Algae contains most of the marine biogenic S, and is the main producer of dimethylsulfide, of which oxidation products contribute ~ 40% acidity of the acid rain. The biogenic S of red algae mainly exists in carrageenan molecules. In this work, 89% of C and 96% of biogenic S in carrageenan was synchronically fixed into biochar to form thiophene S decorated biochar aerogel (SCA), efficiently preventing the loss of C and S elements. More importantly, the presence of thiophene S structure in SCA can “push” electrons into the antibonding orbitals of N2, and simultaneously “pull” the lone-pair electrons from N2, thus endowing the SCA super activity for nitrogen reduction reaction. Experimentally, its NH3 yield rate reaches high as 36.69 μg h−1 mg−1cat, surpassing most metal-free electrocatalysts. Theoretical calculations demonstrate that the thiophene S can promote the absorption and activation of N2, and efficiently lower the energy barrier of N2 protonation.