Abstract
Development of a structurally well-defined small molecule with a high oxygen reduction reaction catalytic activity is a key approach for the bottom-up design of a metal-free carbon-based catalysts for metal-air batteries and fuel cells. In this paper, we characterize the oxygen reduction reaction activities of trioxotriangulene derivatives, which are stable neutral radicals with high redox abilities, via rotating disk electrode measurements in alkaline aqueous solution. Among trioxotriangulene derivatives having various substituent groups, N-piperidinyl-substituted derivative mixed with acetylene black shows a high catalytic activity with the two-electron transferring process exceeding other derivatives and quinones. To reveal the correlation between molecular structure and catalytic activity, we discuss substituent effects on the redox ability of trioxotriangulene derivatives, and demonstrate that a molecule with electron-donating groups yields relatively higher catalytic activities.
Highlights
Development of a structurally well-defined small molecule with a high oxygen reduction reaction catalytic activity is a key approach for the bottom-up design of a metal-free carbonbased catalysts for metal-air batteries and fuel cells
We investigate the Oxygen reduction reaction (ORR) catalytic activities of TOT derivatives 1–5 (Fig. 1), and the substituent effect is discussed in the relationship with redox potentials between their neutral radical and monoanion species
The oxidation potential (Eox) became lower as the electron-donating ability of substituent groups became stronger with the order of Cl, Br (Eox = –0.04, −0.05 V vs. Fc/Fc+) > H (Eox = −0.10 V) > Ph (Eox = −0.33 V)
Summary
Development of a structurally well-defined small molecule with a high oxygen reduction reaction catalytic activity is a key approach for the bottom-up design of a metal-free carbonbased catalysts for metal-air batteries and fuel cells. Since the first report on nitrogen-doped carbon nanotube in 20096, various heteroatomdoped metal-free carbon catalysts[7] have been developed based on carbon nanotube[6,8,9,10,11,12], graphene[13], graphite[14], and nanoshell carbon material namely carbon alloy catalyst[15,16,17,18] These heteroatom-doped carbons are structurally undefined materials and not discrete, because they are prepared by the pyrolysis of small molecules or by doping heteroatoms into carbon atom framework. ORR catalytic activity of small molecules has been studied since the first report in 1964 on the cobalt phthalocyanine complex[21], and various metal complexes of porphyrin, phthalocyanine, 1,10-
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