Department of Physics, Temple University, Philadelphia, PA 19122;
Department of Chemistry, Temple University, Philadelphia, PA 19122.
Proc Natl Acad Sci U S A. 2017 Sep 5;114(36):9523-9528. doi: 10.1073/pnas.1706836114. Epub 2017 Aug 21.
Birnessite, a layered-structure MnO, is an earth-abundant functional material with potential for various energy and environmental applications, such as water oxidation. An important feature of birnessite is the existence of Mn(III) within the MnO layers, accompanied by interlayer charge-neutralizing cations. Using first-principles calculations, we reveal the nature of Mn(III) in birnessite with the concept of the small polaron, a special kind of point defect. Further taking into account the effect of the spatial distribution of Mn(III), we propose a theoretical model to explain the structure-performance dependence of birnessite as an oxygen evolution catalyst. We find an internal potential step which leads to the easy switching of the oxidation state between Mn(III) and Mn(IV) that is critical for enhancing the catalytic activity of birnessite. Finally, we conduct a series of comparative experiments which support our model.
钠锰矿是一种具有层状结构的 MnO，是一种丰富的功能材料，具有在各种能源和环境应用中的潜力，如水氧化。钠锰矿的一个重要特点是 MnO 层中存在 Mn(III)，同时伴有层间电荷中和的阳离子。我们使用第一性原理计算，借助小极化子的概念揭示了钠锰矿中 Mn(III)的本质，这是一种特殊的点缺陷。进一步考虑到 Mn(III)的空间分布的影响，我们提出了一个理论模型来解释作为析氧催化剂的钠锰矿的结构-性能关系。我们发现了一个内部电势阶跃，它导致 Mn(III)和 Mn(IV)之间的氧化态的容易转换，这对于提高钠锰矿的催化活性至关重要。最后，我们进行了一系列的对比实验，支持了我们的模型。
