Boron-Doped Ti 3 C 2 T x MXene for Effective and Durable High-Current-Density Ammonia Synthesis.

Ammonia (NH 3 ) synthesis via the nitrate reduction reaction (NO 3 RR) offers a competitive strategy for nitrogen cycling and carbon neutrality; however, this is hindered by the poor NO 3 RR performance under high current density. Herein, it is shown that boron-doped Ti 3 C 2 T x MXene nanosheets can highly efficiently catalyze the conversion of NO 3 RR-to-NH 3 at ambient conditions, showing a maximal NH 3 Faradic efficiency of 91% with a peak yield rate of 26.2 mgh -1  mg cat. -1 , and robust durability over ten consecutive cycles, all of them are comparable to the best-reported results and exceed those of pristine Ti 3 C 2 T x MXene. More importantly, when tested in a flow cell, the designed catalyst delivers a current density of ‒1000 mA cm -2 at a low potential of ‒1.18 V versus the reversible hydrogen electrode and maintains a high NH 3 selectivity over a wide current density range. Besides, a Zn-nitrate battery with the catalyst as the cathode is assembled, which achieves a power density of 5.24 mW cm -2 and a yield rate of 1.15 mgh -1  mg cat. -1 . Theoretical simulations further demonstrate that the boron dopants can optimize the adsorption and activation of NO 3 RR intermediates, and reduce the potential-determining step barrier, thus leading to an enhanced NH 3 selectivity.