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Utilization of cobalt bis(terpyridine) metal complex as soluble redox mediator in Li-O2 batteries

Utilization of cobalt bis(terpyridine) metal complex as soluble redox mediator in Li-O2 batteries
Utilization of cobalt bis(terpyridine) metal complex as soluble redox mediator in Li-O2 batteries
Redox mediators hold significant promise in reducing the large overpotentials pervasive upon charging of lithium-oxygen (Li-O2) cells. Cobalt bis(terpyridine) (Co(Terp)2) was investigated as mediator of the Li2O2 oxidation reaction using electrochemical, XRD and mass spectrometry measurements and benchmarked against tetrathiafulvalene (TTF). Significant reductions in reversible potential versus Li+/Li are measured for Co(Terp)2 and TTF from diglyme to Pyr14TFSI:diglyme to Pyr14TFSI, attributable to upward shift in the Li+/Li, due to weakening Li+ solvation in this solvent order. The lowering of the reversible potentials has noticeable gains on the kinetics of the charge reaction and greater reduction in charge overpotential are observed with the cobalt complex. However, probing the efficacy of the discharge and charge processes using differential electrochemical mass spectrometry reveal that Co(Terp)2 undergoes CoII to CoI reduction on cell discharge which interferes with the desired O2 reduction; furthermore less than 25% of the O2 consumed on discharge is recovered on charge. On the other hand, TTF allows the ideal 2 e-/O2 on discharge and enables up to 32% O2 recovery on charge. CO2 is a significant charging product as voltages becomes greater than 4.0 V vs. Li+/Li because of electrolyte decomposition. The methodology here developed is valuable to critically evaluate the effectiveness of redox agents in Li-O2 batteries.
1932-7447
16290-16297
Yao, Koffi Pierre Claver
e312b763-ba2e-49f4-a8b9-f290718febac
Frith, James T.
349b19de-36a7-4136-9f2d-af8160311d38
Sayed, Sayed Youssef
4c380851-1ac0-4b2f-a865-0ca40f87f295
Barde, Fanny
52008a6b-91a6-4674-b4c7-0e785b32be54
Owen, John R.
067986ea-f3f3-4a83-bc87-7387cc5ac85d
Shao-Horn, Yang
e55d99c2-6bde-4a3d-8542-48406bd0effa
Garcia-Araez, Nuria
9358a0f9-309c-495e-b6bf-da985ad81c37
Yao, Koffi Pierre Claver
e312b763-ba2e-49f4-a8b9-f290718febac
Frith, James T.
349b19de-36a7-4136-9f2d-af8160311d38
Sayed, Sayed Youssef
4c380851-1ac0-4b2f-a865-0ca40f87f295
Barde, Fanny
52008a6b-91a6-4674-b4c7-0e785b32be54
Owen, John R.
067986ea-f3f3-4a83-bc87-7387cc5ac85d
Shao-Horn, Yang
e55d99c2-6bde-4a3d-8542-48406bd0effa
Garcia-Araez, Nuria
9358a0f9-309c-495e-b6bf-da985ad81c37

Yao, Koffi Pierre Claver, Frith, James T., Sayed, Sayed Youssef, Barde, Fanny, Owen, John R., Shao-Horn, Yang and Garcia-Araez, Nuria (2016) Utilization of cobalt bis(terpyridine) metal complex as soluble redox mediator in Li-O2 batteries. The Journal of Physical Chemistry C, 120 (30), 16290-16297. (doi:10.1021/acs.jpcc.6b02932).

Record type: Article

Abstract

Redox mediators hold significant promise in reducing the large overpotentials pervasive upon charging of lithium-oxygen (Li-O2) cells. Cobalt bis(terpyridine) (Co(Terp)2) was investigated as mediator of the Li2O2 oxidation reaction using electrochemical, XRD and mass spectrometry measurements and benchmarked against tetrathiafulvalene (TTF). Significant reductions in reversible potential versus Li+/Li are measured for Co(Terp)2 and TTF from diglyme to Pyr14TFSI:diglyme to Pyr14TFSI, attributable to upward shift in the Li+/Li, due to weakening Li+ solvation in this solvent order. The lowering of the reversible potentials has noticeable gains on the kinetics of the charge reaction and greater reduction in charge overpotential are observed with the cobalt complex. However, probing the efficacy of the discharge and charge processes using differential electrochemical mass spectrometry reveal that Co(Terp)2 undergoes CoII to CoI reduction on cell discharge which interferes with the desired O2 reduction; furthermore less than 25% of the O2 consumed on discharge is recovered on charge. On the other hand, TTF allows the ideal 2 e-/O2 on discharge and enables up to 32% O2 recovery on charge. CO2 is a significant charging product as voltages becomes greater than 4.0 V vs. Li+/Li because of electrolyte decomposition. The methodology here developed is valuable to critically evaluate the effectiveness of redox agents in Li-O2 batteries.

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jpcc-CobisTerpy060716_submit rev 2b.pdf - Accepted Manuscript
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Accepted/In Press date: 26 June 2016
e-pub ahead of print date: 29 June 2016
Published date: 14 July 2016
Organisations: Electrochemistry

Identifiers

Local EPrints ID: 397946
URI: http://eprints.soton.ac.uk/id/eprint/397946
ISSN: 1932-7447
PURE UUID: cfd1c595-c39d-428c-a8a0-91896060a883
ORCID for John R. Owen: ORCID iD orcid.org/0000-0002-4938-3693
ORCID for Nuria Garcia-Araez: ORCID iD orcid.org/0000-0001-9095-2379

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Date deposited: 12 Jul 2016 15:21
Last modified: 15 Mar 2024 05:44

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Contributors

Author: Koffi Pierre Claver Yao
Author: James T. Frith
Author: Sayed Youssef Sayed
Author: Fanny Barde
Author: John R. Owen ORCID iD
Author: Yang Shao-Horn

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