State Key Laboratory of Physical Chemistry of Solid Surfaces, iChEM, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, China.
Key Laboratory of Advanced Fuel Cells and Electrolyzers Technology of Zhejiang Province, Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences, Ningbo 315201, China.
J Chem Phys. 2023 Feb 28;158(8):084701. doi: 10.1063/5.0139534.
Unraveling the origin of Helmholtz capacitance is of paramount importance for understanding the interfacial structure and electrostatic potential distribution of electric double layers (EDL). In this work, we combined the methods of ab initio molecular dynamics and classical molecular dynamics and modeled electrified Cu(100)/electrolyte and graphene/electrolyte interfaces for comparison. It was proposed that the Helmholtz capacitance is composed of three parts connected in series: the usual solvent capacitance, water chemisorption induced capacitance, and Pauling repulsion caused gap capacitance. We found the Helmholtz capacitance of graphene is significantly lower than that of Cu(100), which was attributed to two intrinsic factors. One is that graphene has a wider gap layer at interface, and the other is that graphene is less active for water chemisorption. Finally, based on our findings, we provide suggestions for how to increase the EDL capacitance of graphene-based materials in future work, and we also suggest that the new understanding of the potential distribution across the Helmholtz layer may help explain some experimental phenomena of electrocatalysis.
阐明亥姆霍兹电容的起源对于理解双电层（EDL）的界面结构和静电势分布至关重要。在这项工作中，我们结合了从头算分子动力学和经典分子动力学的方法，对带电 Cu(100)/电解质和石墨烯/电解质界面进行了建模和比较。提出亥姆霍兹电容由串联的三个部分组成：通常的溶剂电容、水化学吸附诱导的电容和 Pauling 排斥引起的间隙电容。我们发现石墨烯的亥姆霍兹电容明显低于 Cu(100)，这归因于两个内在因素。一是石墨烯在界面处具有更宽的间隙层，二是石墨烯对水化学吸附的活性较低。最后，基于我们的发现，我们为未来如何提高基于石墨烯的材料的双电层电容提供了建议，我们还提出对亥姆霍兹层电势分布的新理解可能有助于解释一些电催化的实验现象。
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