Synthesis and electrocatalytic reactivity for water oxidation of two cerium complexes

<p>Two cerium complexes with and without manganese ion, [MnCe₄(dipic)₆(H₂O)₂₀][Ce(dipic)₃]₂·7H₂O (dipic = dipicolinate) (<b>1</b>) and [Ce₂(H₂O)₄(O₂CMe)₆][Ce(H₂O)₄(NO₃)₂(O₂CMe)]₂·2H₂O·2MeOH (<b>2</b>), have been prepared, and their electrocatalytic reactivity for water oxidation has been investigated. Compound <b>1</b> is a heterometallic 3d-4f compound which possesses four Ce(IV) ions, two Ce(III) ions, and one Mn(II). Compound <b>2</b> is composed of three neutral parts, one of which is a dinuclear cerium molecule lying on an inversion center, and the other two are symmetric monomer units; the four cerium ions in <b>2</b> are all Ce(III). Electrochemical studies of <b>1</b> and <b>2</b> show that <b>1</b> can catalyze water oxidation at the potential ~1.5 V with an overpotential of <i>ca.</i> 900 mV <i>versus</i> NHE. Control potential electrolysis (CPE) experiments at 1.50 V of <b>1</b> displayed a stable current density of 2.5 mA/cm², and the calculated Faradaic efficiency is 60%. However, no electrocatalytic reactivity was observed for <b>2</b>. By comparison experiments, it was found that the electrocatalysis of <b>1</b> may result from the cooperative catalytic effect of the 4f cerium ion and 3d transition metal manganese ion.</p