Metal-free N2-to-NH3 thermal conversion at the boron-terminated zigzag edges of hexagonal boron nitride: Mechanism and kinetics

•DFT study of metal-free thermal conversion of N2 and H2 to NH3.•Nitrogen fixation at the boron-terminated zigzag edges of hexagonal boron nitride.•Full catalytic cycle of the NH3 synthesis at the hydrogenated boron edges is given.•Mechanism of the chemical flexibility of the boron sites and associated kinetics.