Elucidating nano and meso-structures of lignin carbon composites: A comprehensive study of feedstock and temperature dependence

Local Structure Analysis and Modelling of Lignin‐Based Carbon Composites through the Hierarchical Decomposition of the Radial Distribution Function

“…These results agree well with the HR‐TEM and XRD – Scherrer analysis conducted by García‐Negrón et al. ; [9] however, they are in partial disagreement with the trends modeled by McNutt et al [13a] . who states that for the LBCCs synthesized from hardwood lignin by Tenhaeff et al., [8] crystalline volume fraction decreases with increasing reduction temperature.…”

“…Samples reduced at 1050 °C show a primarily amorphous structure with small amounts of nanocrystallites while samples reduced at 2000 °C show primarily graphitic and ordered structures which are most easily observed in the kraft softwood and switchgrass samples. Nanocrystallites in the pine and hardwood samples reduced at 1050 °C and 2000 °C are somewhat difficult to make out visually; however, the XRD and Scherrer analysis confirm their presence with new peaks forming in the XRD pattern as reduction temperature is increased [9] …”

“…In other words, all lignin materials will eventually form an increasingly graphitic structure if the temperature is sufficiently high. Second, differences in the size of the resulting crystallites are most obvious at the highest reduction temperatures, with KSW and SG yielding larger crystallites than HW and YP [9] . We make a third observation upon review of García‐Negrón's elemental analysis of the “other” column for pyrolyzed and reduced lignin, where the “other” column is strongly considered to be mainly oxygen from ether linkages with trace amounts of ash and iron contamination from pyrolysis and ball milling respectively [9] .…”

“…Second, differences in the size of the resulting crystallites are most obvious at the highest reduction temperatures, with KSW and SG yielding larger crystallites than HW and YP [9] . We make a third observation upon review of García‐Negrón's elemental analysis of the “other” column for pyrolyzed and reduced lignin, where the “other” column is strongly considered to be mainly oxygen from ether linkages with trace amounts of ash and iron contamination from pyrolysis and ball milling respectively [9] . Evidence for ether linkages persisting post pyrolysis is present in the experimental RDFs as there is a relatively high intensity plateau centered near 4.6 Å that decreases in intensity with increasing reduction temperature.…”

“…Since the radial distribution function (RDF) is an effective function for evaluating the local structure of powder, single‐crystal, or liquid materials containing amorphous or crystalline domains in isotropic or anisotropic orientation, [11] model analysis usually includes comparison of the experimental neutron or X‐ray RDFs and the simulated RDF [12] . This method allows researchers to directly attribute a complex nanomaterial's structural characteristics to features present in the simulated RDF, [11,13] and in battery specific research it can define local order changes from cycling, nano‐phase quantifications, and ion storage mechanisms [9,10b,12,13b,14] . While this method is effective for testing specific composites, it produces a bottleneck when researching materials where small changes in processing have large effects in the resultant structure and the subsequent performance of the material in application.…”