With excellent layered structures, abundant pores and a high specific surface area, two-dimensional (2D) porous nanostructured materials have been demonstrated to show great potential in supercapacitors. At present, it is highly desirable but remains challenging to prepare different sizes and crystallinity of 2D porous thin sheets so as to further improve the performance of supercapacitors. Herein, 2D porous cobalt-oxalate (Co-OA) thin sheets with different sizes and crystallinity assembled by interconnected nanosheet array frameworks have been successfully synthesized, using cobalt nitrate hexahydrate as a cobalt source and oxalic acid dihydrate as a ligand, through a simple hydrothermal strategy at 220 °C for different reaction times. The as-prepared sample at 220 °C for 20 h, has a high area specific capacitance (1.631 F cm⁻² at the current density of 1.2 mA cm⁻²), good rate capability (80.6% retention upon increasing the current density from 1.2 to 12 mA cm⁻²) and excellent cycling performance (1.5% attenuation at 6.0 mA cm⁻² for 2000 cycles). In addition, one aqueous asymmetric supercapacitor (ASC) is constructed based on the sample synthesised at 220 °C for 20 h as positive electrodes and activated carbon (AC) as negative electrodes. This ASC effectively provides a maximum energy density of 17.675 Wh kg⁻¹ at 900 W kg⁻¹, still maintaining 8.25 Wh kg⁻¹ at 9000 W kg⁻¹, which demonstrates it may be a promising candidate in energy storage for supercapacitors. It is worth emphasizing that this strategy could be extended to fabricate other materials with different sizes and crystallinity.

中文翻译：

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二维多孔草酸钴薄板的尺寸和结晶度控制：调整表面结构以增强水性不对称超级电容器的性能†

具有出色的层状结构，丰富的孔和高的比表面积，二维（2D）多孔纳米结构材料已被证明在超级电容器中显示出巨大的潜力。目前，非常需要制备不同尺寸和结晶度的二维多孔薄板以进一步改善超级电容器的性能，但是仍然具有挑战性。在这里，已成功地通过硝酸钴六水合物作为钴源和草酸二水合物作为配体，通过简单的水热法成功地合成了由相互连接的纳米片阵列框架组装而成的具有不同尺寸和结晶度的二维多孔草酸钴（Co-OA）薄板。策略在220°C下进行不同的反应时间。所制备的样品在220°C下持续20 h，具有较高的面积比电容（1.631 F cm^-2在1.2毫安厘米的电流密度^-2），良好的倍率性能（在增加来自1.2的电流密度12毫安厘米80.6％保留^-2）和优异的循环性能（在6.0毫安厘米1.5％衰减^-2为2000个周期）。此外，基于在220°C下合成20 h的样品作为正极，而活性炭（AC）作为负极，构造了一种水性不对称超级电容器（ASC）。此ASC有效地提供17.675瓦公斤的最大能量密度^-1在900瓦千克^-1，仍保持8.25瓦千克^-1在9000公斤w ^ ^-1，这表明它可能是超级电容器储能的有希望的候选者。值得强调的是，该策略可以扩展到制造具有不同尺寸和结晶度的其他材料。