Metal–support interactions program methane pyrolysis carbon into percolating MWCNT networks for high-areal-loading dry electrodes

CO 2 -free hydrogen via methane pyrolysis (MP) produces a solid-carbon co-product that must be valorized at scale. We show that catalyst-level metal–support interactions (MSIs) program the structure and porosity of MP-derived multi-walled carbon nanotubes (MWCNTs) and, in turn, govern percolation and through-plane transport in Li-ion battery cathodes based on LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811). Alumina-supported Co and Ni catalysts were synthesized by one-step solution combustion, and MSI-driven reconstruction was quantified by X-ray diffraction and H 2 temperature-programmed reduction. Strong Co–AlO x coupling with partial CoAl 2 O 4 formation restricted nanoparticle growth and produced narrower, more graphitic MWCNTs with hierarchical meso–macroporosity and higher conductivity (Co-CNT). Weaker Ni–AlO x interactions permitted coarsening and yielded thicker MWCNTs that packed into dense aggregates with restricted pore throats (Ni-CNT). To quantify dispersion, we introduced a grid-based carbon dispersity value from microscopic analysis and linked it to network formation. Under wet processing, Co-CNTs percolated at loadings as low as 2 wt% and sustained high-rate operation, whereas Ni-CNTs remained network-limited. Under solvent-free dry processing with polytetrafluoroethylene fibrillation, Ni-CNT dispersity increased from 53.3% to 87.5%. This enabled ultrathick electrodes with an areal loading of ∼50 mg cm -2 that approached ∼7 mAh cm -2 at low current densities and retained 56% of the 0.1 C capacity at 1 C, compared with 70% for Co-CNT. These results establish an explicit linkage from catalyst design and MP performance to carbon product attributes and electrode function, and provide design rules for upgrading MP-derived carbons into high-value conductive additives for thick, high-loading NCM811 cathodes. • Strong Co-AlO x MSIs form narrow, graphitic MWCNTs with open porosity. • Weaker Ni-AlO x MSIs allow coarsening; MWCNTs pack dense with tight throats. • Co-CNTs percolate at ≥2 wt% (wet); Ni-CNTs require PTFE-assisted dry mixing. • Dry Ni-CNTs reach ∼7 mAh cm -2 at ∼50 mg cm -2 loading; retain 56% at 1 C.