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Highly Porous Renewable Carbons for Enhanced Storage of Energy-Related Gases (H2 and CO2) at High Pressures

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journal contribution
posted on 18.08.2016, 17:39 by Marta Sevilla, Wantana Sangchoom, Norah Balahmar, Antonio B. Fuertes, R. Mokaya
Hydrochar, i.e., hydrothermally carbonized biomass, is generating great interest as a precursor for the synthesis of advanced carbon materials owing to economical, sustainability, and availability issues. Hereby, its versatility to produce adsorbents with a porosity adjusted to the targeted application, i.e., low or high pressure gas adsorption applications, is shown. Such tailoring of the porosity is achieved through the addition of melamine to the mixture hydrochar/KOH used in the activation process. Thereby, high surface area carbons (>3200 m2 g–1) with a bimodal porosity in the micromesopore range are obtained, whereas conventional KOH chemical activation leads to microporous materials (surface area <3100 m2 g–1). The micromesoporous materials thus synthesized show enhanced ability to store both H2 and CO2 at high pressure (≥20 bar). Indeed, the uptake capacities recorded at 20 bar, ca. 7 wt % H2 (−196 °C) and 19–21 mmol CO2 g–1 (25 °C) are among the highest ever reported for porous materials. Furthermore, the micromesoporous sorbents are far from saturation at 20 bar and achieve much higher CO2 uptake at 40 bar (up to 31 mmol of CO2 g–1; 25 °C) compared to 23 mmol of CO2 g–1 for the microporous materials. In addition, the micromesoporous materials show enhanced working capacities since the abundant mesoporosity ensures higher capture at high uptake pressure and the retention of lower amounts of adsorbed gas at the regeneration pressure used in PSA systems.