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Composition of Oxygen Functional Groups on Graphite Surfaces
The Journal of Physical Chemistry C ( IF 3.7 ) Pub Date : 2022-06-23 , DOI: 10.1021/acs.jpcc.2c01258
Nadia N. Intan 1 , Jim Pfaendtner 1, 2
Affiliation  

The types and compositions of oxygen functional groups on graphite surfaces are heavily subjected to the method in which the graphite is synthesized and processed in experiments, which makes the characterization difficult. The challenge even extends to the modeling of oxygenated graphite surfaces in computational studies. However, the determination of both the types and compositions of oxygen functional groups on graphite surfaces is of paramount importance as it plays a significantly important role in dictating the behaviors and performances of electrochemical systems. For example, the surface structure and composition of the graphitic anode used in lithium-ion batteries (LIBs) determine the quality of a solid electrolyte interphase (SEI) that forms at the electrode/electrolyte interface, which, in turn, substantially affects the stability and lifetime of the devices. To help predict the structure and the composition of the surface oxygen functional groups on graphite surfaces resulting from solution-based syntheses and modification processes, we analyze the adsorption of different oxygen functional groups at both edge and basal sites of graphite as a function of pH under which the solution-based processes may take place. A series of density functional theory (DFT) calculations reveal that at room temperature and for a pH range from 0 to 14, the (112̅0) edge surface of graphite will be fully oxygenated, while the basal sites remain unsaturated. The oxygen functional groups at the edge sites are comprised of mostly hydroxyl and ketonic groups, with carboxyl and carbonyl groups present only in small amounts. Furthermore, we observe the transformation of the carbonyl group into the ketonic group in the presence of empty surface carbon sites, which further stabilize the graphite surface. Meanwhile, carboxyl groups are more stable when all surface sites within a carboxyl layer are all populated. We conclude that the population of oxygen groups that can be found at the edge surface of a graphite in the ascending order is carboxyl < carbonyl < hydroxyl < ketonic. On the contrary to the edge plane, a small amount of oxygen functional groups may be forced to adsorb on the basal surface upon the application of an external potential. The adsorbed groups are found to prefer to cluster together on basal sites in a highly ordered fashion, while the edge surface does not show this preference for adsorption sites.

中文翻译:

石墨表面氧官能团的组成

石墨表面氧官能团的类型和组成很大程度上受制于实验合成和加工石墨的方法,这使得表征变得困难。挑战甚至延伸到计算研究中氧化石墨表面的建模。然而,石墨表面上氧官能团的类型和组成的确定至关重要,因为它在决定电化学系统的行为和性能方面起着非常重要的作用。例如,锂离子电池 (LIB) 中使用的石墨阳极的表面结构和组成决定了在电极/电解质界面形成的固体电解质界面 (SEI) 的质量,而这反过来又会 严重影响器件的稳定性和寿命。为了帮助预测基于溶液的合成和改性过程产生的石墨表面表面氧官能团的结构和组成,我们分析了不同氧官能团在石墨边缘和基部的吸附与 pH 值的关系。可能会发生基于解决方案的过程。一系列密度泛函理论 (DFT) 计算表明,在室温和 0 到 14 的 pH 值范围内,石墨的 (112̅0) 边缘表面将被完全氧化,而基部保持不饱和状态。边缘位置的氧官能团主要由羟基和酮基组成,羧基和羰基仅少量存在。此外,我们观察到在空的表面碳位点存在下羰基转化为酮基,这进一步稳定了石墨表面。同时,当羧基层内的所有表面位点都被填充时,羧基更稳定。我们得出结论,可以在石墨边缘表面发现的氧基团按升序排列是羧基 < 羰基 < 羟基 < 酮基。与边缘平面相反,在施加外部电位时,少量的氧官能团可能被迫吸附在基面上。发现吸附的基团更喜欢以高度有序的方式聚集在基底位点上,而边缘表面没有显示出对吸附位点的这种偏好。
更新日期:2022-06-23
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