A Carbon Electrode Functionalized by a Tricopper Cluster Complex: Overcoming Overpotential and Production of Hydrogen Peroxide in the Oxygen Reduction Reaction

Abstract

A study of the oxygen reduction reaction (ORR) on a screen printed carbon electrode surface mediated by the tricopper cluster complex Cu (7-N-Etppz(CH OH)) dispersed on electrochemically reduced carbon black, where 7-N-Etppz(CH OH) is the ligand 3,3'-(6-(hydroxymethyl)-1,4-diazepane-1,4-diyl)bis(1-(4-ethyl piperazin-1-yl)propan-2-ol), is described. Onset oxygen reduction potentials of about 0.92 V and about 0.77 V are observed at pH 13 and pH 7 vs. the reversible hydrogen electrode, which are comparable to the best values reported for any synthetic copper complex. Based on half-wave potentials (E ), the corresponding overpotentials are about 0.42 V and about 0.68 V, respectively. Kinetic studies indicate that the trinuclear copper catalyst can accomplish the 4 e reduction of O efficiently and the ORR is accompanied by the production of only small amounts of H O . The involvement of the copper triad in the O activation process is also verified.

Bioinspired Design of Hybrid Polymer Catalysts with Multicopper Sites for Oxygen Reduction

“…A pair of broad and redox peaks at~0.29 V vs. reversible hydrogen electrode (RHE) was assigned to the reduction of Cu 2 + to Cu + ( Figure S4a). A linear relationship between reduction peak currents (I) and the scan rate (w), known as Randles-Sevcik plot (Equation 3), [14,22] was shown in Figure S4, that gives a surface coverage of 2.11 × 10 À 10 mol cm À 2 of Cu on the electrode. A linear dependence of peak potentials vs. log scale of the scan rate was obtained, showing a surfaceconfined redox process.…”

“…The turn-over frequency (TOF) was calculated to be 0.74 s À 1 at E 1/2 (see Equation 4). [14] To better assess catalytic activity of Cu 2 + ions, we carried out ex situ titration. The working electrode was prepared with CB and pristine Py-PGMADPA 67 (Poly-CB) and the activity of the film was measured after titrating various volumes of Cu(NO 3 ) 2 solution (0.91 mM in methanol).…”

“…A key intermediate is known to be the di-Cu μ-oxo-bridge formed either intermolecularly [13] or intramolecularly. [14] The optimal distance between adjacent Cu sites is essential to bind O 2 while being able to unbind after the reaction. [11d] In small molecular complexes, the rigid backbone of ligands limits the turnover of Cu sites as reported previously.…”

“…For example, control of the first coordination sphere of Cu centers in molecular catalysts has received continuous interests to mimic the enzymatic activity of Cu oxidases [11a,d,e] . Mono‐, [11a,12] di‐, [11d,e,13] and trinuclear [14] Cu complexes have been synthesized and examined for O 2 activation. Synthetic mimics, however, are less active compared to Cu oxidases.…”

Electrocatalytic Oxygen Reduction at Multinuclear Metal Active Sites Inspired by Metalloenzymes

“…Recently, a study of the ORR catalyzed by trinuclear copper complex [Cu I 3 (7-N-Etppz(CH 2 OH))]ClO 4 (7-N-Etppz (CH 2 OH)=3,3ʹ-(6-(hydroxymethyl)-1,4-diazepane-1,4-diyl) [65]. This compound was originally designed and synthesized as a biomimetic of the active site of the particulate methane monooxygenase (pMMO) in methanotrophic bacteria [66,67].…”