Embodiments of the present disclosure generally relate to carbon foams, processes for forming carbon foams, doped carbon composites, processes for forming doped carbon composites, and uses thereof, e.g., as electrodes. Processes described herein relate to fabrication of carbon foam and materials derived from the pyrolyzation of biomass at supercritical and subcritical conditions for CO2, N2, H2O, or combinations thereof. The process includes exposing biomass to CO2, N2, H2O, or combinations thereof under various parameters for temperature, pressure, heating rate and fluid flow rate. Silicon-carbon composites and sulfur-carbon composites for use as, e.g., electrodes, are also described.