阳离子掺杂α- MnO2的电荷储存
Charge Storage in Cation Incorporated α-MnO2
摘要：
利用α-MnO 2的电化学超级电容器提供了高功率密度和高能量密度的可能性。不幸的是，α-MnO 2中的电化学电荷存储机制以及操作条件对电荷存储机制的影响通常还没有很好地理解。在这里，我们提出了第一个详细的α-MnO 2的电荷存储机制，并解释了α-和β-MnO 2之间的容量差异使用相结合的理论电化学和能带结构分析。我们确定的重要性的带隙，功函数，零电荷点，和隧道尺寸的电极材料，以及pH值和稳定窗口的电解质在确定给定的电极材料的可行性。α-MnO 2的高容量是由于带隙中的阳离子诱导的电荷开关态与电解质允许的扫描电位重叠。电荷切换状态源自掺入材料中的间隙和取代阳离子（H+、Li+、Na+和K+）。间隙阳离子被发现诱导电荷开关状态稳定Mn-O反键轨道从导带。取代阳离子与O[2 p]悬挂键相互作用，这些悬挂键通过Mn空位从价带不稳定以诱导电荷切换状态。我们计算的平衡电化学电位，在这些国家减少和预测的电化学操作条件对他们的贡献电荷存储的效果。我们报告的机制和理论方法是通用的，并可用于计算筛选新材料通过离子掺入改善电荷存储。
英文摘要：
Electrochemical supercapacitors utilizing α-MnO2 offer the possibility of both high power density and high energy density. Unfortunately, the mechanism of electrochemical charge storage in α-MnO2 and the effect of operating conditions on the charge storage mechanism are generally not well understood. Here, we present the first detailed charge storage mechanism of α-MnO2 and explain the capacity differences between α- and β-MnO2 using a combined theoretical electrochemical and band structure analysis. We identify the importance of the band gap, work function, the point of zero charge, and the tunnel sizes of the electrode material, as well as the pH and stability window of the electrolyte in determining the viability of a given electrode material. The high capacity of α-MnO2 results from cation induced charge-switching states in the band gap that overlap with the scanned potential allowed by the electrolyte. The charge-switching states originate from interstitial and substitutional cations (H+, Li+, Na+, and K+) incorporated into the material. Interstitial cations are found to induce charge-switching states by stabilizing Mn-O antibonding orbitals from the conduction band. Substitutional cations interact with O[2p] dangling bonds that are destabilized from the valence band by Mn vacancies to induce charge-switching states. We calculate the equilibrium electrochemical potentials at which these states are reduced and predict the effect of the electrochemical operating conditions on their contribution to charge storage. The mechanism and theoretical approach we report is general and can be used to computationally screen new materials for improved charge storage via ion incorporation.
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