Nanoporous B13 C2 towards Highly Efficient Electrochemical Nitrogen Fixation.

The electrochemical nitrogen fixation under mild conditions is a promising alternative to the current nitrogen industry with high energy consumption and greenhouse gas emission. Here, a nanoporous boron carbide (np-B13 C2 ) catalyst is reported for electrochemical nitrogen fixation, which is fabricated by the combination of metallurgical alloy design and chemical etching. The resulting np-B13 C2 exhibits versatile catalytic activities towards N2 reduction reactions (NRR) and N2 oxidation reaction (NOR). A high NH3 yield of 91.28 µg h-1 mgcat. -1 and Faradaic efficiency (FE) of 35.53% at -0.05 V versus the reversible hydrogen electrode are obtained for NRR, as well as long-term stability of up to 70 h, making them among the most active NRR electrocatalysts. This catalyst can also achieve a NO3 - yield of 165.8 µg h-1  mgcat. -1 and a FE of 8.4% for NOR. In situ Raman spectroscopy and density functional theory calculations reveal that strong coupling between the BC sites modulates the electronic structures of adjacent B atoms of B13 C2 , which enables the B sites to effectively adsorb and activate chemical inert N2 molecules, resulting in lowered energy required by the potential-determining step. Besides, the introduction of carbon can increase the inherent conductivity and reduce the binding energy of the reactants, thus improving N2 fixation performance.