Predictable and targeted activation of biomass to carbons with high surface area density and enhanced methane storage capacity

Abstract

A challenge in the synthesis of activated carbons is that currently there is no way to prepare materials with predictable and targeted properties. In particular, there are no material parameters or characteristics of the starting carbonaceous matter that can be used to predict the porosity and packing density of the activated carbon. Here we report on the synthesis of biomass-derived activated carbons with targeted porosity and packing density that is suitable for methane storage. We show that the ratio of elemental oxygen to elemental carbon (i.e., O/C atomic ratio) of the precursor can be used as a universal predictor of the nature of porosity generated in an activated carbon. We use date seeds (Phoenix dactylifera) as an example of how biomass starting material with a very low O/C ratio, along with choice of mode of carbonisation, can be used to synthesise activated carbons with optimised porosity, as defined by the surface area density, and high packing density that is suitable for methane storage. The carbons store up to 222 cm³ (STP) cm⁻³ methane at 25 °C and 35 bar, which is much higher than any value reported to date for porous carbons, and is comparable to the best metal–organic-framework (MOF). However, the activated carbons are much cheaper (≤1$ per kg) compared to at best 10–20$ per kg for MOFs. Our findings present important insights on directed synthesis of optimised activated carbons and represent a significant step in the development of cheap porous carbons for high volumetric methane (or natural gas) storage. The findings are also applicable to informing the optimised preparation of activated carbons with targeted properties for other applications in energy storage and environmental remediation.