A new water oxidation catalyst: Lithium manganese pyrophosphate with tunable mn valency

Jimin Park, Hyunah Kim, Kyoungsuk Jin, Byung Ju Lee, Yong Sun Park, Hyungsub Kim, Inchul Park, Ki Dong Yang, Hui Yun Jeong, Jongsoon Kim, Koo Tak Hong, Ho Won Jang, Kisuk Kang, Ki Tae Nam

Research output: Contribution to journalArticlepeer-review

103 Citations (Scopus)

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 (Li 2MnP2O7), 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 ∼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 Li2MnP 2O7 < Li1.7MnP2O7 < Li1.5MnP2O7 < LiMnP2O 7. 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.

Original languageEnglish
Pages (from-to)4201-4211
Number of pages11
JournalJournal of the American Chemical Society
Volume136
Issue number11
DOIs
Publication statusPublished - 2014 Mar 19
Externally publishedYes

ASJC Scopus subject areas

  • Catalysis
  • Chemistry(all)
  • Biochemistry
  • Colloid and Surface Chemistry

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