Lyu Dongxun, Märker Katharina, Zhou Yuning, Zhao Evan Wenbo, Gunnarsdóttir Anna B, Niblett Samuel P, Forse Alexander C, Grey Clare P
Yusuf Hamied Department of Chemistry, University of Cambridge, Cambridge CB2 1EW, United Kingdom.
J Am Chem Soc. 2024 Apr 10;146(14):9897-9910. doi: 10.1021/jacs.3c14807. Epub 2024 Apr 1.
Ion adsorption at solid-water interfaces is crucial for many electrochemical processes involving aqueous electrolytes including energy storage, electrochemical separations, and electrocatalysis. However, the impact of the hydronium (HO) and hydroxide (OH) ions on the ion adsorption and surface charge distributions remains poorly understood. Many fundamental studies of supercapacitors focus on non-aqueous electrolytes to avoid addressing the role of functional groups and electrolyte pH in altering ion uptake. Achieving microscopic level characterization of interfacial mixed ion adsorption is particularly challenging due to the complex ion dynamics, disordered structures, and hierarchical porosity of the carbon electrodes. This work addresses these challenges starting with pH measurements to quantify the adsorbed HO concentrations, which reveal the basic nature of the activated carbon YP-50F commonly used in supercapacitors. Solid-state NMR spectroscopy is used to study the uptake of lithium bis(trifluoromethanesulfonyl)-imide (LiTFSI) aqueous electrolyte in the YP-50F carbon across the full pH range. The NMR data analysis highlights the importance of including the fast ion-exchange processes for accurate quantification of the adsorbed ions. Under acidic conditions, more TFSI ions are adsorbed in the carbon pores than Li ions, with charge compensation also occurring via HO adsorption. Under neutral and basic conditions, when the carbon's surface charge is close to zero, the Li and TFSI ions exhibit similar but lower affinities toward the carbon pores. Our experimental approach and evidence of HO uptake in pores provide a methodology to relate the local structure to the function and performance in a wide range of materials for energy applications and beyond.
离子在固 - 水界面的吸附对于许多涉及水性电解质的电化学过程至关重要，这些过程包括能量存储、电化学分离和电催化。然而，水合氢离子（H₃O⁺）和氢氧根离子（OH⁻）对离子吸附和表面电荷分布的影响仍知之甚少。许多关于超级电容器的基础研究集中在非水电解质上，以避免探讨官能团和电解质pH值在改变离子吸收方面的作用。由于碳电极复杂的离子动力学、无序结构和分级孔隙率，实现界面混合离子吸附的微观层面表征极具挑战性。这项工作从pH测量开始，以量化吸附的H₃O⁺浓度，从而应对这些挑战，这揭示了超级电容器中常用的活性炭YP - 50F的基本性质。固态核磁共振光谱用于研究YP - 50F碳在整个pH范围内对双（三氟甲磺酰）亚胺锂（LiTFSI）水性电解质的吸收情况。核磁共振数据分析强调了纳入快速离子交换过程以准确量化吸附离子的重要性。在酸性条件下，更多的TFSI⁻离子吸附在碳孔中，而非Li⁺离子，电荷补偿也通过H₃O⁺吸附发生。在中性和碱性条件下，当碳的表面电荷接近零时，Li⁺和TFSI⁻离子对碳孔表现出相似但较低的亲和力。我们的实验方法以及孔中H₃O⁺吸收的证据提供了一种方法，可将局部结构与广泛用于能量应用及其他领域的材料的功能和性能联系起来。
