We report ambient electrochemical N-2 fixation at low overpotentials by using two-dimensional (2D) -boron. The metal-free catalyst afforded both an excellent NH3 yield rate and faradaic efficiency, approximately two times higher than those of bulk boron. We found that several binding sites, especially those involving icosahedral boron in the 2D material, can indeed catalyze N-2 reduction efficiently with strong N-2 adsorption, thus benefiting initial activation.