Composition of Oxygen Functional Groups on Graphite Surfaces

Abstract

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.

N-Doped and Sulfonated Reduced Graphene Oxide Supported PtNi Nanoparticles as Highly Efficient Electrocatalysts for Oxygen Reduction Reaction

“…The supported materials exhibited the wrinkles sites and sheets-like morphology. The similar molecular structure of oxygen functional groups on graphite surface were described in reference [32]. Figure 2c,d showed the FE-SEM images of GO and PtNi/S-(N)rGO catalyst, respectively.…”

“…The activated sites by N doping also provided the binding of oxygen fun groups. The increase of d-sapcing was attributed to sulfonation groups and oxyge tional groups [32]. The SEM images of PtNi/S-(N)rGO were shown with morphology of the w layers in Figure 2a,b.…”

“…The activated sites by N doping also provided the binding of oxygen functional groups. The increase of d-sapcing was attributed to sulfonation groups and oxygen functional groups [32].…”

Selective Hydroxylation of Carbon Fiber Paper for Long‐Lasting Hydrophilicity by a Green Chemistry Process

“…Computations have demonstrated that oxygenates at the basal sites of graphite are thermodynamically unfavorable. [ 43 ] Therefore, long‐lasting oxygenates must bind at edge sites. We established above that the content of adsorbed water on CFP must be above the critical threshold of 0.5% for hydrophilicity.…”

Use of Inner/Outer Sphere Terminology in Electrochemistry—A Hexacyanoferrate II/III Case Study

“…It is interesting to note that much of the older literature tends to suggest that the hexacyanoferrate II/III couple is an OSET process, although this view seems to be changing, as more examples of the influence of the electrode surface, indicative of ISET are found. This is especially true for carbon-based electrodes, which may possess a range of different surface functional groups, including carbonyls, carboxylic acids (or carboxylates), anhydride groups, epoxides, and peroxy groups, esters as well as sometimes even phenol and quinone groups, amongst others [17,44,55,91,92] Furthermore, microstructural defects such as missing carbon atoms, dangling bonds, metallic impurities, and folds in thin graphene sheets can also occur, which may affect the HET process. Adsorbed oxygen may also play a role in an ET process occurring on such electrode surfaces as described earlier [93,94].…”