Fe azaphthalocyanine unimolecular layers (Fe AzULs) on carbon nanotubes for realizing highly active oxygen reduction reaction (ORR) catalytic electrodes

Autor: Hiroya Abe, Jun Nakamura, Susumu Ikeda, Tomokazu Matsue, Yutaro Hirai, Haruyuki Matsuyama, Hiroshi Yabu, Yasutaka Matsuo
Rok vydání: 2019
Předmět:
Zdroj: NPG Asia Materials. 11
ISSN: 1884-4057
1884-4049
DOI: 10.1038/s41427-019-0154-6
Popis: A new class of Pt-free catalysts was designed that included molecular iron phthalocyanine (FePc) derivatives, namely, iron azaphthalocyanine (FeAzPc) unimolecular layers (Fe AzULs) adsorbed on oxidized multiwall carbon nanotubes (oxMWCNTs). FeAzPcs were dissolved in organic solvents such as dimethyl sulfoxide (DMSO), and catalytic electrodes modified with molecularly adsorbed FeAzPcs were successfully prepared. The optimized composition of the catalytic electrodes was determined, and the electrodes exhibited superior activity for the oxygen reduction reaction (ORR) and better durability than conventional FePc catalytic electrodes and commercial Pt/C due to the electron-withdrawing properties of the pyridinic nitrogen in FeAzPcs. The catalytic electrodes that were molecularly modified with FeAzPcs have higher activities than those composed of FeAzPc crystals and oxMWCNTs. To the best of our knowledge, among all of the conventional catalysts based on modified MWCNTs and oxMWCNTs, this catalyst exhibits the highest activity. Unlike other Pt-free catalytic electrodes, the Fe AzUL catalytic electrodes can be prepared by low-cost processing without pyrolysis and are therefore promising catalytic electrode materials for applications, such as polymer electrolyte fuel cells and metal–air batteries. A unique structure that appears when ring-shaped catalysts are adsorbed onto carbon nanomaterials may help reduce the cost of producing fuel cells. To extract electrical energy from the conversion of oxygen and hydrogen into water, fuel cells normally use platinum catalysts to speed up oxygen-splitting reactions. Hiroya Abe from Tohoku University in Sendai, Japan and colleagues now report that, when absorbed onto carbon nanotubes as a unimolecular layer, iron azaphthalocyanines, complexes that surround an iron atom with four interconnected aromatic rings, are more catalytically active than conventional fuel cell catalysts. The team’s studies revealed that this high activity arises from favorable positioning of nitrogen atoms in the azaphthalocyanine rings. Unlike other iron-based fuel cell catalysts that require high temperatures for preparation, the new complex can be synthesized under milder conditions at a lower cost. We found high oxygen reduction reaction catalysts that are realized by ironphthalocyanine (FePc) derivatives, iron azaphthalocyanines (FeAzPcs) unimolecular layers (Fe AzUL) adsorbed on oxidized multiwall carbon nanotubes (oxMWCNTs). They showed superior ORR activities and durability than conventional FePc catalytic electrodes and commercial Pt/C. The Fe AzUL catalytic electrodes can be prepared by low-cost processing without pyrolysis, unlike other Pt-free catalytic electrodes, and are therefore promising catalytic electrode materials for applications, including polymer electrolyte fuel cells and metal–air batteries.
Databáze: OpenAIRE
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