Tuning the Electrochemical Interface of Ag/C Electrodes in Alkaline Media with Metallophthalocyanine Molecules

Transition metal phthalocyanine (MPc) molecules were shown to be able to modify the electrochemical interface of the Ag catalyst in the alkaline electrolyte. Depending on the binding strength of the MPc (M = Fe, Co, Ni, and Mn) molecules with the OH^– species, the electrochemically active sites of the Ag electrode surfaces can be altered accordingly. A structural model for illustrating the electrochemical interface of the Ag/C catalysts modified by the MPc molecules in alkaline media is proposed, which can be used to elucidate the ORR kinetics observed on various MPc@Ag/C catalysts in AEMFCs. The optimal CoPc–OH and Ag–CoPc interactions resulted in the highest kinetic current density and power density (536 mW cm^–2 at 50 °C) observed with the AEMFCs using CoPc modified Ag/C cathode catalysts in comparison with the Ag/C and other MPc (M = Fe, Ni, and Mn) modified Ag/C catalysts

Nano-Structured Bio-Inorganic Hybrid Material for High Performing Oxygen Reduction Catalyst

In this study, we demonstrate a non-Pt nanostructured bioinorganic hybrid (BIH) catalyst for catalytic oxygen reduction in alkaline media. This catalyst was synthesized through biomaterial hemin, nanostructured Ag–Co alloy, and graphene nano platelets (GNP) by heat-treatment and ultrasonically processing. This hybrid catalyst has the advantages of the combined features of these bio and inorganic materials. A 10-fold improvement in catalytic activity (at 0.8 V vs RHE) is achieved in comparison of pure Ag nanoparticles (20–40 nm). The hybrid catalyst reaches 80% activity (at 0.8 V vs RHE) of the state-of-the-art catalyst (containing 40% Pt and 60% active carbon). Comparable catalytic stability for the hybrid catalyst with the Pt catalyst is observed by chronoamperometric experiment. The hybrid catalyst catalyzes 4-electron oxygen reduction to produce water with fast kinetic rate. The rate constant obtained from the hybrid catalyst (at 0.6 V vs RHE) is 4 times higher than that of pure Ag/GNP catalyst. A catalytic model is proposed to explain the oxygen reduction reaction at the BIH catalyst

Molecular and Electronic Structures of Transition-Metal Macrocyclic Complexes as Related to Catalyzing Oxygen Reduction Reactions: A Density Functional Theory Study

Transition-metal (TM) macrocyclic complexes have potential applications as nonprecious electrocatalysts in polymer electrolyte membrane fuel cells. In this study, we employed density functional theory calculation methods to predict the molecular and electronic structures of O₂, OH, and H₂O₂ molecules adsorbed on TM porphyrins, TM tetraphenylporphyrins, TM phthalocyanines, TM fluorinated phthalocyanines, and TM chlorinated phthalocyanines (here TM = Fe or Co). Relevant to their performance on catalyzing oxygen reduction reaction (ORR), we found for the studied TM macrocyclic complexes: (1) The type of the central TM is the most determinant factor in influencing the adsorption energies of O₂, OH, and H₂O₂ (chemical species involved in ORR) molecules on these macrocyclic complexes. Specifically, the calculated adsorption energies of O₂, OH, and H₂O₂ on the Fe macrocyclic complexes are always distinguishably lower than those on the Co macrocyclic complexes. (2) The peripheral ligands are capable of modulating the binding strength among the adsorbed O₂, OH, and H₂O₂, and the TM macrocyclic complexes. (3) A N–TM–N cluster structure (like N–Fe–N) with a proper distance between the two ending N atoms and a strong electronic interaction among the three atoms is required to break the O–O bond and thus promote the efficient four-electron pathway of the ORR on the TM macrocyclic complexes