Soltani Hamed, Bahiraei Hamed, Ghasemi Shahnaz, Hashempour Mazdak
Department of Physics, Faculty of Science, Malayer University, Malayer, Iran.
Sharif Institute of Energy, Water and Environment, Sharif University of Technology, Azadi Avenue, P.O.Box11365-9465, Tehran, Iran.
Heliyon. 2024 Dec 21;11(1):e41427. doi: 10.1016/j.heliyon.2024.e41427. eCollection 2025 Jan 15.
Manganese dioxide (MnO) is a well-known pseudocapacitive material that has been extensively studied and highly regarded, especially in supercapacitors, due to its remarkable surface redox behavior, leading to a high specific capacitance. However, its full potential is impeded by inherent characteristics such as its low electrical conductivity, dense morphology, and hindered ionic diffusion, resulting in limited rate capability in supercapacitors. Addressing this issue often requires complicated strategies and procedures, such as designing sophisticated composite architectures. This study introduces a straightforward and cost-effective approach to tune and enhance the rate capability of MnO pseudocapacitor electrodes fabricated via the electrodeposition method. Among the electrodeposition parameters, the deposition time and electrolyte concentration, which influence the mass loading, electrode thickness, microstructure, and electrochemical properties, were the primary focus. Various electrodes were prepared potentiostatically in a two-electrode cathodic electrodeposition setup on a Ni foam substrate in a KMnO aqueous electrolyte, with bath concentrations (in terms of Mn ion) of 0.01 and 0.1 M, and electrodeposition times ranging from 1 to 15 min. Optimal rate capabilities were achieved at low bath concentrations and deposition times, primarily due to the structural properties of electrodes prepared under such circumstances. While electrodeposition at a 0.1 M electrolyte concentration resulted in the formation of electrolytic MnO with high supercapacitive rate sensitivity, reducing the bath concentration to 0.01 M primarily led to the formation of birnessite δ-MnO, capable of maintaining a reasonable specific capacitance in the range of approximately 90-100 Fg with almost no sensitivity to the charging/discharging rate, as confirmed by galvanostatic charge-discharge (1-10 Ag) and cyclic voltammetry (10-100 mVs) examinations. Along with the positive structural impacts of the layered birnessite with large interlayer spacing, the porous morphology (vertically aligned two-dimensional interconnected columns) and low thickness (≈2 μm) of the electrode prepared at the lowest bath concentration and electrodeposition time (0.01 M in 1 min electrode) contributed to its fast ionic diffusion kinetics for pseudocapacitive charge storage and the consequent high rate capability.
二氧化锰（MnO）是一种著名的赝电容材料，因其显著的表面氧化还原行为，特别是在超级电容器中，导致高比电容，而受到广泛研究和高度重视。然而，其固有特性如低电导率、致密形态和受阻的离子扩散阻碍了其全部潜力，导致超级电容器中的倍率性能受限。解决这个问题通常需要复杂的策略和程序，例如设计复杂的复合结构。本研究介绍了一种直接且经济高效的方法来调节和提高通过电沉积法制备的MnO赝电容电极的倍率性能。在电沉积参数中，影响质量负载、电极厚度、微观结构和电化学性能的沉积时间和电解液浓度是主要关注点。在两电极阴极电沉积装置中，于泡沫镍基底上在KMnO水溶液电解液中恒电位制备各种电极，浴液浓度（以Mn离子计）为0.01和0.1 M，沉积时间为1至15分钟。在低浴液浓度和沉积时间下实现了最佳倍率性能，这主要归因于在这种情况下制备的电极的结构特性。虽然在0.1 M电解液浓度下电沉积导致形成具有高超级电容倍率敏感性的电解MnO，但将浴液浓度降低到0.01 M主要导致形成水钠锰矿δ-MnO，通过恒电流充放电（1 - 10 Ag）和循环伏安法（10 - 100 mV s）测试证实，其能够在约90 - 100 F g范围内保持合理的比电容，且几乎对充放电速率不敏感。除了具有大层间距的层状水钠锰矿的积极结构影响外，在最低浴液浓度和沉积时间（1分钟电极，0.01 M）下制备的电极的多孔形态（垂直排列的二维互连柱）和低厚度（≈2μm）有助于其赝电容电荷存储的快速离子扩散动力学以及随之而来的高倍率性能。
