OH−-Binding Effects on Metallophthalocyanine Catalysts for O2 Reduction Reaction in Anion Exchange Membrane Fuel Cells

Application of Molecular Catalysts for the Oxygen Reduction Reaction in Alkaline Fuel Cells

The development of precious group metal-free (PGM-free) catalysts for the oxygen reduction reaction is considered as the main thrust for the cost reduction of fuel cell technologies and their mass production. Within the PGM-free category, molecular catalysts offer an advantage over other heat-treated PGM-free catalysts owing to their well-defined structure, which enables further design of more active, selective, and durable catalysts. Even though non-heat-treated molecular catalysts with exceptional performance have been reported in the past, they were rarely tested in a fuel cell. Herein, we report on a molecular catalyst under alkaline conditions: fluorinated iron phthalocyanine (FeFPc) supported on cheap and commercially available high-surface area carbon─BP2000 (FeFPc@BP2000). It exhibits the highest activity ever reported for molecular catalysts under alkaline conditions in half-cells and fuel cells.

Study on the Effects of a π Electron Conjugated Structure in Binuclear Metallophthalocyanines Graphene-Based Oxygen Reduction Reaction Catalysts

The high overpotentials for oxygen reduction reaction (ORR) create an extremely negative impact on the energy efficiency of the air-based battery systems. To overcome this problem, binuclear ball-type metallophthalocyanines containing methoxy substituents (M₂Pc₂(EP)₄, M = Fe(II), Co(II) and Zn(II)) were wrapped with polystyrene sodium sulfonate (PSS) modified graphene oxide (GO), using a facilely “solvothermal π-π assembly” method to prepare M₂Pc₂(EP)₄/PSS-Gr composites. Compared with the commercial Pt/C catalysts, the M₂Pc₂(EP)₄/PSS-Gr composites enhanced the catalytic activity of oxygen reduction reaction. The π electron conjugated structure of the MN₄-type phthalocyanine macrocyclic system strongly influenced the one-step four-electron electrocatalytic process of the M₂Pc₂(EP)₄/PSS-Gr composites. Moreover, the π-π interactions between the M₂Pc₂(EP)₄ and PSS-Gr dramatically enhanced the π electron density in the conjugated structure and oxygen could be reduced more easily. The electrocatalytic activity test was displayed in the order of Fe₂Pc₂(FP)₄/PSS-Gr > Co₂Pc₂(EP)₄/PSS-Gr > Zn₂Pc₂(EP)₄/PSS-Gr. The results indicated that the catalytic performance of M₂Pc₂R_n could be enhanced by the modification of π electron conjugated structure of M₂Pc₂(EP)₄ and carbon materials.

Nonpyrolyzed Fe-N Coordination-Based Iron Triazolate Framework: An Efficient and Stable Electrocatalyst for Oxygen Reduction Reaction

Pyrolyzed base-metal-based metal-organic frameworks (MOFs) with FeN_x coordination are emerging as nonprecious metal catalysts for electrochemical oxygen reduction reaction (ORR). However, surprisingly, nonpyrolyzed MOFs involving Fe-N coordination have not been explored for the ORR. This study concerns the catalytic performance of a semiconducting nonpyrolyzed iron triazolate framework (FeTa₂ ) for ORR in alkaline electrolyte. The FeTa₂ catalyst is studied as composites with different amounts of conductive Ketjenblack carbon (KB). The performance of these FeTa₂ -x KB (x denotes the KB/FeTa₂ weight ratio) composites by onset and half-wave potentials of ORR appears to be superior to most previously documented nonpyrolyzed MOFs. Characterization by elemental analysis, FTIR spectroscopy, XPS, and cyclic voltammetry suggest that N-Fe^III -OH^- sites at the surface of FeTa₂ function as the catalytic active sites. This FeTa₂ also shows very stable activity during ORR, as supported by accelerated durability test of the FeTa₂ -x KB sample (20 000 cycles, ca. 90 h). The framework structure of FeTa₂ remains intact during the durability test, which would help to explain its excellent catalytic durability. This would be the first study demonstrating efficient and stable ORR catalysis by a nonpyrolyzed Fe-N coordination-based MOF material.

Systematic study of transition-metal (Fe, Co, Ni, Cu) phthalocyanines as electrocatalysts for oxygen reduction and their evaluation by DFT

A facile approach is reported to prepare a series of transition-metal phthalocyanines supported on graphitized carbon black (TMPc/GCB, TM: Fe, Co, Ni and Cu) as oxygen reduction reaction electrocatalysts,viaπ–π interaction self-assembly.