Highly efficient tribocatalytic nitrogen fixation of hydrothermally-synthesized Bi₂S₃ driven by mechanical friction

Nitrogen (N₂) fixation for ammonia (NH₃) synthesis is a critical way for achieving carbon neutrality and fostering sustainable development. For the synthesis of NH₃, the sustainable and environmentally-friendly strategies using renewable and clean energy under ambient condition have attracted researchers' interest. Friction exists everywhere. As an emerging catalytic technology, tribocatalysis synergistically integrates the triboelectric effect with electrochemical processes. In this work, efficient tribocatalytic N₂ fixation directly from air is obtained on the friction interface between bismuth sulfide (Bi₂S₃) particles with a narrow bandgap of 1.48 eV and a polytetrafluoroethylene rotary disk at a low-frequency stirring speed. In darkness at room temperature, the maximum generation rates of ammonia radicals (NH₄⁺), after 5 h of friction, are respectively 250.45 μmol L^-1 g^-1 h^-1 and 208.53 μmol L^-1 g^-1 h^-1 under with and without the addition of 10 vol% methanol solution. Active radical negative charges are indispensable to the process of tribocatalytic N₂ fixation based on the electron paramagnetic resonance experiment. Additionally, the factors that affect the NH₄⁺ generation rate, such as the amount of catalyst, stirring speed, contact area and the pH of reaction solution, are explored to optimize catalytic behavior. After three cycles, the Bi₂S₃ catalyst can also maintain excellent performance in N₂ fixation. Based on the excellent catalytic performance of the narrow bandgap Bi₂S₃ material, reasonable synergistic mechanisms are proposed, which provide a reference for the understanding of tribocatalytic mechanisms. This work reports that the abundant and non-toxic Bi₂S₃ catalyst, as a promising candidate, shows great potential for application in tribocatalytic N₂ fixation through harnessing ordinary mechanical energy in nature.