Supercritical carbon dioxide (scCO2) is a non-toxic, inert, and widely used solvent in green chemistry, offering tunable properties such as density, diffusivity, viscosity, and polarity, adjustable through temperature, pressure, or co-solvent addition. This study employs the Design of Experiment (DoE) methodology to optimize scCO2-assisted synthesis of Li-S battery cathodes, presenting the first systematic investigation of how scCO2 conditions affect the structural and surface properties of reduced graphene oxide (rGO) during sulfur decoration. Results show that temperature and pressure significantly influence sulfur integration and cathode performance. By combining DoE with detailed electrochemical impedance analysis using complex nonlinear least squares fitting, the study provides deeper insight into composite electrochemical behavior under varying conditions. An optimal rGO structure with low charge transfer resistance, enabling efficient ion and electron transport, was obtained at 150 bar and 60 °C, balancing sulfur loading and pore accessibility. Conversely, harsher conditions (180 bar, 80 °C) caused sulfur agglomeration and higher resistance, reducing performance. These findings highlight the necessity of precisely controlling scCO2 synthesis parameters to enhance cathode structure and improve electrochemical performance and long-term stability of Li-S batteries.

After being an indispensable intermediate in the oxidative exfoliation route towards graphene, graphene oxide has gained its deserved value in materials science for numerous applications, from catalysis, through energy storage and conversion, to sensor use. In this work, three graphene oxides of tuned morphology and chemistry are used as a simplified model for porous carbon materials in hydrogen storage and as a Li-ion battery anode. The BET surface areas were, respectively, 9, 13, and 535 m²/g, while the corresponding O/C values from the X-ray photoelectron spectroscopy were 0.51, 0.17, and 0.12. Additionally, the samples were thoroughly characterized using scanning and transmission electron imaging, powder X-ray diffraction, thermal stability, and Raman and Fourier transform infrared spectroscopic methods. Hydrogen adsorption isotherms (−196 °C) and their comparison with nitrogen uptake revealed that pore accessibility, porous confinement, and surface chemistry, i.e., both morphology and surface chemistry, contribute to efficient adsorption. In the anode application, by contrast, surface chemistry was the single most defining factor for performance.