Electrochemical Nitrogen Reduction Reaction Performance of Single-Boron Catalysts Tuned by MXene Substrates.

A boron (B) center, which has an electronic structure mimicking the filled and empty d orbitals in transition metals, can effectively activate the triple bond in N2 so as to catalyze the nitrogen reduction reaction (NRR). Here, by means of density functional theory, we have systematically investigated the catalytic performance of a single B atom decorated on two-dimensional transition metal carbides (MXenes). The B-doped Mo2CO2 and W2CO2 MXenes exhibit outstanding catalytic activity and selectivity with limiting potentials of -0.20 and -0.24 V, respectively. Importantly, we have found that, although a high tendency of B-to-adsorbate electron donation can promote the hydrogenation of *N2 to *N2H, it would also severely hamper the *NH2 to *NH3 conversion due to the strong B-N bonding. Such an electron-donation effect can be reasonably tuned by the transition metal in the MXene substrate, which enables us to achieve optimized catalytic performance with a certain moderate degree of electron donation.