A New Water Oxidation Catalyst : Lithium Manganese Pyrophosphate with Tunable Mn Valency

Title
A New Water Oxidation Catalyst : Lithium Manganese Pyrophosphate with Tunable Mn Valency
Authors
박지민김현아진경석이병주박용선김형섭박인철양기동정희윤김종순홍구택장호원강기석남기태
Keywords
Water Splitting; Catalysis; Biomimetics; Li2MnP2O7; Mn valency; Water oxidation
Issue Date
2014-03
Publisher
Journal of the American Chemical Society
Citation
VOL 136, NO 11, 4201-4211
Abstract
The development of a water oxidation catalyst has been a demanding challenge for the realization of overall water-splitting systems. Although intensive studies have explored the role of Mn element in water oxidation catalysis, it has been difficult to understand whether the catalytic capability originates mainly from either the Mn arrangement or the Mn valency. In this study, to decouple these two factors and to investigate the role of Mn valency on catalysis, we selected a new pyrophosphate-based Mn compound (Li2MnP2O7), which has not been utilized for water oxidation catalysis to date, as a model system. Due to the monophasic behavior of Li2MnP2O7 with delithiation, the Mn valency of Li2-xMnP2O7 (x = 0.3, 0.5, 1) can be controlled with negligible change in the crystal framework (e.g., volume change similar to 1%). Moreover, inductively coupled plasma mass spectrometry, X-ray photoelectron spectroscopy, ex-situ X-ray absorption near-edge structure, galvanostatic charging discharging, and cyclic voltammetry analysis indicate that Li2-xMnP2O7 (x = 0.3, 0.5, 1) exhibits high catalytic stability without additional delithiation or phase transformation. Notably, we observed that, as the averaged oxidation state of Mn in Li2-xMnP2O7 increases from 2 to 3, the catalytic performance is enhanced in the series Li2MnP2O7 < Li1.7MnP2O7 < Li1.5MnP2O7 < LiMnP2O7. Moreover, Li2MnP2O7 itself exhibits superior catalytic performance compared with MnO or MnO2. Our study provides valuable guidelines for developing an efficient Mn-based catalyst under neutral conditions with controlled Mn valency and atomic arrangement.
URI
http://pubs.kist.re.kr/handle/201004/50875
ISSN
00027863
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