Nano- and mesoporous boron carbon nitrides with very high surface areas up to 1560m²g^-1 are obtained by pyrolysis of a graphitic carbon nitride (TiPg-C₃N₄ infiltrated with a borane complex. This reactive hard-templating approach provides easy composition and texture tuning by temperature adjustment between 800 and 1400°C. The process yields B_xC_yN2OyH11, materials as direct copies of the initial template with controlled compositions of 0.15≤x≤0.36, 0.10≤y≤0.12, 0.14≤z≤0.32, and 0.11≤v≤0.28.The nano and mesoporosities can also be tuned in order to provide hierarchical materials with specific surface areas ranging from 610 to 1560 m²g^-1. Such high values, coupled with resistance against air oxidation up to 7000C, suggest potential materials for gas storage and as catalyst supports. Indeed, it is demonstrated that these compounds exhibit high and tunable H₂ uptakes from 0.55 to 1.07wt.% at 77 K and 1 bar, thus guiding further search of materials for hydrogen storage.