 Vulcan 上，并在热解前后作为氧还原反应（ORR）的电催化剂进行了研究。通过从头算分子动力学模拟还模拟了热解过程，并计算了与 FeTPP 和 CoTPP 的金属中心相互作用后 O 离解的最小能量路径。热解后，FeTPP 表现出最佳性能，可将 O 完全还原为 HO，从而增加了极限电流并降低了过电势。各种催化剂的塔菲尔斜率在热解过程后没有变化，这表明 ORR 的机制不受热处理的影响。TEM 图像、X 射线衍射、XPS 光谱、Fe Mössbauer 和 DFT 模拟表明，在高温下大环络合物没有分解，大环络合物的几何形状得以保留。观察到金属-氧（M-O）结合能和 M-N 键长的微小变化，这归因于热处理引起的大环和 Vulcan 基质不规则表面之间的分散相互作用，从而与 O 分子更好地相互作用。本文应用的理论策略很好地模拟和解释了 M-N-C 活性位的性质以及对 ORR 的性能。
