A New Water Oxidation Catalyst : Lithium Manganese Pyrophosphate with Tunable Mn Valency
- A New Water Oxidation Catalyst : Lithium Manganese Pyrophosphate with Tunable Mn Valency
- 박지민; 김현아; 진경석; 이병주; 박용선; 김형섭; 박인철; 양기동; 정희윤; 김종순; 홍구택; 장호원; 강기석; 남기태
- Water Splitting; Catalysis; Biomimetics; Li2MnP2O7; Mn valency; Water oxidation
- Issue Date
- Journal of the American Chemical Society
- VOL 136, NO 11, 4201-4211
- 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.
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