The role of the modulated intrinsic electromagnetic field characteristics inside the carbon nanopores on molecular hydrogen densification

•Intrinsic electromagnetic field can be modulated by tuning pore diameters and atomic compositions of carbon nanopores.•The modulation of intrinsic electromagnetic field inside a carbon nanopore is highly connected to the degree of H2 densification.•H2 densification in carbon nanopores with sub-1 nm diameters can be explained in terms of IEMF interaction more positively.•H2 densification may be possible even in larger than 1 nm in diameter, contrary to the conventional concept.