Layered metal–organic frameworks (MOFs) have emerged as promising materials for next-generation supercapacitors. Understanding how and why electrolyte ion size impacts electrochemical performance is crucial for developing improved MOF-based devices. To address this, we investigate the energy storage performance of Cu₃(HHTP)₂ (HHTP = 2,3,6,7,10,11-hexahydroxytriphenylene) with a series of 1 M tetraalkylammonium tetrafluoroborate (TAABF₄) electrolytes with different cation sizes. Three-electrode experiments show that Cu₃(HHTP)₂ exhibits an asymmetric charging response with all ion sizes, with higher energy storage upon positive charging and a greater charging asymmetry with larger TAA⁺ cations. The results further show that smaller TAA⁺ cations demonstrate superior capacitive performances upon both positive and negative charging compared to larger TAA⁺ cations. To gain further insights, electrochemical quartz crystal microbalance measurements were performed to probe ion electrosorption during charging and discharging. These reveal that Cu₃(HHTP)₂ has a cation-dominated charging mechanism, but interestingly indicate that the solvent also participates in the charging process with larger cations. Overall, the results of this study suggest that larger TAA⁺ cations saturate the pores of the Cu₃(HHTP)₂-based electrodes. This leads to more asymmetric charging behavior and forces solvent molecules to play a role in the charge storage mechanism. These findings significantly enhance our understanding of ion electrosorption in layered MOFs, and they will guide the design of improved MOF-based supercapacitors.

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了解电解质离子尺寸对导电金属有机框架超级电容器性能的影响

层状金属有机框架（MOF）已成为下一代超级电容器的有前途的材料。了解电解质离子大小如何以及为何影响电化学性能对于开发改进的 MOF 器件至关重要。为了解决这个问题，我们研究了 Cu ₃ (HHTP) ₂ (HHTP = 2,3,6,7,10,11-六羟基苯并菲)与一系列具有不同阳离子的 1 M 四烷基四氟硼酸铵 (TAABF ₄ ) 电解质的储能性能尺寸。三电极实验表明，Cu ₃ (HHTP) _{2对所有离子尺寸均表现出不对称充电响应，在正充电时具有更高的能量存储，并且对较大的TAA} ⁺阳离子具有更大的充电不对称性。结果进一步表明，与较大的 TAA ⁺阳离子相比，较小的 TAA ⁺阳离子在正充电和负充电时表现出优异的电容性能。为了获得进一步的见解，进行了电化学石英晶体微天平测量，以探测充电和放电过程中的离子电吸附。这些揭示了Cu ₃ (HHTP) ₂具有阳离子主导的充电机制，但有趣的是，溶剂也参与了较大阳离子的充电过程。总体而言，本研究的结果表明较大的TAA ^{+阳离子会饱和Cu} ₃ (HHTP) ₂基电极的孔隙。这导致更加不对称的充电行为，并迫使溶剂分子在电荷存储机制中发挥作用。这些发现显着增强了我们对层状 MOF 中离子电吸附的理解，并将指导改进的基于 MOF 的超级电容器的设计。