High content Fe(III) electrocatalyst for the oxygen reduction and evolution reactions. Spectroscopic, electrochemical, and theoretical insights

• Published in: International journal of hydrogen energy 2025-02, Vol.101, p.605-616
• Main Authors: Loyola, César Zúñiga, Zitolo, Andrea, Troncoso, Nicolás, Carrasco, Juan, Choque, Sergio, Abarca, Gabriel, Zagal, Jose H., Orellana, Walter, Tasca, Federico
• Format: Article
• Language: English
• Subjects: Fe phthalocyanine; Fuel cell cathode; Oxygen evolution reaction; Oxygen reduction reaction; Penta-coordination; Zn-air battery
• ISSN: 0360-3199
• DOI: 10.1016/j.ijhydene.2024.12.385

X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS), DFT simulations, and standard electrochemical methods were used to analyse the high Fe(III) content of the synthetized Fe phthalocyanine (FePc) axially coordinated to 4-amino-3-nitropyridine (NPy). XPS analysis reveals that NPy exerts a high electron-withdrawing power on the Fe centre causing a shift to a more positive value of E0’Fe(III)/(II) contrasted to FePc-CNT with a ΔE0’ = [E0’FePc-NPy-CNT(III)/(II) - E0’FePc-CNT(III)/(II)] = 56 mV, which evidence the possibility to fine-tune this value. XAS and XANES analyses indicate a decreased electron density in the metal centre causing lower interactions with O2. Consecutively, the Fe2+/Fe3+ ratio changes from 0.95 to 0.51 for FePc-CNT and Fe-NPy-CNT, respectively. The electrocatalytic studies of the oxygen reduction reaction (ORR) in alkaline media, show better performances than the commonly used Pt 20% electrocatalyst in terms of overpotential (ΔE0’ = [E0'onsetFe-NPy-CNT - E0'onset Pt0] = 35 mV) and similar TOF rates at 0.9 V vs. RHE (∼1.00 e− site−1 s−1). DFT calculations show that both FePc-Py-CNT and FePc-NPy-CNT catalysts have nearly equal interactions with O2 (−0.37 eV and −0.32 eV, respectively). However, the O2 bond distance in the FePc-NPy-CNT system is 11% greater compared to the FePc-Py-CNT system explaining the superior performance of the FePc-NPy-CNT catalyst for the oxygen reduction reaction (ORR). Additionally, the interaction with H2O is stronger in the -NPy-configuration, which is consistent with the experimental results. [Display omitted] •High spin and Fe(III) content electrocatalyst was synthetized using NPy and FePc.•The NPy-presence decreases the electron density in the metal centre•NPy exerts a high shift in E0’Fe(III)/(II) allowing to fine-tune this value.•Lower interactions with O2 and TOF values for the ORR similar to Pt catalyst.•The OER is negatively affected by the high Fe(III) content.