Nanoporous activated carbon cloth as a versatile material for hydrogen adsorption, selective gas separation and electrochemical energy storage

The efficient storage of energy combined with a minimum carbon footprint is still considered one of the major challenges towards the transition to a progressive, sustainable and environmental friendly society on a global scale. The energy storage in pure chemical form using gas carriers with high heating values, including H₂ and CH₄, as well as via electrochemical means using state-of-the-art devices, such as batteries or supercapacitors, are two of the most attractive alternatives for the combustion of finite, carbon-rich and environmentally harmful fossil fuels, such as diesel and gasoline. A few-step, reproducible and scalable method is presented in this study for the preparation of an ultra-microporous (average pore size around 0.6 nm) activated carbon cloth (ACC) with large specific area (> 1200 m²/g) and pore volume (~ 0.5 cm³/g) upon combining chemical impregnation, carbonization and CO₂ activation of a low-cost cellulose-based polymeric fabric. The ACC material shows a versatile character towards three different applications, including H₂ storage via cryo-adsorption, separation of energy-dense CO₂/CH₄ mixtures via selective adsorption and electrochemical energy storage using supercapacitor technology. Fully reversible H₂ uptake capacities in excess of 3.1 wt% at 77 K and ~ 72 bar along with a significant heat of adsorption value of up to 8.4 kJ/mol for low surface coverage have been found. Upon incorporation of low-pressure sorption data in the ideal adsorbed solution theory model, the ACC is predicted to selectively adsorb about 4.5 times more CO₂ than CH₄ in ambient conditions and thus represents an appealing adsorbent for the purification of such gaseous mixtures. Finally, an electric double-layer capacitor device was assembled and tested for its electrochemical performance, constructed of binder-free and flexible ACC electrodes and aqueous CsCl electrolyte. The full-cell exhibits a gravimetric capacitance of ~ 121 F/g for a specific current of 0.02 A/g, which relative to the ACC's specific area, is superior to commercially available activated carbons. A capacitance retention of more than 97% was observed after 10,000 charging/discharging cycles, thus indicating the ACC's suitability for demanding and high-performance energy storage on a commercial scale. The enhanced performance in all tested applications seems to be attributed to the mean ultra-micropore size of the ACC material instead of the available specific area and/or pore volume.