TY - JOUR
T1 - Spectroscopic Investigation for Oxygen Reduction and Evolution Reactions with Tetrathiafulvalene as a Redox Mediator in Li-O2 Battery
AU - Qiao, Yu
AU - Ye, Shen
N1 - Funding Information:
This work was supported by the Advanced Low Carbon Technology Research and Development Program (ALCA), specially promoted research for innovative next generation batteries (SPRING) from the Japan Science and Technology Agency (JST). The authors want to express their special thanks to Prof. Kubo and Mr. Kumura from NIMS for guidance on the preparation of the porous carbon electrode employed in this study. Q.Y. acknowledges a scholarship from the China Scholarship Council (CSC). The authors thank Prof. Kohei Uosaki for his stimulating discussions and comments. The authors thank Dr. Can Liu and Miss Yingying Zhou for their assistance with some of the experiments.
Publisher Copyright:
© 2016 American Chemical Society.
PY - 2016/7/28
Y1 - 2016/7/28
N2 - To develop a lithium-oxygen (Li-O2) battery with a high specific energy, the electrochemical oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) have been systematically investigated on gold and porous carbon electrodes in a DMSO-based electrolyte solution containing tetrathiafulvalene (TTF) as a redox mediator by using in situ UV-vis absorption spectroscopy and surface-enhanced Raman vibrational spectroscopy (SERS) in combination with ex situ infrared and Raman spectroscopies. Our results demonstrate that TTF definitely reduces the overpotential for the OER process and restrains the decomposition of the carbon electrode and solvent during the OER, while the functionality of the redox mediator can change with the electrode materials and morphologies. No free TTF+ was observed in solution during a round-trip galvanostatic ORR/OER cycle on the gold electrode surface. The electrochemically generated TTF+ was mainly consumed by the oxidative decomposition of lithium superoxide (LiO2) in solution but not lithium peroxide (Li2O2) on the electrode surface formed during the ORR, different from that previously proposed. On the other hand, Li2O2 and Li2CO3 were observed during the ORR on the porous carbon electrode surface both in the TTF-free and TTF-containing solutions. The TTF+ can mediate the oxidation of the Li2O2 during the OER. Furthermore, the accumulation of free TTF+ was observed in solution during a round-trip galvanostatic ORR/OER cycle on the porous carbon electrode. The amount of the excess TTF+ in solution well corresponds to that of the byproduct of Li2CO3 formed on the carbon electrode surface. TTF is unlikely to work as an ideal redox mediator at the porous carbon electrode as expected. A better understanding for the mechanism and surface reactions for the ORR/OER cycle on these electrodes has been achieved by the present study.
AB - To develop a lithium-oxygen (Li-O2) battery with a high specific energy, the electrochemical oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) have been systematically investigated on gold and porous carbon electrodes in a DMSO-based electrolyte solution containing tetrathiafulvalene (TTF) as a redox mediator by using in situ UV-vis absorption spectroscopy and surface-enhanced Raman vibrational spectroscopy (SERS) in combination with ex situ infrared and Raman spectroscopies. Our results demonstrate that TTF definitely reduces the overpotential for the OER process and restrains the decomposition of the carbon electrode and solvent during the OER, while the functionality of the redox mediator can change with the electrode materials and morphologies. No free TTF+ was observed in solution during a round-trip galvanostatic ORR/OER cycle on the gold electrode surface. The electrochemically generated TTF+ was mainly consumed by the oxidative decomposition of lithium superoxide (LiO2) in solution but not lithium peroxide (Li2O2) on the electrode surface formed during the ORR, different from that previously proposed. On the other hand, Li2O2 and Li2CO3 were observed during the ORR on the porous carbon electrode surface both in the TTF-free and TTF-containing solutions. The TTF+ can mediate the oxidation of the Li2O2 during the OER. Furthermore, the accumulation of free TTF+ was observed in solution during a round-trip galvanostatic ORR/OER cycle on the porous carbon electrode. The amount of the excess TTF+ in solution well corresponds to that of the byproduct of Li2CO3 formed on the carbon electrode surface. TTF is unlikely to work as an ideal redox mediator at the porous carbon electrode as expected. A better understanding for the mechanism and surface reactions for the ORR/OER cycle on these electrodes has been achieved by the present study.
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U2 - 10.1021/acs.jpcc.5b11692
DO - 10.1021/acs.jpcc.5b11692
M3 - Article
AN - SCOPUS:84979892845
VL - 120
SP - 15830
EP - 15845
JO - Journal of Physical Chemistry C
JF - Journal of Physical Chemistry C
SN - 1932-7447
IS - 29
ER -