Experimental evidence of an upper limit for hydrogen storage at 77 K on activated carbons

An upper limit for hydrogen storage at 77 K on activated carbons was clearly observed in the present experimental work. Such a limit is around 6.4 wt.%, i.e., close to the theoretical limit of 6.8 wt.%. Results of hydrogen storage were obtained in three independent laboratories using volumetric and gravimetric devices. Lab-made activated carbons (ACs) were found to have higher capacities than those of the commercial material AX-21. A maximum excess hydrogen storage capacity of 6.0 wt.% at 77 K and 4 MPa was obtained. This maximum was reduced to 0.6 wt.% at 298 K and 5 MPa. ACs with surface areas (SBET) as high as 3220 m2 g−1 were prepared from chemical activation of anthracites with alkali (Na and K) hydroxides. At 77 K and 4 MPa, excess hydrogen storage capacity was directly correlated with SBET for ACs having SBET values lower than 2630 m2/g. Hydrogen uptake at 77 K also correlated with micropore volume and strongly depended on average pore diameter.