The Relevance of Carbon for Energy Transition: Ways to Assess Its Surface Properties and Standardize Their Characterization
Authors: Özcan Fatih , Amin Amin , Caidi Adib , Lange Thomas , Peinecke Volker , Segets Doris 
Published: February 2024

Technical carbon blacks (CB) are well-established materials that gain increasing attraction in the context of electrification and transition towards renewable energy sources. Their availability, low price, and favorable properties (e.g., conductivity, specific surface area) make them ideal candidates as additives in batteries or as support material for electrocatalysts, e.g., in fuel cells [1]. However, due to the vast number of producers and manufacturing processes large variations in their properties can be observed making product quality control difficult.
To this end, we report on ways and methods to standardize the characterization of CB materials that are specifically designed for fuel cell and battery applications. By applying analytical centrifugation (AC) and combining it with complementary methods (e.g., electrical conductivity measurements, Boehm titration), we identify parameters like particle size, morphology, and surface properties that are influential for the overall value chain in electrode manufacturing. This helps to minimize the effects of material inherent property fluctuations as well as process-related fluctuations on the final electrochemical performance.
Four different CBs were investigated, and their various properties were assessed. Our results show that the degree of graphitization and hence the electrical conductivity in a CB can be correlated with the overall surface basicity. Moreover, these properties can be linked with their dispersibility features on the ink formulation level and studied via liquid phase characterization using Hansen Parameters (Fig. 1) [2]. In brief, the higher the basicity of a CB surface is, the better the interaction with non-polar/mildly polar aprotic solvents becomes. This is especially true when oxygen-containing surface functional groups that cause a higher overall polarity of the material are missing.
Figure 1: Hansen interaction space (for polar, disperse and hydrogen bonding interactions) showing the location of various solvents that are used as probe liquids for determining the Hansen Similarity Parameters of the respective CBs in 3D space (a) and 2D representations (b-d).
To conclude, we were able to identify differences in CB materials by applying AC-based characterization techniques. Those differences can have a huge impact on the overall process chain of electrode production as they are decisive not only in formulation considerations but also in the subsequent processing steps. In the future, we will focus on closing the process chain and try to apply our characterization routines for an efficient identification of decisive process parameters at every stage of production. Additionally, we want to transfer knowledge gained from lab-scale techniques (e.g., sonication methods) to industrially relevant mixing procedures. By this, we will give electrode manufacturers tools at hand for a fast characterization of feed materials to save costly and lengthy adjustments of processes due to quality fluctuations. An accelerated implementation of green energy solutions is sought by this approach.

References

[1] L. M. Roen, C. H. Paik, and T. D. Jarvi: Electrocatalytic Corrosion of Carbon Support in PEMFC Cathodes, Electrochem. Solid-State Lett., vol. 7, no. 1, p. A19, 2004.
[2] S. Süß, T. Sobisch, W. Peukert, D. Lerche, and D. Segets, Determination of Hansen parameters for particles: A standardized routine based on analytical centrifugation, Adv. Powder Technol., 29, 1550–1561, 2018.

Figure 1