This review presents the state-of-the-art with respect to synthesis of activated carbons, and their use as electrode materials in supercapacitors and as hydrogen storage materials.

Sustainable porous carbons have been prepared by chemical activation of hydrothermally carbonized polysaccharides (starch and cellulose) and biomass (sawdust). These materials were investigated as sorbents for CO₂ capture. The activation process was carried out under severe (KOH/precursor = 4) or mild (KOH/precursor = 2) activation conditions at different temperatures in the 600–800 °C range. Textural characterization of the porous carbons showed that the samples obtained under mild activating conditions exhibit smaller surface areas and pore sizes than those prepared by employing a greater amount of KOH. However, the mildly activated carbons exhibit a good capacity to store CO₂, which is mainly due to the presence of a large number of narrow micropores (<1 nm). A very high CO₂ uptake of 4.8 mmol·g⁻¹ (212 mg CO₂·g⁻¹) was registered at room temperature (25 °C) for a carbon activated at 600 °C using KOH/precursor = 2. To the best of our knowledge, this result constitutes the largest ever recorded CO₂ uptake at room temperature for any activated carbon. Furthermore, we observed that these porous carbons have fast CO₂ adsorption rates, a good selectivity for CO₂–N₂ separation and they can be easily regenerated.

This perspective review paper provides an overview on recently developed carbon material technology synthesised from the hydrothermal carbonisation (HTC) approach, with a particular focus on the carbon formation mechanism, perspectives on large scale production, nanostructuring, functionalisation and applications. Perceptions on how this technology will be developed especially with regard to application fields where the use of HTC-derived materials could be extended will also be introduced and discussed.