Functional metal–porphyrazine derivatives and their polymers. Part 11. Secondary fuel cells based on oxygen reduction at a platinum electrode modified by metal–2,9,16,23-tetracarboxyphthalocyanine covalently bound to poly(2-vinylpyridine–styrene)

Abstract

A new type of secondary fuel cell is described in which molecular oxygen evolved by electrolysis of water in the charging process is stored in polymer matrix of metal–2,9,16,23-tetracarboxyphthalocyanine covalently bound to poly(2-vinylpyridine–styrene)(M = Fe^III, Co^II, Ni^II, and Cu^II) on a platinum electrode, and then electrocatalytically reduced in the discharging process in 30% KOH aqueous solution. The constant-current charge–discharge curve for the platinum electrode modified by the cobalt–copolymer, charged for 30 min at 500 µA, followed by a 100-µA discharge, showed a stable plateau at about –0.24 V vs. saturated calomel electrode. The discharge capacity was 833 A h per kg of the cobalt–phthalocyanine, about 20 times that for the corresponding electrode modified by vacuum deposition of monomeric cobalt–phthalocyanine. For this cell there was no significant decay in its characteristics after over 30 charge–discharge cycles. After the charge the e.s.r. spectrum showed a signal assigned to a Co^III–pc–O₂^– radical [pc = phthalocyaninate(2–)]. The higher capacity of the cobalt–copolymer complex seems to be due to the activation and storage of dioxygen evolved upon charging. The capacity decreased in the order Co^II > Fe^III Cu^II > Ni^II. The cathodic reactions of the electrode modified by the cobalt-copolymer are discussed.