Four-electron reduction of O 2 over multiple Cu I centers: Quantum theory
A series of copper complexes were tested theoretically for oxygen electro reduction, beginning with bare Cu and Cu + centers, with and without N-bearing ligands, and ending with one, two, and three H 2N–Cu–Imidazole Cu I centers. Adsorption energies for reaction intermediates formed during the four...
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| Published in: | Journal of electroanalytical chemistry (Lausanne, Switzerland) Switzerland), 2007-09, Vol.607 (1), p.90-100 |
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| Main Authors: | , , |
| Format: | Article |
| Language: | eng |
| Subjects: | |
| Online Access: | Get full text |
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| Summary: | A series of copper complexes were tested theoretically for oxygen electro reduction, beginning with bare Cu and Cu
+ centers, with and without N-bearing ligands, and ending with one, two, and three H
2N–Cu–Imidazole Cu
I centers. Adsorption energies for reaction intermediates formed during the four one-electron reduction steps to water were calculated, using B3LYP hybrid density functional theory, and then used in a linear free energy relationship to predict the reversible potential for each step. Cu
I sites not poisoned by O(ads), OH(ads), and H
2O were sought, and so initial screening was based on the predicted reversible potentials for O(ads) reduction to OH(ads) and OH(ads) reduction to H
2O and the adsorption bond strengths of O
2 and H
2O. The Cu
I centers in H
2N–Cu–Imidazole and H
2N–Cu–Imidazole had the best properties in this screening. The former was used to model four-electron reduction by copper laccases, some of which have very little overpotential. On the basis of calculations on a model for 3-Cu
I catalytic sites composed of three H
2N–Cu–Imidazole in loose association, the following conclusions were reached: (i) the reduction potential for OH bonded to the model is higher than calculated for Pt, which is consistent with the higher observed overpotentials for Pt compared to lacasses; (ii) H
2O bonds weakly to the Cu
I centers and does not poison them; (iii) model-dependent heat losses were calculated for non-electron transfer steps and it is shown how they contribute to the overpotential for the overall four-electron reduction. Finally, it is shown that CH
3S–Cu–(Imidazole)
2 possesses the electron donor–acceptor properties that allow it to be an intermediate in electron transfer to the catalytic site. This study shows that loosely coordinated Cu
I centers present opportunities for four-electron oxygen reduction at low overpotential. |
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| ISSN: | 1572-6657 1873-2569 |